Have you finished doing the troubleshooting yet? You should know if it's the proportioning valve. Since the brake system is not original anymore, I would take it out also.

 

No I haven't made time to get out there yet, I'm hoping to get it figured out by this weekend. I'm willing to bet its the pv, ill keep this updated once I figure it out.

 

So I got the truck fixed....and I was betting against the Proportioning valve being the culprit.....I was WRONG!!

I decided to check all the mechanical things one last time before tearing into the hydraulics and the Proportioning valve.

What I ended up finding was once the lug nuts were tightned down they were basically clamping the rotor and the brake pads together. I spaced out the things out with some 1/8" spacers between the rotor and the hub. Now everything spins super smoothly after the lug nuts are torqued down.

Long story short, if you are using the RuffStuff brake caliper mounts make sure you check which year Sterling Axle you have because you may need spacers...or read their website...because I didn't.

During the conversion process I also swapped in Front F350 brakes and the F350 master/booster. After driving it with everything working the way it's supposed to I am EXTREMELY impressed with the stopping power this truck has.

Thanks again for everyones help!!

 

I did a similar rear disc conversion in a toyota landcruiser and there was a small device I had to remove to alleviate pressure in the rear lines. It did the exact same thing you described with your bronco before removal. Also, I think a disc/drum master is ok...seen it done lots of times retaining the stock master. That is my 2¢.

Looks like it is solved