Lotus Elan

Diff Rebuild

PostPost by: GregoryNorthwood » Sun May 19, 2024 10:12 am

I have recently taken apart my differential to replace shims, bearings, CWP, and put a quaife lsd in. I also bought an alloy nose housing from TTR which came with a spacer washer included.

My question is whether I can trust that shim thickness for correct meshing, and all I have to do is torque up the input shaft nut to remove backlash. I don’t really want to have to send the diff somewhere to be rebuilt.

Thanks in advance,
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PostPost by: promotor » Sun May 19, 2024 1:29 pm

Different brands of bearings consistently give different readings for pinion height so supplying a diff case with a shim without the exact bearings that was used to do the assessment is incorrect to me.
I am guessing that these TTR supplied cases are assessed by measuring where the bottom of the bore for the pinion head bearing is machined to and not by assessing where the top of the pinion bearing that contacts the pinion shim actually sits.

You can quite easily wonder "how can different bearings give different readings". Looking at a workshop manual aside from Lotus Elans, for example the Morris Minor diff (used in Lotus Elites) overhaul section states that bearings have a tolerance on thickness on both pinion and side bearings and they need assessing individually.

This plays out in the Ford / Lotus diffs but is only important on the pinion bearings as the side bearings aren't shimmed like the Morris Minor diffs are due to having side adjusters.

Backlash is adjusted by the side adjusters, and getting the correct backlash figure may still give the result of an incorrect contact patch. Used diffs may not like being set to factory figures as they may have been running slightly out of this position quite happily as things wear over time,
Contact patch is controlled by a mixture of pinion depth as well as relative position to the crownwheel by the way of the side adjusters. Unfortunately aluminium cases do not allow the side bearings to be moved across by the side adjusters as the bores for the bearings are tighter than cast iron ones to allow for heat expansion. It is a more labour intensive process with aluminium casings.

You could build it up and see if you get lucky. Just don't drive it very far if it ends up noisy and you might have a chance of rectifying it changing the settings.
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