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Brake fluid/E36 ABS bleeding
Greetings,
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...
Herman
********** Message follows **********
Date: Fri, Jan 13, 1995 11:30 AM PST
Subj: 3-series brake info.
To: HermanC2
Herman,
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 3 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!
Happy Motoring!
Michael