Originally Posted by nostaw22
When I did the conversion I didn't bother changing proportioning valves, and the brakes work fine, so if you do nothing it will be "OK".
I was talking to my mechanic about it and he said there is a spring which helps hold residual pressure, which is different for the drum / disc brakes. He said just pull the spring from the GC proportioning valve rear output line and use it to replace the spring in the XJ proportioning valve's rear output. I haven't done this yet since the brakes don't seem to drag using the stock XJ proportioning valve and I don't have a GC proportioning valve.
Not sure if this helps, but it may save you some hassle.
Your mechanic is correct. Just put the GC spring in the XJ prop. valve.
1992 XJ 2" lift -- RIP
2000 XJ 3" lift -- Australian Ford Big Brakes up front, rock rails, ZJ rear discs (with WORKING parking brake), C4x4 rear bumper/tire carrier, Hella H4 headlights, IPF driving lights, OEM skid plates, OME springs/shocks, JKS LCA's, JKS Sway Bar links.