Caterham Rear Diff Cover

I’ve replaced the rear suspension mounts with roller bearings, but in the the process discovered that there was no way to remove the differential.

The rear chassis is different to the standard Haynes Roadster as it has much more triangulation. This makes the access to the differential very tight. It makes the removal very tricky; a bit like one of those puzzles you get at Christmas.

Once the differential was in place I added one bracket after another until suddenly I realised that there was no longer room to twist and rotate the differential out of its hole. It very nearly came out; in several directions; but every time it simply got wedged. All of the brackets I had tack welded in place had to be removed.

Haynes Roadster Rear Differential Mounts

As you can see in the above shot, all but 3 of the Sierra differential mounts have been removed. I was never happy with the top rear mount (centre of above picture) as it was only possible to use fairly short bolts.

Step in the Caterham Differential Cover. The shot below shows the difference between the standard Sierra cover (bottom) and the Caterham item.

Caterham Sierra Differential Cover

Caterham have produced their own cover without the long nose at the top and machined down a couple of the strengthening ribs. The top mount is incorporated into two of the large torx bolts that secure the cover. In my opinion this is a much stronger system. I much prefer this system to the other option: that of using a later model Ford Scorpio cover.

Without this long nose I probably could have removed the diff, but I had already beaten of the remaining mounts.

Haynes Roadster Rear Differential Brackets

The new differential mounts are totally removable. In place, the flat brackets already hold the diff very solidly. The boomerang shaped bracket is probably just for show, but it does give good piece of mind. If in future I decide that too much differential noise is transferred into the chassis, the job of urethane insulating it, would become much easier too.
(The silver paint is a quick non-permanent coating to stop them rusting)

Whilst the differential and all of its associated bracketry was out of the way, I remade all of the suspension mounting points to incorporate roller bearings.
– A very time consuming job.

See here:

Haynes Roadster roller bearing suspension mounts

This was the 4th time I had made these brackets in one form or another. The first time there was 0% anti-squat, the second 95%, the third with 20% and now finally, I have 20% and roller bearings. Luckily, this time I still had the alignment jig left over from the last incarnation.

The rear suspension now moves up and down with no detectable resistance. Whereas before, the urethanes had sufficient grip to slow the hubs, complete with disks and callipers from descending in under a minute. This new lack of friction has not been at the cost of vibration and noise absorption. As a quick test, I gave the hub a thump with a lump hammer. If I had simply used rose joints all around, I would have expected the chassis to ring like a bell. Apart from the metal on metal ‘clank’, the noise was quite dull and clearly deadened in comparison to when I clouted the chassis. The urethanes were doing a great job.

For Christmas, I got a set of 4 AVO coil-overs. I’m going to use these instead of the huge DRZ400 motorbike units. With these gone, I’ll need to make up some new shock mounts and rocker arms. Once these are complete, I’ll be able to make the rear suspension push rods and finish off the rear hubs. – That’s after I’ve finished mounting the steering rack.

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