brakes
 

I was looking at brakes today at autozone for the 78 how do i tell if it is jb7 or jb8 brake system.It i a one ton 4wd

Re: brakes
 

i think its a rotor sizes might say in your info in the dash.

Re: brakes
 

The JB7 system runs a vacuum boost with 1.28" front discs and 2.5" rear drums whereas the JB8 system uses the hydroboost setup with larger discs (1.53") and larger drums (3.5").

Re: brakes
 

True that, however I guess somewhere in the '80s things changed cause my hydroboost module that came off an '80s 1-ton diesel has to use a JB7 master cylinder (for a '79 C30), the JB8 one that's supposed to fit it has a bore in the piston that is too deep for the hydroboost rod. I'd suggest just pulling a wheel and measuring yer current rotors, they will be thinner than the brand new ones but they will still give you an idea of what to get. Check the rear drums too, just to make sure.

Re: brakes
 

does it make a differance in telling that it has a dana 60 in the front.Also whne measuring the rear brake does 3.5 inches the meauserment of the shoe width or the drum width

Re: brakes
 

dunno about the front axles I'm running the JB7 hydroboost master cylinder for a 1-ton with my half-ton rotors and calipers without any issues. The 3.5" should be shoe width, you will need to pull drums for that and that can be pretty nasty depending on yer axle's rust developments. Really best way would be to pull a front wheel and measure the rotor thickness, if it's about 1.5" you should have the JB8, and if it's around 1.25" it's the JB7, but even then I'd check with the actual part dimensions at AutoZone cause stuff gets mislabeled sometimes. As I said, I have to run a '70s JB7 master cylinder on my '80s JB8 hydroboost system, and I only figured that out cause I had measured the bore depth of the original hydroboost master cylinder in the junkyard.

Re: brakes
 

Thank you I'll measure the front rotors tonight