On my 69 corvette when I bleed all four calipers and the master cylinder, the brake pad is nice and hard but as soon as I start the engine the brake paddle gets soft and easily goes to the floor. I don’t know what’s going on. Any suggestions would be great. Thanks

 

is it power or manual brakes, I'm guessing power and you may have a booster vacuum leak. Do a search for booster trooubleshooting of you have it. If you don't you still have a bubble in the lines. In that case multiple cycles is what cleared mine, then I got a motive power bleeder and it made one man bleeding fast and clean.

Your going to be asked what order your bleeding them in. Passenger rear inner then same outer. drivers side inner then outer then passenger front, drivers front last is usually my order.

 

Bad Master Cylinder......

 

Do a word search in General Forum and Technical Forum "brakes" (& Advil/just kidding about the Advil search ).......lots of advice.

 

A bad brake booster will only make the brake pedal hard or cause a vacuum leak and make the engine run rough. It will not affect brake fluid leakage or a sinking pedal.

First make sure none of the calipers are leaking. Then go inside the car and pump the brake pedal until it's hard, once you have a hard brake pedal hold pressure on it with your foot and if it leaks down the master cylinder is bad and needs to be replaced.

If you are not sure about the brake bleeding procedure on C3 Corvette below is the procedure.

According to the service manual,

left rear inner, left rear outer

right rear inner, right rear outer

left front

right front

 

I guess I have been doing it wrong for a lot of years.....I wonder why people tell me the bake pedal in my corvettes are the best they have ever seen..... Maybe I have to change how I do it....

master cylinder

passenger side rear inner, passenger side rear outer

driver side rear inner, driver side rear outer

passenger side front

driver side front

 

My post makes no sense... I'll post back later after I figure this out.

I pulled the 1978 service manual and don't agree with it. I'll pull some other manuals tomorrow and compare.

 

I wish I had saved my original post but I didn't. So.. I'll try to type what I remember I posted.

First, go to this post and read it.. it's locked so I can't quote and I won't copy and paste another mans work.

https://www.corvetteforum.com/forums...fo-please.html

From what I'm reading, there has to be an air issue in the system on your car. The best way to tell if the booster is working is to push the pedal down, start the car and see if the pedal moves. If it does the booster is working. If it stays in the same position the booster is defective.

A non working booster should not hurt the pedal travel with the engine on or off, it it's not working the pedal won't move. If it is, the pedal will travel downward (as you describe).

So.. back to the age old question about what is the right way and wrong way to bleed brakes. Go read the thread, it's an awesome thread.

If you read the link I posted above, you'll see there are deviations in the service manuals from 66-82. I've pulled the 1970 manual today and I pull the 1978 manual as well, both gave a different procedure to bleed the brakes on a C3. One said start with the left rear (78) one said start with the nearest to the master cylinder.. go figure.

If I were you, and it's a big... (IMHO), I'd find someone with a pressure bleeder and have them bleed the brakes for you. Periodically air bubbles can get trapped in the calipers and with a pressure bleeder you can open the valve, lightly tap the caliper and these bubbles will dislodge. But for my money, the best way (and the only way we do them) is a pressure bleeder as prescribed in all the service manual.

Willcox

 

That’s also the sequence that I follow. Start with the longest line and work back to the shortest.