Lotus Elan

Differential clearance.

PostPost by: Bigbaldybloke » Sun Oct 20, 2019 4:36 pm

My car is an early Plus 2 with a Spyder sheet metal chassis. I?ve fitted a diff brace and after a bit of juggling of washers and mounts I have a few millimetres clearance between the diff and bottom chassis rail as shown in the photo.
fbb0488d-2a38-410e-9089-33bb17bc0283.jpeg and
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PostPost by: baileyman » Mon Oct 21, 2019 1:25 am

Russ Newton suggested to me that my diff should be angled same as the transmission so the drive shaft u-joints should perfectly cancel their errors. I suppose that is right, but I'll swear there was and is very little wiggle room for the diff, so I am leaving it where it is.

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PostPost by: prezoom » Mon Oct 21, 2019 2:33 am

Place an angle finder on the front crankshaft pulley and record the angle. Then place the angle finder on the differential pinion flange. The angles should be the same.
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PostPost by: rgh0 » Tue Oct 22, 2019 10:19 am

The bottom plate on the Spyder chassis is the same location as the Lotus chassis. The top plate where the diff mounts is also the same. What is different I believe is the depth of the top plate structure which is less on Spyder with it space frame tubes compared with the bent sheet metal Lotus used.

Thus more clearance with the Spyder chassis to remove the diff.

Where you locate the diff versus the top and bottom plates in not critical except for getting at least one washer or the brace above the diff to spread the load from the mounts and at least 4 mm below the diff to stop it hitting the chassis.

The range between the two is small especially if the chassis bottom plate has been bent by jacking in the past. Bending it back down again can help and is easy to do.

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PostPost by: davidj » Wed Oct 30, 2019 5:12 pm

Just for the record, I have fitted the diff with approx 4mm clearance between the lower edge of the diff flange and the chassis. I used two thick washers and the diff brace and 4" bolts, 1/4" longer than standard. From this I guess the Spyder chassis has 1/4" higher more clearance than the standard chassis.

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PostPost by: persiflage » Mon May 22, 2023 4:52 pm

More diff woes :(
1972 Sprint. Lotus replacement chassis in mid 1990s.
Prior to fitting new driveshafts I removed the diff. to attend to a slight leak. Refitting has shown up a very tight clearance issue at the bottom. I’ve replaced the original fit 3mm spreader washers with new 1.7mm ones but my cardboard feeler gauge is still a very snug fit at 0.57mm.
11E3F53B-3766-4FA3-A0C0-154F1B87790E.jpeg and

The diff mounts were of course replaced at the same time as the chassis but have virtually no road use, maybe 1200 miles.
Could they have deteriorated to such an extent just by sitting? They appear to be fine.
I have read comments regarding the build quality/accuracy of replacement chassis ( mine needed to be relieved to ensure the exhaust manifold didn’t knock) and I’ve measured the distance between top and bottom chassis rails at the diff mounts as 250mm left side and 260mm right side (approx).
The bottom rail isn’t deformed by jacking.
Can anyone with a Lotus chassis confirm those figures as it isn’t detailed in the manual drawing.
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