Fixed Brakes - Broken again
Thread Starter
Safety Car
Joined: Feb 2006
Posts: 3,557
Likes: 0
From: Ridgeway VA
Fixed Brakes - Broken again
'75 with 10 year history of brake problems - last week new master cylinder and bleed done by a good mechanic. In the last 4 years everything has been done except - brake line front to back, front brake rubber hoses (that means all other brake lines are new) . Took for a ride today and almost have to stand on brakes and light comes on.
Possibilities - new booster just after 3 years, new lines yet not replaced? Any others had this ongoing problem?
Possibilities - new booster just after 3 years, new lines yet not replaced? Any others had this ongoing problem?
Melting Slicks
Joined: Dec 2006
Posts: 2,669
Likes: 3
From: Kingston Ontario
Check rotor runout. If you had a good pedal a week ago and you don't have it now I would say runout or you have a leak somewhere. The light coming on indicates that your system failure is in one half of the system, front or back. Check master cylinder for levels and then check rotor runout. 
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,851
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
If you have excessive rotor run out the caliper can suck air in the system and not leak fluid out the caliper! It will most likely not show up in the reservoir. I know. . . I know. . . it breaks the law of displacement, but it can happen.
To find a rotor with excessive run out can be real easy by cheating if you do not have access to a dial indicator.
Remove the wheels to obtain access to the brake calipers. Remove the brake pad pin and paint it with an off color paint. Install the pin back in the car and drive it. A rotor with excessive run out will wear the paint right off the pin.
Just an old bubba trick but it will ID any rotor problem pretty quickly.
Willcox
To find a rotor with excessive run out can be real easy by cheating if you do not have access to a dial indicator.
Remove the wheels to obtain access to the brake calipers. Remove the brake pad pin and paint it with an off color paint. Install the pin back in the car and drive it. A rotor with excessive run out will wear the paint right off the pin.
Just an old bubba trick but it will ID any rotor problem pretty quickly.
Willcox
3rd Gear
Joined: Nov 2006
Posts: 3
Likes: 0
I might stating the obvious, but have the pads been replaced lately? I had a chain reaction situation on my '71 where one caliper would blow, and fluid would get everywhere. Then, since those pads were soaked, the pressure rose to the other calipers causing those to blow (leak), and so forth. I overhauled all four calipers with the O-ring type seals and installed new (non-soaked) brake pads, and the pedal is as stiff as ever. Pressure bleeding about six times around with the Motive also helped out a tad.
Safety Car
Joined: Sep 2005
Posts: 4,213
Likes: 643
From: Orange County Ca
2 thoughts here. New master cylinder. Was the indentation that the push rod goes into EXACTLY the same. If not, the push rod may not bottom in the indent, and the cylinder travel may be affected. If the ports and the piston don't line up correctly, things don't work right.
Also you mention the "light" comes on. This could mean that the equalizing valve has upset, and is blocking 1/2 of the brake lines. This could be a result of a lot of air in some calipers or lines.
Also you mention the "light" comes on. This could mean that the equalizing valve has upset, and is blocking 1/2 of the brake lines. This could be a result of a lot of air in some calipers or lines.
Tech Contributor
Joined: Aug 1999
Posts: 15,154
Likes: 3,959
From: Connecticut, USA
sounds like air in the system. If you search my name you'll find my post on dialing in rotor runout to under 002" If the bearing endplay is also 002" and the brake hoses,calipers good then you should be able to get a good system. If they last only a short time you have runout issues.
30 years ago my buddy's 68 was so bad we used to bleed the brakes every sat afternoon to go out on sat night! The runout was the problem, once the rivets are removed and the rotors turned or replaced this is usually a problem until corrected. New rotors won't fix it.
30 years ago my buddy's 68 was so bad we used to bleed the brakes every sat afternoon to go out on sat night! The runout was the problem, once the rivets are removed and the rotors turned or replaced this is usually a problem until corrected. New rotors won't fix it.
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Melting Slicks
Joined: Apr 2002
Posts: 2,337
Likes: 14
From: Norfolk VA
What is your take on this brake system? I am converting to the C5 brake system because of these issues, Checking runout, heavy rusty air pumping calipers. I a proponent to the floating caliper system. I guess Chevy thinks so and they went back to a fixed, multi piston (not sure if the pistons float on the current C6 brakes) caliper system without springs behind the pistons. The C3 brake system is a pita.
