Locking brakes

[mikes67]

I have a 69 C20 4wd that had the front drum system replaced with a 71 disk brake system. Under normal conditions the pickup stops perfectly, but in a panic situation the back brakes lock up before the front. I've replaced the master cylinder, power booster, and the porportioning valve. Not sure what size the rear brakes are, but they are standard for the pickup. The lugs on the front are bigger than the rear.

Any idea on what I can look at?

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http://www.chevworld.com

[bobs409]

Check to see if it's both rear wheels. When this happens see if one or both are over heating by feeling the wheels/drums. (carefull) You should be able to keep you hand on them without burning yourself. an over heated brake will lock up.

It may be a sticking emergency brake cable, worn out brake springs, etc.

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63 Impala*66 Chevelle SS*69 Chevelle*69 C10 Stepside*71 Cheyenne 20*72 Chevelle

Parts for sale:
http://www.angelfire.com/trek/mr409/items4sale.html

[bigvinnie]

had the same problem, but my fix was probably more obvious than yours.... the rear axle seals were leaking and soaked the brake shoes, which made them grab terribly... replaced the seals and the shoes and the problem was solved.

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'72 short step, 350, 700R4, tilt, ps, pdb, a/c, lowered coils, etc., other work in progress... San Diego, CA
http://www.ixpres.com/vlusardi/chevtrk.htm

[Fast68Chevy]

check rear axle shaft seals(wheel seals) if they are leaking onto shoes then they will cause brakes to grab like that, also if it does it when bed is unloaded, then no wonder.. back of truck is light and those brakes are huge for it
lugs are bigger in 71-up on all trucks when they went to disks, are 9/16" studs, unlike 1.2" in pre 71(on most all trucks)

good luck

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Randy- Lincoln, IL
randy@ccaonline.com 2177353230
-71 C-10 350/CH465/3.07, assemble it, yeah right, that'll happen in this world,(not)
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[Longhorn Man]

When you replaced the prop valve, did you get one for a '69....or a '71?


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'69 G.M.C. 350/350. Trying to clean up the left over damage from the Dope-Smokin-Old-Man
I've been dubbed the Longhorn Freak/Fanatic/Expert, I just hope I can live up to it.
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Andy, in Columbus Ohio

[wHATANERD]

I just completed the same swap, installing 72 brakes on my 69, I used a new Master Cyliner, proportioning valve, flex hoses, and new front lines, all ordered for a 72. I also rebuilt the rear wheel cylinders, and have no leaks, The rear brakes seem to be doing all the stopping, the system has been bleed, and get good preasure, and no air, but the rear brakes are locking up before the front brakes stop. If you find a solution please let me know.