Help - Intermittent brake failure
Thread Starter
5th Gear
Joined: Mar 2007
Posts: 5
Likes: 0
Help - Intermittent brake failure
1988 Corvette 35th Anniversary, under 40,000 miles. Every so often the brakes completely fail - all the way to the floor but after 4 pumps will work one time then fail totally again. If I park the car for a while all will work again until the next time (could be weeks or months). I had the master cylinder replaced and there are NO leaks anywhere (none before replacement as well). I'm at a total loss and nobody seems to know the reason. Today I purchased a used ABS computer - just in case it may be that. I have always wondered because the ABS light never shows when the engine is started?
ANY thought would be REALLY appreciated.... Thanks!
ANY thought would be REALLY appreciated.... Thanks!
Last edited by raparriott; Sep 3, 2007 at 02:08 PM.
Instructor
Joined: Aug 2007
Posts: 212
Likes: 0
From: www.C4guru.com Everywhere!
My understanding of the ABS system is when the light IS lit, you still have brakes but you have no ABS. I think you have a bad master cylinder. Mine went out twice and the second time I bought a new one. I bought a remanufacutred one from Autozone the first time. If it was a hard pedal, then it would be a brake booster. You shouldn't drive it like that. Put on a new master cylinder, bleed the system and you should be good to go if that is the problem. You may also just have air in the lines. You could bleed them and just see if that helps but if not m.c. is shot.
Thread Starter
5th Gear
Joined: Mar 2007
Posts: 5
Likes: 0
Well we think alike about the master cylinder - but I just replaced that last month and it was not a rebuild it was a GM new and this morning I had the same issue happen - a scary thing for sure and most unsettling. The GM service manager said he frankly had no clue as to what could be the problem. I am taking a stab at the ABS as I wonder if the computer somhow redirects the fluid pressure or as may be in this case does something wrong. This is so frustrating and I never know when it will happen there seems to be no pattern.
Thanks for your response....
Thanks for your response....
Le Mans Master
Joined: Sep 2006
Posts: 6,050
Likes: 147
From: Phoenix AZ
2021 C4 of the Year - Modified Finalist
no brakes
If your brakes fail after using them for a while like in traffic, I would suspect either condensation in the calipers or outright brakes bled with a bleeder bottle that was allowed to sit with the bottle neck open to atmosphere, and was contaminated with water.
Brake fluid has an affinity for water. It will absorb it, and when it is let to settle, the water will make it's way down to the calipers and boil when you are using the brakes.
boiling water turns to steam. steam is compressible.
When you pump the brakes, you remix the brake fluid and the water, and cool the water down enough so that it doesn't boil, and you have the same thing over and over. every day, every cooling cycle.
cool they work, hot they fail
Brake fluid has an affinity for water. It will absorb it, and when it is let to settle, the water will make it's way down to the calipers and boil when you are using the brakes.
boiling water turns to steam. steam is compressible.
When you pump the brakes, you remix the brake fluid and the water, and cool the water down enough so that it doesn't boil, and you have the same thing over and over. every day, every cooling cycle.
cool they work, hot they fail
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
Was the master bench bleed first before installation. If there is any question, I would remove it, bench bleed and reinstall.
Then I would bleed and flush all lines.
Depending on results, I would go from there. If you can hold your foot on the brake and it does not sink, chances are the new master is OK.
Then I would bleed and flush all lines.
Depending on results, I would go from there. If you can hold your foot on the brake and it does not sink, chances are the new master is OK.
Pro
Joined: May 2004
Posts: 712
Likes: 26
From: Santa Maria CA
Check the rubber vacuum hoses. I had the same symptoms on another car and after taking the car to 3 shops and replacing almost all the parts it was discovered that a soft vacuum hose would occasionally collapse on itself and the pedal would go to the floor - no brakes. The problem was finally fixed with a $2 piece of hose.
Team Owner
Joined: May 2002
Posts: 24,337
Likes: 25
From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
The booster vacuum hose is thick, I don't see it collapsing. I also don't see any way a pinched vacuum hose could do anything close to what you're saying.You have hydraulic fluid in the system that is about impossible to compress. A vacuum hose isn't going to change that.
Really wet fluid or an intermittent failing m/c sounds like the culprit to me. Both could let the pedal drop when the fluid warms up, but feel fine cold. Personally I've never experienced boiling fluid though.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
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
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
Just wondering why you had the original master replaced in the first place. Is this the same problem as the first master cylinder had. Or is this a new problem with the replacement master. If this is a new problem, then I agree the new master might be defective.
Team Owner
Joined: Dec 1999
Posts: 34,873
Likes: 487
From: Lacey WA RVN 68-69
NCM Sinkhole Donor
I would inspect all of the hard brake lines and connections that you can see. Make sure all of these connectors, blocks and threaded ends are not leaking. Any slight leak can cause air to be sucked into a hard line as line presure is released.
You could have leaky seals at the caliper pistons. That could also introduce air into the system. With the low mileage on the car, the caliper seals may have dried up or stuck to the bore and may have cracked.
Replacement C4 calipers can be expensive so you might try rebuild kits for them.
You could have leaky seals at the caliper pistons. That could also introduce air into the system. With the low mileage on the car, the caliper seals may have dried up or stuck to the bore and may have cracked.
Replacement C4 calipers can be expensive so you might try rebuild kits for them.
Thread Starter
5th Gear
Joined: Mar 2007
Posts: 5
Likes: 0
Thanks for your question. I replaced the master cylinder with an new OEM for exactly this same problem. Since it is intermitant I thought the problem had gone away but unfortunately no such luck.
I recently spoke with a person that asked if the ABS proportioning valve behind the drivers seat could cause this sort of isse but I do not know. I have purchased and am waiting for a used ABS computer as well. I have always wondered why the ABS light does not come on before the car is started for a short time to tell me the system is working. It will be my luck that maybe a light bulb is out in the display panel - LOL.
If you have any more thought I'm all ears. The master cylinder was replaced by an in area man that builds custom hot rods for a living and has done so for years, he's in his 60's. He also spoke to the service manager at the local Chevy dealership and they both had believed it was the MC but as you can see the issue is still at hand. I wish I was more knowledgable in these matters but am having to depend on the kindness of people like you. Thanks again for your message.
I recently spoke with a person that asked if the ABS proportioning valve behind the drivers seat could cause this sort of isse but I do not know. I have purchased and am waiting for a used ABS computer as well. I have always wondered why the ABS light does not come on before the car is started for a short time to tell me the system is working. It will be my luck that maybe a light bulb is out in the display panel - LOL.
If you have any more thought I'm all ears. The master cylinder was replaced by an in area man that builds custom hot rods for a living and has done so for years, he's in his 60's. He also spoke to the service manager at the local Chevy dealership and they both had believed it was the MC but as you can see the issue is still at hand. I wish I was more knowledgable in these matters but am having to depend on the kindness of people like you. Thanks again for your message.
Le Mans Master
Joined: Mar 2004
Posts: 8,700
Likes: 298
From: Ft. Lauderdale Fl
Well we think alike about the master cylinder - but I just replaced that last month and it was not a rebuild it was a GM new and this morning I had the same issue happen - a scary thing for sure and most unsettling. The GM service manager said he frankly had no clue as to what could be the problem. I am taking a stab at the ABS as I wonder if the computer somhow redirects the fluid pressure or as may be in this case does something wrong. This is so frustrating and I never know when it will happen there seems to be no pattern.
Thanks for your response....
Thanks for your response....
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
The ABS pump and computer is behind the driver. The proportioning valve is in the master cylinder. Probably your ABS pump and brake computer that might relate to your ABS light is probably a different problem from you loosing the brakes. The ABS light problem could even be a bad light bulb and should be checked out first.
I have heard of the valves in the ABS pump getting a blockage and not let pressure go to a particular line. But not familiar with a problem with the ABS that would permit the pedal to go to the floor.
It was said that a bad brake caliper could suck in air but not leek which is true. But usually with air in the system it does not recover the have a good brake pedal and then go bad again. Only a brake line bleed would show if there was any air in the lines or not.
If you are running out of options, perhaps you need to get a second opinion from another shop, maybe one that works on sports cars or specializes in vettes.
Good luck.
I have heard of the valves in the ABS pump getting a blockage and not let pressure go to a particular line. But not familiar with a problem with the ABS that would permit the pedal to go to the floor.
It was said that a bad brake caliper could suck in air but not leek which is true. But usually with air in the system it does not recover the have a good brake pedal and then go bad again. Only a brake line bleed would show if there was any air in the lines or not.
If you are running out of options, perhaps you need to get a second opinion from another shop, maybe one that works on sports cars or specializes in vettes.
Good luck.
Burning Brakes
Joined: Apr 2005
Posts: 1,109
Likes: 2
I guess that changing to a more viscous brake fluid could help.
I was reading about a fluid called ATE blue, which is DOT3 and 4, so it might help. I will try this , braided stainless steel lines and again a new Master cylinder + speed bleeders to make things easier.
I always think if new Corvettes gave this kind of trouble. Maybe it would be interesting to use the GM brake fluid recomended for the car.
Just a thought.
Safety Car
Joined: Jul 2004
Posts: 3,835
Likes: 30
Was the master bench bleed first before installation. If there is any question, I would remove it, bench bleed and reinstall.
Then I would bleed and flush all lines.
Depending on results, I would go from there. If you can hold your foot on the brake and it does not sink, chances are the new master is OK.
Then I would bleed and flush all lines.
Depending on results, I would go from there. If you can hold your foot on the brake and it does not sink, chances are the new master is OK.
1st Gear
Joined: Mar 2023
Posts: 1
Likes: 0
Had the same thing happen to me but I ended up in a ditch
[QUOTE=raparriott;1561768103]1988 Corvette 35th Anniversary, under 40,000 miles. Every so often the brakes completely fail - all the way to the floor but after 4 pumps will work one time then fail totally again. If I park the car for a while all will work again until the next time (could be weeks or months). I had the master cylinder replaced and there are NO leaks anywhere (none before replacement as well). I'm at a total loss and nobody seems to know the reason. Today I purchased a used ABS computer - just in case it may be that. I have always wondered because the ABS light never shows when the engine is started?
ANY thought would be REALLY appreciated.... Thanks!
[/QUOTE
I had the same thing happen to my 89 l98 first time it was simple and the cap on the master was loose thinking nothing of it I put it back on and went to move it everything seemed fine few weeks later I was playing around coming into my yard and spun out into the ditch because a no breaks had to pull the e-brake and ended up swapping ends into the ditch in front of my house bent up my bumper a little bit but nothing too bad
ANY thought would be REALLY appreciated.... Thanks!
[/QUOTE I had the same thing happen to my 89 l98 first time it was simple and the cap on the master was loose thinking nothing of it I put it back on and went to move it everything seemed fine few weeks later I was playing around coming into my yard and spun out into the ditch because a no breaks had to pull the e-brake and ended up swapping ends into the ditch in front of my house bent up my bumper a little bit but nothing too bad