Author Topic: 1975 C10 Scottsdale Power Brake help  (Read 1666 times)

Offline Jlitz

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1975 C10 Scottsdale Power Brake help
« on: August 31, 2014, 01:55:50 PM »
Hello All
I put power brakes on my non-power truck and started having problems
The front brakes drag and fluid comes out of the top of the MC after driving a while. I guess it expands when hot from dragging.

The truck came with manual JB1 brakes and I put a JB3 power set up on it.
The only difference I can see is the brake MC.
The large reservoir is switched from the back to the front from the JB1 to the JB3 MC.
I can not find a JB1 power MC.
I checked the clearance between the booster rod and the MC and it is not pushing on the MC when the brake pedal is not pushed.
I even tried adding washers between them on the mounting bolts to guarantee it
I also pulled the MC off the booster when the brakes were dragging and they did not free up.
I changed MC's and I still had the same problem.
I did look up the part numbers for the proportioning valve and they are the same
Then I went back to the manual brakes and the problem went away.

Now my question is what is the difference between the master cylinders inside other than piston size, and how do I fix the problem

Offline Jlitz

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Re: 1975 C10 Scottsdale Power Brake help
« Reply #1 on: September 07, 2014, 07:02:03 PM »
Hello all

I did get it repaired
Friday I was off and put the power unit back on again, same problems.
So I live near a u-pull-it and got a master cyl off of a truck there.
I put it on and drove the truck for about 20 miles and the truck seemed ok.
Today I took the truck to a car show and put about 110 miles on it without any problems.

I took the parts back to Auto zone and they gave me a full refund with core charges and told me to keep the new booster.
It was a good day. I ended up with power brakes on my truck for only ten dollars and it all works.

Offline bake74

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Re: 1975 C10 Scottsdale Power Brake help
« Reply #2 on: September 07, 2014, 10:01:54 PM »
     Glad to hear you got it fixed, sorry that nobody got to this post that could answer it.  A lot of times we can only get to so much in 1 day.
#1: The easiest and most obvious solution to any problem is 99% of the time correct.
#2: There is no such thing as impossible, it just takes longer.
  74 k10, 77k10    Tom