Restoration Impossible: Rebuilding the Rear End

Sep 27, 2017 update to the Lotus Elan project car

The bespoke Lotus housing, combined with stub axles, is mated to a standard Ford differential to make the Elan have independent rear suspension.
The stub axles, new bearings and gasket came from R.D. Enterprises. Now the entire unit is ready to put together.
And now our differential is ready to be installed, Bushings hold the top of the differential to the frame and torque rods with rubber bushings allow the bottom of the differential sight movement under acceleration.

Before undertaking the rear suspension rebuild and assembly, we wanted to get the differential rebuilt and in place. This is critical because the suspension’s Roto-flex couplings and half shafts mount to this differential.

Based on a common English Ford unit, the front half of the differential is nothing fancy. What makes this differential special is not the ring and pinion gears and bearings, but the bespoke Lotus cast rear housing and differential mounting bushings used on the Elan.

The early Elan was offered with a 3.9:1 final drive. In an effort to improve the car at highway speeds, the later cars were offered with 3.7:1 final drive gears. Since we had a late parts car and had already updated our engine to the later car’s slightly higher horsepower figure, we felt safe in using the later and lower (numerically) final drive, which would make our car run lower rpm at higher speed.

Of course, in a rather long list of things that would have been good to know before we started on this project, the flange that connects to the driveshaft on the later differential has a different, wider bolt pattern than that of the early differentials.

Thankfully, we were able to get the driveshaft back out of our still bare chassis, and make the correction. We just had to use the flange off of a later driveshaft we had in our parts stash.

As for the rebuild, the Ford gears are robust and were in good shape, so we cleaned, painted, added new lubricant, and installed new bearings and gaskets into the differential housing.


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Reader comments:

wschaub
Sept. 29, 2017 7:52 a.m.

Did you install the stiffening bracket that spans the upper mounting ears on the aluminum casting?  Lotus added these to later Elans.  If not, it may be worth considering.  I'm following this restoration with great interest as I am restoring a 1972 Elan that has been sitting since 1987.

Tim Suddard
Tim Suddard Publisher
Oct. 12, 2017 6:20 a.m.

In reply to wschaub:

I did not add those stiffening bracket. We are trying to restore this as close to original as possible. I did stiffen the engine mounts, as they were torn.

wschaub
wschaub New Reader
Oct. 12, 2017 3:03 p.m.

You may want to talk to Ray @ R.D.  That differential bracket was a running change Lotus made, I think with the Sprint.  It is a pain, even with the body off.

Tim Suddard
Tim Suddard Publisher
Oct. 15, 2017 7:43 a.m.

In reply to wschaub:

I have been talking to Ray at least once a week, about every step in the restoration. He has been a great resource and a great guy.

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