hard to diagnose brake issue

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e24nut
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hard to diagnose brake issue

Post by e24nut »

i have had my e24 for several years. when I purchased it I occasionally noticed when I applied the brakes after the car had been parked that as pressure was applied on the pedal I would feel a slight resistance in the pedal travel that would only happen on the first application of the brakes. I assumed it was a faulty or sticking brake caliper piston and had BMtech in Melbourne look at the issue. they replaced the accumulators and had the calipers reconditioned - but no problem was found. I have also noticed that when driving then car on a slight decline with the brakes on that the pedal travel gradually increases which is unnerving but braking would stop the car normally. I raised this issue with BMtech and they insisted that the brake function was completely normal. during this period I also had the common leaking master cylinder seals so I decided to replace the master cylinder with a new unit.

So, new discs, reco calipers, new accumulators and master cylinder but the above mentioned symptoms slight resistance mid pedal travel and increased pedal travel while applying brakes gently on long downhill roads (but still normal stopping power) still persist.

Yesterday I noticed increased pedal travel while driving in traffic which progressively got worse tho the point that the car would stop with decreased braking performance and pull to the left as that happened. this persisted for a few minutes and the brakes then randomly returned to normal function and are still working fine. brake fluid is clean and reservoir levels normal - no leaks detected.

So I am at a loss with how to deal with this. I took the car to the local brake place and they couldn't fault it. I have replaced just about the entire braking system and the same symptoms persist. my gut feel is that it is a sticking piston on one caliper - but would this cause the pedal travel to dramatically increase? Both front calipers have been reconditioned. I even had bmtech remove the caliper and return it to the reconditioner to have it checked - no problem.

anyone had a similar issue or any advice or ideas?

much appreciated

Nut
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Re: hard to diagnose brake issue

Post by GazM3 »

Assume brake fluid is replaced and flushed clean. May be a sticking caliper/s especially if it pulls to one side and there is increased brake dust on the wheel of the offending side
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daz635
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Re: hard to diagnose brake issue

Post by daz635 »

Did you change the brake lines. Sometimes the brake lines can look ok on the outside but have collapsed internally acting like a check valve when hot and not releasing pressure.
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e24nut
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Re: hard to diagnose brake issue

Post by e24nut »

Thanks for that.I replaced the hoses about 4 years ago with bmw genuime parts. I hope i will get a few more years out if them . The old ones had blistered...it could explain the poor function and pulling to the left though

It still does not explain the pedal travel and the little clunk when i press the brake the first time after startup that jas been present since i bought the car

Thx

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Re: hard to diagnose brake issue

Post by Brucey »

"the little clunk" only has one cause; it is the pushrod from the brake servo making contact with the back of the MC. IME this either indicates that the servo is faulty, or the MC is not returning fully.

If the servo is not working properly then the brake effort will be higher than normal. If you have not done so as yet, check the basic function of the hydraulic system that powers the servo.

1) run the engine for a few minutes and turn it off

2) remove the cover from the hydraulic reservoir

3) eyeball the fluid level inside (if necessary remove the mesh screen to see the oil level). The oil level should be low.

4) with the engine still off, Apply the foot brake (with a significant pressure), whilst an assistant observes the reservoir. Each application of the brake should discharge oil into the reservoir, raising the level

5) after 12-20 applications of the brake the oil discharge should cease and the pedal should firm up. The reservoir should be brim-full of oil.

6) start the engine; the oil level should drop to its normal (low) level in about 15 seconds. If it does not drop then (for whatever reason) the 'bomb' is not being filled with oil.

A common fault with the brake system is that 'the bomb' fails and this means that after one application of the brakes there is no oil pressure other than what is generated by the pump at that moment. On a long twisty downhill run (in a car with an autobox especially) the engine may not be turning very fast and in combination with a small fault with the pump etc a failed 'bomb' and the demands of the steering box, the hydraulic system may fail to generate enough pressure to work the brakes normally.

However this would not explain the long pedal, or the pulling to one side. The only things that are very likely to cause these things is a fault in the MC, or possibly some other cause of brake dragging.

One of the many common faults with the MC is that the compensation ports are drilled at an angle and left knife-edged. This can shave parts of seal off every time the brake is used, leaving the MC full of rubber shavings that will eventually stop the brakes from working. An erratic long pedal and pulling to one side may result if a shaving gets trapped in the poppet valve (not all MCs) in the compensation port for front piston in the MC. It is possible that the MC may not return fully anyway if the MC is starting to stick.

If the servo is faulty it may be leaking ATF into the space between the servo and the MC (there is a drain hole but this may be partly blocked; IME the first seal or part that fails on the servo is the oil seal around the pushrod). If the phenolic guide bush in the back of the MC is soaked in ATF and/or brake fluid, it can swell up, resulting in erratic sticking of the MC, mainly when the MC is hot.

If the MC sticks (or sticky caliper piston, or failing brake hose) some or all of the brakes will drag and this means that they may get so hot that some boiling occurs in one circuit. This will also make the bake pedal long (on repeat application) if the boiling manages to open a compensation port briefly and pushes fluid through it. [If the brakes have been dragging the discs will be unusually hot when you stop.]

IIRC there is a small oil filter at the entry into the brake servo. This should be checked, as should the pushrod seal. It goes without saying that the pushrod seal only sees whatever back pressure is in the return line for the oil that is discharged from the brake servo; this pressure should be low but if the return line is clogged for whatever reason, (or the breather in the top of the ATF reservoir is clogged) then the back pressure will be higher than normal which will result in oil burping past the pushrod seal, even if it is in good condition.

I hope this has given you some ideas of things to check.

cheers
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e24nut
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Re: hard to diagnose brake issue

Post by e24nut »

Thanks Brucey. Much appreciated
Nut
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e24nut
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Re: hard to diagnose brake issue

Post by e24nut »

Thanks for all the great advice. after much investigation and implementing brucey's recommendations, I have found that the left front caliper is slightly gripping causing it to overheat and is consequently boiling the brake fluid in the caliper and reducing its performance. this explains excessivH pedal travel and pulling to the left. here is the issue. I have had this caliper reconditioned twice, no, 3 times by my BMW mechanic. I have returned it faulty and both times, I have got the car back and the brakes are "working fine" but the problem keeps reoccurring. should I recondition again or replace the entire caliper with a new unit. any thoughts?

apart from this I have replaced all brake lines, new servo and master cylinder 12 months ago ( the slight clunk in the pedal on startup has happened since I purchased my shark 7 years ago.

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daz635
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Re: hard to diagnose brake issue

Post by daz635 »

Have you checked the length of the shackle from your brake pedal to the booster. Being a RHD late car I assume the booster and master cylinder are both on the RHS.

If this adjustment is out it can cause the booster to pressurise and activate the master cylinder slightly when the car heats up. This can cause the calipers to stick on

Even a couple of mm can cause a slight issue. Having changed the master cylinder and booster, the length of the rod and shackle may have changed.

Good write up half way down the page 3 here by JCS and Brucey

http://bigcoupe.com/phpBB3/viewtopic.ph ... r&start=50

Easy way to test. Wait until caliper is dragging and pull clevis pin at brake pedal to see if it releases.
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e24nut
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Re: hard to diagnose brake issue

Post by e24nut »

Thanks daz

If the shackle length was incorrect would that lead to dragging on one brake only? Interestingly the front left caliper is clealy a problem as the disk temp is some
40 degrees hotter than the right. I havent been able to drop the clevis pin out of the shackle as yet but i am wondering if this was the problem would all of the brakes would be sticking?

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Re: hard to diagnose brake issue

Post by e24nut »

Brucey i have checked the servo function and is behaving as it should. The little clunk which from your advice is the servo pushrod has been with the car since i bought it 8 years ago and the bom. Since then i have replaced the mc 2 years ago as well as brake lines. I have tried at least 5 time to get an explanation from bmtech who report back that brake funtion normal. Is the pushrod issue serious? I only happens after the first application of the brakes after starting i asked bmtech on many occasions to try to explaing the clunk (servo pushrod) but they never have been able to identify it. I have had the front calipers reconditioned but after i discovered that the left front caliper was sticking i took it back to bmtech who sent the caliper back to the brake reconditioning subcontractor it was returned "no fault found". Bmtech thought it may be a bad set of pads and replaced them under warranty - after that they reported that the front left was ko longer dragging. But clearly the fault has not been identified. I am reluctant to take it back as the expense of tracing such a fault i think may be prohibitive. Is it possible that the brake pedal "clunk" after starting is a sticky caliper piston releasing when cold and then inteittently sticking? If i check the small filter you describe will that show any seal fragments as you described. If the servo is performing normally as per the check procedure is the pushrod problem an issue given that it has been happening for many years? I am wondering if i should replace the entire caliper on the front left to see if that fixes the problem before ndetaling a detailed and expensive analysis of the entire brake system ? Interestingly, i took my shark on a 300km trip yesterday and brake function was fine in both heavy traffic and in the highway at 110 km/h. The fault did not reoccur at all except that on return i found that he left disk was 40°c hotter than the right s clearly the problem still exists but its severity has dminished. Sorry about the ling reply but this one has got me stumped and your response has been the most insightful given the frustration i have had trying to get my mechanic to explain. Having said that bmtech have looked after the car for many years and i trust them. But not getting any joy on this. I appreciate you advice on this
Cheers
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daz635
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Re: hard to diagnose brake issue

Post by daz635 »

I feel your pain and frustration mate
Took me 2 years to sort out my braking issue.
Mine was similar to yours in that my left hand calliper was sticking when the car heated up. Mine was sticking badly eventually causing the steering to shake and boil the fluid in the calliper. Yours is evidently not sticking as bad as mine which is going to make it difficult to diagnose.
When I first purchased my car it had this issue and my mechanic changed the master cylinder and it fixed the problem. Two years later the issue was back again. Went thru everything the same as you lines, callipers, discs, bomb ect. In frustration I replaced the master cylinder again and bingo problem solved.

As brucey has said above any foreign material inside the cylinder can cause it to stick causing one of the ports to be partially blocked.

In answer to the above question yes if the rod is slightly out of adjustment only one caliper will start to stick on not all of them. It usually will happen when the braking/steering system heats up and the fluid pressure increases

If you are not having any joy with Bmtech can I suggest you contact Addam Smith at BMWrecking on the Gold Coast and have a chat. He is an absolute expert on these cars and their issues and willing to help anybody with problems.

https://www.facebook.com/BMWrecking-Gol ... 960016698/
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Re: hard to diagnose brake issue

Post by cgswift »

Nut,
When you found the front caliper had increased 40C, by chance did you record any temperature change in the opposing rear caliper as well? If not, this should rule out the master cylinder as the culprit. Interesting issue, you have my mind tumbling. Toph
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e24nut
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Re: hard to diagnose brake issue

Post by e24nut »

Hi toph. Both rear brakes are consistently about 45° centigrade. Interesting. Definitely only the front. Funny thinh is that even though the caliper is sticking you wouldnt notice it driving the car. Thanks
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Re: hard to diagnose brake issue

Post by e24nut »

Thanks daz. I had a long chat to joe brogno at bmtech and showed him your correspondence. Will be going in for a further inspection in early jan.
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Re: hard to diagnose brake issue

Post by Brucey »

I agree it is sounding more and more like a MC fault. The reason you get one brake only dragging when the MC goes faulty is that

a) the rear brakes don't come on at low system pressures (there are brake bias valves that ensure that this happens on all E28-based models apart from M635CSi/M6 versions) and

b) the two compensation ports in the MC don't open at the same time as one another.

The MC commonly goes bad through the bushing at the rear of the MC swelling up and binding. This at first manifests itself only when the MC gets hot (in traffic) but eventually it will be all the time. One front brake drags (it is most often the RH one but this may vary) except when everything is stone cold. The calipers can be exchanged or rebuilt and this makes no difference.

You can diagnose this issue by relieving the pressure in the affected brake circuit; just slacken the relevant union on the MC and let a little fluid out into a rag and the problem may have instantly cured itself for a short while.

The bushing at the rear of the MC swells up because it is either contaminated with brake fluid or ATF from the servo. If there is any kind of a leak in this area a MC could go bad in a year or two. If you can remove the bushing (not easy) and machine the bore a few thousandths bigger then this may cure the problem too, at least for a while; the bushing may continue to swell over time.

The 'clunk' on first application of the brakes indicates a faulty MC and/or a faulty servo.

My suggestion is that you replace the MC and the end seal in the servo; also make sure that the drain hole between the two isn't blocked. Worst case is that you have a spare (good) MC and you have wasted a few quid on a small seal.

hth

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e24nut
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Re: hard to diagnose brake issue

Post by e24nut »

Brucey - thanks for your reply - I think you have nailed it and what you describe is exactly what is happening with my e24. I have had the caliper recoed twice and the fault only occurs with when the car heats up in traffic. unfortunately I had problems with the seals on the MC causing cavitation in the hydraulic fluid which made the power steering make a ridiculous noise and I had to replace the MC (1500aud) 3 years ago. I will use your note to clarify the issue with BMtech who haven't been able to diagnose the problem. looks like another expensive repair!

thanks again
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Re: hard to diagnose brake issue

Post by Brucey »

the PAS hydraulic system is completely separate from the brake MC; the only commonality is that the PAS fluid is also used to operate the brake servo (booster) which is bolted to the brake MC. At 1500 AUD and with those symptoms that sounds like a price for a new servo (or other part of the PAS/servo system) rather than a new MC per se. It would be helpful to know exactly what has been done to your car.

The most common causes of noise/cavitation in the PAS system are

1) an air leak on the feed line to the pump or

2) a clogged filter at the exit of the PAS reservoir

But if the fluid level is low (and NB checking the level in the reservoir requires a special procedure), or air gets into the system it can make a terrible noise; bubbles don't immediately settle out of the oil (even when it is hot) and if frothy oil passes through the pump it makes a terrible noise.

Unfortunately the number of people that understand these cars very well is very small indeed now (if it was ever large... :roll: ) and the process of playing parts change bingo is getting both difficult and incredibly expensive. You would be amazed at how many people have changed out their PAS pump, PAS box, etc when really they needed a new filter or a new feed hose, or just the clips being properly tight on the old one.... :roll: .....

Anyway, do the test I have suggested in which you slacken a brake pipe union on the MC and see if that makes any difference; if it does then the brake MC is bad. [BTW If you don't know which pipe is which, the pipes are marked at the ABS unit.]

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Re: hard to diagnose brake issue

Post by daz635 »

Totally agree with Brucey

The number of people that actually worked on the car when it was new or have experience with it is tiny in Australia due to small numbers in which it was sold in this Country

Even some BMW shops are going to struggle if they have no experience with the left of field issues that this car has. Plus changing parts to try and fix a problem without diagnosing the exact issue is going to get very expensive, very quickly

E24 Nut are you on the Australian E24 Owners Facebook page. Somebody may be close to you and come and offer some advice / help. They are all extremely helpful

https://www.facebook.com/groups/AussieSharksE24/
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e24nut
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Re: hard to diagnose brake issue

Post by e24nut »

Problem solved even though the mc was reconditioned 3 years ago i decided to replace it with a new unit. After sourcing one in germany and waiting a month for delivery all is good! Thanks to all who offered advice!
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Re: hard to diagnose brake issue

Post by Brucey »

glad it is fixed now; the slight mystery is that the previous MC went bad so quickly. I wonder if there is a weep of PAS fluid from the servo that is getting onto the guide bushing at the back of the MC and making it swell up; I have seen this before.

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Re: hard to diagnose brake issue

Post by e24nut »

I think that was the issue as the mechanic at bmtech thought it was probably a seal related issue. To their credit they didnt charge me for labour due to the number of unsuccessful attempts at a fix.

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