When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
The motive bleeder is what I have. I've pumped 3 quarts through the system so far with it. I don't get any air. Brake pedal still spongy.
I spoke to a guy at one of the big Corvette parts houses today. He said he'd worked there for years and had not heard of any consistent problems with the reproduction calipers or master cylinders. He said "that's just Corvette brakes" and seemed to think it was a very common problem. He basically just told me there has to be air in there somewhere.
I kind of doubt it at this point, but unless the calipers are bad I'm not sure what else to do.
Originally Posted by J.Abbott
I know someone recommeded the vacuum bleeder, I would not. I was not a fan of anything except the old way of doing it until I saw how GM did it and by accident a new company started making a small pressure bleeder. They sent me one in like 03 or 04 and we used it on the race can and I could not believe how easy and how awesome it was. It was a Motive bleeder and you can find them anywhere, it is a life safer on bleeding the older Vettes as well and it is the only way I would do it now.
You reached the point where you need to pinpoint what's at fault here. And the best way to do that is to isolate parts.
You need to isolate the master from the entire brake system. Is the master at fault or the calipers at fault?
You don't even have to remove the master for the test.
When bench bleeding, a master cyl can give false presentation of having lots of pressure.
What you can do with a screwdriver in a bench vise is no where near what the leverage of a brake pedal will do to the master later. (over 400 lbs of pressure)
Just a quick note here. Somewhat common for people to push a screwdriver / piston in too far. That can damage the MC piston rings / seals.
Warranty is void if the piston is shoved in more than 1 & 3/8". (According to the label on the box)
NAPA sells short length brake-lines with brass fittings. You will need two test lines. The front port and rear port on the master are different Dia & TPI.
Get creative on how to block off the other end of the lines.
Unhook the vehicles brake-lines from the master. Install your test lines.
Hop in the drivers seat. You should be able to stand on the brake pedal.
If you can, look elsewhere.
If you can't, there's the problem.
Of course, the entire system will need re bleeding.
The motive bleeder is what I have. I've pumped 3 quarts through the system so far with it. I don't get any air. Brake pedal still spongy.
I spoke to a guy at one of the big Corvette parts houses today. He said he'd worked there for years and had not heard of any consistent problems with the reproduction calipers or master cylinders. He said "that's just Corvette brakes" and seemed to think it was a very common problem. He basically just told me there has to be air in there somewhere.
I kind of doubt it at this point, but unless the calipers are bad I'm not sure what else to do.
Ok sometimes it comes down to definition and what you are comparing too. A power brake C3 will feel different than a standard brake setup. When I say a brake is spongy, when you push the pedal down it will stop and then continue down until it bottoms out on the floor. That is when there is air in the line. If the brake feels soft but comes to a hard rest before the floor that is not a spongy brake, that is just a power setup and how they feel. A standard brake is very solid and the pedal does not travel very far. If you feel that you have air in the line always bleed from the furthest from the MC first. So right rear, outside of the caliper, then inside of the caliper, then LR, RF then LF. If you are using the motive make sure you put a clear line on the bleeder valve so you can see if you are pushing out any air. Once it is solid you should be good to go. I usually make two trips around just to be 100%.
Ok sometimes it comes down to definition and what you are comparing too. A power brake C3 will feel different than a standard brake setup. When I say a brake is spongy, when you push the pedal down it will stop and then continue down until it bottoms out on the floor. That is when there is air in the line. If the brake feels soft but comes to a hard rest before the floor that is not a spongy brake, that is just a power setup and how they feel. A standard brake is very solid and the pedal does not travel very far. If you feel that you have air in the line always bleed from the furthest from the MC first. So right rear, outside of the caliper, then inside of the caliper, then LR, RF then LF. If you are using the motive make sure you put a clear line on the bleeder valve so you can see if you are pushing out any air. Once it is solid you should be good to go. I usually make two trips around just to be 100%.
My pedal gets some resistance after about an inch of depression, then I can get it to go to about 1" from the floor but not all the way. Definitely too soft, not "hard". It is standard brakes, not power.
I approached this by clamping the soft brake hoses at all 4 corners which gave me a rock hard pedal.
If fact, clamping only the front hoses gives me the same rock hard pedal.
Originally Posted by HeadsU.P.
You reached the point where you need to pinpoint what's at fault here. And the best way to do that is to isolate parts.
You need to isolate the master from the entire brake system. Is the master at fault or the calipers at fault?
You don't even have to remove the master for the test.
When bench bleeding, a master cyl can give false presentation of having lots of pressure.
What you can do with a screwdriver in a bench vise is no where near what the leverage of a brake pedal will do to the master later. (over 400 lbs of pressure)
Just a quick note here. Somewhat common for people to push a screwdriver / piston in too far. That can damage the MC piston rings / seals.
Warranty is void if the piston is shoved in more than 1 & 3/8". (According to the label on the box)
NAPA sells short length brake-lines with brass fittings. You will need two test lines. The front port and rear port on the master are different Dia & TPI.
Get creative on how to block off the other end of the lines.
Unhook the vehicles brake-lines from the master. Install your test lines.
Hop in the drivers seat. You should be able to stand on the brake pedal.
If you can, look elsewhere.
If you can't, there's the problem.
Of course, the entire system will need re bleeding.
I approached this by clamping the soft brake hoses at all 4 corners which gave me a rock hard pedal.
If fact, clamping only the front hoses gives me the same rock hard pedal.
when you bleed the right front caliper and then the left are you tapping the caliper with a hammer or rubber mallet to dislodge any air bubbles?
I read another thread from 2011 where a C3 owner had pretty much the same problem as I'm having. Don't see he ever got it fixed. Many responses said that all C3s had soft brake pedals.
I read another thread from 2011 where a C3 owner had pretty much the same problem as I'm having. Don't see he ever got it fixed. Many responses said that all C3s had soft brake pedals.
Another question about those Chinese calipers. Did you have to hold in the four pistons with a tool of some sort in order to insert the pads? The reason I'm asking is I was wondering if the piston springs are missing in the front calipers.
I approached this by clamping the soft brake hoses at all 4 corners which gave me a rock hard pedal.
If fact, clamping only the front hoses gives me the same rock hard pedal.
Then the clue lies in the front brakes.
You clamp the front hoses, firm pedal.
Release the clamp, pedal drops.
Did the aftermarket front calipers come with a copper crush washer?
The GMs do. Goes on the hose connection. (fronts only)
Then the clue lies in the front brakes.
You clamp the front hoses, firm pedal.
Release the clamp, pedal drops.
Did the aftermarket front calipers come with a copper crush washer?
The GMs do. Goes on the hose connection. (fronts only)
He should be leaking without the copper washer but the hoses would be suspect. Which hose did you use, do they have a DOT number on them? If not I would replace them with ones that do, you could be expanding the hose when pushing further down on the pedal. Standard brakes should be pretty firm.
Did you ever resolve your problem? I'm in the same situation. I replaced EVERYTHING but the comb valve on my '79 using Wilwood calipers, pads, rotors and lines. My pedal still goes to the floor before the car stops. I'm reluctant to drive it very far. When the engine is shut down and the vacuum is gone, the pedal is hard as a rock. Very frustrating.
Did you ever resolve your problem? I'm in the same situation. I replaced EVERYTHING but the comb valve on my '79 using Wilwood calipers, pads, rotors and lines. My pedal still goes to the floor before the car stops. I'm reluctant to drive it very far. When the engine is shut down and the vacuum is gone, the pedal is hard as a rock. Very frustrating.
Al
You didn't mention master, what if anything did you do?
Still in progress. Rebuilt all calipers with CSSB o-rings and replaced all flex hose with new rubber. Waiting on a replacement LF hard line that i destroyed trying to break it loose. Have not touched MC yet. Hope it is not necessary. Bought the tool to keep combo valve centered. Hoping to start bleeding by end of week (26 Feb).
I forgot to mention that I replaced the MC, too. Today I bedded in the new brakes. The car does stop, but the pedal touches the carpet on hard stops. It's not possible to lock the wheels up. When I checked the temp of the wheels, they were hot to the touch. So, the brakes are working. I've owned this car for over 30 years and never had, what I would call comfortable pedal travel. These things are just under-braked.
I forgot to mention that I replaced the MC, too. Today I bedded in the new brakes. The car does stop, but the pedal touches the carpet on hard stops. It's not possible to lock the wheels up. When I checked the temp of the wheels, they were hot to the touch. So, the brakes are working. I've owned this car for over 30 years and never had, what I would call comfortable pedal travel. These things are just under-braked.
they are not under-braked, something is wrong with your system. You bench bled the master? What brand master did you use?
After 20 years of road racing, I have found that a spouse/significant other/son or daughter is an invaluable part of brake bleeding. I have tried every variant of brake bleeder in the past, and have found someone pressing on the pedal gives the most consistent solid pedal. I do use a pressure type one-man bleeder to get the bulk of the bleeding done, then call in the human factor to complete this job. This way you don't wear out your welcome making them push endlessly before getting any initial results.
Marc in Indy
1957 Corvette 283/245 4 speed
1973 Honda Civic SCCA GT5 vintage race car with the VSCDA
Exactly what I have been told (about 1,000 times).
Well 68 did have a lot of one-year parts!
Hopefully it still has the pressure switch inside.
And for your viewing pleasure here is a NOS GM Adjustable Proportioning Valve # 3878944
Only known factory installation was on L88s, and 4-wheel J56 disc brake Z28s.
Possibly ZR-1s or ZR-2s with J56 HD brakes.
It can be yours for only $2500! LOL On NCRS.com.
And to think I ran one on my 70 Z28 pro-solo car, because it was "cheap" (almost free)!
Who knew?
It is the one mentioned in the Chevy Power Book, which even gave a chart of the pressures at different adjustments. Just turn the ****. It did make a huge difference in how much rear braking power I got. I could finally lock the rears before the front LOL. And when I got it tuned just right, I got up to 1.27G braking. In the 80s.
I have one still in the GM box and I only want $1k for it
Hi FWillson, I came across this post as I'm having the same problem on my 1976 Corvette. New back calipers and pads but can't seem to bleed the system to a hard pedal. The difference between our cars is mine has power brakes. I have a hard pedal when the car is not running. As soon as I crank the car, the pedal goes to the floor and won't pump up. I've run 2 quarts of brake fluid through the back 2 new calipers the old fashioned way with someone pumping and holding the pedal for me. I then purchased a Motive power bleeder and tried that. Nothing has worked so I'm wondering if the master cylinder somehow got screwed up when I replaced the calipers. Did you ever find a solution to your problem? I've bled the brakes on many many cars and have never had this problem and it's driving me crazy! Thanks Jay
