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Brake Fluid Recommendations and Bleeding ABS

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Boggie
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Brake Fluid Recommendations and Bleeding ABS

Post by Boggie » Fri Aug 17, 2018 7:28 pm

Hi All,

I am halfway through the M635 brake refurb. New BMW MC and all new steel lines, custom Goodridge SS hoses, rebuilt and coated calipers, EBC discs and Redstuff pads etc. The only things I will retain are the ABS unit and fluid reservoir (currently in the dishwasher with the washer bottles- don't tell the wife).

Couple of questions please: Any recommendations on what (UK available) fluid works well in these cars and are there any special procedures to bleeding a car with ABS system (this is my first 'modern' car restoration)? I will be on my own so was going to use my EasyBleed (I.E. pressurise the reservoir). I have researched both questions but have conflicting results. You guys are more likely to have the right answers... :)

Cheers,
Ian
1985 M635CSI
Classic Car Collector & Restorer.

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Brucey
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Re: Brake Fluid Recommendations and Bleeding ABS

Post by Brucey » Fri Aug 17, 2018 10:45 pm

if the system has been broken apart completely the ABS system will probably have air in it (in contrast to 'a normal bleed'). This air won't wholly come out unless the ABS pump is used, ideally during the bleed procedure. There is a whole piece about this in the workshop manual, and I think there is a special test unit that feeds the ABS computer dummy signals so that each channel can be actuated separately.

If you are not able to find a way to run the pump but you are able to get a pedal that feels a bit like a brake, you can provoke the ABS unit to work by (say) driving the car on wet grass and deliberately locking the wheels. This only works above 15mph, so try to be safe doing it. It may also be possible to run the car up (in gear so that the rear axle is doing >15mph) on axle stands and provoke the front ABS that way when the brakes are applied.

BTW M635CSi brakes have no compensation valves in the rear lines so bleed easier, but (in contrast to other E24) the rear brakes come on even at the slightest brake application.

If you have a vacuum pump, this can be a useful diagnostic tool; if the fluid level in the reservoir appears to rise when it sees vacuum, it is a pretty fair bet that there is air somewhere in the system. Repeat applications of vacuum will often pull air out of crevices in the system in a way that won't happen using other methods.

Re brake fluid, there are lots of fancy fluids out there but few have much real advantage over glycol based fluids like DOT4 or DOT 5.1 and retain full compatibility with seals and the ABS system. If you plan to adhere to the recommended fluid change schedule in future, a standard fluid is probably the best idea.

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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Boggie
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Re: Brake Fluid Recommendations and Bleeding ABS

Post by Boggie » Sat Aug 18, 2018 9:21 am

Thanks Brucey!

Great info. I particularly like the idea of running the car on stands (my car is currently on 4x 6 ton lorry stands) and fooling the ABS unit into thinking the wheels have locked. Will the fact that the fronts are not turning but the rears are be enough to trigger the ABS pumps or does the unit have to see the fronts spin then stall?

As I am now not replacing the lines from master cylinder to ABS unit (they are in excellent condition - if it ain't broke...) I was hoping not to introduce air into the ABS unit but changing the MC may be a problem.

DOT 5.1 is probably the way to go due to the higher boiling point and my local Halfords has the Comma 5.1 in stock.

Will let you know how I get on.
Cheers,
Ian
1985 M635CSI
Classic Car Collector & Restorer.

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Brucey
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Re: Brake Fluid Recommendations and Bleeding ABS

Post by Brucey » Sat Aug 18, 2018 9:45 am

Driving the car on wet grass certainly gives the ABS system a workout but I have never had to do this on the stands so I don't know what the ABS system will do exactly; it is possible that it will just flag a fault if the front wheels are not turning at the same speed (the symptoms are, so far as the ECU is concerned, indistinguishable from sensor failure, and this I have seen; the ABS light comes on above 15mph; whether this leaves you with any ABS action or not I am not sure).

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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Boggie
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Re: Brake Fluid Recommendations and Bleeding ABS

Post by Boggie » Sat Aug 18, 2018 11:05 pm

Interesting information in the BMW E24 Manual I found a link to. It says you connect the charging system (I.E. Easy Bleed) to the MC, push and hold down the brake pedal, open the bleed valve on the furthest caliper away (presumably with bleed pipe attached and submersed), pump the brake 12 times then close the valve and move to the next caliper. Going to need to enlist the other half to help out...

Will let you know how I get on.
1985 M635CSI
Classic Car Collector & Restorer.

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Brucey
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Re: Brake Fluid Recommendations and Bleeding ABS

Post by Brucey » Mon Aug 20, 2018 8:54 am

IME that prodecure should work OK when the system has not been completely broken apart, and it is certainly the thing I'd do first.

However when the system has been apart (for weeks or months) there is more danger of there being air in the ABS pump (and a certainty that there is badly moisture-comtaminated fluid within it) and this doesn't always make its way out of the system under its own steam.

http://www.stoptech.com/technical-suppo ... ke-systems

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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Boggie
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Re: Brake Fluid Recommendations and Bleeding ABS

Post by Boggie » Tue Aug 21, 2018 7:35 pm

I have a pedal!
Don't know what you guys were worried about.... :)

I used a pressurised EasyBleed system at 20Lb/Sq" and bled the system as a 'normal' car. IE started at the furthest wheel, left rear then right rear, left front and so on. Initially I thought I was in trouble as the left rear was not bleeding as I expected. However, upon inspection I have a blocked nipple (no breast-feeding jokes please). Once I had swapped it for an old spare the whole system was bled in around 20 minutes. I am very happy to say that I now have a nice firm pedal and all 4 calipers are grabbing discs.

Brucey, thanks for the link below. I still have around a litre of premium DOT5.1 so once I have the MOT I will get the car out somewhere quiet and low traction (there is a nice gravel lane near me) to cycle the ABS a few times. I have ordered a new set of nipples and dust caps from BMW as it looks like someone has taken a set of mole grips to a couple of mine. When I fit them I will have to do a minor bleed anyway, just to ensure I do not introduce air when I swap them over. So, pushing through the remaining new fluid would seem to be a good idea (especially as the container has been opened).

Incidentally, whilst I had the reservoir under pressure, I flushed through the clutch system. You should have seen what came out! It looked like someone had washed muddy hands in a pint of cloudy cider. There were lumps of god knows what in there. I hope this might make my clutch feel better and raise the biting point to a sensible place (rather than near the floor where I often stall).

I now have one day to fit the reconditioned diff, sort out the Heath Robinson washer wiring, fit the new BMW in-tank lift pump and do a little bit of welding. Then it should be a simple matter to bolt on the new BBS 009/010 wheels, get him back on the ground and fit number plates before taking a drive to my not-so-local tame MOT guy.

Happy days...
1985 M635CSI
Classic Car Collector & Restorer.

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