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From digest.v7.n282 Tue Sep 16 09:39:19 1997
From: Andrej Gaspari <>
Date: Tue, 16 Sep 1997 09:52:28 -0400
Subject: <E28> Brake bomb install

Here's the procedure (perhaps someone could add this to the FAQs?):

  • -Discharge the hydraulic booster system by pressing the brake pedal until the fluid level in the reservoir stops rising and the pedal gets rock hard.
  • -Make sure the regulator is spotless. Remove the hydraulic lines and the wires to the pressure switches. You do NOT need to drain the system - you will lose only a few drops of fluid. (1)
  • -Unbolt the regulator and remove it (the bomb is attached to the bottom.) Place the regulator in a vice. Use a strap wrench to spin off the old bomb. (2)
  • -Spin on the new bomb and tighten with the strap wrench.
  • -Replace the regulator and the hydraulic lines and wires. Top off the fluid if necessary (10mm from the top of the reservoir with the system totally discharged.)

(1) Use a flare wrench to remove the hydraulic lines. If you don't have metric wrenches, SAE flare wrenches will work.

(2) Some people prefer to remove the bomb with the regulator in the car. If you choose to do this, make sure you brace regulator adequately, as the mounting bracket is not very strong.

I also suggest that you replace the pressure switches at the same time - they seem to wear out and start to leak regularly. You cannot put them in the wrong positions - the threads are different.

> Sorry for the WOB, but does anyone have available the procedure for
> installing a brake bomb on a 1985 535i? Or, can anyone reference the
> Digest listing that carried the procedure? Also, I have been told that
> the swap can be made with everything left in place (including the brake
> fluid reservoir) - can anyone verify this?

  • --
  • -AEG

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