Lotus Elan

Tapped Diff Flange

PostPost by: Foxie » Thu Aug 29, 2019 12:48 pm

I'm changing over diffs at the moment, and see I need the larger PCD flange (77.79mm/3.063")

Burton supply two types of flange: The old type with drilled holes, and a new type with tapped holes. ( Both are drilled to take both PCDs, both are the same price )

The flange with tapped holes seems to be preferable, ( after all the struggles I've had with the old type )

Has anyone any views on this ?

:)
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PostPost by: promotor » Thu Aug 29, 2019 2:13 pm

Have you got any links to the flanges you mention?
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PostPost by: Foxie » Thu Aug 29, 2019 4:47 pm

promotor wrote:Have you got any links to the flanges you mention?


https://www.burtonpower.com/catalogsear ... FLANGE+ENG :)
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PostPost by: promotor » Thu Aug 29, 2019 5:35 pm

Foxie wrote:
promotor wrote:Have you got any links to the flanges you mention?


https://www.burtonpower.com/catalogsear ... FLANGE+ENG :)


The black finish flange is only for mk1 & mk2 escort etc not for Elan - it has a different PCD and the outer diameter is 108mm, the plain finish one fits both early and late elans and is 92mm outer diameter (which covers both 86mm O/D and 92mm OD found on Elans).

So I'm guessing the one you need - unless you've got a non-standard propshaft in your car - is the plain finish one that is double drilled.
The black one only has 6 holes so isn't double drilled - 4 holes are threaded and 2 holes are plain holes - the 2 plain holes are presumably there so that you can use a flange holding tool without damaging the threads when tightening the pinion nut up. They're the holes I use when setting diffs with that flange.

HTH.
Last edited by promotor on Thu Aug 29, 2019 11:06 pm, edited 1 time in total.
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PostPost by: MarkDa » Thu Aug 29, 2019 6:12 pm

I would have preferred the clear holes purely on the basis that you have lock nuts and can use bolts to avoid bridging the shear line with threads on set screws.
But it would seem that you have no choice anyway :)
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PostPost by: Foxie » Thu Aug 29, 2019 6:29 pm

Well, that's cleared up that !

And I take the point of avoiding threads in shear, if there had been a choice.

Thanks all :)
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PostPost by: promotor » Thu Aug 29, 2019 11:10 pm

Foxie wrote:Well, that's cleared up that !

And I take the point of avoiding threads in shear, if there had been a choice.

Thanks all :)


Something to consider with the aftermarket flanges is that they don't come with a flange shield nor are they machined to accept one. I think it is a massive oversight to not include a shield or machine the flange to accept one from an original flange.
It's purpose is not only to keep dirt and water from going directly into the seal surface but also helps to hold the seal in should the breathing system fail and a build up of pressure tries to push the seal out. A quick way to make a pinion look like an ice-cream cone is to not have any oil in the diff!
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PostPost by: 2cams70 » Fri Aug 30, 2019 1:06 am

Foxie wrote:And I take the point of avoiding threads in shear, if there had been a choice.


It's all good. That's the standard flange design on later Mk1 and all MK2 Escorts (except the OEM flange has a seal shield). It's designed so the friction acting between the two flanges as a result of bolt clamping force takes the shear load. The larger PCD, bolt diameter and flange surface area actually reduces the loading on the bolts. From an engineering perspective it's a better design than the earlier one.
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PostPost by: promotor » Fri Aug 30, 2019 7:17 am

2cams70 wrote:
Foxie wrote:And I take the point of avoiding threads in shear, if there had been a choice.


It's all good. That's the standard flange design on later Mk1 and all MK2 Escorts (except the OEM flange has a seal shield). It's designed so the friction acting between the two flanges as a result of bolt clamping force takes the shear load. The larger PCD, bolt diameter and flange surface area actually reduces the loading on the bolts. From an engineering perspective it's a better design than the earlier one.


In addition the diff flanges should be spigoted to the propshaft flange- as the diff flange has a recess and the prop flange itself has a step that fits into it - so it's not just friction holding things together and taking load. Much the same as a 4-bolt flywheel on a Twincam.
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