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Anybody happen to have the master cylinder removed and brake booster installed, and willing to measure how much the rod between the booster and the master cylinder moves with full movement of the brake pedal?
No matter what I do the brake pedal sinks almost to the bottom with no resistance.
The rod length is right, measured to have about 0.010'' play.
When the pedal is pushed to the floor with a bleeder open only a very small amount of fluid comes out.
Gravity bleed, lift the rear of the car, everything has been tried.
It's the third master cylinder I try, and the correct size for power brakes.
I dont have mine off so i cant get you a measurement.
You say you have tried 3 masters so then something must be off somewhere with what you have setup.
Power brakes use an 1 1/8" bore master. As this is harder to push on due to the larger bore size but the booster makes that easier to push.
Power brakes have the clevis mounted to the LOWER hole in the brake pedal (furthest from the fulcrum) closest to the pedal pad.
Manual brakes use a 1" bore master as this is easier to push but requires more travel to accomplish the same movement as the power based master cylinder.
Manual brakes have the clevis mounted to the UPPER hole in the brake pedal (closest to the fulcrum) furthest from the pedal pad.
Then there is the difference of the piston cup depth in various years. The ’76 and earlier Corvette used the deep style master cylinder shown on the right, while the ’77 and later C3 models used the shallow style shown on the left (its more of a dimple than a hole).
Is it possible someone put in a booster/master combo of a different year and you maybe are trying the wrong master for that combo? Just a thought.
I dont have mine off so i cant get you a measurement.
You say you have tried 3 masters so then something must be off somewhere with what you have setup.
Power brakes use an 1 1/8" bore master. As this is harder to push on due to the larger bore size but the booster makes that easier to push.
Power brakes have the clevis mounted to the LOWER hole in the brake pedal (furthest from the fulcrum) closest to the pedal pad.
Manual brakes use a 1" bore master as this is easier to push but requires more travel to accomplish the same movement as the power based master cylinder.
Manual brakes have the clevis mounted to the UPPER hole in the brake pedal (closest to the fulcrum) furthest from the pedal pad.
Then there is the difference of the piston cup depth in various years. The ’76 and earlier Corvette used the deep style master cylinder shown on the right, while the ’77 and later C3 models used the shallow style shown on the left (its more of a dimple than a hole).
Is it possible someone put in a booster/master combo of a different year and you maybe are trying the wrong master for that combo? Just a thought.
Thanks for the input, but I have the right diameter and depth master and the clevis is in the correct hole on the pedal arm
What brand/place are you getting these master cylinders from? Often the parts house are selling masters that are not actually corvette, but come off other vehicles and might work in a corvette.
What brand/place are you getting these master cylinders from? Often the parts house are selling masters that are not actually corvette, but come off other vehicles and might work in a corvette.
One repro original style, believe it was from Zip Corvette.
One Willwood.
One SSBC aluminum (looks like the original)
The one from Zip should match the closest providing the correct info was relayed to the vendor.
IDK, its frustrating for sure.
Just curious. When you bench bleed, you are not pushing the piston in too far are you? That will destroy the piston seals, void warranty and cause "pedal to the floor" syndrome. Check out my profile > photo albums > bench bleed, about the screwdriver trick.
The one from Zip should match the closest providing the correct info was relayed to the vendor.
IDK, its frustrating for sure.
Just curious. When you bench bleed, you are not pushing the piston in too far are you? That will destroy the piston seals, void warranty and cause "pedal to the floor" syndrome. Check out my profile > photo albums > bench bleed, about the screwdriver trick.
That could be an issue. But why would the seals be damaged by doing this on a new master cylinder? I get that it happens with a used one that may have rust in the "unused" part of the bore.
Would fluid be leaking to the outside if that happened?
Still curious about how much travel there is supposed to be.
Last edited by Danish Shark; Jan 22, 2020 at 03:09 AM.
When I bought my rebuilt MC, a huge label on the box said: Do Not Force Piston In More Than 1 3/8" or you will void the warranty.
I did some research. It seems the piston seals (2) can actually be forced beyond the cylinder wall ends, inside the MC bore. Then, what happens is, the seal (piston ring) flips itself over or rolls over on the return stroke. When that happens, the seal or seals are damaged. This scenario is quite common for us people new to the system of bench bleeding. Or in laymans terms: Who dah thunk?
Take a look at my profile > photo album > bench bleeding for some ideas.
From: Las Vegas - Just stop perpetuating myths please.
Well I would inspect the pedal assembly. I've had the clutch pedal pin on the lever fail at the tiny spot welds that fasten it to the pedal arm. Had to make a better pin out of a grade 8 bolt and use a full bead weld to hold it in.
Here's a great thread on upgrading the whole pedal assembly: https://www.corvetteforum.com/forums...-bearings.html
I'm sure you know about the need to bleed the master cylinder on the bench/out of the car but in case it was overlooked I will mention it. Brake master needs to be bleed in horizontal level.
Well I would inspect the pedal assembly. I've had the clutch pedal pin on the lever fail at the tiny spot welds that fasten it to the pedal arm. Had to make a better pin out of a grade 8 bolt and use a full bead weld to hold it in.
Here's a great thread on upgrading the whole pedal assembly: https://www.corvetteforum.com/forums...-bearings.html
I'm sure you know about the need to bleed the master cylinder on the bench/out of the car but in case it was overlooked I will mention it. Brake master needs to be bleed in horizontal level.
Hope this can help.
Well, yes & no. Horizontal, nose up, nose down. Three positions.
A bubble will be trapped in the piston bore and it has to come out the tiny hole in the reservoir. That's why you tilt the MC. To get the bubble to rise & escape.
Well I would inspect the pedal assembly. I've had the clutch pedal pin on the lever fail at the tiny spot welds that fasten it to the pedal arm. Had to make a better pin out of a grade 8 bolt and use a full bead weld to hold it in.
Here's a great thread on upgrading the whole pedal assembly: https://www.corvetteforum.com/forums...-bearings.html
I'm sure you know about the need to bleed the master cylinder on the bench/out of the car but in case it was overlooked I will mention it. Brake master needs to be bleed in horizontal level.
Hope this can help.
I have been wondering is something is wrong with the pedal assembly, or maybe something is bent.
I can't quite figure out what the pedal assembly is mounted on? I assume that it is not just the fiberglass firewall? Is it bolted to the frame somehow?
If the whole pedal assembly is tilted downward it will make a huge difference.
I have been wondering is something is wrong with the pedal assembly, or maybe something is bent.
I can't quite figure out what the pedal assembly is mounted on? I assume that it is not just the fiberglass firewall? Is it bolted to the frame somehow?
If the whole pedal assembly is tilted downward it will make a huge difference.
Pedal assembly is bolted to the firewall and the brake booster.
It doesn't matter what length someone else's booster rod is. There are so many combinations of different valve manufacturers, different M/C castings, etc. etc that each application needs to install a rod that fits their hardware. This means that the rod length must equal the depth of the pocket in the apply valve + the depth of the booster pocket + the thickness of the gasket between the booster and master cylinder (if you use one). That rod can be a few thousandths shorter, but it can not be longer than that total amount or the brakes will be partially applied.
It doesn't matter what length someone else's booster rod is. There are so many combinations of different valve manufacturers, different M/C castings, etc. etc that each application needs to install a rod that fits their hardware. This means that the rod length must equal the depth of the pocket in the apply valve + the depth of the booster pocket + the thickness of the gasket between the booster and master cylinder (if you use one). That rod can be a few thousandths shorter, but it can not be longer than that total amount or the brakes will be partially applied.
Hi
It is not the brake rod lenght I am asking about. It is how far it moves with full movement of the pedal.
I have measured the movement om my car and it is 25mm or one inch.with full pedal travel.
Why aftermarket master cylinder verses factory manual master cylinder. = just curious
3 of my cars have been manual & never had any complaints or problems
Why aftermarket master cylinder verses factory manual master cylinder. = just curious
3 of my cars have been manual & never had any complaints or problems
Blast from the past
Manual brake cars are different, or at least on my manual car I never noticed this behaviour.
Now I have one with power brakes, and it seems like the Vettes just have horribly low brake pedal, so very very little brake pedal travel.
I learned to live with it; just pretend it isn't scary.
absolutely correct about pushing seals too far when bench bleeding MC and even can happen when bleeding each wheel with MC installed in car and ramming brake pedal to floor...need to go slow and just far enough - I have your exact pressure bleeder setup -.works perfectly, is fast with only one person and overall I believe does a much better thorough job, while eliminating two person bleeding using brake pedal and damage to MC seals.
Brake booster rod movement
