Lotus Elan

Plus 2 S differential story and question

PostPost by: TomMull » Mon Feb 19, 2024 9:55 pm

diff 1.jpg and
Just finished setting up the differential from my strange Plus 2 S. I won’t bore you with the story of the car except to say I bought it sight unseen from California after a fairly positive paid condition report. Turned out the chassis had been welded and re-welded several times and was totally useless, but that is another story. The front shock towers tore the bobbins in the body too but I’m fairly good with fiberglass.

So I’m putting a new chassis under it now and in the process of moving all the suspension and mechanicals to the new chassis. We got the differential out of the old one and as soon as we got the front of it lower than the back, the oil ran out through the pinion splines. It poured out as if we’d removed the drain plug.

Here’s what we found: The flange nut was finger tight and the crush spacer was not crushed, which accounted for mots if not all of the leak. The car could not have been driven in that condition.

Inside there was better news; the ring and pinion appeared to be new, new bearings too. There was absolutely no sign of wear. On the other hand, the outside of the case had 50 years of crud on it. Did someone put a ring and pinion in it without cleaning the crud? Apparently so. The stub axle bearings were old so we replaced them and the seals.

I’m of limited differential experience to say the least but a friend and I got it set up so the preload, backlash and pattern look good.

I’ve had the car in a corner for a few years and now I’m getting optimistic about it’s resurrection. It will be a while before I get to try it on the road on the road but differential sure looks pretty now.

Feather by feather the goose is plucked.


Oh and the reason I posted this was to ask if anyone has had problems with the bolts threaded into the aluminum housing on the differential. I got them all torqued to 25 ft/lbs but some were a bit looser than others.
Tapping into cast aluminum does not seem like the best idea to me. Would studs with loctite set in the aluminum and nuts on the ferrous diff casting side be better?
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PostPost by: smo17003 » Mon Feb 19, 2024 10:45 pm

I had my diff rebuilt using studs rather than bolts. In the UK they're available from TTR. Their website actually shows a new Elan diff assembly built with studs. https://www.tonythompsonracing.co.uk/parts/final-drive/
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PostPost by: alan.barker » Tue Feb 20, 2024 5:02 am

if the threads are stripped i would fit Wire Thread Inserts.
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PostPost by: gus » Tue Feb 20, 2024 1:17 pm

Loctite is always a good idea.

Next thing to check, are the diff output shafts the necked down style?
If so, you ought to replace them
Had one shear in 1987 or so and it requires complete teardown to get all the little bits out
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PostPost by: TomMull » Tue Feb 20, 2024 1:58 pm

Gus,
I’m not familiar with the “necked down style axles”. Mine got somewhat of a test pounding them out with a big slide hammer. Car is a ‘70 Plus 2 S.

Alan,
No stripped threads but some wear noted. Also quite limited thread depth due to blind holes in the casting.

Smo17003
I think studs are the way to go. They would provide better use of thread depth since they go in finger tight to near full thread depth without worry of breaking the casting and can be secured with permanent loctite.

Thanks for all the replies,

Tom
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PostPost by: smo17003 » Tue Feb 20, 2024 2:11 pm

Studs and nuts were of course fitted to Cortina's with the same basic diff unit (albeit into a steel housing). Perhaps using bolts saved Lotus a few more pennies?
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PostPost by: gus » Tue Feb 20, 2024 5:40 pm

Look in the parts manual, the output shafts in that period had a necked down section between the bearing surface and the splines. It is not this section that fails but where the splines enter the differential. Remove yours and look at this area carefully, they will slowly start to twist and eventually snap. The later ones where the diameter is straight between splines and bearing surface do not suffer from this. It isn't the necked down section that breaks, it is poor material or heat treating, once they changed to later style they are fine.
Shouldn't take a slide hammer to get them out...
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PostPost by: TomMull » Tue Feb 20, 2024 7:55 pm

Gus,

Thanks for the heads up.It would appear that I do have the stepped drive shafts but I'll go with them for now. Have lots of other worries.

The drive shafts were very difficult to remove the first time I took them out. I used a slide hammer attached to a three legged puller. I hammered against the weight of the differential assembly; might have gone easier if I had found a way to secure the diff.

I cleaned the lands for the bearings and polished with 600/1000 grit. I used a hammer and a brass drift pin to put them back in with new bearings. I somehow forgot one of the inner snap rings, not unusual for me, so had to take them both out again. Same story with the slide hammer.

I've noticed that others have had this problem with the axles. Perhaps I'm doing something wrong? The good news is that they do come out.

Tom
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PostPost by: Craven » Tue Feb 20, 2024 9:30 pm

FWIW,
[attachment=0]P1020694.JPG
Attachments
P1020694.JPG and
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PostPost by: elanfan1 » Tue Feb 20, 2024 9:39 pm

Hope you’re laiming against the condition teportproviders
Steve

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PostPost by: alan.barker » Thu Feb 22, 2024 2:06 pm

Hi Tom don't use Loctite on threads in Alloy or next time the screw are removed the threads wil be stripped.
No ptoblems fitting Wire Thread Inserts in blind holes. They will be stronger than threads tapped direct in Alloy.
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PostPost by: elancoupe » Thu Feb 22, 2024 2:35 pm

Next time you want to remove the output shafts, take a heat gun to the outside of the area where the bearings rest. Removal will be far less difficult. :)
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PostPost by: alan.barker » Thu Feb 22, 2024 3:13 pm

+1 and if bearings have been fitted before using Loctite because of bad fit it will be destroyed.
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PostPost by: TomMull » Thu Feb 22, 2024 6:06 pm

Just to be clear on a couple of issues.
1, Following a previous suggestion re using studs rather than bolts in the aluminum housing, those studs would use loctite, not the bolts as original. I agree with no loctite in aluminum, the point was well taken. My experience though is that bolts with loctite, red or blue, can be removed without damage using a judicious amount of heat.
2.The stub axles were stuck. I got 1 out after a couple of rounds with the slide hammer. The second one did not move but heating to 135C released it and it came out bit by bit just as the first. I am surprised to hear that this is unusual. (I will admit the the slide hammer is not the best tool to get equal force on each arm but it was what I had.)
I did not measure the interference fit, wish I did now. I wonder how accurately those aluminum housings were machined.
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PostPost by: alan.barker » Thu Feb 22, 2024 7:06 pm

When i worked in Aerospace Industry all threads in alloy had wire thread insert/ helicoil fitted. Lots of wirelocking also.
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