Brake Booster Malfunction?
Thread Starter
8th Gear
Joined: Apr 2019
Posts: 8
Likes: 1
From: Brussels Belgium
Brake Booster Malfunction?
Howdy, several months (years) always the same problem with the brake pedal? there are no leaks and so on! I changed the 4 calipers, master and all the lines and hoses.
the brakes are amazing working well! did a brake test yesterday on the brake test roller bench! all 4 correct, when the corvette is cold; the pedal goes only 5 mm. in! brakes like a European car
. never the less. when I drive 25 miles and more
everything warms up! and the pedal goes 1" or more downwards? and is not feeling spongy? sometimes goes more than 2" in. the day after engine stone cold! everything works fine again?
their is only one line (steel) for the vacuum to the booster from the carb. the booster and valve/filter are 43 years old? but after several hours when I pull the vacuum valve a bit out! there is still a sissi vacuum sound to hear.
so he works! I think. can it be a MC problem it's the third one now in time? the push rod length? any suggestion? P.S. when the Cor is warmed up and I pushed the pedal downwards again there is always a sound too hear at the pedal,
like an air compression release?
the brakes are amazing working well! did a brake test yesterday on the brake test roller bench! all 4 correct, when the corvette is cold; the pedal goes only 5 mm. in! brakes like a European car
. never the less. when I drive 25 miles and moreeverything warms up! and the pedal goes 1" or more downwards? and is not feeling spongy? sometimes goes more than 2" in. the day after engine stone cold! everything works fine again?
their is only one line (steel) for the vacuum to the booster from the carb. the booster and valve/filter are 43 years old? but after several hours when I pull the vacuum valve a bit out! there is still a sissi vacuum sound to hear.
so he works! I think. can it be a MC problem it's the third one now in time? the push rod length? any suggestion?
P.S. when the Cor is warmed up and I pushed the pedal downwards again there is always a sound too hear at the pedal,like an air compression release?
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
Your MC testing is done with the engine running. What does the pedal do with engine off?
The fact that the booster still holds vacuum long afterwards indicates its fine.
You keep swapping out masters. So, I question if you damaged the seals inside by improper bench bleeding.
When you insert a screwdriver on the MC piston, a distance of no more than 1 & 3/8 inches will bleed the MC.
Any more than that can damage the piston seals internally and void the warranty of the master.
Why can't you overextend the master piston when it's mounted on the car?
The brake pedal hitting the carpet is the max travel.
The fact that the booster still holds vacuum long afterwards indicates its fine.
You keep swapping out masters. So, I question if you damaged the seals inside by improper bench bleeding.
When you insert a screwdriver on the MC piston, a distance of no more than 1 & 3/8 inches will bleed the MC.
Any more than that can damage the piston seals internally and void the warranty of the master.
Why can't you overextend the master piston when it's mounted on the car?
The brake pedal hitting the carpet is the max travel.
Thread Starter
8th Gear
Joined: Apr 2019
Posts: 8
Likes: 1
From: Brussels Belgium
Your MC testing is done with the engine running. What does the pedal do with engine off? with the engine off it blocks and want go in.
The fact that the booster still holds vacuum long afterwards indicates its fine.
You keep swapping out masters. No, it's the third Master in 43 years, this one is 2 years old bought it compleet remanufactured; I never pushed the pedal further than halfway when bleeding with two persons and now I did gravity bleed.
will do it again end this week.
So, I question if you damaged the seals inside by improper bench bleeding.
When you insert a screwdriver on the MC piston, a distance of no more than 1 & 3/8 inches will bleed the MC.
Any more than that can damage the piston seals internally and void the warranty of the master. I know.
Why can't you overextend the master piston when it's mounted on the car? ??
The brake pedal hitting the carpet is the max travel.
The fact that the booster still holds vacuum long afterwards indicates its fine.
You keep swapping out masters. No, it's the third Master in 43 years, this one is 2 years old bought it compleet remanufactured; I never pushed the pedal further than halfway when bleeding with two persons and now I did gravity bleed.
will do it again end this week.
So, I question if you damaged the seals inside by improper bench bleeding.
When you insert a screwdriver on the MC piston, a distance of no more than 1 & 3/8 inches will bleed the MC.
Any more than that can damage the piston seals internally and void the warranty of the master. I know.
Why can't you overextend the master piston when it's mounted on the car? ??
The brake pedal hitting the carpet is the max travel.
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
Well lets backup. I don't think you are following me.
You may be buying a fourth master in 43 yrs. To me, that is a lot of swapping-out. Some of these C3s on this forum still have the original master.
I am not a big fan of using the two-person brake pedal method of bleeding the brakes. But it's your car.
When all these past masters cylinders were in the vise on your work bench, did you insert a screwdriver more than 1 & 3/8 inches? (Need to convert to metric)
You stated you have no leaks. Well, that's no external leaks. You have no idea if you have an internal leak. And an internal leak can and often happens inside a master that was not bench bled properly.
The piston seals could be damaged, the brake-fluid is slipping (leaking) past the seals. Invisible to the eye. You still have some braking but not 100%.
You may be buying a fourth master in 43 yrs. To me, that is a lot of swapping-out. Some of these C3s on this forum still have the original master.
I am not a big fan of using the two-person brake pedal method of bleeding the brakes. But it's your car.
When all these past masters cylinders were in the vise on your work bench, did you insert a screwdriver more than 1 & 3/8 inches? (Need to convert to metric)
You stated you have no leaks. Well, that's no external leaks. You have no idea if you have an internal leak. And an internal leak can and often happens inside a master that was not bench bled properly.
The piston seals could be damaged, the brake-fluid is slipping (leaking) past the seals. Invisible to the eye. You still have some braking but not 100%.
Last edited by HeadsU.P.; Sep 4, 2024 at 06:58 PM.
