1968 brakes non power disc

[GrantHile]

I think I know the answer to my question but I'd like some input before I buy a new proportioning valve. I had my rear brakes lock up after hitting the brakes rather hard one night and after sitting for short time they were ok. I tryed replacing the master cylinder and couldn't seem to get the rear to bleed. So I returned the master and got another but after the 3rd its not that. I took off the valve and it seemed to be clear but maybe when pressured it close's the rear. Anyway if anyone has had this happen please advise Thanks for any help Grant

[Terry F.]

Re: 1968 brakes non power disc

Weird....people on the board have had that one happen before. You might just want to search the archives.

I would study a chevrolet service manual. Make sure the master cylinder does not have check valves in the holes that the brake lines screw into. I seem to recall passenger cars having something like that and the manual instructing you to remove them on corvette.

The rubber flex hoses are capable of colapse internally. You might disconnect them where they attach to the frame and flush the system that way.

It may be the little valve but I have not had them do that on me. Not to say that they won't, just not my experience (yet?).

Later, Terry

[Wayne W.]

Re: 1968 brakes non power disc

Check the rubber hoses. They tend to collapse from the inside causing the condition you describe.

[Jim T.]

Re: 1968 brakes non power disc

Grant your discription of the rear brake malfunction is very similiar to the experience I had on my original owner 68. My problem was with the right front wheel, a new rubber brake hose and the problem was gone. New brake hoses on the rear is a inex*****ve replacement of a saftey item. I would not check or replace anything else until you replace the hoses.

[Jim B.]

Re: 1968 brakes non power disc

I think that the weakest part of a 68 is the braking system. My original owner 68 non power brakes have locked up as you described. But mine only locked on one wheel which was hard to deal with. After disassembly the problem turned out to be the caliper piston which gouged out a groove in the sleeve and then locked into place. I had the same problem with bleeding but mine only cleared once or twice then locked up permaently. I had to replace the caliper. The car was still worth it. I would certainly agree with replacing ALL rubber components if they are not new. Good luck.

Jim Boudreaux
#38390

[Michael W.]

Re: 1968 brakes non power disc

'68 Corvettes DO NOT have a 'proportioning valve' in the true sense of the word. There is nothing internal to this valve to regulate or limit pressure to the rear or front brakes. It serves simply as a manifold to sense pressure differential between the two systems (in the case of a leak) and turn on a warning light. The shuttle valve does need to be centered to be able to bleed the rears successfully.

Look elsewhere for your problems.

[Tom S.]

Re: 1968 brakes non power disc

Grant
I'll bet it's the hose. I just went through that last week with my 69. I have std. brakes as well.The inside of the hoses colapse and after it sit's a few minutes the fluid seep's back and wheel free's up.Good to go until you apply the brakes again. Tom