24. IRS

The Independent Rear Suspension (IRS)

It has been a while since I have written an article about the restoration of my E-Type. That is mainly due to the fact that I have been living and working in California for the last 4 months. It is hard to do much more than order parts when your restoration project is 3000 miles away! But I am back and am pleased to be able to report progress on a major sub-assembly, that being the independent rear suspension unit, the IRS.

The IRS as used on the E-Type and subsequently used by Jaguar for their sedans such as the XJ6 was a major departure and improvement for their automotive lineup. In an era when most cars came with a solid rear axle mounted on a set of leaf springs, the Jaguar IRS represented a major technological leap forward. Even today, it is held in great favor by custom car builders and hot rodders as the basis for some of their creations. In my case, the IRS had been residing as a rusty lump in the parking area outside my shop, waiting for eventual attention.

Its turn came during my Christmas vacation, when I was home and looking for a project to tackle. Bodywork on the car was substantially done, the front sub-frame and suspension was hung, and all I lacked to allow me to land the car on four tires was the rear suspension unit.

I can tell you right now that the IRS is somewhat complicated and not a simple piece to refurbish. I had noted that professional restorers like Classic Jaguar were asking close to $5000 to restore an IRS. Before I started the job, this seemed like a large sum but in restrospect I can understand that they earn their money, as there are a lot of tricky and time consuming aspects to the job.

The first time consuming aspect is getting all the pieces apart. After 40 years of rust and corrosion, there are parts that do not want to come apart! Products that attack the corrosion such as Kroil or PB Blaster are a must. A hydraulic press is also mandatory.

The major parts of the IRS are the center differential unit, the halfshaft axles, the swing arms, the hub carriers, the splined hubs, the cage, and the radius arms. The hub carriers are aluminum, the rest of the parts are steel. I managed to get all of these parts disassembled over a period of several days, using solvents, great force, and swearing. The big steel pieces went into my bead blast cabinet for cleaning and the smaller pieces went into the parts washer. Once I had all the parts cleaned up, I was able to inspect them for damage. I decided to replace the radius arms simply because the rubber bushings at each end were permanently corroded into position and I would have destroyed the arms getting the bushings out. I decided to replace the splined hubs, as the splines were very worn from years of delivering the torque from the axles to the tires. As a matter of course, I ordered all new bearings and rubber parts. Then I went ahead and applied black urethane paint to all of the steel parts.

I spent some time reading my Bentley manual regarding it instructions on refurbishing the IRS. Frankly, the instructions for the differential unit intimidated even me, the dedicated do-it-yourselfer! I decided to send the differential out to Dick Maury at Coventry West in Atlanta for rebuilding. Dick has a very good reputation and I knew the unit would be in safe hands. At that point, my Christmas break came to an end and it was off to California for several months of work.

When I got back in April, it was time to begin re-assembly. By the way, a book that I found to be helpful when putting the IRS back together was “Jaguar 6 Cylinder Engine Overhaul: 1948-1986 (Including I.R.S. and S.U. Carburettors.” It is available through Amazon.com. I have not mentioned it specifically but the disc brake calipers, as well as the parking brake mechanism are mounted directly to the differential unit. I had bead blasted and painted all the parts previously. I had also had the disc brake calipers re-sleeved to ensure I had a clean sound surface for the rubber seals to slide in. I carefully assembled the brake parts and mounted them to the differential, along with new rotors. At this point, you can re-attach the differential to the cage. But first, you might want to test fit the cage to the chassis of the car. The cage connects to the chassis via rubber mounting blocks.

Once the differential is attached to the cage, it is time to start installing the half shaft axles. If you haven’t already done so, you should install new universal joints. The “fulcrum shafts” that connect the swing arms to the cage come stock with an amazing array of roller bearings, oil seals, and washers. I choose to go with a kit sold by Classic Jaguar that replaces many of these parts with bronze bearings. This simplified installation quite a bit but it was still a trick to get everything lined up.

When you get to the outer end where the hub carrier is involved, there is a very fiddly bit about measuring and installing spacer washers to give you 0.002″ to 0.006″ of end float at your hub bearings. This is another area where the pros earn their keep but I think I managed to set things up properly (I hope!). When you are finished connecting the half axle shaft, the swing arm, the hub carrier, and the hub together, you are about done. Don’t forget to install the radius arm before its mounting hole is blocked off by the hub carrier.

It was with great satisfaction that I stood back and admired the final IRS assembly. The restored IRS always represents a “photo op” in anyone’s restoration effort. I took several shots for my restoration diary. The last step is to use a transmission jack to hoist the thing up into the car. That will come later.