This is my first time fabricating an air bag suspension. Could find very little on the web for Jag IRS on bags, so looking for any advise or comments, so here goes......
This is where I'm at so far. This is a Series III Jag IRS with a later model Jag XJS locking differential(basically a Dana 44). 3.54:1 ratio and will be using a 5 speed WC T5 out of a V8 Camaro (with an S10 tail shaft to get the shifter in about the right position in the cab). Everything is just tacked together at this point.
Engine is down 3 deg and the diff is up 3 deg. Still need a lower support rod or rods to keep the diff from tilting under hard acceleration.
I'm sure there is better IRS out there than the Jag to start with, but this is about nostalgia and a plush ride, not corner carving ability.
I didn't like the stamped sheet metal cradle the Jag IRS comes mounted in so I fabricated this 'ladder' that supports the diff. It is mounts to tabs welded into the frame rails. The end tube has urethane bushings and the ladder bolts in with a single 1/2" diameter bolt on each side. Inboard Jag brakes are a PITA to service, so I made it so the whole IRS would 'drop out' with these two bolts. A little shimming will also be possible to get the alignment correct with the use of some washers. (sorry about all the painter's tape)
The air bag is mounted on a trailing arm that hangs from the Jag's lower control arm outboard pivot point to a cross member about 3' in front of the rear axle. The pick-up point of the front of the trailing arm is on the same axis as the inboard pivot of the Jag's lower control arm. I mounted it this way so the force of the airbag would not create a moment or torque on the needle bearings in the lower control arm.
The Boss wheels put the tires too close to the rear fenders and were close to the bed sides too, so I narrowed the Jag IRS about 2.5" (mini tubs are next). Cut the lower control arm on a band saw, sleeved it and put it back together. Took out the Jag axles and made new half-shafts out of parts in the Spicer catalog (the Jag half shafts are a forging, and I had some real doubts that they could successfully be shortened, but I'm told the Cobra kit car guys do it) Camber is about one degree negative and will be shimmed to zero at ride height.
The air bags are Slam RE5 with the internal bump stop for compression. The shock will have to provide the extended limit. Need recommendation on shocks that will work well with airbags. Travel will be about 5.5". With the bag aired-out the running boards will be about 3-4" off the ground. I may box the frame around the rear IRS mounts and notch the frame with a half circle of pipe to let it drop a little lower.
Another shot of the rear end. The bearing carrier now hits the frame rail when the bag is aired-out, so will have to trim the outer 'bell' of the bearing carrier about 1/4" to clearance it.
This is the 49 GMC that the Jag IRS is under. (had to pull the steering wheel up out of the way - granddaughter likes to stand on the seat and pretend she's driving) Fenders waiting on the mockup of the IRS to be done so I know where to cut the bed sides for the mini tubs. I put the rear end center line at 36" from the end of the frame rail - if anyone can confirm that's a good measurement to get the wheel centered in the fender I'd really appreciate it.
Phil