Re: E28 Brake bomb

[Jerry Chyo <jerryc@xxxxxxxxxxxx>]

At 07:16 AM 11/18/98 -0500, John wrote:
>I know I don't have an E36 ///M3, Z3, ///M Coupe or Roadster, or other "late
>model" Bimmer, just a "lowly" E28 (they rule you know!)...but I received only
>"one" response to my request for assistance on my brake telltale lighting
>up/ATF loss in the Power Steering reservoir (prior to calling my mechanic).
>Please set aside the beers Bubbas and try to help me on this one!!!!!!  

Stop it John :^0.  Seriously, sometimes you have to post more than once to
get a response.  I would have responded earlier, but some *guy* has been
taking up so much bandwidth talking about intake dynamics and leafblowers
that I probably cruised right by it....and if you ever say "lowly E28"
again, I'll send the E28 police to take your car from you.

>My car appears to have a leak somewhere in the power assist for my brake
>system.  The brakes operate "perfectly"..no hard pedal, no travel to the
>floor, etc.  just the dumb brake warning light coming on after the car has
>been driven some...it usually comes on "without" depressing the brake pedal
>even!

SOunds like a brake bomb.  My car is doing the same thing right now and a
reviewed the archives last night (a pretty good place to start when you
have a problem) and this is what I found out.  The first thing to test is
whether your brakes are hard to push right after you turn the engine off.
The bomb is supposed to save up (hence "accumulator") pressure (up to 1000
lbs.) in the event the engine shuts down while you are driving.  This
allows youto have power assist even when the motors off.  If you have no
power assist when the motors off, it isn't saving up pressure.

>I crawled under the car last night to inspect where the ATF fluid is coming
>from and found the underside of the floor pan soaked with something...ATF I
>assume, BUT looking at all the hoses and fittings, including the underside of
>the brake booster and the master brake cylinder, they looked dry as a bone!
>The brake fluid is not leaking either.

Thats a good sign.

>The only place that looked wet at all was the brake "bomb" (all grimy on the
>outside surface) and the pressure regulator (grimy too) where the low and
high
>pressure switches reside.

Thats not a good sign.  Mine's ugly right now too.

>If the booster was leaking how could the bomb be all grimy(it resides above
>the booster as you know)?  

If the boosters leaking too, then the bomb must be leaking.  I would bet
your bomb is shot.  Seems like theres a question on this every week.

>Is it possible to have a leaking brake accumulator "bomb" that still
functions
>well enough that the pedal feels completely normal?

Yes.  It doesn't really do anything until the engine gets shut off (if I'm
wrong, soeone educate me so I don't kill myself thinking my brakes are okay
for the rest of the week).

>The brake fluid reservoir is "full", and if not for the ATF leak I'd think
the
>sending unit on the brake fluid reservoir had gone south.

You must have a 528e.  The big six cars don't have ATF.  If you have a big
six, that's not ATF.  You should also replace the filter in the bottom of
the hydraulic fluid canister while your at it.

>I would really appreciate some input on this....if it's an easy fix like
>replacing the brake bomb and a couple switches, I'm up to the task, but I
>don't want to fool around with the big $ items like the regulator or the
brake
>cylinder(just yet anyway!)

Hope this helps.

Jerry Chyo
'88 M5
'72 tii

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