Installing a Differential in a Spitfire

by Brian Neuschwander

Here is how you do it:

Roll the diff under the car on a floor jack.

Elevate the diff until you can put the rear bushing "ears" into the slots in the frame. This will locate and hold the rear of the unit temporarily.

Then continue to elevate the unit while guiding the front bushings around the mounting studs.

Install lower front bushing halves, washers, and nuts, but do not tighten all the way down yet.

Use the jack to raise and lower the diff as needed to align the rear bushings with the bolt hole through the frame. It is easiest to see from the right side on account of brake line obstruction if you look from the left. You may need a lever to force the diff forward slightly to get alignment of all the holes.

When aligned insert the pointed bolt. Use your old rocker shaft (you did save your old rocker shaft, right?) to pound the bolt through the bushing sleeves and frame holes.

Now tighten the front bushing bolts properly.

Install the nut on the rear bolt from the left side. If you attach several ratchet extensions you can get enough play and length to work through the brake tubing to reach the nut.

Tighten properly. If you are lucky the bolt will be jammed in there so as not to need a wrench on the other end.

That's all. It is the easiest part of the operation. Be sure to have the exhaust off the car first. Mine is a one piece custom pipe and glass pack that attaches with a flange at the header and a couple of hanger bolts near the back. Simple, fast, and accessible. I contemplated running it out the side in front of the rear wheels like a Caterham, but there is not enough ground clearance. It would be nice to work on the rear end without removing the exhaust.

And remember to put it up on proper jackstands. I have had the spit slide off the jacks before. Just a warning.


Douglas Braun also added:

Don't forget to put anti-seize compound on the long bolt. Otherwise you will be forced to saw apart the bolt (a VERY painful task) the next time the diff has to be removed.

Mark Haynes also adds:

When raising the diff into place, if you find it's not moving after getting the ears into place, that the axle flanges can/do get hung up on the output flanges, If you lift on the offending wheel/hub, you can usually get it free, sometimes you'll have to get a bar under it so that it doesn't go right back when you let go. With 2 people it's about a 1 hour job removing and replacing the diff.

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