Rear Axle

The Rear Axle has a standard Jaguar XJS 2.88:1 Ratio Diff with Power loK (Limited Slip Diff). I bought the rear axle a long time ago from a young chap on eBay.  I used it to make all of the chassis mountings early on in the project when I was making the necessary chassis mods, but then just left it sat in the corner of the workshop.  It was only when I bought a Rear brake upgrade kit that I decided to start work on it.

It was then that I realised that there was a problem.  The brake kit consists of some custom mounting brackets that bolt up to the output shaft bearing housings.  When I offered up one of the brackets, it was clear that there was no way it would ever fit.  The reason being that the mounting brackets had a pattern of 5 holes but the bearing housings on the sides of the Diff only had 3 mounting points. 

After a little research it was clear that the Diff I had was a Dana unit rather than the more common Salisbury.  This in itself would not be a bad thing, other than all of the aftermarket brakes etc that I had would only fit a Salisbury.  On further investigation, I also found out that the Dana unit is not as resilient as the Salisbury either.  So I decided that there was only one way to go, I had to find a Salisbury.  It needed to be a 2.88:1 Ratio as I wanted the tall gearing so I started looking for one at all the Jaguar suppliers I could find, but no one seemed to have any.  I finally found one and got some pictures of it emailed to me first to make sure that it was what I wanted.

Here you can see the correct Salisbury Diff on the right hand side of the Picture with a later XJ40 Salisbury diff on the left.  Note the completely different mounting styles.  The later XJ40 type are not as versatile as the earlier diffs so don't tend to be used in any Rod or aftermarket applications. 

The Diff I managed to get hold of is out of a late XJS, from the casting identifications I can tell that it is one of the 89-95 HE XJS units (HE stands for High efficiency, although I am not sure what it is that makes it a High efficiency).

Luckily the Diff casing is exactly the same with regards to the mounting points and the Arm and shaft mountings, so I can use the components I already had from the other diff. 

I Stripped all of the component parts down and then cleaned them all up to see what I had.  The lower arms were pretty rusted so I ended up getting them shot blasted.  I was going to see if I could get them chromed but in the end I decided to paint them the same as the chassis as they were badly pitted after being blasted.

Here you can see all of the rear axle components after I painted and clear coated them.  Now I just need to be really careful when it comes to assembling it all so that I don't mark them.

The lower suspension arms are usually fitted with needle roller bearings, but I have decided to go with a slightly different approach.  I am using UHMD (Ultra High Molecular Density) bushes instead.  They are essentially a plastic bush that is very hard wearing and resistant to abrasion, it looks a little bit like PTFE but is much harder.  The bushes replace the needle bearings, but retain the inner sleeves and the large flat washers. 

Here you can see the bushes prior to being fitted.



The bushes are simply pushed into the ends of the arms and then the inner sleeves pushed in to the bushes. Here is what they look like in place.



So after painting everything and then setting about assembly I found out that the drive shafts were no good. After fighting with the modified half shafts for half the day and then having the use of one of the local garages 30 Ton Press to try and get the UJ's in the end of them I reluctantly came to the conclusion that there was no way the UJ's were ever going to go in properly. 

It was clear that the ends distorted when they were welded to the point of making it impossible to fit the UJ's correctly. The problem is that the when the UJ is in place the Circlips (Snaprings) used to hold them in place have no way to go into the grooves.  It looks like the distance between the grooves, which should be the same as the total outside length of the UJ is in fact about 1mm less that the length of the UJ.  I contacted Wisbech Engineering who modified the shafts to explain the situation and they told me to send them back to them for them to sort them out. 

I sent them back and they promptly returned them again telling me that they were now ok, but when I got them it was clear that all they had done was ground down the Circlips to half their thickness, this in itself I regarded as a bodge, but even worse was the fact that the ends of the Shafts were so tight under the pressure that they were essentially seized. So being very unhappy I sent them back again. 

This time Wisbech mailed me to say that they were going to remake them as they couldn't see any other way to get them right.  The interesting thing was that they also told me that this was not a new problem and that they had seen the same issue in the past but had made a jig some years back and had not seen it since. 

So a few weeks later I got the new shafts back, they are definitely new shafts and they seem to be a lot better than the original ones as the UJ's now move.  I decided to leave the entire shaft assemblies together this time when painting them again.

I painted the Shafts and the Diff casing together as you can see here:







The diff with the polished cover in place before I bolted it up to the chassis.



I had to drift the bearing races and cages into the hub carriers and onto the hubs.  You can see from the photos here that I coated the parts in Copper ease first.  This is just in case they need to come out again. 


Here you can see the majority of the Rear end components assembled, I still have a bit of an issue to resolve in getting the correct Camber set, but this should not be too much of a problem.


Here is the rear end view with the Air Ride Shockwaves in place.



After making sure that everything went together it was time to pull it all apart again and set it all up correctly.  This meant getting the bottom arm mounting brackets shimmed correctly then I could start to put everything together for a final time (hopefully!). 

When I dismantled the diff I found that there were a number of shims under only one side bracket and more under the front than the rear, so when I came to re assemble I decided to do the same and only shim the one side.  Using one side as a datum it was a matter of making sure that the brackets were exactly parallel and that the centres were correct for the tie strap.

To make sure that the brackets were parallel I measured the distance between the bottom diff mounting plate holes, rather than just measure them with a tape I used the bottom plate itself to check the clearance on the holes.  To set the correct distance between the pivot centres I simply used the tie strap itself.  Doing this I found that I needed 2 shims under the front and 1 under the rear.  Once I was happy with the shimming I correctly set the torque on the mounting bolts and then safety wired them.  To finish them off I put a coat of paint over the bolts just to tidy them up a little.

Here you can see the bracket on one side after being safety wired in place.  I want to try and find some new top mount bolts in good condition/new that are drilled for safety wire too, as the new bolts that Jaguar now supply are just a standard bolt with thread lock applied. 


I went with a billet Ali tie strap with a simple ball milled design as you can see here.  The rear is now all built with new shafts etc.  I just need to get the washers I need now to be able to fully tighten everything up.


Here is the axle with the the Rear diff cover now attached and the blanking plate in place.



Some pics with the rear radius rods in place and my attempts at working out the air pipe work too.