75 Power brake issues
Thread Starter
Instructor
Joined: Apr 2004
Posts: 115
Likes: 2
From: Kissimmee, FL
75 Power brake issues
My 75 vette power brakes go down to the floor with little stoppage.
Bled all 4 brakes and fluid level good, no leaks. Brake pads also good.
Could it be master cylinder and/ or booster?
Thanks
Bled all 4 brakes and fluid level good, no leaks. Brake pads also good.
Could it be master cylinder and/ or booster?
Thanks
Melting Slicks
Joined: Jun 2011
Posts: 3,114
Likes: 598
Start with bleeding the Master cylinder while on the car.
Try this.
Get the last bit of air out from the brake master cylinder. - CorvetteForum - Chevrolet Corvette Forum Discussion
Once this is done I usually do a pressure bleed of each caliper bleeder.
So you dont waste brake fluid capture the bleeder fluid into a jar and recyle into the MC.
I pressure bleed using the adapter / clamp on the MC.
I use 15-20 PSI at the MC.
Le Mans Master
Joined: Aug 2006
Posts: 7,419
Likes: 1,555
From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
You have to continue to troubleshoot
You said that no leaks at the calipers but were both sides of the master cylinder full?
The M/C can leak into the booster.
To test the M/C:
Plug one line with the other connected and see if the pedal is rock hard then reverse the plug and the line and test again.
The pedal should be rock hard in both tests, if not the M/C is bad.
The M/C can leak into the booster.
To test the M/C:
Plug one line with the other connected and see if the pedal is rock hard then reverse the plug and the line and test again.
The pedal should be rock hard in both tests, if not the M/C is bad.
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,809
From: Cool Northern Michigan
Caution if you plug the MC for testing. Do Not Use a Bolt. There is a flare inside those ports on the side of the MC. A bolt can destroy the casing.
You can make two test lines out of short lengths of steel pre-made lines at NAPA, about a foot long. You will need the port hole diameter and TPI from both ports which are different, but both are common sizes. Then plug the end of the test line or simply pinch it off. There may be 400 lbs of pressure on the line from the brake pedal.
Keep in mind that after testing the MC you have introduced air into the entire system.
You can make two test lines out of short lengths of steel pre-made lines at NAPA, about a foot long. You will need the port hole diameter and TPI from both ports which are different, but both are common sizes. Then plug the end of the test line or simply pinch it off. There may be 400 lbs of pressure on the line from the brake pedal.
Keep in mind that after testing the MC you have introduced air into the entire system.
Le Mans Master
Joined: Aug 2006
Posts: 7,419
Likes: 1,555
From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
Some M/C bleed kits have the correct size plugs which are 9/16 X 18 and 1/2 X 20.
If you get the hard lines just get the correct fittings.
The rear calipers have 2 bleed screws, do the inners first then the outers.
If you get the hard lines just get the correct fittings.
The rear calipers have 2 bleed screws, do the inners first then the outers.
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Team Owner
Joined: Jun 2001
Posts: 43,136
Likes: 155
From: Thomson Georgia
I have been told that may be my issue. I am currently rebuilding my calipers and replacing the rubber hoses. They do wear out eventually.