How to Change Brake Fluid

or Bleed your Brakes

From: joe@senner.org (Joe Senner)
Subject: Re: BMW: Bleeding ABS I Brakes
Date: Wed, 16 Aug 1995 17:41:49 -0500 (CDT)

]a) Do I bleed the modulators before or after the calipers. My impression from
]the Haynes manual is that the modulators are first but I'd rather ask the
]experts (and I got confused moving back and forth between the chapters).

You'll want to pull new fluid from the master cylinders (hand/foot) through the system, extracting at two points, the modulators and the calipers.

Drain or otherwise extract the bad fluid from the reservoir. I soaked it up with a wad of paper towels. You don't want to pump more bad fluid through the system. Refill with new fluid.

Set the lid back on, or cover with a rag. When you pump the lever, fluid will squirt out!

Watch the fluid level and _don't_ let it go dry. You're starting over if that happens :-)

Attach your drain hose to the modulator bleed screw and crack it open with a 10 mm wrench. If you're using just a plain old hose to bleed with, apply pressure to the brake lever and crack the bleed screw open just a little until fluid begins to flow. Close the bleed screw _before_ your lever is all the way to the end of its travel. This prevents you from sucking air back into the system.

If you're using a valved drain hose, you can pump the brake lever at with the bleed screw cracked open slightly and get the fluid flowing. The one way valve will prevent fluid/air from sucking back in when you release the lever for another pump. The valved bleed hose works best if you put some teflon tape on your bleed screws (removing them all the way, obviously). I've done it without though.

If you've got a vacuum bleeder, start sucking on the nipple until you see clear fluid :)

When you're getting clear fluid out of the modulator, move your hose attachment to the caliper and go at it again.

]b) How much DOT 4 brake fluid am I going to use (more or less)? I don't want ]to run out halfway through the job.

I didn't use all of one normal sized bottle, can't remember how many ounces, but they're common. Not much bigger than your hand. 1 pint?

]c) Are there any common errors/ "gotchas" that I should know about before I ]begin?

Brake fluid eats paint. Just keep that in mind, and take your time.

--
Joe Senner
K Whiner MC#3

 

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