Diff Brace – Fabricate A Race Bred Diff Brace.

The standard differential brace supplied with the lotus elan, is in many elan owners minds, inadequate. And not only that, it is a hindrance when it comes to removing or installing the diff into the elan chassis.

There are many elan owners, who, when faced with the removal of the diff, would very much prefer to think about doing something else, the reason for the reluctance to tackle the removal of the diff is because they can be dogs of things to remove and replace.

Well, despite all of the problems one reads about on the forums, the diff can be removed fairly quickly and with out much drama, but in order to do that, there needs to be some minor mods done to the chassis and two distinct locations on the diff cast iron casing.

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The brace is often the obstacle when it comes to working with the diff, the angle brace in itself is strong enough, but it is the way that it’s designed and attached that causes the problem, the standard original brace is a simplistic piece of light sheet metal angle.

It is a wonder that who ever came up with the design had not given it further thought in order to make it easier for the elan mechanic/owner/enthusiast to remove and replace the diff.

Below, we illustrate how a high strength, lightweight diff brace can be fabricated. This particular design of brace was used on the race track for many years, it is well designed and totally integrated with the diff case & alloy rear housing.

Lotus diff minus the brace.

As can be seen, the plate follows the profile of the front cast iron diff housing, and is secured via the four 5/16″ banjo studs at the front. the sheet metal is formed to wrap partially around the outer ears of the alloy carrier, where much of the strength is required, because the outer ears of the alloy cases are prone to cracking and breaking, but this design of brace will definitely prevent any breakages.

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The sheet metal is best welded with Oxy/Acet or TIG welding method. Note also the small washers that have been brazed onto the brace, the washers are machined from round stock and then brazed to the sheet metal in the appropriate place. Making the templates will take more time than it will to make the sheet metal bracket.

Note how compact and neat this fabricated diff brace is. It is designed to be an integral part of the diff, and when installing, or removing, the diff and brace are removed as one… no fiddling, cussing or getting frustrated trying to get diff, angle brace, and getting the bolts and holes all lined up.

The diff brace secured to diff makes removal and installation of the diff much easier.
Watch the video Here.

1. Next time the diff is out of your elan, take a look underneath the rear cross member, there will be scratches on the under side where the lower diff housing  scrapes on the cross member during removal. To avoid this, a small portion of the metal needs to belled or raised about 1.5mm in order to allow that little bit extra movement/clearance for the diff, (Every bit counts) this is a small mod that can be done when a full chassis/body restoration is being carried out.
2. At the front of the diff under the very front of the casing, (See below) there is an excess of cast iron left from the casting and factory machining process, there is also a machined recess jig locating hole which is used during manufacture. The jig locating hole will never be used again, so that cast metal lug can be removed with a large angle grinder.

   

   This is a shot of the diff upside down in the bench vise. The casting protrusion which should be removed is the raised bit where the wording in red is placed in the photo above. It is surprising just how much easier the installation and removal of the diff becomes once these small mods are employed. The removal of the cast material will not harm the diff casting, it is just excess metal.

   

   The photo above illustrates where the lower diff nose jams and scrapes on the lower chassis tray, when this happens the top part of the diff alloy housing is pressed against to top rear cross member, and this is where the removal becomes difficult and the cussing and swearing begins.

   

   This photo shows where the cast iron metal has been removed, the removal of metal removes the possibility of 98% of the snagging that occurs during removal or installation. The writer notes that the last time the diff was removed, it almost fell out into his arms, and I’m not kidding, no more trying to hold the tongue at the correct angle in hope that the diff will come out easy… because I know that it will, I have three diffs with different ratios, and if I had two extra alloy rear casings and output shafts I would not be very concerned with having to carry out a change over… and get it done in a pretty short time frame.

   

   Here is another trick that will expedite removal of the diff from the elan chassis. Before the upper diff mount bolts are undone, create two wedges from pine or some other soft timber, then gently tap the wedges under the diff from each side. The timber wedges will support the heavy diff and allow easy removal of the upper mounting bolts.

   Before removal of diff, tap the wedges out carefully, then proceed to wriggle the diff out of the chassis, from the left side only. And if you can do the mods outlined above, I reckon that next time the diff will come out in the blink of an eye.

   These ideas we are sharing with you are gleaned from hands on workshop experience with our S2 elan, there are lots of little tricks and mods that can be used to make elan ownership easier and make these delightful sports cars more enjoyable to work on. And lets face it, they are very different to the normal car. There is a process to follow when working on a lotus.