Ok I'll check for any leaking tomorrow. However, The reservoir never goes down
in fluid level.
It also does this: with the motor off, the pedal feels tight at the top. It is
only when the motor is running that the 1-2" pedal sink take place.
Could it be a faulty air valve in the power brake booster?
It developed over time. The last time it occurred, I replaced the rear drums
and shoes, and the front pads. Then a complete bleed, statring wiht the master
cylinder, then three times around the wheels as per Haynes manual. The brakes
worked good after that. But a few months later the slop at the top of the pedal
and brakes grab came back.
Well - the easy answer is do what you did last time. Blah! That sucked,
didn't it? The slop at the top of the pedal implies a leak and air getting
into the lines. The first thing I'd do is to inspect the rear wheel
cylinders, all of the brake lines, etc. for any sign of fluid leaking. I'd
be looking for even small signs. I'm sorry - I don't know if the '96 Grand
Am has drums in back or disks. If it has disks, then you can obviously
ignore the wheel cylinder idea. Still - look for leaks.
If you cannot find any leaks, then I think I'd go for the master cylinder
next. In fact, I think the master cylinder might be closer to the front of
my mind. Make sure you bench bleed the new cylinder before you install it
in the car.
The brake grab is what is throwing me. I've only encountered severe grab
when a bolt backed out of a caliper and allowed the caliper to rotate into
the wheel upon braking. Now, that was grab! Absent any other ideas or
thoughts with respect to the grabbing, I think I'd hit the master cylinder.
$40 and a core.
Another thought Bill...
How old is the brake fluid in the car? Brake fluid assumes moisture from
the atmosphere and you can get into a situation where with water in the
lines you have no pedal, since water does not compress. At a point however,
you will begin to compress the brake fluid that is in the lines. Perhaps
that could explain the grabbing and the soft pedal.
If your fluid is more than a couple or a few years old, or, if it looks
dark, then purge it and replace with new. You can do this by simply gravity
bleeding the brakes and keeping the reservoir topped off, or you can pump it
out with the pedal while keeping the reservoir topped.
Thanks for the replies, guys.
As for the grab, I will go for one more short drive to see what wheels are
grabbing first. Then I will put the car up and inspect everything.
One last question: if I do replace the master cylinder, it there any concers
with removing the ABS unit that is directly attached to it?
Uh, Dave - there is a slight error in your otherwise good advice. When
water is heated enough to turn into a vapor, it doesn't compress, it
expands. Try boiling a sealed container of water and you will see that!
True, but, it's expansion is not enough to overcome the high pressures in a
brake system. Vehicles in the mountains often loose their brakes because the
moisture in their system vaporizes and the pedal goes to the floor. In
everyday driving, there usually isn't enough heat generated to be a problem.
Not really - just don't horse anything. But... better advice has been put
forward by Dave and some others - namely to investigate the vacuum booster
first. Take a look back at the couple of responses that directed you that
way and look there first.
The valve is not replaceable.
I will assume no one adjusted either of the rods in order to make it
do what it is doing.
Look for a diagram on the net of how a booster works.
When you push on the brake pedal, it opens a valve that lets
atmo. pressure push on the diaphram which helps push on the
rod to the MC. If too much air gets in too fast it will do
exactly as you describe.
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