Got a problem on my '62 Invicta... after driving ashort distance, the brakes stay 'on'... locked up. Doesn't happen immediately, but after a short drive of 3-5 miles or so. First symptom is brake lights staying on, then they slowly drag more and more (after each push of the pedal) until they basically lock up. Once it happens, the car has to sit while they slowly free back up. Have had the problem ever since I swapped the factory booster/cylinder for a Corvette-style dual cyl with 7" dual-diaphragm booster. Master cyl is 1" bore, same as stock. Car still has stock drums all around. The booster fit straight into the stock firewall holes, so plunger aligns with brake pedal fine. Plunger isn't too long because pedal has plenty of free play away from the firewall when disconnected from plunger. Disconnecting the vacuum tot he booster doesn't change anything. I've bled these things several times, but the problem won't go away - drives fine for a while, then at some point the brakes stick 'on' until they are allowed to free back up on their own. Thoughts here...? Did I miss something obvious? Need new return springs on the shoes to counteract the new master...? Wheel cylinders are recent, but maybe I should rebuild them based on these symptoms...? Help would be appreciated here.... gotta get this ***** up to Austin, and I don't wanna trailer it!
sounds like one of the rubber brake lines is collapsing. It won't let the pressure bleed off at first but will after it sits. I've had the same problem on a couple of cars. Try to isolate which one it is and replace. I'd replace all of them if thats possible. TP
you did miss something,I had the same problem on my 32. Somewhere along the brkelines or even the booster there is heat getting to it. I wrapped my exhaust with moroso heat shield wrap where it was close and cured the problem. The 7" booster seems to be effected by this much easier.
sounds like maybe a speck of dirt or rust blocking the small bleed hole in the reservoir. i would get the fluid out and make sure the holes are all clear.
your brake fluid is boiling somewhere in your system,i'm guessing a bad master cylinder,or your pedal linkage is binding
Since the problem started only after replacing master cyl/booster, START THERE, check for sufficient pushrod clearance between booster and master cyl. Easy way is to loosen nuts holding m/cyl to booster leaving about 1/8 in. clearance. If that corrects problem, slide m/cyl out enough to inspect pushrod, probably has adjuster on end, shorten about 1-2 turns at a time and drive again.
Good stuff guys - thanks. Definitely a couple of things here that I didn't think about. I'll let ya know what happens.
Your rod from the pedal to the MC is too long.............. I have the opposite problem.....rod is too short
I think Ponch62 is on to it Mine did the exact same thing sometimes I could drive 30 miles or so before it would do it. It was the rod legnth I just shorted it up a bit and it aint done it since
I know you say you bled them several times, but I say there is still air in the lines. I've seen this same symtom on numerous occasions. Every time it was air in the lines. As the braking system heats up, the air expands until the brakes lock up. When the system cools, the brakes function properly. Please try to bleed them some more and see if it helps.
Hey Blakey Blake! how fresh was the brake fluid you topped the new master off with? it sounds like a contaminated system to me. which would require the replacement of all the rubber lines and rubber peices. you didn't mix silicone and dot 3,did you? ahh hell. if you don't get it figured out by monday next, call me. I can spend some time here at the shop with you till we get it lined out.
How the hell would I know...? If the plunger rod was too long, would they be locked up all the time and not just after I put a few miles on it? Besides... like I said above, there's no 'pressure' on the plunger that would be relieved by shortening it... the brake pedal hangs freely, so that it can actually swing up to the bottom of the dash if it wasn't connected to the plunger rod. The length of the plunger rod now is exactly the same as the stock unit. I guess I'll start with a complete bleed... all the way down with new fluid... and what that gets me. I'l also check the MC ports for rust and crud. Then I'll move on to collapsed rubber lines and rebuilding wheel cyclinders.
Had the same thing happen to me after rebuilding my master cylinder ad "adjusting the slop" out of the pushrod....adjusted the rod too much. I say your pushrod between M/C and booster is too long or there is a spec of **** in the return hole of the M/C...seen that happen too.
They are talking about the plunger rod from the boster to the master cylinder, not the plunger rod from the pedal to the booster.
The slightly too long pushrod may be causing your brakes to constantly drag, creating heat and expanding any water or air in your brake lines, that would lock them up. I think there is some kinda heat issue. But what do I know, my brakes are a tree.
where did the new "booster" etc come from? was it MBM BRAKES? OR PIRATE JACK? if so.. the rod is too long.. not by much.. but whats happening is that the brakes are dragging ever so slightly, as you drive they heat up the drums discs whatever.. and eventually lock up.. you can guess how I know.. if you dont have parts from MBM or pirate jack.. please disreguard the above post..
I have had the same problem too. My rear disc brakes would lock up tight after about 3 - 5 miles. Front brakes were not locked. On mine the rubber hose from the body to the differential was bad and working like a one way valve. Is the problem with all four or just the front or just the rear or just one wheel? Good luck. This problem drove me crazy for quite some time. Let us know what you find.
This happend on my car. I replaced all the wheelcylinders and rubber lines. It still did it. Apperently the matercylinder was just corroded up. I got a new one and everything works like new. These were completlr stock break's though. It's either that or your rod is to long.
i would suspect the m/c . you said the problem showed up after you changed it duh. are you sure you have what you think you have? a drum bk. cyl has a built in ck valve and will build line pressure.
I don't remember seeing adjustment on the rod b/t the booster and master, but I'll check that. Even before they eventually lock up, the brakes feel very tight... very little pedal travel. I thought this was a good thing, but maybe not. I'll dig in next weekend and let you know what I find. Thanks again.
I'm with Eddie and the rest of the guys over the amount of free play you have !!!!!! LOLs Had the same fauly with a single m/c of a frogeye sprite I rebuilt. In that situation backed off the adj rod into the m/c. a couple of turns at a time til it cured. Seems to be an inability of the hydraulic pressure built up by the m/c to dissipate? Hell of a mouthful for a friday! Least its better than having no dam brakes - thats not recommended at all.
My experience is that a tight adjustment from pedal to booster will let the vacuum on booster pull the diapham into mastercylinder,therefore creating a drag on brakes..
Master cylinders for disc/drum systems will not work on all drum systems,remove the vette m/c and replace with one for a 67 and up chevy truck or other 67 and up gm car with drum brakes all the way around. Jeff
Following up - since I'm in Austin trying to remodel the new/old house before we move in, and the Buick still sits in Houston, I paid my local machanic to tear into this in his spare time. Sounds like the plunger rod between the booster and master was too long, which surprises me because 1.) the booster/master was delivered as a 'set', and 2.) was not adjustable that I recall. Believe me, if something appears to be adjustable, I'll adjust it... I'm compuilsive like that. Anyhow, that seems to be it - shortening the rod will get it on the road again. Once it arrives in Austin, I might set aside some time to tweak it... maybe take the advice of using the Chevy truck master for drums... but the big 'emergency' has been fixed. I was not gonna trailer that ****er to Austin. Thanks for the suggestions, guys... and big shout to HOTRODPRO? for the offer to help out.
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