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Type 44 bomb replacement & brake question
At 11:35 AM 10/4/1998 -0400, you wrote:
>Mike,
>
>Question, how were you able to figure out whether problem with you brakes
>was the bomb or something else. I have an 84 5ks, and I sometimes have to
>push the pedal all the way to the floor for the brakes to engage, and other
>time not. I can usually reproduce it if I push the brake pedal down
>slowly. Is this symptomatic of a bad bomb? Thanks in advance for your
>help, I just saw your post, and thought you would be a good person to ask,
>since you've recently been through this sort of thing. BTW, I'm relatively
>new, just signed up mid-summer, and mostly just read posts, trying to
>collect knowledge. When I do post its usually a quesiton, hopefully soon I
>will be able to end the one way relationship. Anyway, if you could help me
>out, I'd be grateful.
>
>Thanks again,
>
>Steve
>
>PS- as a college student, I must ask, how much does the bomb cost? :)
>
Steve -
Don't feel bad about being new at this - we all started there once (except
maybe Phil Payne, who was evidently born with a microfische in his mouth .
. .).
What you are describing is more indicative of a bad (failing) master cylinder.
Step one is to carefully bleed the brakes - the rears are a little tricky
since the compensating valve (just in front of the left rear wheel) tends
to trap air. If this cures the problem, great! You'll need another person
to help you - it's a little difficult to be both in the car pumping the
brake pedal and under the car opening and closing the bleeder screws (SOAK
them in penetrating oil before you start - if you break one off, you'll
need a caliper).
What I usually do is go to one of the tire places, let them put the car up
on a lift with me in it, and I pump while the monkey lad opens and closes
the bleed screw. They are morons, but in this case there is only one moving
part at each wheel, so they can figure it out.
Changing the master cylinder is no big deal. They cost about $50 from
Discount Auto parts, Pep Boys, etc. If you get this just right and are even
a little bit lucky, you won't have to bleed the brakes. (Advise you do it
anyway.) Sinking pedal indicates bad master cylinder. If you can pump it up
and it is then OK for one or two immediate brake applications, it is air in
the lines (bleed).
The bomb is a pressure accumulator. Whether it is good or bad does not
affect pedal position or repeatability, just pedal effort. To check the
bomb, drive the car, park it and turn it off. Apply the brakes until the
pedal feels "hard" - it is a very distinct feeling. If your bomb is shot
(and on an 84 it probably is - they seem to last about 7 years), the pedal
will become "hard" in 10 or fewer pumps - in fact, if the bomb is
completely shot, it will be hard all the time - you essentially have NO
power assist. Good bombs give 25 or so pumps before the pedal gets hard.
The reason they used this system is that most of these cars were turbo. In
regular cars, manifold vacuum is used to draw the fuel-air mixture into the
engine - turbo cars have a pump (the turbo) to FORCE the fuel-air mixture
in, so you get more horsepower, but you also have positive pressure in the
intlet manifold. There is no convenient vacuum source on turbo cars, so
Audi used a hydraulic booster instead of a vacuum booster for the brakes.
Works very well, it's just different (and more expensive to fix).
It is unfortunately possible to have all three of these problems at the
same time - replace master, bomb and bleed brakes needed. Another failure
mode for the master cylinder is the brakes drag after driving for ten or
twenty minutes - this is a failed check valve in the master - cure is
replace the master. These cannot be successfully rebuilt in the field, so
don't waste time trying, even if you can find a kit. Just replace the
master with an aftermarket (guaranteed) rebuilt, bleed the brakes, and from
your description, that should do it.
Incidentally, I've owned almost 100 cars since I was 18 - while this is
definitely not the most reliable of the lot, it is absolutely the most
satisfying - and I intend to keep it.
Best Regards,
Mike Arman
Oh, yeah, the bomb costs about $200 on sale, about $260 normally - see the
vendor list - sometimes it goes on sale - make sure you get the right one
for your car - there are gasket/seal ring differences from year to year. I
think yours is the 671C version, but I'm NOT sure!