So I have a 99 D 4wd and I've been thinking about doing a rear disc conversion and have a few questions. I've heard that I can just pull off my drum backing plate and the disc "backing plate" (if thats the right word for it) can bolt right up to my 9.25 axle housing, it sounds right to me. I was thinking about going to the junkward and getting the backing plate, calipers, brackets, ect and swapping the parts. I would rebuild the calipers and get new pads and rotor if I needed. Also I would be putting in a dura grip or the stock trac lok carrier with new carrier bearings and alxe bearings seals. But just wanting to confirm this brake conversion is possible. And what do I need to do with the combination valve. Or should I get it from the donor D as well?

 

You're better off finding a 2003 rear end with the same gear ratio. Honestly, and I say this because I did a rear disc swap on my 1998 using 2003 parts and I ran into a big problem that required cutting and welding.

The big problem, the mounting flange on the ends of the axle tubes. The drums have a thin backing plate, and the calipers use a bracket which is .5" thicker. The discs do not use a backing plate in the same sense that the drums to...it's just sheet metal.

I used a hole saw, cut the flanges out, and welded them back into place but further inward by near 3/4". Then, the caliper brackets bolted up, disc, then caliper.

The reason I had to go through that trouble was because I bought a donor rear end with the wrong gear ratio, and on top of that the gears were shot. I could have swapped my gears into the donor axle, but at that point I figured it was easier to just cut and move the flanges.

The E-brake cable is also different, and the hard lines are different between years so I bent my own lines.

My advice...find a whole axle with the same gears and simply swap axles. It'll be a lot easier and almost as expensive.

 

But as long as I get the parts from an axle thats the same gear ratio I would be fine except for the E-brake cable right? You never did anything with the residual pressure valve? Wouldnt that cause your real brakes to drag since theyve been converted to disc?

 

Not just parts...the whole axle. The flanges are welded to the axle. The drum flanges are welded further towards the ends because the drum back plate is thinner than the caliper brackets. That means that the flanges on the disc axles are welded inward further than on the drum axle. Unless you want to cut and weld those flanges, you need to swap the whole axle.

That way EVERYTHING reconnects. The soft brake line goes right into the distribution block on the axle, just disconnect the drum E-brake cable and install a disc E-brake cable, and you're done.

I was told I would need a '03 master but I did not. Also, the '03 does not have a distribution block and my 1998 did. I was told I could leave it as is or remove it...which I did. I still have front bias braking, and my rear brakes do not drag.

I would recommend replacing the rear soft lines as they tend to swell over time and trap pressure.