Lotus Elan

Raising the Final Drive Unit

PostPost by: jkolb » Mon Dec 29, 2008 6:45 pm

I am about to begin reinforcing my frame heretofore stock) and am considering raising the final drive by 1/2 inch to reflect the fact that the ride height will be decreased through a fully adjustable suspension. It seems that this would be a good idea, though I've not read of anyone who has modified the frame to accommodate the change. What do you think? Has anyone done this modification?

Jerry
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PostPost by: jimj » Mon Dec 29, 2008 11:19 pm

Butchering the chassis would not be a good idea and pointless. By lowering the ride height you would not increase the amount the drive shafts could deflect upwards, you are reducing the amount of travel in the suspension.
Jim
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PostPost by: cabc26b » Tue Dec 30, 2008 4:57 am

Jerry -
You can move the diff up by fitting the TTR mounts instead of the stock units. I have done this on a couple of cars. I also use the diff bracket and make sure the rods that control fore and aft movement are upgraded along with rreinforcing the chassis fixtures for the rod attachment. I run stiffer springs. and I am not looking for long travel with UJ's and sliding splins.

I try to be systematic when I do things like this.

George
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PostPost by: jkolb » Tue Dec 30, 2008 2:10 pm

I am doing the full 26R reinforcement, and using TTR's uprated mounts. Installed as stock, these mounts do not increase the height of the differential materially with respect to the inner wishbone pivots. It is my understanding that the TTR frame builds in an increase in dif height, and I am trying to accomplish that by shimming up the TTR mounts with 1/2 inch aluminum "pads". This, however, brings the dif into conflict with the rear crossmember. I can do this and reinforce it in a manner that will not reduce its strength, but am looking for some input as to whether this will be helpful. It would seem to reduce the drive shaft angles in a car that is being lowered, but is it material? Is there something I am missing? The car is almost exclusively a track/race car.

Jerry
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PostPost by: rgh0 » Tue Dec 30, 2008 9:16 pm

Jerry

How are you intending lowering the car? I get most of the lower ground clearance in my Elan from the smaller diameter 175/60 tyres I use. The suspension has only been lowered a little so that the drive shaft is aproximately horizontal with normal diff location. This produces a ground clearance of about 100mm under the body / chassis and about 50mm under the exhaust which is about as low as practical for me at least.

Even if you lower the suspension substantially further so that you had say a 20 mm rise in the drive shaft from diff to wheel hub I dont believe this would be a problem as all the types of drive shaft join can tolerate normal running at this sort of angular deflection. However lowering the suspension this far starts to limit travel substantially which will affect handling adversly in other ways.

regards
Rohan
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PostPost by: cabc26b » Tue Dec 30, 2008 10:37 pm

Sorry - my recollection is the mounts I got were shorter than the ones I took off, agree with the nominal lift comment though, espcially when you add the bracket. On the frames Not following you - The ttr frames ( they're done by Miles) don't modify the rear cross member holes -
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PostPost by: jkolb » Tue Dec 30, 2008 10:55 pm

Excellent point Rohan. I am afraid that I got off track thinking that the lowering would be mostly by virtue of the adjustability of the rear coils.

Thanks for the input! sometimes there are things that we can do, but that we shouldn't.

Jerry
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PostPost by: jkolb » Tue Dec 30, 2008 10:58 pm

Re my frame comment. Tom at Dave Bean Engineering told me that the crossmember was higher in the TTR/Miles frame to raise the dif. I have never compared them. If you have yours out of the car I will measure my original and post later today.

Jerry
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PostPost by: Davidb » Thu Jul 23, 2009 10:14 pm

Do we have an update on this?
While I don't recall any differences in the upper mounts for the diff casing on my 26Rs I do recall that both cars had the suspension pick up points raised on the chassis at the rear.
DB
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