July 2006  IRS and Differential

First the finished paint job. It took a while but it was well worth the wait, the finish is absolutely stunning! But on to more mundane things - the dreaded Independent Rear Suspension....

The IRS is extremely heavy and awkward to manhandle - 2 people struggle to move it! Added to which it is invariably filthy and rusty. With hindsight, while I had it on a trailer, I should have had it steam cleaned. Although I took lots of pictures during the strip down they were not a great deal of use with the IRS in this state. Parts came off with  handfuls of grease and after disassembly I was still unclear on how to reassemble it.

After shot blasting, parts were again brush painted with POR15. As the car was sitting well previously I decided to reuse the springs but the cleaning and painting of these is tedious and given the low cost of replacements I wouldn't do it again. New Gaz adjustable shocks were fitted.

The tag on the original differential shows 46 crown wheel teeth to 13 pinion gear teeth giving the normal 3.54:1 ratio for US cars. This will give high engine revs at motorway speeds and mostly negate the 5th gear in my new gearbox. Standard for UK cars was 3.07:1 but this may give me too high a 5th gear so I've compromised with a 3.31:1 differential from a later car. Top gear engine revs will now be reduced by 13% over the standard UK setup.

Just like the original differential the condition of the replacement is unknown but they are supposedly very rugged so the plan is to check inside and change the input and output shaft oil seals which are of the old leather type. The casing was painted before disassembly to keep mating surfaces clean.

So much for plans; the output shaft bearings show signs of wear, which is not that unusual due to the axial load exerted by the suspension. What I didn't expect was the type of bearing, instead of the usual Timkin roller bearings there was a single, double race angular contact bearing which is no longer available. SKF supply a replacement kit which includes shims as the bearing is slightly narrower. The problem is in how to set the preload, the old bearing had a split inner race so the securing nut torque took care of this. The new bearing, although still a dual race angular contact type, has has a solid inner so the nut can be fully tightened. Not being able to find any further information I reassembled it by shimming the bearing cap to provide 3 'thou of preload. If anyone knows the correct procedure please let me know.

The pinion oil seal was replaced and the nut torqued to 70 ft/lbs so as not to further compress the crush spacer which sets the pinion preload. Engineer's blue indicates that the gears still mesh correctly.

WARNING!

I've heard stories of these IRS assemblies loosing circlips from the drive shaft universal joints and even the rear end collapsing as the drive shaft disconnects from the wheel hub; if true, this appears to be the reason. One circlip groove on both splined hubs was machined off centre with the machine tool barely scoring one side (click on the image for a closer view). The fact that both yolks had the same problem makes me think that there are a lot more out there in the same condition! I had a local machine shop re-cut the grooves, this does lead to an increased diameter groove but with new circlips it doesn't seem to be a problem.

The rest of the reassembly followed the workshop manual, with the exception of the outer fulcrum bearing oil seals. The original is a complex arrangement using a felt seal and from the emulsified grease and rust seen in the disassembled bearings this seems to act as a wick to soak up water. Following information found on the jag-lovers website it was replaced with a modern lip seal, type CR11123.

Finished at last!

Series 2 callipers and disks have been used with the later differential and the difficult to access brake bleed points have been extended to the top of the IRS cage as this is accessible via a removable panel in the boot of a series 1 car.  Mostly these extensions are fed to the bottom of the cage and accessed from under the car, the downside is that the bleed point becomes the lowest part of the system giving potential air-lock problems.

The safest way to move this weighty unit. Now, back to the restorers for refitting.

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