Lotus Elan

Diff flange - advice sought on size!

PostPost by: dunclentdr » Sun Sep 11, 2016 10:04 pm

I have managed to pick up a nice rebuilt diff with Quaife ATB LSD - the diff has a larger size flange to fit with the prop, the diff that was on the S2 originally has the smaller flange.

I'm building up on a 26R chassis from TTR - is it possible to fit the diff with larger flange and also obtain a propshaft with the larger flange too?

Thanks

David
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PostPost by: bill308 » Mon Sep 12, 2016 2:29 am

Hi David.

There are actually 3-possible pinion flanges that will fit an English axle. Lotus used two of them, a 2.75 inch PCD bolt circle on the smaller one as fitted to the 3.9:1 final drive ratios and a larger 3.125 inch PCD one usually fitted to the 3.55:1 and possibly the 3.77:1 final drive ratios. I have the third style fitted to my newly built up final drive, it has a 3.5 inch PCD and TTR tells me there aren't any drive shaft yoke flanges available that will fit it. So I need to replace it as the new shock absorbing prop shaft TTR provided, is fitted with the small yoke, with a 2.75 inch PCD. I would prefer the 3.125 inch PCD pinion flange and prop shaft yoke. The new pinion flange I ordered from TTR is also available from Burton Power and is drilled with holes to fit both the 2.75 and 3.125 PCD bolt circles.

Given the chance, I would swap my 2.75 inch PCD prop shaft yoke flange with a 3.125 inch PCD one. TTR says the small 2.75 inch flange (and 3.125 inch flange) is made of steel and is plenty strong, but with my new engine putting out 165 lb ft of torque, I would prefer the 3.125 inch version. The loads should be lower on the bolts with the larger bolt circle.

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PostPost by: elated » Mon Sep 12, 2016 11:19 am

I seem to recall that the flange bolt holes are not in a true PCD
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PostPost by: bill308 » Mon Sep 12, 2016 12:54 pm

Hi Gordon.

Can you explain, "I seem to recall that the flange bolt holes are not in a true PCD"?

My research finds that PCD is the abbreviation for Pitch Circle Diameter. In other words, the diameter of a circle, sweeping through a collection of holes, equidistant from a central point.

I have found PCD is customarily used to by suppliers to describe the bolt pattern on drive shaft and pinion flanges.

Bill
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PostPost by: dunclentdr » Mon Sep 12, 2016 3:07 pm

Bill

Thanks for the information - I may have to end up fitting a new, smaller, pinion flange - I was kind of hoping there may be suppliers of propshafts with the larger flange - does anyone know?

David
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PostPost by: promotor » Mon Sep 12, 2016 3:54 pm

Is there a reason that you can't swap just the prop yoke for a larger one? Does your prop use a standard U/J? If so I would just swap the yoke for a larger one and fit a (quality) U/J with a grease nipple while you're at it.

You could buy a cheap flange attached to a propshaft and swap it over.

Mk2 Escort prop flange should fit your prop with no issue.
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PostPost by: dunclentdr » Mon Sep 12, 2016 8:40 pm

That's a very helpful suggestion, thank you!
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PostPost by: promotor » Tue Sep 13, 2016 4:17 pm

dunclentdr wrote:That's a very helpful suggestion, thank you!


No worries. Far better than disturbing the diff flange. Just check that you have adequate room under the floor for a bigger flange to fit (and not get in the way when trying to remove the diff from the car) - outside diameter of a large flange is approx 106mm.
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PostPost by: bill308 » Thu Sep 15, 2016 9:53 pm

Thanks promotor, I believe you are correct. My final drive/transmission builder is looking into it with his drive shaft supplier. The yoke flange was apparently fitted to Escort Mk2's with the Atlas rear end.

In the mean time, I ordered up a new pinion flange drilled for both Lotus bolt patterns. I sent this to my builder two days ago. My builder says he will likely have to replace only the pinion seal and crush spacer, all without opening up the casing. So, not as big a deal as I thought.

The other thing is my shock absorbing drive shaft is fitted with the small yoke flange as fitted to the 3.9:1 rear ends. I'm thinking I really want to replace it with the larger Lotus yoke flange as fitted to cars with the 3.55:1 rear end ratio, for lower shear loads on the bolts. The engine will produce up to 165 lb ft of input torque so multiply this by my first gear ratio of 2.66:1 and the loads start to get big especially when flywheel inertia is added to the total.

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PostPost by: 2cams70 » Fri Sep 16, 2016 12:43 am

Be careful if using an Escort flange on the driveshaft side. Although it may match with the flange on the diff there were a variety of different styles of universal joint used depending on the driveshaft supplier. Some had staked in place U/J's, some had U/J's retained with circlips on the inside, others with them retained by circlips on the outside. Some diff flanges had tapped bolt holes others untapped. I would expect the Elan would have the early circlip on the outside type (same as Cortina) but don't know for sure. MK2 Escorts all had the big flange, MK1's had different sizes depending on whether it was a standard or performance variant.

Burtons have an aftermarket "multifit" type flange (see link) which expect this is the same as what you are using on the diff side.

http://www.burtonpower.com/pinion-flang ... xeng6.html

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PostPost by: bill308 » Fri Sep 16, 2016 10:51 pm

Hi 2cams70.

The pinion flange shown in you link is the one I will be fitting to my final drive. It was sourced from TTR.

Bill
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PostPost by: promotor » Sat Sep 17, 2016 9:58 am

bill308 wrote:Hi 2cams70.

The pinion flange shown in you link is the one I will be fitting to my final drive. It was sourced from TTR.

Bill


These don't come with a seal shield and they aren't available separately for some reason either! As far as I can remember you can't make a Ford one fit so you have to make do without.

Genuine Ford parts (in this case a complete flange) is still as good as it gets 50 years on!
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PostPost by: CBUEB1771 » Sat Sep 17, 2016 1:08 pm

elated wrote:I seem to recall that the flange bolt holes are not in a true PCD
Gordon


The bolt hole centers are on a PCD, you are probably recalling that they are not uniformly spaced at 90 degree increments around the PCD, they are in a rectangular pattern rather than a square pattern.
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PostPost by: 2cams70 » Sun Sep 18, 2016 1:33 pm

Assuming the Elan has a driveshaft with circlips on the outside of the U/J and that you want to use the large PCD diameter flange the most likely source for donor parts will be a Mk2 Cortina GT or 1600E.

The only other Ford models with this combination of parts are the Mk2 Lotus Cortina or a Mk1 Escort Twin Cam / RS1600 / Mexico. These aren't likely to be donors given their rarity.

The diff on these models will also have the large PCD flange with the front seal dust shield installed.

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PostPost by: Chancer » Sun Sep 18, 2016 2:35 pm

I used a 1600GT for the driveline on my first Westfield some 30 years ago, I had to remove the large flange and fit a smaller one, being someone who never throws anything away I most likely still have the larger flange.

Is it now a rare and sought after item? Is it worth me digging through my boxes of bits when I return to the UK?
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