Power brake booster replacement,c3

[Joseph K.]

Can anyone provide me with any :"Don'ts" on the removal of a PB booster from a 1975 corvette? The box it is in says unloaded, does that me it needs to be "Loaded" once in the car. The job looks pretty innocent and I have mechanical background but wanted to see what you guys thought first. How do I tell if the one I have is working or not?, other than the brakes don't work so well. Is there a way to test these? rebuild them if it is original to the car? Thanks in advance for any reply..Kirby

[Jim T.]

Re: Power brake booster replacement,c3

Don't know where you would get the parts to rebuild one. The part that requires the most patience is laying under the dash and removing the retaining nuts, they are a interference fit from start to finish. Only power brake unit that I have had that went bad was on my 85, it would not hold pressure when the brakes were applied.
I have done this more than once and no problems. Unbolting the brake lines to the master cylinder, cap them. After you install the master cylinder to the new power and ready to hook up the brake lines to the master cylinder, just connect the brake lines loose enough so that the leaking brake fluid fills the lines and connection, should be no air in the lines with this procedure, tighten the line connections. I did not have to bleed the brake calipers.

[Kurt G.]

Re: Power brake booster replacement,c3

Joe, I had the same delemna with my 72 last winter. Chances are, it's not the booster. I made several calls to shops around the country and they all told me the problem was most likely my master cylinder. Son of a gun, they were right. Pulled the old master cylinder off, had it rebuilt and along with rebuilt calipers and some new pads, my little gal stops just as well as she did the day she rolled off the factory floor.

[Martin N.]

Re: Power brake booster replacement,c3

JOSEPH-

When you say "brakes don't work so well" can you be more specific describing your braking problem? I.E.: low pedal, hard pedal, no pedal? Booster problems usually are hard brake pedal complaints.

Marty

[Kurt G.]

Re: Power brake booster replacement,c3

My problems were a real soft pedal. To get braking I had to push to the floor. Compound that with 35 year old untouched calipers and every stop was a very cautious one. Needless to say I didn't get to drive my car much. If the booster goes out your pedal pressure will be pretty much like the pressure you would have with non-power brakes.

[Jim T.]

Re: Power brake booster replacement,c3

The only power brake booster I have experienced going out was on my 1985 Corvette. My 70's still works great. Anyway on the 85 I could still stop the car and when stopped with application on the brakes the pedal would go down and I could faintly hear air escaping. Bought a brand new identical booster from Auto Zone at a very reasonable price and it is the same Australian manufacture as my original factory installed brake booster. How often does that happen?

[Michael B.]

Re: Power brake booster replacement,c3

Test your booster by depressing the brake pedal several times with the engine off. It should become very stiff. Now, with a lite to moderate pressure on the pedal, start the engine. If you feel the pedal drop a little (vacuum assisted) under your foot, the booster is working.

Remove your foot from the pedal and turn off the engine. Go to the engine compartment and pull the check valve and hose from the booster. You should hear the rush of air filling the vacuum in the booster. If not, you have an internal leak. You can have a booster that leaks internally and still give some boost, but its days are numbered.

The term "Loaded" refers to whether the booster comes with a new master attached and adjusted or not. "Unloaded" is just the booster. The biggest difficulty will be reaching the mounting nuts on the interior side of the firewall. Save yourself some grief and remove the driver's seat first and give yourself some working room. Have a good selection of 3/8 extensions, universal joints and wobble sockets at the ready. You do not need to remove the cluster to get to these nuts.