Major Brake issues 1978
Thread Starter
7th Gear
Joined: Apr 2013
Posts: 7
Likes: 0
Major Brake issues 1978
Hey everyone I'm new to the site and am having some pretty major brake issues with my 1978. It is my first project car and I have been tinkering with it for a few years and it has not yet seen the road. Whenever I press the brake pedal when the car is not running I have solid brakes. When the car is running I press the pedal and it goes immediately to the floor. I have replaced the master cylinder, power booster, all four calipers and have repeatedly flushed the line to make sure there is no air. It may be something trivial and obvious but any help would be greatly appreciated.
Melting Slicks
Joined: May 2003
Posts: 2,076
Likes: 281
From: Dyersburg TN
vette brakes are tough to get all the air out. I recommend a Motive bleeder. Also as noted in pref post, bleed all (rears have 2) in the correct order.
also not saying this is it, but I put a new MC on once that had a low pedal. Swapped it for another and great brakes.
double check for leaks
good luck
also not saying this is it, but I put a new MC on once that had a low pedal. Swapped it for another and great brakes.
double check for leaks
good luck
Thread Starter
7th Gear
Joined: Apr 2013
Posts: 7
Likes: 0
I appreciate all the advice. I did bleed the master cylinder a few times but I will go ahead and bench bleed it. And when I have a free afternoon after class I will attempt to re-bleed every inch of the line including the 2 on the rear calipers. It still doesn't make sense as to why I would have pressure just fine when the engine is not running and then nothing as soon as It starts. Could It be an issue with some vacuum component? Thanks
Thread Starter
7th Gear
Joined: Apr 2013
Posts: 7
Likes: 0
Is there anyway to tell If my master cylinder is bad before I drop the money on a new one. I replaced it last year as I began working on the car as the first component when I discovered my brake problem? Thanks
Instructor
Joined: Mar 2013
Posts: 215
Likes: 0
From: Sunshine Coast Qld
Have you got any line clamps? If you have, or can beg, borrow or steal 4 of them, put one on each of the flexible lines to the calipers. Now start the car, if the pedal still goes to the floor, either the master cyl is buggered or has air trapped in it. If the pedal is hard, release one line clamp at a time until you find the offending brake line with air in it. It's best to do this with a friend releasing the line clamps while you feel the pedal movement.
Edit to add - DO NOT USE LOCKING PLIERS...only the proper plastic line clamps.
Edit to add - DO NOT USE LOCKING PLIERS...only the proper plastic line clamps.
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Race Director
Joined: Mar 2006
Posts: 14,112
Likes: 28
From: Florida
Remove the lines out of the master, plug the ports and you should be able to stand on the pedal without it going down.
Melting Slicks
Joined: Jul 2010
Posts: 2,503
Likes: 33
From: McGrady NC
St. Jude Donor '15-'16
There are several ways to do it, but I have had very good luck with gravity bleeding the brakes. Get the car off the ground and remove all four wheels. Make sure the master cylinder is full. Leave the cap loose so you can check it often and easily top it off. Starting from the passenger side rear, open the top outside bleeder. A flexible plastic tube on it will minimize the mess. Let it run/drip until the fluid is clean and clear. Keep an eye on the master cylinder and keep it full. Once the stream is slow and steady, close it and move to the other rear brake and repeat. Then the passenger front and driver front. Keep the MC full and watch for a clean steady stream of fluid from each bleeder. This process worked very well for me after I replaced everything. Note: you do have to bench bleed the master cylinder first. No way around it.
Melting Slicks
Joined: Mar 2007
Posts: 2,520
Likes: 11
From: Hinckley OH
Melting Slicks
Joined: Nov 2010
Posts: 3,363
Likes: 32
From: Bowtie, Pennsyltucky
St. Jude Donor '13-'14-'15,'21
There are several ways to do it, but I have had very good luck with gravity bleeding the brakes. Get the car off the ground and remove all four wheels. Make sure the master cylinder is full. Leave the cap loose so you can check it often and easily top it off. Starting from the passenger side rear, open the top outside bleeder. A flexible plastic tube on it will minimize the mess. Let it run/drip until the fluid is clean and clear. Keep an eye on the master cylinder and keep it full. Once the stream is slow and steady, close it and move to the other rear brake and repeat. Then the passenger front and driver front. Keep the MC full and watch for a clean steady stream of fluid from each bleeder. This process worked very well for me after I replaced everything. Note: you do have to bench bleed the master cylinder first. No way around it.
I've had good luck using this method.
