Which master cylinder
 

I am in the process of swapping 1 ton axles into my 1986 GMC K10. The dana 60 has the J8 calipers (I think), the rotors are 1.5" thick. I am in the process of swapping the 11" rear drums to 13" drums to make sure the E-brake will work with my current setup (14 bolt is out of a '78 so it has the old style E-brake).

My question is 2 fold, a) will I need a new master cylinder and b) if so which one? I am thinking one from a single rear tire K30 will do the trick but I am not sure. Any help will be appreciated.

Re: Which master cylinder
 

the answer is "no". Stock master cylinder will work fine.

Re: Which master cylinder
 

I'd suggest changing it. Looking on rockauto, a k10 came with a 1-1/8" master cylinder. A k30 use a 1-5/16" master. That 3/16" difference isn't just a discrepancy.

Your current master will likely function well enough for initial testing. I'd suggest using it, and see how you like it. Because it's a smaller bore relative to what your calipers/slaves were designed to operate with, you'll likely have a deeper pedal, less pedal effort required, and possibly a squishy pedal feel. Upgrading to the larger bore size should counter those annoyances.

If you don't like the pedal feel once you have the truck back on the road, it should be easy enough to swap for a k30 master at that point. I'd say there's no need to swap it now.

Re: Which master cylinder
 

Thanks for they reply, I have driven a couple trips now and it is like you said it would be. I think I will drive a bit on it and decide then. Again thanks, for the reply!
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