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Date: Tue, 5 Dec 1995 10:26:12 -0500
From: (Pete Read)
Subject: Bleeding ABS Brakes

igor kogan asked:
>Can somebody tell me is there is anything special about bleeding
>brakes on 1991 M5. I understand that it is a ABS and never did
>anything with ABS before. May be there is a FAQ on the subject

I've changed/bled my E28 M5 brake fluid six times in the past 18 months (for driver's schools). No problems to report using both the standard foot pump (two person) method and more recently, the EZ Bleed that uses tire pressure (left front reduced to 20 psi).

With either method, I run clear hose from the bleed nipple and submerge the open end in the catch container brake fluid so air can't be drawn back into the caliper. The EZ Bleed still needs some foot pumping to speed things up. Just open the bleed nipple and assist by pumping the brake. Increasing the pressure beyond the recommended 20 psi may eliminate the need for foot pumping, but I haven't tried.

The Gunson EZ bleed cost $33 from:
John Abbot, Auto Expert Products Co.
Boca Raton, FL
Ph: (407)483-7898

Your specific question about special ABS bleeding methods has been asked several times on the BMW-digest list. I've been working my way backwards through the archived files. I cut and pasted the following answer in my personal notes as it seemed to make the most sense.

Copied Message from the BMW-digest list

>Subject: Brake fluid/E ABS bleeding
>Following are comments from an ITT/Teves (OEM brake supplier) employee
>to questions I posed on Ate Super Blue brake fluid and bleeding the E36
>brake system with ABS. Thought the list might find it interesting...
>********** Message follows **********
>Date: Fri, Jan 13, 1995 1:0 AM PST
>Subj: 3-series brake info.
>To: HermanC2
>Ate brake fluid is glycol based. We at ITT take a rather dim view of
>silicone based brake fluids; the compatibility between your ABS and
>silicone brake fluid is not the greatest. It turns out that the
>hydraulic control unit of your ABS was designed to work with
>conventional (DOT 3 and DOT 4) fluids; silicone fluids can affect
>the sealing performance of some of the internal valves over time. By
>the way, the same applies for other ABS units (Bosch, etc.) too:
>Use only DOT or DOT 4 brake fluid (DOT 5 is the silicone fluid).
>DOT 4 is similar to DOT 3, with the only real difference being a
>slightly higher boiling temperature with DOT 4. Any brand name DOT 3
>or 4 fluid is fine. The newer the can, the better, and don't leave
>the can open in your garage -- it will soak up moisture from the air.
>(That's why you always see the warning "use only brake fluid from a
>sealed container").
>When servicing 3-series brakes, there is a special (dealer) tool
>available to bleed the brakes. It works by talking to the ABS
>controller and putting the ABS into a special "bleed" mode, cycling
>the ABS valves and running the pump.
>Needless to say, the tool is not exactly cheap. Happily, IT IS
>possible to replace the brake fluid in a 3-series by just bleeding
>out each caliper individually and topping up the master cylinder
>(that's what I do on my own car). As long as the system is never run
>dry of fluid, you don't need to worry about bleeding the ABS unit.
>However, if you do happen to run the ABS unit dry, the unit will expel
>any trapped air when the ABS is activated. This air, which has now
>moved from the ABS unit to the brake lines upon ABS activation, can be
>then removed from the brake system by bleeding conventionally at the
>calipers. Try about 6 ABS stops or so, on the slipperiest surface you
>can find, to bleed the ABS unit. BE EXTREMELY CAREFUL and CAUTIOUS
>when attempting this; the ABS AND THE ENTIRE BRAKING SYSTEM WILL act
>strangely when you do this.
>Be sure to follow the owners manual recommendations for brake fluid
>replacement; the brake fluid naturally absorbs water over time,
>lowering the boiling point of your fluid and eventually causing
>corrosion of the brake system. Excessively dark fluid is bad,
>indicating moisture or other contamination. Replace it! Note that
>your owner's manual does not allow DOT 5 fluid!

End of Copied Message from the BMW-digest list

Pete Read
88 M5

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