I’d read many threads on the disk brake conversions out there and the monkeying w/ prop valves and mc’s boosters ect.
What I ended up finding was that the D60 brakes (JB8) Bendix type were only 4% smaller than the fronts of the 2004 2500 that would have come w/ the rear end. So I decided I was going to use the MC from the 2004, but that it may be a challenge. I was also going to gut the factory combo valve as shown in the Atron writeup.
Well the combo valve didn’t come off as well as I’d hoped. The line for the rear would absolutely not come off. Ended up having to cut the hardline. Once I got the valve out I took it to the bench. Put a pipe wrench on it and the back of the combo valve spun out, but the fitting still would not. So I put some heat to it, and eventually it relented.
By the time I got it open and started examining everything. 40 years had taken it’s toll on that valve. It was cruddy’d up and pretty nasty. It would have been a giant PITA to salvage that thing. I started looking at the replacement parts and found that a few places made solid brass replacements that were basically already gutted, and some other ones that had a prop valve built into them.
Decided that I didn’t want to either cut and reflare all 5 lines to use one of the ones w/ adjustable prop valve in them and went with one of the solid brass gutted replacements.
Took a try or 2 to get the line reflared where I had to cut it but eventually it relented and got a leak free connection.
Now putting the MC in was a challenge. I learned a few things and will put them here for future reference.
In ’81 the hole in the booster for the MC snout changed to a larger diameter. I’d heard of people using some much later ones but having to swap the mounting bracket on the booster and having problems w/ the push rod to the brake going metric
So I decided to just try an 81 booster. And… It was a direct fit. All the threads, the mount everything was EXACTLY the same except that the mounting hole was now the ‘new’ larger bore.
80 vs 81
old 80 mc 1.1" bore vs 1.4" bore
The new MC would physically bolt right up to that booster and that booster would bolt right into my truck. With one exception.
The resovoir on the new mc was a full on quart and was HUGE! So, I decided to space down the booster at the firewall using some washers. It was a bunch of washers to get it down far enough and it still grazes the fire blanket under the hood but it does fit.
I also had to remove a piece of bracket on the A/C compressor – looked like it was for a different application, and it was extremely tight. After removal there’s plenty of space.
There is one gotcha when putting in that master cylinder. You have to convert the rear line thread from 9/16-18 to 1/2-20. I tried a conversion fitting I found locally (the only one) and the fitting didn't seal. The cone inside wasn't proud enough to contact the flare. But I did find one from Wilwood, which was the only other one I found. If you don't like the adapters you can reflare the line, but the fittings for that is even rarer. The combo of the 1/2-20 thread w/ the 1/4" line side is rare.
Allstar Performance Inverted Flare Nuts ALL50118
Wilwood Brake Line Fittings 220-8575
Which leaves me to the present day. Got everything together and went for shake down run…
Shake was the operative word. I’m going to ask a mod to see if they can merge that thread onto this one as I think it will be more appropriate at this point. (was merged, but put in the front of this)
Things left to do on this build.
Replace carpet
Replace seats
Clean up under dash wiring
Build rear bumper
Build new steps/rock sliders (yes I’m short fat and old. I need the step portion)
Build a combo trans/tcase mount / belly skid.
