c3 hard brake pedal
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3rd Gear
Joined: Aug 2019
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c3 hard brake pedal
1969 vette with power brakes were always good then one day pedal goes farther down and brake light comes on and pedal gets real hard. does not go to floor. does not use fluid. does stop with all four wheels. replaced mc no change. checked all calipers and all is good. what do I check next
Le Mans Master
Joined: Aug 2017
Posts: 8,336
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From: Cool Northern Michigan
Will assume the ENTIRE system was bleed after the MC swap?
Was the MC bench bled?
You likely have seepage somewhere. Doesn't always show up right away on the floor. Keep looking.
Was the MC bench bled?
You likely have seepage somewhere. Doesn't always show up right away on the floor. Keep looking.
Is my vette stock?? HAHA
Joined: Oct 2015
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From: Im not allowed to tell you
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does the pedal go down and not come fully back to the top? You can pull it back to the top with your toe? Its you brake booster. I did a lot of research and another thread on this a month ago or so. Theres either a spring internal that fails or a vent that doesnt allow the pressure to equalize when you release the pedal. Pretty easy fix. Make sure your pedal rod is adjusted properly when you replace the booseter. CSSB has a tool for it. I used a micrometer.
http://www.cssbinc.com/brake-boosters-corvette.aspx
http://www.cssbinc.com/1968-76corvet...tmenttool.aspx
http://www.cssbinc.com/brake-boosters-corvette.aspx
http://www.cssbinc.com/1968-76corvet...tmenttool.aspx
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,809
From: Cool Northern Michigan
Ok. I think I know what might be happening here,
Symptom: Pedal to low
Changes: New MC
Question: How much of a gap do you have between the Booster Rod and the end of the MC piston? This is very critical and gets over looked by many.
Different manufactures / suppliers of M.C.s may have different designs on the end of the MC piston.
There is a specialty tool that measures that gap. OR
By removing the MC mounting nuts but not the brakelines, move the MC forward. You can place a gob of Silly Putty on the end of the booster rod. Tighten the two MC nuts. Remove the nuts, measure the gap by carefully scrapping the putty out of there.
I don't remember that exact clearance, but seems to me it was 0.060. If there is no gap, the brake pads are forced against the rotors constantly.
If there is way too much gap, the pedal is low before good solid braking. Certain year C3s had adjustable booster rods, in or out / shorter or longer. Others had no adjustment. Some had a adjustment at the brake pedal arm. Manual brakes had a deeper piston in the MC end. PB had a shallower, and so on.
Symptom: Pedal to low
Changes: New MC
Question: How much of a gap do you have between the Booster Rod and the end of the MC piston? This is very critical and gets over looked by many.
Different manufactures / suppliers of M.C.s may have different designs on the end of the MC piston.
There is a specialty tool that measures that gap. OR
By removing the MC mounting nuts but not the brakelines, move the MC forward. You can place a gob of Silly Putty on the end of the booster rod. Tighten the two MC nuts. Remove the nuts, measure the gap by carefully scrapping the putty out of there.
I don't remember that exact clearance, but seems to me it was 0.060. If there is no gap, the brake pads are forced against the rotors constantly.
If there is way too much gap, the pedal is low before good solid braking. Certain year C3s had adjustable booster rods, in or out / shorter or longer. Others had no adjustment. Some had a adjustment at the brake pedal arm. Manual brakes had a deeper piston in the MC end. PB had a shallower, and so on.
Last edited by HeadsU.P.; Aug 10, 2019 at 06:15 PM.
