jackvtte

Anyone tell me what the symtoms are of a faulty vacuum booster? I just bled my brakes, front and rear, and the brake light illuminates (intermittely). I have a LR caliper that has leaked but doesn’t seem to at the present. The seal from the Master to the booster seems good; the brakes are a bit spongy and I hear a “WHOOSH” when I pump them to stop. Anyone give me ‘what’s next’? :cheers:

mapman

jackvtte,

I would look through the diagnosis section on Brakes in the Chevrolet Corvette Shop Manual for your year car to help identify or eliminate problem sources. Can you identify the source of the "WHOOSH" sound? Can you get an assistant to operate the brakes while you search for the sound.

The brake warning light is addressed in the shop manual section on brakes, operation of the combination valve. The valve and switch are designed so that the switch will "latch" in the "warning" position once a failure has occurred. To turn off the light the failure must be repaired and application of a pedal force require to develop 450 psi line pressure.

If it is the power brake booster, there have been several threads recently discussion the PITA it is to remove the 4 nuts under the dash that hold the booster to the firewall. Mine was pretty easy but I had the steering column out of the car.

tersian

I know you just bled them but there is a definate order they need to be bled in, otherwise you just move air around in the system. I don't have the order with me right now, but almost sounds like you still have air in the system.

Marks69BB

:iagree: You need to start at the caliper farthest from the MC (pass rear) first, then drivers rear, pass front, and last, drivers front. Did you replace the MC? If you did, did you bench bleed the MC before you installed it? If you didn't, it sounds like you may need a new MC. Also, never let the MC go dry or you'll have to start bleeding the system all over again. It sounds like you still have air in the system. Your booster is probably ok. When it comes to brakes, corvettes are a biotch and have to be bled over and over again to get the proper pedal feel. The last time I did mine, it needed a new MC and it took us all day to get the pedal pressure right. :banghead:


[Modified by Marks69BB, 10:51 AM 2/12/2003]

IETEK

I just went through this I bought a 77 that had set up for about 5 years I ended up having to replace 3 calipers and a master cylinder. Your problem sounds like a Master cylinder ($15.00 @ auto zone) . Mine did the same thing. If your Brake Booster was bad, you would more than likely experience a elevated or rough idle from the engine since a bad booster would more than likely cause a vacuum leak. Also I found the rear brakes were tough to bleed since the the proportioning valve puts most of the fluid pressure on the front brakes.
I would suggest that you use some type of vacuum brake bleeder or you can even use your engine vacuum and clear tubing to do the job, simply crack the bleeder and connect the tubing to the bleeder port. Let the engine vacuum pull the fluid through the lines as well as evacuating any air.
You can also use a pressurized type bleeder you can make yourself. Check the archives on the forum for a "how to" on making one, it's real simple but does a great job. And remember to follow the recomended bleed sequence for your year model because it may vary year to year.
As for the leaky caliper do your self a favor and change or rebuild the caliper before you have to pull a Flinstone. If it blows out you more than likely will have little if any brakes And if you drive like I do from time to time your gonna' be in a bind when they go out !!! :D


Hope this helps, IETEK

PatG

Do not buy the $15 MC from any auto parts store unless you happen to enjoy replacing your MC every year or so.

jackvtte

I have a ’79.
The WHOOSH sounds like it is coming from in front of the pedal. I can narrow it down with help. The brakes were bled in the proper order (furthest from MC first). The MC is about 4 yrs old from Chicago Corvette. It’s been about 8 years since I replaced all four calipers with S/S and 3 years since replacing the proportional valve. Your posts have been very helpful. Thanks to all. ;)

mapman

Is this inside the car (under the dash) or outside (under the hood)?

Is the WHOOSH only when the car is running, or do you have the same noise after the car has set for some time?

If the noise is under the dash, do you have cruise control on the car?

Chris O'

The "whoosh" is the air coming through the filter on the pedal side. Might need a new foam filter? (Mine does it as well).

If your booster was shot your brakes would be rock hard (no assistance).

Pump the pedal, clamp all 4 rubber lines and get someone to unclamp and reclamp one by one. You will feel a noticable drop in the pedal at the offending caliper. Undo both fronts and then the and rear to see which circuit is worse.

:cheers:


[Modified by Chris O', 3:54 PM 2/13/2003]