Bad Brakes
Thread Starter
Racer
Joined: Mar 2015
Posts: 306
Likes: 20
From: Greenville SC
Bad Brakes
Guys< I started a thread back on 8/29 regarding issues with brakes. I have 79 L48 w/ all new calipers, m/c and booster. Run probably over a quart of fluid thru lines. 3 different mechanics have bled the brakes. I still have a pedal that goes to the floor. The car stops but I am afraid that one day it won't.
I can have someone assist in pumping the pedal while I go around all 4 wheels and bleed. There is always a firmer (acceptable) pedal when I do this. However when I start the car pedal goes back to floor. M/C was bench bled and I bled it on the car. I have plenty of vacuum. Rotors are smooth and I don't think runout is a possibility.
I can't even find anyone who even wants to look at my car now. This started in March and I have about 1000 bucks invested. Any advice is appreciated.
I can have someone assist in pumping the pedal while I go around all 4 wheels and bleed. There is always a firmer (acceptable) pedal when I do this. However when I start the car pedal goes back to floor. M/C was bench bled and I bled it on the car. I have plenty of vacuum. Rotors are smooth and I don't think runout is a possibility.
I can't even find anyone who even wants to look at my car now. This started in March and I have about 1000 bucks invested. Any advice is appreciated.
Race Director
Joined: May 2006
Posts: 18,736
Likes: 2,582
You mention another thread, why did you start a second one where you may end up with the same suggestions?
Did you ever answer the question about checking the booster pushrod to master clearance?
Did you disconnect the brake lines at the master, plug the ports, and check if the pedal still goes down?
https://www.corvetteforum.com/forums/c3-tech-performance/4435917-position-of-rear-bleeders-2.html#post1602093046
Did you ever answer the question about checking the booster pushrod to master clearance?
Did you disconnect the brake lines at the master, plug the ports, and check if the pedal still goes down?
https://www.corvetteforum.com/forums/c3-tech-performance/4435917-position-of-rear-bleeders-2.html#post1602093046
Last edited by MelWff; Sep 20, 2020 at 10:48 AM.
Racer
Joined: Nov 2019
Posts: 336
Likes: 173
From: Canadian living in southern France
Guys< I started a thread back on 8/29 regarding issues with brakes. I have 79 L48 w/ all new calipers, m/c and booster. Run probably over a quart of fluid thru lines. 3 different mechanics have bled the brakes. I still have a pedal that goes to the floor. The car stops but I am afraid that one day it won't.
I can have someone assist in pumping the pedal while I go around all 4 wheels and bleed. There is always a firmer (acceptable) pedal when I do this. However when I start the car pedal goes back to floor. M/C was bench bled and I bled it on the car. I have plenty of vacuum. Rotors are smooth and I don't think runout is a possibility.
I can't even find anyone who even wants to look at my car now. This started in March and I have about 1000 bucks invested. Any advice is appreciated.
I can have someone assist in pumping the pedal while I go around all 4 wheels and bleed. There is always a firmer (acceptable) pedal when I do this. However when I start the car pedal goes back to floor. M/C was bench bled and I bled it on the car. I have plenty of vacuum. Rotors are smooth and I don't think runout is a possibility.
I can't even find anyone who even wants to look at my car now. This started in March and I have about 1000 bucks invested. Any advice is appreciated.
I have a '76, and have replaced the flex hoses, master cylinder and front pads while doing a minor restoration when I bought it. I've done exactly the same things you have, plus, using a pressure bleeder, (twice), checking the proportioning valve, checking the booster, and then resorted to dancing around the car and chanting. Still no brakes with the engine running and the booster engaged.
Of the dozen or more cars I've done serious work on, including full restorations, I have never met up with anything like it. I'm seriously starting to wish I'd never bought the car, I'm sick of it. Working on it has become a chore instead of a hobby.
I'm starting again tomorrow afternoon, trying a few new things that came up in this forum and popped into my head in the middle of the night.
Anything I come up with that helps, I'll post it on your thread right away, guaranteed.
Safety Car
Joined: Aug 1999
Posts: 4,862
Likes: 118
From: Texas
Do you find that you have air in any of the calipers when you bleed the brakes. For years, I fought ongoing air in the calipers until I installed o-ring caliper pistons.
If you aren't pulling air into the calipers, you might have a bad master cylinder, or incorrect pushrod clearance as previously mentioned.
The suggestion to disconnect the brake lines and plug the master cylinder is a good one. If you do that, and pedal still goes to the floor, you know thare where your problem is located.
If you aren't pulling air into the calipers, you might have a bad master cylinder, or incorrect pushrod clearance as previously mentioned.
The suggestion to disconnect the brake lines and plug the master cylinder is a good one. If you do that, and pedal still goes to the floor, you know thare where your problem is located.
Last edited by RatRacer; Sep 20, 2020 at 11:16 AM.
Racer
Joined: Mar 2011
Posts: 490
Likes: 99
From: The South
I had a chronic issue with my brakes - replaced calipers multiple times. It was runout - bad rear spindle - had to be replaced. Closely check your runout - you can do it with a cheap tool from Amazon. Worth every penny.
Thread Starter
Racer
Joined: Mar 2015
Posts: 306
Likes: 20
From: Greenville SC
I have not plugged the M/C. I did take the lines loose to bleed the M/C. I trust the mechanic who installed the booster did it properly he has re-bled the lines 3 times since putting the booster on. Besides I have had the same problem before we put the new booster on. Someone suggested I have someone
"stomp" the pedal and that may aid in removing air. Yes I bought a vacuum bleeder Pumped that sucker a hundred times. Why would runout be an issue if you have a good pedal then it went to the floor when you start car???
Do I just use pipe plugs to block the M/C? I'll check Amazon for the tool you mention.
"stomp" the pedal and that may aid in removing air. Yes I bought a vacuum bleeder Pumped that sucker a hundred times. Why would runout be an issue if you have a good pedal then it went to the floor when you start car???
Do I just use pipe plugs to block the M/C? I'll check Amazon for the tool you mention.
Race Director
Joined: May 2006
Posts: 18,736
Likes: 2,582
Different things can cause the same symptoms so just trusting your mechanic checked doesn't work.
You have to ask.
Yes a pipe plug with correct size/thread will work.
You have to ask.
Yes a pipe plug with correct size/thread will work.
Last edited by MelWff; Sep 20, 2020 at 01:42 PM.
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Racer
Joined: Mar 2011
Posts: 490
Likes: 99
From: The South
I have not plugged the M/C. I did take the lines loose to bleed the M/C. I trust the mechanic who installed the booster did it properly he has re-bled the lines 3 times since putting the booster on. Besides I have had the same problem before we put the new booster on. Someone suggested I have someone
"stomp" the pedal and that may aid in removing air. Yes I bought a vacuum bleeder Pumped that sucker a hundred times. Why would runout be an issue if you have a good pedal then it went to the floor when you start car???
Do I just use pipe plugs to block the M/C? I'll check Amazon for the tool you mention.
"stomp" the pedal and that may aid in removing air. Yes I bought a vacuum bleeder Pumped that sucker a hundred times. Why would runout be an issue if you have a good pedal then it went to the floor when you start car???
Do I just use pipe plugs to block the M/C? I'll check Amazon for the tool you mention.
You changed a bunch of parts and had multiple people work on the car - its a shot in the dark as far as what's wrong - folks are just trying to come up with all possible reasons to help you out.
Why not start with the simplest thing that was suggested - block all the lines to your M/C and then test. That isolates it down to just your booster and M/C.
I mentioned runout issues because that's what I experienced, but it was after I would bleed and get a firm pedal and then drive the car for a short while.
Thread Starter
Racer
Joined: Mar 2015
Posts: 306
Likes: 20
From: Greenville SC
OK thank you gentlemen for the help. I checked on the runout tool suggested. It's over $300. How else can I check the runout? I will block off the M/C first thing in the morning.
I get better info from you guys than the people I pay. Thanks all.
I get better info from you guys than the people I pay. Thanks all.
Melting Slicks
Joined: Oct 2012
Posts: 2,156
Likes: 273
From: Dunedin NZ.
I have not plugged the M/C. I did take the lines loose to bleed the M/C. I trust the mechanic who installed the booster did it properly he has re-bled the lines 3 times since putting the booster on. Besides I have had the same problem before we put the new booster on. Someone suggested I have someone
"stomp" the pedal and that may aid in removing air. Yes I bought a vacuum bleeder Pumped that sucker a hundred times. Why would runout be an issue if you have a good pedal then it went to the floor when you start car???
Do I just use pipe plugs to block the M/C? I'll check Amazon for the tool you mention.
"stomp" the pedal and that may aid in removing air. Yes I bought a vacuum bleeder Pumped that sucker a hundred times. Why would runout be an issue if you have a good pedal then it went to the floor when you start car???
Do I just use pipe plugs to block the M/C? I'll check Amazon for the tool you mention.
I can't see anywhere in the thread what the pedal feel is like with the engine off. If the pedal is hard with the engine not running the issue is not air in the system. JMPO
Melting Slicks
Joined: Oct 2012
Posts: 2,156
Likes: 273
From: Dunedin NZ.
A dial gauge and magnetic base can be purchased online here for less than $50.00 so you you should be able to find one for a comparable price where you are, this should be sufficient to check your rotor runout, you may have to get creative with a bracket to hold the base where you need it though!
Racer
Joined: Mar 2011
Posts: 490
Likes: 99
From: The South
$45.99
It's what I purchased and used. You have to fiddle around with it to get it to set just right, but I was able to use it to measure runout on the front and rear.
But it sounds like you need to start with isolating the master cylinder from the rest of the system and starting there first, based on what you've described.
Last edited by gguillot; Sep 20, 2020 at 04:59 PM.
Le Mans Master
Joined: Jan 2001
Posts: 6,742
Likes: 1,384
If you properly blocked all the ports, and there is no resistance, then your master cylinder isn't working properly.
Did you get, or make, a pressure bleeder? I don't even try to bleed my corvette brakes without a pressure bleeder.
Did you get, or make, a pressure bleeder? I don't even try to bleed my corvette brakes without a pressure bleeder.
Thread Starter
Racer
Joined: Mar 2015
Posts: 306
Likes: 20
From: Greenville SC
I took the M/C out. There was some air in the front section. Checked the length of booster rod, looked to be right length. No change in pedal, Gonna make a pressure bleeder and blow the system OUT, Thanks again, Guess just trial and re try,
Melting Slicks
Joined: Oct 2012
Posts: 2,156
Likes: 273
From: Dunedin NZ.
When the system is correct the pedal should only have a small amount of travel and then be rock hard with the engine off. A small amount of air makes a big difference when it trapped in the master cylinder.
Good luck I hope you can resolve the issue!
Good luck I hope you can resolve the issue!