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Hydro brake mystery

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Hydro brake mystery

Post by ZesCoupe » Mon Jun 11, 2018 2:00 pm

Hi All,

Read loads of posts here and other forums but still can't find anything to answer my brake problem. It doesn't fit with the usual symptoms.

The shark hadn't run for some time and I replaced all the front brake lines a couple of weeks ago. The garage that did the obligatory test to be able to get it back on the road refreshed the fluid and bled it with their special apparatus. Pedal felt fine but then yesterday an enormous squeal started while driving on the highway at about 120 kmh. Convinced this was the PS pump but it disappeared after a while. Later after the car had been standing for a while I found suddenly that I had a hard pedal, but the brakes worked although needing a lot of effort. The brake warning light (exclamation mark) was also flashing so I limped it home and did the accumulator check. Fluid level pumped up OK but needed extreme force on the pedal where there was very little travel. After that starting the engine didn't lower the fluid to where it should be, so I presume the accumulator was not refilled. The level is still at the top of the reservoir.

Today I took it all apart. Pump itself looked OK, no obvious damage inside and the seals where OK. The accumulator had no leaks and I could feel the membrane with a plastic rod about a centimeter or so below the opening. I assume it's intact, it was replaced a few years ago. As for the regulator, I saw no leaks when removing the return pipe connection (as read somewhere) but apart from that......

So the question is where could the fault lie? Accumulator, regulator, pump? Any help apreciated.

Regards,
Martyn
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Re: Hydro brake mystery

Post by VintageRacer » Thu Jun 21, 2018 1:53 pm

Sounds like the accumulator went bad again. The squeal is interesting and could have been a slipping belt which would cause you to lose pressure and a hard pedal. Check your belts for slippage or even throw on a new belt and see if that helps (its cheap and easy). Or you could just delete the hydroboost and covert to an E28 vacuum setup.

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Re: Hydro brake mystery

Post by ZesCoupe » Thu Jun 21, 2018 5:15 pm

Thanks for the input VintageRacer.

Update from my side. Had already fitted new belts and they were adjusted correctly. Managed to "borrow" a new accumulator, that didn't help at all but while talking to a contact at the local BMW dealer we came to the conclusion that as both the power steering and the brake booster functionality were not working correctly it would probably be a supply thing. On further inspection of the pump there was considerable scoring of the aluminium plate between the two halves that sits against the vane assembly. No idea what could have caused that - maybe dry running with some impurities in the oil maybe. That was possibly the noise I heard but anyway I decided to get a new pump. The local BMW dealer needed more than a week to get a remanufactured exchange unit but I managed to find a BMW specialist who had the last brand new Meyle in stock and shipped it to arrive next day.

So I fitted that and took it for a test drive. The problem had disappeared - and then it was back - and then it was OK again etc. etc. One minute heavy steering and hard pedal, a few minutes later everything as it should be. But by the time I got home again it was back to the original situation :( :
  • Hard pedal
  • No power steering
  • Reservoir full
  • No drop in level with engine running
  • Flashing warning light at idle, steady light at higher revs
I dismantled the whole assembly once again and flushed all the lines and assemblies. I had acquired a used Regulator for next to nothing but had no idea if was any good. It looked clean enough but then again you don't know what's bad inside. Swapped that out but it hasn't changed anything, I'm beginning to suspect the Regulator. It's said that the Regulator almost never fails but with my luck it probably has. I can't honestly think of anything else it could be seeing as the problem is with both the brakes and steering. Guess I'l have to bite the bullet and shell out for a new one €€€!!! :roll:

Couple of extra points. Filter is not that old, a number of years but very few kilometers. Filter and reservoir were cleaned, had some grey residue (possibly aluminium) on the walls but nothing much on the inside of the filter area. I have a magnet sitting there to collect any steel particles coming from the steering box but that was relatively clean.
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Re: Hydro brake mystery

Post by hornhospital » Thu Jun 21, 2018 9:35 pm

Doesn't one of the power steering hoses have a restrictor in it? Do you suppose it's clogged? Just guessing, but at this point, what else could it be?
Ken Kanne
'84 633CSi "Sylvia"; '85 635CSi "Katja";'87 325is "Odette"; '93 325is "Elvira"; '95 M3 "Ashlyn"

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Re: Hydro brake mystery

Post by ZesCoupe » Thu Jun 21, 2018 10:05 pm

Well Hornhospital if that's the case it's the first I've heard of a restrictor :-? . As I said, I've flushed all the lines anyway, they seem perfectly clean. It's the restriction aspect which makes me think of the regulator, it regulates what goes to either the steering box or the brake servo.

In the tech article "Hydro braking system" it states:
The power steering pump supplying the pressure for this system has a maximum operating pressure of about 130 bar (1900 psi), however the working pressure for the H31 system is regulated at 35 ? 57 bar and only needs about ten percent of the fluid volume that is needed for the power steering. With that in mind it is obvious that any problem with the pump pressure or volume would show itself first as a problem in the power steering.
The last sentence seems to point to the cause but as the pump is brand new (I drove less than 100km) seems to be ruled out. Runs as sweet as a nut anyway - no noises. Only thing left is some sort of restriction in the regulator.

I had hoped that maybe Brucey or Chris Wright would have joined in but they don't seem to be around at present, they usually have some good insights into problems like this ](*,) . I've had some interesting PM discussions with Brucey in the past.
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Re: Hydro brake mystery

Post by VintageRacer » Fri Jun 22, 2018 5:28 pm

Check your supply line from the reservoir to the pump. Over time this line can degrade and collapse. Also check the filter for clogs. This could also be a fluid supply issue.

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Re: Hydro brake mystery

Post by Brucey » Thu Jun 28, 2018 8:51 pm

I agree with the above post (and this is a common problem area) but then again there has to be some kind of restriction in the system output somewhere in order to generate pressure.

The fact that there is grey (presumably non-magnetic) sludge in the reservoir is somewhat worrying; normally I'd assume that this means that there must be an aluminium (or rubber?) part somewhere that is wearing and that this also makes a blockage in the filter assy more likely.

I wonder if the problem originally lay in the pump and that what you are experiencing now is collateral damage arising in part from that.

If the pump is starved of oil it will be noisy and it will wear faster than normal and this tends to push hard steel particles (from the pump vanes) into the system. These ought to be harvested by a magnet if you have one fitted. The pump will of course fail to generate pressure if the pressure relief valve in it is jammed open.

Occasionally the hoses have been known to fail in such a way as the hose liner generates a flap of material that can sporadically impede the flow. If this were to happen in the main pressure line (from the pump to the regulator block) then this would explain the symptoms, i.e. that it is intermittent, that the PAS doesn't work, that the accumulator doesn't charge with fluid, and that there is unusual debris in the system (which might be bits of failing hose?).

If the accumulator doesn't charge with fluid there are only two reasons for this, either that the accumulator never sees enough pressure (eg because of some kind of fault upstream ) or that the accumulator itself is faulty. My understanding is that a failed accumulator will have a leak past the diaphragm so that it may

- hold oil when removed (thus be heavier than a known good unit) and/or
- the rubber diaphragm inside the unit might be easier to push back slightly (eg with a length of dowl)

unfortunately failed units have been of little interest to me in the past (and have obviously failed before they came out of the car) so they have just gone in the bin. Maybe someone with a failed unit can say if there are obvious symptoms when a failed accumulator is out of the car?

My understanding is that there must be a fixed orifice that limits the flow through the regulator to the accumulator (to a small fraction of the full pump flow), else you would lose PAS pressure whenever the accumulator is being charged, and the accumulator would be able to charge very much more quickly than it does. My understanding (which might be in error) is also that the pressure in the main feed line is measured in the regulator block but it is otherwise passed straight through to the steering box and that it is normally limited by a pressure relief valve in the PAS box and/or the pressure relief valve that is built into the pump.

Note that if this is correct, then the bulk of the flow returns into the reservoir from the PAS return line, not the return line from the regulator block, and that if there is any contamination arising from those parts of the system that see full flow, it may be localised thereabouts rather than throughout the reservoir.

Some suggested tests;

- remove the sintered metal filter in the base of the reservoir and see if it is clean. If in any doubt replace it; it is not expensive.
- check the feed hose to the pump for any leaks/bad joints (although if it is leaking air in the pump becomes noisy, which is obvious; if the filter is clogged then the hose can be sucked flat and intermittently block the flow like that, moreso when the oil is cold).
-remove the main pressure line and blow compressed air through it; note any blockage or emerging debris
- do the same with the return lines (esp from the PAS box and the regulator unit)
- disassemble the pressure relief valve in the pump (and PAS box if there is one) and make sure that it is OK and not jammed/damaged
- be sure that you are using the correct fluid specification in the system (i.e. ATF, not any other PAS fluid)

If my understanding of the system is flawed I apologise in advance and please point out any obvious errors.

cheers
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Re: Hydro brake mystery

Post by ZesCoupe » Fri Jun 29, 2018 12:11 am

Well thanks for jumping in Brucey, I value your input. An update from my side is possibly necessary as I have been busy with this for the past couple of weeks.
  • Checked the high pressure lines again - they are all clear, no stoppages.
  • Changed the supply hose from the reservoir to the pump. It's now a spiral reinforced silicone type with new hose clamps.
  • The new regulator (ATE) arrived from Germany today but it has not helped the situation. Possibly spent €450 for nothing.
  • Removed the filter in the reservoir to see if there was any further residue but it's clean. Filter is definitely not blocked anyway.
  • The pump is quiet but I don't see much movement of the fluid (definitely ATFII) in the reservoir, even at higher revs.
  • The new regulator included new switches but now I am getting a fixed warning light on idle and a flashing on higher revs.
Tomorrow I'm planning to look at the pump. It was brand new last week from Meyle, not an exchange unit and felt quite tight when I installed it. I can't imagine that it was already faulty but you never know.

One positive out of this so far is that through all my research I have accumulated a lot of information from various sources which has given me much better insight into the workings of the H-31 system. One German language document from ATE was very descriptive of the workings and testing of the various elements. My German is crap but it is not dissimilar to Dutch, which I do speak, so I have created an English version. First using Google and then reading the original to try and improve the translation. The problem with translation is that the word order in Dutch and German sentences is back to front compared to English. I also found some much better graphics than the original German document which I have added within the text sections. Having read and edited it a number of times I now believe that it is a pretty accurate description of the workings. I have added it here for anybody who is interested. NB. This file was updated 20th August '18

H31 Hydraulic Brake System.pdf
(1.02 MiB) Downloaded 15 times

Only thing I haven't looked at is the booster itself, although having begun to understand the workings I can't see how that would cause both lack of both brake and steering assistance. It shows no signs of leakage anyway.

Just one more thought. How important is the restrictor in the line from regulator to the steering box? I have a made up high pressure replacement line.

Regards,
Martyn
Last edited by ZesCoupe on Mon Aug 20, 2018 11:32 am, edited 1 time in total.
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Re: Hydro brake mystery

Post by VintageRacer » Fri Jun 29, 2018 1:35 am

I can tell you 100% that you can run a line directly from the pump to the box without a restrictior. I have done just that on my Group A car using an E28 line. I didn’t have a restrictor on my car in the line from the regulator to the box so I’m not sure which markets or cars had that.

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Re: Hydro brake mystery

Post by ZesCoupe » Fri Jun 29, 2018 8:20 am

Yes - I read that in another thread. Some people say it is just to cut down any aeration but it doesn't show up on for instance the E32's (well as far as the steel section being visible in the middle of the hose - see realoem image). In any case just running the power steering would by-pass the brake problem.
Screen Shot 2018-06-29 at 10.02.22.png
Screen Shot 2018-06-29 at 10.02.22.png (117.05 KiB) Viewed 825 times
Pre '87 E24 hoses also cost 50% more than post for some reason but both are NLA, which is why I got one made up. Both the regulator and accumulator are identical for all E23, E24, E28 and E32 models.

Having read the ATE H-31 manual I can't see what kind of influence it would have on the workings of the system - unless it influences the pressure being built up as measured by the regulator. That is not discussed in the ATE manual. The new Meyle pump I bought delivers 120bar according to the specs. The original for my model was 110bar and apparently later models had a 130bar pump. As I said I'm going to look at the pump today. Also going to try and source a high pressure gauge to do the measurements as detailed in the ATE manual.

Regards,
Martyn
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Re: Hydro brake mystery

Post by Brucey » Fri Jun 29, 2018 12:11 pm

the regulator unit is the same for E24 and E32 but for some reason the third (return) hose on the regulator unit is not shown in the E32 diagram.

In the E24 diagram this is clearly shown (21 and 23)
Image

Obviously early E24s had vacuum brake servos and had a simpler PAS arrangment, much like the one you end up with if you delete the regulator etc from a race car.

Also, apologies for not having replied to your PM; I have been 'off the case' for a while.

BTW I like your pdf very much but it is perhaps worth adding a comments/footnotes section; one comment I would make is that the brake servo is relatively easy to strip apart and there are only a few wearing parts inside; you can get the servos rebuilt via this very forum.

cheers
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Re: Hydro brake mystery

Post by Brucey » Fri Jun 29, 2018 12:39 pm

thinking about it there (surely?) must be a pressure relief valve (or at least something that restricts the flow when the PAS is not being used) in the PAS box, else the regulator flow control piston (#2) would always see a large pressure differential (even when the steering is not being moved) and the #2 piston would always be leftwards (as per the diagram).

It seems to me that a possible explanation for the whole thing is that your steering box is faulty, and does not constitute enough of a flow restriction to cause the accumulator to ever, er, accumulate at all, and obviously does not provide pressure to cause the PAS to work either.

It might be that this was a known fault and that a simple palliative would to add a restriction to the line connecting the regulator to the PAS box (if this is what you mean?); this would always give some pressure at the accumulator, (and therefore servo brakes) even if the fluid flow was unrestricted through the PAS box.

cheers
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Re: Hydro brake mystery

Post by ZesCoupe » Fri Jun 29, 2018 1:06 pm

Thanks Brucey for the comments about the document. I think you may be correct about adding a comments or footnotes section, maybe if anybody wants to share comments I could always incorporate it, that would also mean versioning. I never saw it as definitive because some aspects of the translation have been a sort of best logical guess, if you see what I mean. I was having second thoughts about the correct sensor to remove when doing a pressure test as described, may have to recheck and modify.

Getting back to my present problem. I'm beginning to think you may be correct about the restriction but I can find no definitive answers anywhere in my searches of the net. The last incarnation of the hose was available according to realoem until 2014 and I just checked with the dealer - NLA!

So that leaves secondhand parts - which are getting to just as expensive. :roll:
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Re: Hydro brake mystery

Post by ZesCoupe » Fri Jun 29, 2018 1:11 pm

BTW..

That particular view when selected on realoem for my model (5351) informs me that there are no parts for my model:
Screen Shot 2018-06-29 at 14.30.30.png
Screen Shot 2018-06-29 at 14.30.30.png (124.61 KiB) Viewed 812 times
Don't know which year/version that would be but there are some noticable differences. For mine it shows this:
Screen Shot 2018-06-29 at 14.24.41.png
Screen Shot 2018-06-29 at 14.24.41.png (101.77 KiB) Viewed 812 times
Steering box is certainly different. Mine has a return feed with just a jubilee clip to fix the hose. The other has a banjo fitting
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Re: Hydro brake mystery

Post by Brucey » Fri Jun 29, 2018 9:15 pm

oops the illustration I used was for RHD parts; just meant to show the return hose from the regulator unit (not present in the E32 illustration). The banjo fitting on the PAS box is needed to allow clearance to the bodywork in a RHD car.

If my guess is correct then you don't need any kind of restriction in any hose unless there is also a fault in the steering box so that it does not restrict the flow in any way.

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Re: Hydro brake mystery

Post by plip1953 » Mon Aug 13, 2018 5:35 pm

Hi All

I'm new to this forum, but have owned my 1988 E24 635 CSi RHD for over 25 years.

Rather than start a new thread I thought I'd first see if any of the previous information in this thread my be pertinent to my particular issue.

The story is as follows:-

a few weeks ago, after a lay up over nearly 4 year, Is set about getting the car ready to put back on the road. It started first turn of the key (as it always had done, regardless of how long it's been left unused) and everything seemed in order. But to get it back on the road properly I had to take it for the mandatory UK MOT safety and roadworthiness check. No problem on that score either. As an aside I'm very fortunate that my local garage owner once himself owned an E24 and knows his way round these cars extremely well, so I am very confident that all was checked out throroughly and found to be in good order at the time of the test.

And then yesterday I set off early for the BMW(UK) Car Club National Festival event about 150 miles from my home. Everything was running fine, but shortly before reaching the event, under light braking, there was a load screeching noise as if the fan belt was slipping very badly or a stone had lodged itself between a brake pad and disc. My son was driving at the time so I wasn't totally sure what to make of it all.

The noise then started to be very intermittent and it soon became clear that it didn't happen only when the brakes were being applied. So the stone in the brakes theory went out the window. But my son also felt a strange sensation from the steering as if it was momentarily locking up! Anyway, we were close to our destination so carried on and got parked up. Someone outside the car heard the noise and pretty confidently suggested a loose fan belt - it was that kind of noise.

A bit later on I ventured under the bonnet and indeed the fan belt did seem a bit loose. I tightened it up and felt reasonably confident this would do the trick. But what I hadn't realised is that the power steering pump is driven from a completely different belt (which is quite new and not noticeably loose). Doh!

Later on we started the journey home, again with my son driving, and the noise started occurring again, but for no more than a few seconds at a time, and the "locking" of the steering was also present albeit very briefly. Throughout all of this he said the brakes felt entirely normal.

Much of the next 70 or 80 miles was motorway cruising and there was no further noise until we came off the motorway and had to negotiate a short amount of in town driving before I dropped my son off. From this point on I drove the last 60 miles, again mainly motorway. But this time the noise would occur every few miles and last around 5 seconds - it was almost predictable and very consistent. And it seemed not to matter whether I was accelerating or even braking, but of course there was virtually no steering input being applied.

But when I took the slip road to exit the motorway and almost immediately negotiate two roundabouts the noise became constant and all power steering was lost! Fortunately I was half ready for this and wrestled the car safely trough the roundabouts and then the noise stopped and power steering resumed as normal and stayed like that for the remaining couple of miles to home.

Today, I checked the belt tension and it's possibly in need of a slight re-tensioning - which is pretty easy. I also checked he power steering fluid level. It was about 15mm below the level of the reservoir with engine off. I pumped the brake pedal several times, but it didn't rise any further. I then started the engine and the level dropped quite rapidly and to below the mesh strainer. I subsequently removed the strainer to see just how far below and it was at least 10mm. I switched off and applied the brake pedal around 20 times and the fluid level returned to it's previous level 15mm below the top of the reservoir.

At no time during today has the loud screeching noise occurred.

The pump is the original, so 30 years old, and so are all the other steering and braking components except that I changed the pressure accumulator around 10 years ago (but probably only 3k miles have been travelled since).

Any thoughts on why it's screeching and what's happening when it does. I guess it must be coming from the pump, but is it conceivable that the pump would effectively seize for regular periods of around 5 seconds at a time while cruising at motorway speeds?

I'd be grateful for any ideas as what might be going on, or at least a checklist of what to test out next?
Phil
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Re: Hydro brake mystery

Post by ZesCoupe » Mon Aug 13, 2018 9:12 pm

Hi Plip? (you didn't sign the post with your real name so...),

Welcome to the forum. As you have read I have had some ongoing problems recently which are still not completely solved but more of that later.

As to your problem, I do recognise what you describe and it sounds like the pump protesting, maybe cavitation due to air ingress caused by poor flow? I would think that the first thing to do would be to drain and flush the WHOLE system and clean the reservoir plus filter which you'll find at the bottom. I would think that after that many years you will find an awful amount of crud (metal and other particles) in there and the filter will also be up for renewal. This is described in a number of threads ( can't actually find them on the spur of the moment). You didn't mention any braking problems so I presume the regulator and accumulator are functioning correctly thus you seem to be getting some pressure from the pump.

Check all the hoses, that they are in good condition. They deteriorate over time, also on the inside where they tend to de-laminate. You can sometimes see small black particles which could be rubber or fabric amongst the crud. Problem with the hoses is that most are NLA from BMW. I had one made up today by a local firm supplying hydraulic hoses, fittings etc. Luckily they are quite happy to deal with non business (hobby) people like me and they only charge me peanuts.

Worst case scenario: If the problem is actually in the steering box it could be an expensive exercise as exchange units at the BMW dealer or recognised ZF agents are running at €2500 (mainland Europe). If you are a MORE than competent mechanic it is possible to rebuild it yourself but finding the parts is difficult as BMW does not supply a full rebuild kit any more, only the gasket set. This is also described in other threads (also on Bimmerforums)

After flushing and refilling with fresh ATF (Bentley says Dexron II but have read many posts where owners are using later versions with no ill effects) the system should be bled by turning the steering hard lock to lock for a few minutes. This should get the air out of the system. You will see some froth at first but that should settle down. One further point - place a small magnet in the reservoir to collect any steel particles. I have used a magnet from a small loudspeaker with a hole drilled through the middle to fit over the shaft in the reservoir. I placed mine inside the filter element as this is the only place that steel particles should enter - from the steering box return line. The other return lines would normally only return aluminium particles mainly from the pump where the steel vanes slowly erode the aluminium interior parts. You can recognise this as a grey paste-like deposit. You may also need to repeat the process after some running as some difficult areas take time to flush and you may find more crud appearing. If a such a complete clean doesn't help then you'll have to get back to us.

For anybody else following the thread I'll be writing an update any day soon. At the moment busy testing pumps on an off car rig - seems some so-called re-manufactured pumps are still very sub-standard and I'm very unhappy with certain BMW specialist companies and their well known suppliers.

Regards,
Martyn
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Re: Hydro brake mystery

Post by Brucey » Tue Aug 14, 2018 12:20 am

the fact that when you get the noise you lose the PAS means the belt is slipping and the pump is not turning.

It could be as simple as the belt needing to be tensioned (it needs to be pretty tight) or the belt could be the wrong one (right length, wrong section) which means that no matter how tight it is set, it will be prone to slippage.

So check the belt tension, check the belt itself (type and condition) and take it from there.

BTW the most useful thing you can do is to add a magnet to the PAS reservior; this will take out all the abrasive crud that is in the system. The filter won't remove this stuff because the particles are too small and pass through the filter.

cheers
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Re: Hydro brake mystery

Post by plip1953 » Tue Aug 14, 2018 7:44 am

Thanks for the responses so far. Btw, my real name is Phil, sorry I didn't sign off with it #-o

I've been trying to get my heard round exactly how the system works. Am I right in thinking that the function of the accumulator is purely to provide an store of residual pressure for the braking side of things? But that demands on pressure made by the steering box will always needs to be met from in real time by the pump?

Assuming the above is broadly correct, I'm then on to thinking how the screeching noise (which looks like it must be belt slippage?) could occur at several mile interval of motorway cruising during which there are no demands on the brakes and only marginally on steering assistance. Could this be that (for whatever reason) pressure in the brake accumulator drops below a certain level, and it then places a demand on the pump to restore pressure back to where it needs to be? If so, would it be reasonable that the duration of that re-pressurisation process takes around 5 seconds?

This kind of begs another question inasmuch as how long/well should pressure should be maintained in the accumulator if no demands are actually being made on the brakes? Is every few miles normal or should the intervals be much further apart? I think I would expect the answer to be the latter.

As regards sludge/metal particles in the system, I did have a complete fluid and sintered filter change not very long a go (several years, but very few miles), and the state of the fluid currently seems pretty much ok to me. But I'll either change it anyway or at least install a magnet in the reservoir.

Phil
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Re: Hydro brake mystery

Post by ZesCoupe » Tue Aug 14, 2018 9:08 am

Hi Phil,

Good point of Brucey's, always worth a check of the belt tension and condition. Could be as simple as that but my own experience where the belt was new and tension correct showed that the functionality was intermittent, although not with the screeching. It also generally needs some resistance to the pump rotation to cause it - unless of course it is really slack.

As to your assumption that the accumulator is a store of residual pressure for the brake booster, this is correct. The regulator, the connector block where the accumulator screws into, regulates the division of pressure. Information is a little sketchy but it seems that there will never be more than 10% of the flow being used for the charging of the accumulator so shouldn't affect steering assistance at all. If it's full - it's full and the pump will be constantly pumping fluid around the system and at this time there is actually very little pressure in it. Pressure builds up when the valves react in order to fill the accumulator and when full will revert to the normal position where the fluid and pressure in the accumulator is maintained. When you pumped the brakes with the engine off you released this pressure and the fluid returns to the reservoir, that's why the level rises. Pressure will also build when the steering box (due to torque reaction created internally by the turning of the steering wheel and the resistance of the tyres on the road surface) creates a state where the pressure can build to the 110-130 bar of the pump specs, this would necessarily cause a resistance in the pump and therefore the noise (either from belt slippage or something internal). With the filling of the accumulator the pressure will never get beyond 57 bar so will not cause so much resistance. I haven't actually managed to work out completely what actually happens in the steering box, so this is a fairly generalised view. If you are driving straight the fluid will just flow through the box back to the reservoir. The regulator itself has only a mechanical function as to how the fluid flows through it but is not serviceable. Although not generally known to fail the valves internally will be sensitive to crud in the fluid. I attached a document earlier in the thread, not written entirely by me it's a translation of a German language document from ATE with some better images. This should explain what should be happening when all is OK.

I was also thinking that you didn't mention any dashboard lights coming on or flashing. The one that shows problems with the system is left of the handbrake lamp. It is triggered by the two sensors in the regulator which measure pressure and pressure difference between two zones.

Just to summarise it seems that:
  • No problems with braking
  • No brake warning light indications
  • Intermittent noise from the pump or belts
  • Intermittent lack of steering assistance
  • Comparatively recent filter change and flush
We can possibly therefore assume ( 8-[ ):
  • The regulator and accumulator are OK
  • Belt could be slipping - easiest check
  • Pump could be faulty - needs a test rig setup to check
  • Steering box is faulty - worst case scenario
I should first do as Brucey suggested and check the belt. Secondly do an inspection of the fluid in the reservoir and inside the filter. As I said it can take a while for all the crud leftover from the previous flush to appear. Any other checks will obviously be more involved - high pressure gauges etc.

One niggling point that I noticed in your post is that you completed the drive home and the next day checked the level which was at the correct "full" position. This would mean that the accumulator was discharged, confirmed by the fact that you started the engine and the level dropped. So my question would be "why did the accumulator discharge itself?"

After all that I am off to the garage to continue with my own investigation.

Regards,
Martyn
"If a job's worth doing, it's worth doing well" My Dad (1921-1995)

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Re: Hydro brake mystery

Post by plip1953 » Tue Aug 14, 2018 3:17 pm

Thanks again Martyn

I checked the belt tension again today, and much as I'd like that to be the only issue it doesn't seem especially slack, so I'm not holding my breath on that one!

I still do't feel there is a logical explanation for the noise occurring every few miles on the motorway if nether steering or brakes have been used. In those running conditions I'd expect the accumulator to hold pressure without a problem, Do you agree? I'll do another, more controlled check of the rate of rise in in level of fluid in the reservoir with the engine off and left more than a short time.

Thinking back a while, I did have a bit of a fiddle about with the "adjuster screw" on the steering box. The steering was exhibiting a noticeably amount of steering wheel travel before any actual turning effect and this was effectively eliminated after my trial and error method of adjustment. But my concern now is that I might have introduced a different kind of problem. Any thoughts on this?

Phil
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Re: Hydro brake mystery

Post by ZesCoupe » Tue Aug 14, 2018 5:57 pm

I checked the belt tension again today, and much as I'd like that to be the only issue it doesn't seem especially slack, so I'm not holding my breath on that one!
Condition is also important - also of the pulley. Needs friction to hold of course.
I still do't feel there is a logical explanation for the noise occurring every few miles on the motorway if nether steering or brakes have been used. In those running conditions I'd expect the accumulator to hold pressure without a problem, Do you agree?
Yes - I would expect it to hold pressure, it builds up initially easily enough. I wouldn't expect the accumulator to have much effect on anything other than the brakes (or rather lack of assist). In that situation the only thing that logically springs to (my) mind is some form of air ingress on the intake (non-pressurised) side. As Brucie has mentioned in previous discussions it is possible that there is no visible leak but that air is drawn in. It could be some form of intermittent cavitation causing the noise. Air in the fluid will make it less able to take compression, meaning that the when used the assistance (certainly of the steering) would not be sufficient, but maybe I'm feeling around in the dark there. This is worth a read: https://www.bimmerforums.com/forum/show ... luid-level

Further to the subject of air ingress and cavitation, I was talking to the owner of Hydroline in Veenendaal here in The Netherlands last week. He does specialist rebuilds of pumps, boxes and racks, he also has a load of good information on his website but it's in Dutch so no point in leaving the url. Anyway he says that air in the system is not only recognisable by a "cappucino froth" on the surface of the fluid but also, when running apparently normally, by the presence of what look like tiny floating sparkling particles. Actually very tiny air bubbles which you can see by shining an LED lamp into the reservoir.
I'll do another, more controlled check of the rate of rise in in level of fluid in the reservoir with the engine off and left more than a short time.
Not exactly the same problem but worth the read anyway: viewtopic.php?t=25955
Thinking back a while, I did have a bit of a fiddle about with the "adjuster screw" on the steering box. The steering was exhibiting a noticeably amount of steering wheel travel before any actual turning effect and this was effectively eliminated after my trial and error method of adjustment. But my concern now is that I might have introduced a different kind of problem. Any thoughts on this?
My first thought was "Oh shit!". It's an area which many try to avoid. I have read a number of threads on various boards on the subject. It's not an absolute no-no but you need to be aware of what you're doing. Having said that I read on this thread that Brucie himself used a "highly unscientific method" [-o< : viewtopic.php?t=18036. It is suggested by some that it could cause premature wear and I suppose that if you take it up too much it could cause binding maybe.

The point about reading these other (sometimes seemingly unrelated) threads is that they get you thinking differently about your own problem and maybe inspecting things which you had initially discounted or overlooked.

By the way, I seem (he says cautiously) to have solved my own problem. More on that when I have the update ready.

Regards,
Martyn
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1986 635CSi
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Re: Hydro brake mystery

Post by ZesCoupe » Wed Aug 15, 2018 10:24 am

Hi everybody,

Well it's been a month and a half since I last posted about my problem. Since then it's been a complete roller coaster ride where just about everything has been disassembled, cleaned, rebuilt, whatever....

The last thing I discussed with Brucey was that the steering box was possibly faulty - going on the assumption that the pump was new (Meyle) and therefore OK. That being said I was still planning to look first at the pump and after canvassing my contacts I managed to get hold of a high pressure hydraulic test meter. Using various fittings we managed to set a Heath Robinson test rig connected to the pump and reservoir. Result - no pressure! So phoned the supplier - very friendly and helpful, not in stock but would send a replacement from Meyle a.s.a.p. It arrived a few days later and I returned the first one.

So fitted the new one only to find still no assistance - brakes or p/s. Back to the drawing board ](*,) - still going on the assumption that the pump was new and OK (you probably guess where this is eventually going). Next step then the steering box. Not to go into too much detail, the disassembly repair and reassembly are described in detail here and on other forums. It is for an E31 but the core components are the same. Unfortunately the rebuild kit from BMW is NLA, only the gasket kit is still available, this includes the seals and o-rings needed to reseal the box. I did manage to work out that some of the teflon rings needed are available with a part number that belongs to the older E9 and 2500 models. The o-rings from the set were on back order at BMW with no known date so I sourced them through a general supplier here in NL (Zamro).

Biggest problem with the breakdown was getting the arm off the output shaft. Pullers weren't going to make it so I ended up making a frame from some serious steel so that I could use the hydraulic press to press the shaft out of the arm:
IMG_2055.JPG
IMG_2055.JPG (134.61 KiB) Viewed 486 times
If you look carefully you can see that bits have been added to increase the strength vertically as initially it was just bending. Eventually it seemed strong enough and when the arm finally came loose there was a loud crack like a rifle shot - unbelievable! The rest of the the dismantling and cleaning was simple.

The rebuild went according to the online instructions and the neatly repainted box was re-installed. Result - nothing, nada, still the same so I got in touch with a guy in the north of the country who specialises in E28's (same chassis, same system). We came to the conclusion that maybe my rebuild was not quite good enough so I drove up to see him and picked up a used steering box. That was cleaned and installed. Result - no change :x

What now :-k .

To be continued...
Martyn
Last edited by ZesCoupe on Wed Aug 15, 2018 11:48 am, edited 1 time in total.
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Re: Hydro brake mystery

Post by ZesCoupe » Wed Aug 15, 2018 11:23 am

Phase 101 or so :(

Phoned another contact - Rini from Hydroline in Veenendaal NL (mentioned in the previous post to Phil). After another long discussion he was fairly adament that it could ONLY be caused by the supply side and that although apparently new there must be a fault in the pump. Supplier I bought the pump from (Offenga in Franeker - north of NL) were informed by Meyle that their pumps were new - not re-manufactured. Rini says categorically that there are no new pumps being made for these older models. The known large manufacturers are buying up old cores for re-manufacture and according to him most of the rebuild work is being done in Eastern Europe (cheap). They are reusing cores that are way past their sell by date and the work is sloppy. He said to look closely at the safety bypass valve - it could be stuck or not positioned correctly.

So pump again removed - by now getting really sick of the smell and feel of ATF. Dismantled the pump to find that he was correct. Firstly the by-pass valve was installed too low, the fluid could leak past the first ring of the piston meaning no-pressure build up. The photo's were taken later of my old pump as I had no use of the (phone) camera while working with dirty hands. This shows how the valve should be sitting and the piston retained by the clip should be able to move freely.
Photo 1.jpg
Photo 1.jpg (90.73 KiB) Viewed 484 times

Next I looked at the vane impeller side of the pump. When I got hold of the "butterfly" cover above the impeller I found that it could be moved 1-2mm side to side. This was not correct, it should be quite solid.
Photo 2.jpg
Photo 2.jpg (103.55 KiB) Viewed 484 times

After removing the cover I found that the whole assembly was even looser and that the pins were only marginally protruding above the steel cage. They should be long enough to engage fully in the cover.
Photo 3.jpg
Photo 3.jpg (89.68 KiB) Viewed 484 times

With the cage removed I found that the holes to retain the pins were worn and extremely loose for some reason. They appeared to have been drilled a little deeper in order to hold the pins a little better. They should sit quite firmly as in the picture.
Photo 4.jpg
Photo 4.jpg (107.75 KiB) Viewed 484 times
So having ascertained what was wrong I set about correcting it just as an exercise to prove if I was correct or not. Firstly the clip was removed from the bypass valve and the piston removed cleaned and tested that it was moving freely. Clip replaced at the correct level. Using some foil I then adjusted the height and stability of the positioning pins so there was no movement and replaced the cage and cover. Now it was stable as intended.

Pump back in the car, reconnected with new copper rings and started the refill procedure. After going through the procedure to expel all air in the system for a few minutes the oil in the reservoir settled down. The level had dropped indicating that the accumulator was charged and when I looked inside the car the brake warning light was out and I had brake assistance once more. Steering also felt good although the car was slightly off the ground. Emptied the accumulator, checked the level, cleaned the engine compartment and myself from any oil and took it for a test drive. Hey presto it felt like new again \:D/

This was yesterday and in the evening I sent a detailed email to the suppliers with the photo's telling the same story. This morning they phoned me very apologetically and informed me that this was the fourth time that they had similar experiences with so-called new Meyle pumps. They have deleted them from their catalogue. As I needed another core as my old pump is not completely usable we made a deal that they refunded me most of the costs and I can keep the pump to hopefully make one new one. The front body of my old one is perfect but the back isn't, also the 'butterfly" cover is damaged. So I shall try to use the front body of mine so that the pins are correct, the impeller/cage section, the "butterfly" cover plate and the rear body from the Meyle and that should be OK.

Just shows that:
  1. New parts are not always to be trusted
  2. First rule of Project Management - NEVER ASSUME
At least now I can almost call myself a guru on the H-31 system.

Regards,
Martyn
Last edited by ZesCoupe on Wed Aug 15, 2018 11:50 am, edited 1 time in total.
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1986 635CSi
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Re: Hydro brake mystery

Post by plip1953 » Wed Aug 15, 2018 11:40 am

Well done for sorting your issue :D

Maybe I should pay for you to come over to the UK to sort mine out :lol:
Phil
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