C3 brake trouble again.

[John Sanford]

I recently posted a couple of questions on why I didn't have any brakes on my 74. Several advised replacing the master cylinder. I replaced both the master cylinder and the booster with rebuilt ones. When I poured the fluid out of the old MC, some fluid also came out of the booster vaccuum check valve. (Hmmmm, I wonder if the booster was bad, lol.) When I installed the new booster and master cylinder I had to turn my idle screw up four times just to make the engine idle(because of the new booster.) We bled the brakes on all four wheels starting with the one farthest from the MC. Now when I drive the car, the pedal goes all the way to the floor, but it has GOOD brakes on the floor. All four wheels will lock up now, but why does the pedal go all the way to the floor before they do? The car does have a big cam. Now am I faced with the problem of not enough vaccuum, ---Maybe a vaccuum canister would work. Any hints? Thanks John

[Craig S.]

Re: C3 brake trouble again.

John - there is a threaded adjustment shaft on the booster that controls the pedal height as I recall, seems like it controls the relative point of engagement of the booster. I think I also recall an adjustment between the booster and the master cylinder.....sorry for the vague response without referencing my service manual. At any rate, I believe the correct set up process is covered in the Chevrolet Chassis or Overhaul service mauuals to obtain proper settings on the booster to get the pedal height correct....Craig

[Gary S.]

Re: C3 brake trouble again.

You might try rebleeding the brakes. There are numerous threads about the hassles of bleeding Corvette brakes. Two or three attempts to get a good pedal are not unusual, if this board is any indication.
Gary

[Wayne K.]

Re: C3 brake trouble again.

John,

Did you bench bleed the master cylinder before installing it ? I've seen many posts advising this be done to get proper pedal.

[Jeff A.]

Re: C3 brake trouble again.

Have replaced the master cylinder and brake booster on my 70. There is an adjustment on the master cylinder/booster connection. Replacing the booster is a pain when you try to put the clevis rod back on the brake pedal linkage. It took me an hour of on my back time.

My car has been bled several times when then fluid was replaced. Each time the pedal has come up after driving it for awhile. It keeps getting better and better. I use the highest boiling point DOT fluid that I can get and invested in a vacuum pump to bleed them. I checked my shop manual and the Assembly Instruction Manual. Neither has a great picture of the connection. Good luck.

[Henry Pozzuoli]

Re: C3 brake trouble again.

I have not change a booster in years but have had many battles bleeding these brakes, esp. if you did not bleed the MC first. Sometimes the system fights itself it thinks that there is a leak while your bleeding and shuts off the fluid and the air to that wheel. I have had luck just gravity bleeding or using a hand suction device of one type or another to suck the fluid through. Just watch out you don't run the MC dry.