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Old 03-01-2010, 10:27 PM
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Why do my brakes lock up sporadically?

I've got a '69 Camaro with power brakes & 4 wheel drums. Its got new shoes all around, wheel cylinders, flex lines, and a master cylinder. All that stuff got put on about a year & a half ago & its been parked ever since. Now, I'm bringing the car back to life & find that the brakes are weird. First time I touch the brake pedal, and I mean TOUCH it, very light...the front wheels both lock & skid. After that, they're touchy but not undrivable as long as I'm gentle. Then, sporadically, the left or right front will lock up on normal braking again, then be just fine. I have a good firm pedal at all times, no leaks, no nothin'. It's weird. For obvious reasons, I don't really think it'd be a good idea leaving the neighborhood with brakes that are this unpredictable so I kind of want to get it straightened out.

So, hot rod gurus, what do ya think?

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Old 03-02-2010, 07:16 AM
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Why do my brakes lock up

drums rust after sitting for a while ?
you say no leaks , should quit .
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Old 03-02-2010, 08:28 AM
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Pull the rear drums first, and check it out. If they are rusty, sand them clean. The rears will tell you what the fronts are like with half the work.
A good bleeding of the entire brake system and brake adjustment might help also.

Check for fluid seepage around the wheel cylinder boots. Rubber parts get old and harden over time and may need to be replaced.

The pistons inside the wheel cyl. may be sticking inside the cyl. bores after sitting for so long. They may need honed out or replaced.

This brings up another question, How's your tires?
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Old 03-02-2010, 09:23 AM
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Tires are good, they too are about a year & a half old, no miles on 'em, and no signs of rotting out while they sat. Assuming I don't have more work drama or something else come up to keep me from getting home at a sane hour, I'll pull the drums tonight & see what I find in there. Wheel cylinders were all new when I parked it last year so I doubt they're shot...but they were installed by the same shop who told me that transmission was bad, so there's no telling.

Assuming I don't find any leaking seals or something stupid like a big greasy handprint on the friction material (wouldn't put it past these jokers who did the work) hopefully it's just an adjustment issue. Looking online, I found that I should adjust them out 'til the drum won't spin, then back it off about 4 clicks so that with the tire on it can spin about 1 full rotation before stopping. Does that sound about right?
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Old 03-02-2010, 09:33 AM
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Why do my brakes lock up

run them down and turn several times to remove all the rust were shoes seat the drums the back off till it will spin .
easier than removing , but you can drive around with foot on brake pedal lightly and do the same .
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Old 03-03-2010, 07:53 PM
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ok, so the rear brakes seem to be adjusted well, with the tire on & spin as hard as I can & it makes about 1 full rotation before stopping...which is what I've read on a couple pages to be correct. The front on the other hand, I spin it with the wheel on & it spins too fast for me to be able to count how many rotations it gets before it stops. So, I need to adjust them. Now am I on crack, or is there no adjustment hole in the backing plate of the front brakes? I can't find it anywhere. Do I have to take the wheels & drums off to adjust?
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Old 03-03-2010, 08:06 PM
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Originally Posted by Bill-E-BoB
ok, so the rear brakes seem to be adjusted well, with the tire on & spin as hard as I can & it makes about 1 full rotation before stopping...which is what I've read on a couple pages to be correct. The front on the other hand, I spin it with the wheel on & it spins too fast for me to be able to count how many rotations it gets before it stops. So, I need to adjust them. Now am I on crack, or is there no adjustment hole in the backing plate of the front brakes? I can't find it anywhere. Do I have to take the wheels & drums off to adjust?
some backing plates have the slot , but blank needs removed , punch out .
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Old 03-03-2010, 08:08 PM
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Are you sure they used the right master cylinder and proportioning valve? if you have a master for disc/drum instead of drum/drum it would make the fronts lock up like that because the disc/drum master cylinder puts out a larger volume to the fronts for the disc brakes which require a larger volume of fluid to operate.
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Old 03-03-2010, 08:22 PM
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tempest, that's quite possible...it hasn't stopped right since the master cylinder got installed. It doesn't look like the old one either, instead of the normal lid held on by a retainer, it has a 9/16 bolt in the center of it that holds the lid down. Is there a way I can tell by looking at it whether it should be for a disc brake car or all drums?

Olds, I can't even see anywhere on these plates that could be punched out. Definitely not the normal rubber plugs at the bottom of the backing plate like normal on rears...
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Old 03-03-2010, 08:34 PM
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Originally Posted by Bill-E-BoB
tempest, that's quite possible...it hasn't stopped right since the master cylinder got installed. It doesn't look like the old one either, instead of the normal lid held on by a retainer, it has a 9/16 bolt in the center of it that holds the lid down. Is there a way I can tell by looking at it whether it should be for a disc brake car or all drums?

Olds, I can't even see anywhere on these plates that could be punched out. Definitely not the normal rubber plugs at the bottom of the backing plate like normal on rears...
metal cast plugs the shape of rear ?
the master have same size reservoir , and line size same coming out it ?
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Old 03-03-2010, 08:38 PM
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Why do my brakes lock up

some drums have the plug on front , did you notice one ?
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Old 03-03-2010, 09:31 PM
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ahh there we go, adjustment hole is on the front of the drum. So I adjusted 'em down 'til they locked the wheels...loosened 'em enough to just barely turn & spun the tires a few times to rub off any rust that may have formed as it sat, then loosened it about a turn & a half further to where each wheel would spin a little over 1 full rotation when I spun it by hand. Then I tested it & there is no change. rolling back & forth it still jerks to a stop, driving down the road half the time it pulls to the right trying to go off the road & the other half the time the left front locks & skids.

So the master cylinder, both reservoirs are the same size, and the line closest to the firewall is bigger than the other one. These are the same hardlines that were on the old master cylinder though...

I'm still stumped.
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Old 03-03-2010, 09:45 PM
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Why do my brakes lock up sporadically?

you pulling hair , i did that once ,did you bleed good ?
tape the bleeders leave open barely and put hose on bleeder and other end in bottle of fluid to see bubbles gone and suck back in fluid when you let off the brake pedal ?
shoes are on right ? short shoe to front ?
your not over working them brakes not giving time to seat ?
you did brake clean them new drums of the oil first ?
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Old 03-03-2010, 10:05 PM
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pedal feels perfect so I don't think it needs to be bled again, I might as well try that tomorrow if nothing else comes up though. I can't say for sure whether the shoes are on right or the drums are grease-free, I had a shop do the brakes & with how many other parts of the job they screwed up, I wouldn't be surprised to pull a drum off & find that they forgot to put one of the shoes in & duct taped the retaining spring into place or something.

By the way, found the box for my master cylinder...it's a Fenco M1505. Anybody know if that's the right one for a power drum/drum setup?
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Old 03-04-2010, 12:23 AM
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That's for front and rear drums. Correct. If you still have the receipt with mileage on it and the shop that did the work is still in business, you might want to pay them a visit.

PS: DON'T LEAVE THEM ALONE WITH IT!
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