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Disc brakes locked up

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breckwrecking

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Kittery
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ME
Was driving my 81 around the other day and started to notice some brake drag. Pinpointed it down to the two front disc brakes. I took the calipers off and was able to compress the piston once with a clamp and then after that couldn't. I replaced the mc last summer with a remanufactured one. I am going to try to replace the rubber lines with new ones today. Just wondering if anybody has had this happen before, or have a suggestions? It has manual brakes and I bled everything when I put in the new mc. Just think its weird its both sides. Thanks for any suggestions.
 
Could be an issue with the multi function valve. If you open the bleeder, will it release the caliper or does it stay locked? If it stays locked, your issue is prbably in the calipers or multi function valve, if it releases, I'd look at the master.
 
From the factory, the multi function valve (somewhat inaccurately referred to as a proportioning valve by some) would be located on the inner frame rail just below the brake master. It's not a very good location so some folks move them up next to the master cylinder.

Not my photo, but this is what you're looking for-

BrakeLines11.jpg
 
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Did you fill the reservoir all the way to the top? You need to leave some air gap so the fluid can expand when it is heated from braking. If you do not then it will compress the calipers and cause drag and then lock up.
 
I've also heard of it happening when someone replaces the mc and they got a shaft (goes between mc and booster). If the shaft is a hair too long, the brake fluid expands and the front brakes drag. Simular to Kane's answer.
 
So, embarrassingly enough I have no idea how the '81 calipers remount. I've never seen the set up before and can't find much i go on them. I bought new calipers and pads, but I can't get the bottom slide piece to bang back in. It gets about halfway across the mounting bracket and then starts eating into the caliper metal. Half no idea how these are supposed late up. Any suggestions would be awesome, thanks.
 
Don't think they slide across to install. IIRC, they drop on from above and you need to get the lower/rearward end of the caliper to hook in place before you align the mounting holes.
 
IMG_0411-copy.jpg


Found this on the internet for you, there is a piece of spring steel between the caliper and retaining fitting that should take up much of the slop in the caliper but a lot depends on how worn the mounting arms are and how straight that spring steel is after the years.
I put antiseize on all moving parts, back of the pads and that retaining bolt.
Good luck!
 
Thanks! Finally found the right angle to put the slide bar back in. Super easy once you figure that out! One of the new calipers still seems slightly seized, so might buy a new block install that as well.
 
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