Limited Slip Differential

During my initial build, I kept reading about how a limited slip differential (LSD) was very useful to have, particularly if you had lots of power. Around two weeks prior to my SVA, I saw an advert selling a Sierra XR4x4 back end complete with LSD for £250. I was very interested, but the guilt about how much my car had cost took over, so I decided that it was something I could obtain later.

I was originally going to replace my differential with a Quaife ATB LSD as part of my winter 2002/3 upgrades, but it quickly became clear that I just wouldn't have enough time to complete all of the changes I wanted to make. This was decided to be a luxury rather than a necessity, so was scheduled in for the following winters upgrades (talk about forward planning ;o)

On 31st January 2003, I was browsing the parts for sale on Find-It when I spotted an advert selling an XR4x4 back end complete with LSD for £150. The advert had been there since 9th January and never having seen one so cheap before, I wasn't too hopeful of it still being available. Not being one to give in so easily though, I contacted the seller, Mark, and after a couple of exchanged e-mails, I had my name down to pick it up. Mark was on holiday during the middle of February, so I agreed to pick it up when he returned. I phoned him to arrange the collection, and during the conversation, I was told that if the calipers were seized, he would sort some others out. This made me wonder whether he had more than one unit.

I was speaking to my Dad, asking about borrowing his car and trailer so I could pick up mine and told him what Mark had said about the calipers. Dad was interested in getting one for himself if there was another one for sale. I e-mailed Mark and he had another one, so I arranged to collect that at the same time as mine.

The collection day, Saturday 1st of March came, so I picked up my Dads car and went over to near Wisbech where Mark lived. I collected two complete rear ends, then dropped one off at my Dads house and brought the other to mine. As can be seen from the picture below, the trailing arms are nicely rusted, but then the unit had just come off the back of a car around 10-15 years old, so this was no surprise, although the calipers look in very good condition. This isn't of particular importance as I have some plans including the use of rear discs and calipers from a Peugeot 205 GTI which are smaller, therefore lighter, and have a lot better handbrake mechanism than the Sierra.

XR4x4 Back End As Collected
XR4x4 Back End As Collected

I agreed to only leave it outside the back of the house for a couple of weeks and in fact dismantled within the first week. It was then stored in the garage until I had time to work on it.

Moving forwards a few months to February 2004 (okay, 12 months!) and I have finally got round to looking at the XR4x4 rear end. Apart from being covered in dirt and some surface rust, the trailing arms and sub frame appear to be in good condition, as do the drive shafts. I had previously removed the back from the diff to drain most of the oil out whilst it was in storage, so took the opportunity to look at the internals which look in very good condition with no signs of wear.

Having spent many hours cleaning and painting the previous donor components, I decided to take the easy option and took the trailing arms, complete with hubs still attached, and the sub frame to the local powder coaters and had them shot blasted and powder coated. I still reconditioned the drive shafts and diff myself as the risk of grit getting into sensitive components was too much, brush painting them with red oxide primer and then hammerite.

The condition of the original bushes and gaiters looked good, but I took the opportunity to replace them whilst the job was relatively easy to do. Getting the old bushes out was extremely easy as they were just drilled out. The trailing arm bushes were replaced with Rally Design PolyRace polyurethane bushes and the sub frame bushes by the original Ford items as they are stressed in a different way in the Tiger than their original application and consequently the polyurethane ones wouldn't work.

Getting the first of the sub frame bushes installed took around 1½ hours due to having to work out a technique. However, the second one took a matter of a few minutes. The tools and technique I used was as follows:

Work in progress - page not complete!

Since driving the car with the LSD installed, I found the rear end to be very unpredictable, with little notice the rear end was due to let go. I think this is largely down to the fact that the pre-load on the discs in the LSD is configured for a 1.2 ton car, and not something weighing half that. Consequently, we opened up the diff and removed the friction discs to make the diff open. Whilst this may compromise the traction you can achieve on uneven surfaces, it makes the car inherently safer, particularly on the limits of grip.

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