Re: Is it the "bomb" or master cylinder? 5000

[Kneale Brownson <knotnook@traverse.com>]

The brake pressure accumulator (aka the "bomb" because half its innards are
under pressure) stores pressure for supplying boost to the brake system,
Gregory.  A bad bomb has limited or no storage.  You can test the bomb by
running the engine briefly so the pump can take it to maximum pressure,
shutting down the engine and pumping the brake pedal repeatedly.  A good
bomb will give you twenty or more pumps before the pedal becomes very
stiff.  The idea is that if you lose engine power under an emergency
braking situation, you'll still have power braking.  

If your bomb tests good, you may have a bad master cylinder, a bad booster
or a combination of the two, as I understand it.   If you want to take the
cheapest approach in the event the bomb is OK, some here have advocated
replacing the booster first because it's the least expensive.   When I
replace mine, I'll do both.

Kneale Brownson



At 10:31 AM 6/12/99 +0000, Gregory Dillon wrote:
>Over the last three weeks I've had symptoms of brake problems.  I believe I
>need to change either the Master Cylinder or the "bomb" (what a name).  But
>which?
>
>Here is what has happened.
>
>The Check Diagnositics graphics showed the picture of the "bomb."  I added
>petrosin fluid, it was at the min mark and problem seemed to be corrected.
>
>Twice in as many weeks when stuck in traffic jam type traffic for over 40
>minutes, -stop, shift, start, stop, swear . . .- my brakes have gone from
>stopping at the top of pedal travel to more that half way to the bottom.
>
>Second time, again in long traffic jam same thing.  Brakes only stopping
>near bottom of pedal.   I turned off the car checked fluids and
>temperatures.  Again the brakes fixed themselves somewhat and improved more
>as I drove home.  Back to normal the next morning.
>
>Yesterday, the "bomb" graphic showed for a second, and then turned itself
>off during the auto diagnostic startup functions.
>
>Should I change the bomb or the master cylinder?
>
>Greg Dillon
>
>