69 lousy brakes
Thread Starter
2nd Gear
Joined: Sep 2023
Posts: 3
Likes: 0
69 lousy brakes
So, the other day I took my 69 out for a drive. Not to far away is a steep hill 25mph limit with a 15mph left turn at the bottom. About half way down my brakes faded to the floor. I hit them several times and got enough braking to make the corner without incident. I've since rebuilt the master cylinder and bled about a gallon of brake fluid through the system. No air remains. I did bench bleed the master before reinstalling. I now have "some" braking. But, at 35mph the brakes won't lock up. If something pulled out in front of me I'd hit it before stopping. Any help is appreciated.
Instructor
Joined: Feb 2011
Posts: 186
Likes: 63
From: a little West of Houston Texas
1 post
no location
How did you bleed the 4 calipers ? pressure bleeder, vacuum suction, a helper
Lots of information on the internet = upper right hand corner, hit the google tab & search
no location
How did you bleed the 4 calipers ? pressure bleeder, vacuum suction, a helper
Lots of information on the internet = upper right hand corner, hit the google tab & search
Team Owner
Joined: Jan 2007
Posts: 53,648
Likes: 878
From: Southern Cal Ca
St. Jude Donor '22
So, the other day I took my 69 out for a drive. Not to far away is a steep hill 25mph limit with a 15mph left turn at the bottom. About half way down my brakes faded to the floor. I hit them several times and got enough braking to make the corner without incident. I've since rebuilt the master cylinder and bled about a gallon of brake fluid through the system. No air remains. I did bench bleed the master before reinstalling. I now have "some" braking. But, at 35mph the brakes won't lock up. If something pulled out in front of me I'd hit it before stopping. Any help is appreciated.
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
Not as an insult, but you say you rebuilt the master?
This is exactly why I have said for years that unless you are a experienced brake specialist, just buy a rebuilt. You could have killed somebody just to save a few bucks.
I am all for rebuilding caliper with kits. Reason being that if one caliper fails, you still have brakes. If a booster fails, you still have brakes. If the proportioning valve fails, you still have brakes. But when the master fails it could result into property damage, injury or death.
I don't know why you lost your brakes. But your first order of business is checking MC fluid level again. And check all four corners for wet spots.
You may need to fabricate some MC test lines and isolate the master from the entire brake system.
This is exactly why I have said for years that unless you are a experienced brake specialist, just buy a rebuilt. You could have killed somebody just to save a few bucks.
I am all for rebuilding caliper with kits. Reason being that if one caliper fails, you still have brakes. If a booster fails, you still have brakes. If the proportioning valve fails, you still have brakes. But when the master fails it could result into property damage, injury or death.
I don't know why you lost your brakes. But your first order of business is checking MC fluid level again. And check all four corners for wet spots.
You may need to fabricate some MC test lines and isolate the master from the entire brake system.
Thread Starter
2nd Gear
Joined: Sep 2023
Posts: 3
Likes: 0
Safety Car
Joined: Sep 2005
Posts: 4,222
Likes: 643
From: Orange County Ca
How is your pedal? Hard or mushy?
Mushy is probably air in the system. Many threads here to help get it out.
Hard could be your booster, if you have pb. When mine went out, I did have a little braking left, but not much. Pedal was super hard, bit it only had 10%??? braking. New booster fixed it.
Master cylinders have 2 different plug hole dephs in the rear that would be a problem if you got the wrong rebuild kit.
Etc.
Mushy is probably air in the system. Many threads here to help get it out.
Hard could be your booster, if you have pb. When mine went out, I did have a little braking left, but not much. Pedal was super hard, bit it only had 10%??? braking. New booster fixed it.
Master cylinders have 2 different plug hole dephs in the rear that would be a problem if you got the wrong rebuild kit.
Etc.
Le Mans Master
Joined: Aug 2006
Posts: 7,425
Likes: 1,559
From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
Hi and welcome
See posts 2 5 6 & 7
https://www.corvetteforum.com/forums...ke-issues.html
https://www.corvetteforum.com/forums...ke-issues.html
Last edited by Peterbuilt; Sep 14, 2023 at 05:37 PM.
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Melting Slicks
Joined: Sep 2006
Posts: 2,812
Likes: 469
From: Wichita Kansas
When mine failed years ago, I (had to) use the parking/emergency brake lever to control my braking until I got home. If you are fortunate enough to have one that works, don't forget it is there to help in emergency. It can't replace regular braking but it's better than nothing. Also, downshifting is available. With these old cars, you gotta be thinking of a way out all the time.
Racer
Joined: Jan 2008
Posts: 295
Likes: 58
From: Arvada Colorado
1st Gear
Joined: Aug 2023
Posts: 1
Likes: 0
From: Texas
Vacuum bleeders just do not work very well at all. They pull air in around the threads of the bleeder. If this is all you have, gravity bleed the lines and then follow up with your pal.
This happened to me. Didn’t dawn on me what was happening until about the 4th time around. I globbed some anti seize around the outside of the bleeder so it didn’t suck air. Worked like a charm.
This happened to me. Didn’t dawn on me what was happening until about the 4th time around. I globbed some anti seize around the outside of the bleeder so it didn’t suck air. Worked like a charm.
Thread Starter
2nd Gear
Joined: Sep 2023
Posts: 3
Likes: 0
Not as an insult, but you say you rebuilt the master?
This is exactly why I have said for years that unless you are a experienced brake specialist, just buy a rebuilt. You could have killed somebody just to save a few bucks.
I am all for rebuilding caliper with kits. Reason being that if one caliper fails, you still have brakes. If a booster fails, you still have brakes. If the proportioning valve fails, you still have brakes. But when the master fails it could result into property damage, injury or death.
I don't know why you lost your brakes. But your first order of business is checking MC fluid level again. And check all four corners for wet spots.
You may need to fabricate some MC test lines and isolate the master from the entire brake system.
This is exactly why I have said for years that unless you are a experienced brake specialist, just buy a rebuilt. You could have killed somebody just to save a few bucks.
I am all for rebuilding caliper with kits. Reason being that if one caliper fails, you still have brakes. If a booster fails, you still have brakes. If the proportioning valve fails, you still have brakes. But when the master fails it could result into property damage, injury or death.
I don't know why you lost your brakes. But your first order of business is checking MC fluid level again. And check all four corners for wet spots.
You may need to fabricate some MC test lines and isolate the master from the entire brake system.
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
Don't get me wrong, I like O Reilley's but real good odds they sold you the wrong MC.
Their parts book, like many other stores will list: Fits All Vettes from '68 to "82.
Wrong. There are manual masters, there are PB masters and to add confusion GM changed the design of the piston where it contacts either a booster rod or the brake pedal rod.
And what that does is changes the critical gap. That gap should be 0.060 or around 1/16".
When you bench bled, did you tilt the master up & down? And, did you force the piston in too far? That could damage a piston seal.
Click on my avatar, then photo album brake bleeding for some ideas.
I agree with others about the Mity Vac method. But avoid touching brake pedal until done. Nothing but trouble doing so.
It seems in the last few years, bleeder screws are slightly undersize. I bought some from three different stores and none of them were the same exact dia. Just junk.
When vac bleeding these sloppy bleeder screws give the illusion of lots of air bubbles in the system. The false bubbles are removed but the real bubbles are still in the lines.
Vac bleeding is fine for one or two calipers but not all six bleeders. If you don't want to invest in a Motive pressure tank, then consider the gravity method.
I suspect the MC still has air as does "some" of the calipers.
Their parts book, like many other stores will list: Fits All Vettes from '68 to "82.
Wrong. There are manual masters, there are PB masters and to add confusion GM changed the design of the piston where it contacts either a booster rod or the brake pedal rod.
And what that does is changes the critical gap. That gap should be 0.060 or around 1/16".
When you bench bled, did you tilt the master up & down? And, did you force the piston in too far? That could damage a piston seal.
Click on my avatar, then photo album brake bleeding for some ideas.
I agree with others about the Mity Vac method. But avoid touching brake pedal until done. Nothing but trouble doing so.
It seems in the last few years, bleeder screws are slightly undersize. I bought some from three different stores and none of them were the same exact dia. Just junk.
When vac bleeding these sloppy bleeder screws give the illusion of lots of air bubbles in the system. The false bubbles are removed but the real bubbles are still in the lines.
Vac bleeding is fine for one or two calipers but not all six bleeders. If you don't want to invest in a Motive pressure tank, then consider the gravity method.
I suspect the MC still has air as does "some" of the calipers.
Last edited by HeadsU.P.; Sep 16, 2023 at 08:05 AM.
Le Mans Master
Joined: Jan 2001
Posts: 6,728
Likes: 1,379
Get, or make, a pressure bleeder. Stop wasting your time with that vacuum contraption. If you have not replaced the hosed at the corners then do it now and THEN pressure bleed. I recommend the braided SS hoses since you're gonna do it.
Just do the hoses if they're more than a couple of years old already. I didn't believe it either but it made all the difference on another vehicle I was working on..... I could not believe that the hose would be affected as such just because I emptied the system when replacing pads.... I thought I was doing a good thing by replacing all the fluid. I believe the hose(s) {both fronts} swelled internally when I emptied the fluid..... and they could never allow the brake fluid to work properly no matter how well I was bleeding them...... SO, if you have not changed the corner hoses, then just do it.
Just do the hoses if they're more than a couple of years old already. I didn't believe it either but it made all the difference on another vehicle I was working on..... I could not believe that the hose would be affected as such just because I emptied the system when replacing pads.... I thought I was doing a good thing by replacing all the fluid. I believe the hose(s) {both fronts} swelled internally when I emptied the fluid..... and they could never allow the brake fluid to work properly no matter how well I was bleeding them...... SO, if you have not changed the corner hoses, then just do it.
No insult taken. I've spent 40yrs in construction safety so I understand safe operating equipment. Why the brakes failed to begin with, is beyond me. But rest assured, the car was tested on a private road so no property or person except me was put at risk. That being said. I not only rebuilt the original master but purchased a new master from the local parts store (O'Reilly's). I have bench bled the master twice and about a gallon of new fluid through all four calipers. All air seems to be removed. Brake pedal seems good until I start the engine, then goes soft. If there is still air in the system, I'm at odds on how to remove it. Thanks again for any help.
