Lotus Elan

Diff mounting

PostPost by: s28ven » Mon May 18, 2020 8:36 pm

I’ve fitted new diff mounts with new bolts from Mick Miller and new spacer washers as per the below, except the bolt is in the other way.
F6395FFD-4DA9-4337-92DF-57C28A664133.png and


The issue is I can’t get the nut on far enough to reach the nylock. I have released the torque bars incase the were holding the diff down slightly although it hasn’t made a difference.

There is a slight gap between the washer and the outer rubber on the mount, is this correct?
82AE5F84-25FF-4D39-B483-9E862BFB50B8.jpeg
82AE5F84-25FF-4D39-B483-9E862BFB50B8.jpeg (36.76 KiB) Viewed 425 times


I have another washer on the top of the mount aswell, should this washer be as thick as the bottom two?

737F8083-EE5A-4CCA-BF6C-15BB5D9D9A19.jpeg
737F8083-EE5A-4CCA-BF6C-15BB5D9D9A19.jpeg (63.7 KiB) Viewed 425 times


Thanks,

Steven
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PostPost by: tdskip » Tue May 19, 2020 2:04 am

Is there a reason why you mounted the bolt in the other orientation? Not criticizing, just curious and it may help others with a response.
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PostPost by: s28ven » Tue May 19, 2020 5:23 am

Simply to avoid removing the CV’s. It’s on an S3 so the bolts are much more accessible from the top than on a plus 2.

Thanks,

Steven
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PostPost by: alan.barker » Tue May 19, 2020 7:32 am

I know silly question but Have you checked the length of old bolts with length of the new ones
Alan
ps you can just put one big penny washer and you don't need two.
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PostPost by: s28ven » Tue May 19, 2020 7:45 am

When my dad put it together he would simply have used a bolt that fitted so I don’t want to go on the length of the existing. I would have thought coming for Sue they would be ok though.

It’s more the gap between the washer and the mount rubber that’s causing me to think there is an issue somewhere. If the washers were against the rubber then I would just have removed a washer.

I am unsure if the Internal metal sleeve is against the washer as it’s quite difficult to see in there.

Thanks,

Steven
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PostPost by: alan.barker » Tue May 19, 2020 8:05 am

I see what you mean the metal tube bonded in middle of mounting is too long.
Some others have had this problem and shortened the Tube.
I have just replaced the Frustacones on my sprint and i bought from TTR no problem.
Alan
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PostPost by: sprintsoft » Tue May 19, 2020 8:22 am

Hi Steven,

What gap have you got underneath the diff I.e. between the bottom of the diff and the flat part of the chassis?

Iain
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PostPost by: elanner » Tue May 19, 2020 1:41 pm

s28ven wrote:I am unsure if the Internal metal sleeve is against the washer as it’s quite difficult to see in there.

It is. Otherwise you would be crushing the Frustacone and have no problem tightening the nut up to the nylon.

You're overthinking this. Buy longer bolts! :D

The metal sleeve is fine. When the diff rotates so that the arms move vertically (one up, one down) one of the big washers will bear up against the metal sleeve, driving it into the Frustacone. The small gap between the washer and Frustacone will shrink to the point that the washer may start to bear directly on the Frustacone, limiting the shear on the metal sleeve. At one time I thought, like you, that the large washers were supposed to be hard against the Frustacone, but I finally realized that a small gap between them when static simply doesn't matter and may reduce transmission of vibration and noise.

Nick
Last edited by elanner on Tue May 19, 2020 2:49 pm, edited 1 time in total.
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PostPost by: bitsobrits » Tue May 19, 2020 2:48 pm

Nick wrote: When the diff rotates so that the arms move vertically (one up, one down) one of the big washers will bear up against the metal sleeve, driving it into the Frustacone. The small gap between the washer and Frustacone will shrink to the point that the washer may start to bear directly on the Frustacone, limiting the shear on the metal sleeve.


The primary rotational forces of a ring and pinion will be in the plane of the ring gear (in this case vertical) along the axis of the pinion. Which is to say the force/motion of the Elan differential under load will be up (and under decel down) at the 'nose' of the differential as the pinion tries to 'climb' the ring gear. Hence the fore/aft torque rods to the lower part of the diff housing.

A properly mounted Elan diff should exhibit almost no perceptible movement in normal operation.
Steve

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Formerly:
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Elan S3 1967 FHC airflow
Elan S4 1969 FHC
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Esprit S2 1979
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PostPost by: elanner » Tue May 19, 2020 3:08 pm

Thanks, that makes sense. Of course, the diff arms clearly deal with considerable loads based on Lotus strengthening the area twice during the production run (first with a beefed up rear cover, second with the Sprint brace). The Frustacones must take a bit of a beating.

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PostPost by: s28ven » Tue May 19, 2020 7:33 pm

sprintsoft wrote:Hi Steven,

What gap have you got underneath the diff I.e. between the bottom of the diff and the flat part of the chassis?

Iain


Iain, I will measure later but the below gives an idea.

24E5FF72-C87A-4D19-953C-F19AA0C2C4D8.jpeg and
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PostPost by: sprintsoft » Tue May 19, 2020 8:18 pm

The clearance looks fine, I had wondered if you had fitted it too low.

My bolts I removed were 95mm measured from under the head to the end if that helps?
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PostPost by: SENC » Tue May 19, 2020 8:44 pm

According to Buckland, they should be 3-3/4". If you go longer, you would be advised to change course and install the bottom-up so that only the head extends below the diff arms... there isn't much space between them and the donuts, which is probably why they were installed at Lotus in this direction.

I seem to recall the center tube seeming slightly long when I replace mine a couple years ago, but once done up no issue.

How thick are your washers (should be 1/8" each), 1 on top 2 on bottom?
Henry
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