zeeker

1965, 300 HP, Manual brakes, 4-speed
My problem....This happened last fall as I was putting her to bed. Might drive 10 blocks or 10 miles. Applying light brake pressure to stop, lift foot off pedal, and it continues to stop by itself. Drive another block and it does the same thing, only worse. Finally just locks up TIGHT! I finally got it back in the garage, jacked up the back and could not turn the rear wheels. My brain said to rebuild the rear calipers so I did. They are already SS lined so I bought new pistons and seals. installed and bled. Repair looked good. Well, that cured NOTHING! Happened again yesterday on it's first trip around the block. After nursing it back to my driveway, It was locked up again. As I sat there (for a couple of minutes) scratching my head, suddenly it released and started rolling backwards. I don't know what to do next. The master cylinder looks original. or could the rear calipers just be junk....or could it be in the rear-end? Can anybody help me troubleshoot this? Sure as hell can't drive it this way. Thanks zeeker

856666

If this was mine I would rebuild the master cylinder and flush all the fluid. It should solve the problem IMO.

If it was one rear side or the other I would say the flex hose is suspect but since both are doing this I would go Master Cyl.

If you want to prove the brakes are the problem, drive it to the point of lock up then crack a rear bleeder to release pressure and it should move freely

Phil

GTOguy

My thoughts, too. Rebuild the master. If problem persists, probably a bad flex hose.

DansYellow66

Nothing is ever sure but it sounds like a classic case of bad rubber hoses that have collapsed inside. Step on the brake pedal and fluid is forced past them but once the pressure is released the lining collapses keeping pressure in the brake caliper. The more stops the worse it gets until the brakes are dragging and hot as heck if not locked tight.

rfn026

First, I've had really good experiences with White Post rebuilds.


The Numbers are Important to Me.

I'm not a huge fan of home rebuilts. When you hone the m/c you rather obviously increase the bore diameter. No one sells oversize O-rings. OEM seals might last for a while. You'll be back into it shortly.

Most of the factory rebuilts are done offshore. Enough said.

Before you ship off the m/c flush the entire system with denatured alcohol. Keep flushing until you get clear liquid.

If this were me I would just do everything. You may not need it but as long as .......

Richard Newton
Always Break in New Rotors

AZDoug

Your brake pedal return spring is OK, right?

I never would have thought no spring would be a problem, but in some cases, no or broken return spring will not allow the brakes to release. I ran into the issue about 5 years ago, on a different vehicle.

Doug

maroon67

If it was one rear side or the other I would say the flex hose is suspect but since both are doing this I would go Master Cyl.

If you want to prove the brakes are the problem, drive it to the point of lock up then crack a rear bleeder to release pressure and it should move freely

Phil[/QUOTE]

I agree with the rubber brake hose diagnosis. Just because they look good on the outside does not mean the inside has not deteriorated. When one rear wheel locks up you will not be able to rotate the other by hand. Good luck.

BTW Beautiful car.

GCD1962

A very common cause. You can't tell at all by looking at the hose as it happens internally. Replace all of them, not just one.

MikeM

Next time it locks up, pop the cap on your MC and see if the compensating port is blocked. If it is, it will hold pressure on the brakes.

No sense answering what can cause this until you confirm that's what is or is not the problem.

DansYellow66

A good point. And a weak pedal return spring can prevent the MC piston from returning enough to uncover the compensating port.

zeeker

Thank You so much for the guidance fellas. I suspect that it is the original and since it will never be judged (at least not by me) I'll just spring for a new one. Are some better than others? I also have in my stash a complete set of new hoses. When I rebuilt the rear calipers, I also bought a Motive pressure bleeder. Man, does that work slick. Thanks again, guys. I'll let you know the outcome..........zeeker

pop23235

Try it again and when you sense the "lock up" place your toe under the brake pedal and lift. If it releases, that confirms either your spring is bad or the master is not releasing residual pressure - similar problems.

rfn026

If you're going with new make sure you save the old one. Someone might want it down the road.

Over the years I've had good luck with NAPA parts.

Richard Newton

frankturbo

Same thing happened to my 69 last year , put on a GM repo MC , end of problem...

zeeker

Okay, I proclaim my brake problem healed! I replaced all four hoses and the Master cylinder. Since they don't give Silicone brake fluid away, I changed them all at the same time. Otherwise I would have had to bleed them twice so I don't really know which solved the problem. I do know that it took some serious pushing to get a piece of .082 thick safety wire thru the rear hoses. It just fell thru the new ones. There was also quite of bit of crud in the bottom of the cylinder. Knowing the OP, I think he was a little lax in cleaning things up when he switched to silicone. But then again, that was 27 years ago. The repair went great UNTIL I tried to screw the fitting into the cylinder. TIGHT! #%$&* rebuilt shi&. Naturally it started to cross-thread. STOP
I took the other end loose and snaked out the steel line for some file work in the vice. Much frustration later I got it to fit properly. A proper tap for the cylinder end would have been much easier but who the hell owns one of those? Not me! Next time I'll buy that fitting and play with it in the vice when I'm bench bleeding. Can you guys tell if this is a 1965 unit?