Lotus Elan

5 speed and diff

PostPost by: mcclelland » Wed Jul 15, 2015 9:31 pm

Hello all,

could anyone tell me what is the correct diff ratio fitted with the Lotus 5 speed box?? Was there an option of the 3.77 or 3.54 or just one fitted as standard??
If there was an option which would be best to fit for al-round driving......and also if there was an option I take it there is a gear box drive that needs to be changed to give the correct speed??

Many thanks in advance for your help. George.
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PostPost by: rgh0 » Thu Jul 16, 2015 9:22 am

My 1973 Plus 2 130/5 came with a 3.55 diff which I believe was standard in the car. The speedo drive is the same as with the 4 speed box and uses the same ratio as when it was used with a 3.55 diff.

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PostPost by: CBUEB1771 » Thu Jul 16, 2015 8:15 pm

rgh0 wrote:My 1973 Plus 2 130/5 came with a 3.55 diff which I believe was standard in the car.


Interesting, I wonder what differences there were based on geographical market and importer input. Very few Lotus 5 speed boxes ever made it to the US and anything other than a 3.77 CWP in a +2 is very rare here.
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PostPost by: rgh0 » Thu Jul 16, 2015 8:31 pm

I suspect he lower power of the US emissions engines prompted Lotus to keep the 3.77 diff in US cars

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PostPost by: mbell » Thu Jul 16, 2015 9:13 pm

I didn't think any 5 speed boxes made it to the US in federal spec cars (N code), I haven't seen any on the various registers. I thought they'd stopped the federal version before the 5 speed box was commonly available. So only UK or Euro spec car with 5 speed boxes are in the US.

I should really go out and test the diff on my car to confirm what it is....
'73 +2 130/5 RHD, now on the road and very slowly rolling though a "restoration"
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PostPost by: CBUEB1771 » Thu Jul 16, 2015 9:16 pm

rgh0 wrote:I suspect he lower power of the US emissions engines prompted Lotus to keep the 3.77 diff in US cars


Good thought, another round of certification tests might also have killed the 5 speed for the US market.
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PostPost by: mbell » Fri Jul 17, 2015 12:27 am

Had a look in my manual and it suggests that the 3.77 is standard for the plus 2 and 3.55 is optional. But my manual doesn't include the 5 speed box info.

Would have thought it be strange to add a taller gear to the box and go to a taller diff by default.
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PostPost by: stugilmour » Fri Jul 17, 2015 4:01 am

My '69 Federal four speed originally had the 3.77. I replaced the four speed with a MT75 five speed. After using the car a bit and needing diff service, I changed the final drive to 3.54 with a C&P from eBay. Really like the combination; runs about 3,500 RPM at 80 mph. As it is a Lotus, feel free to pick the ration you like. :) David has done up a great spreadsheet the provides RPM and speed in all the gears, making it easy to check things out pretty thoroughly.

What is the fifth O/D ratio in the Lotus box? I think my MT75 is 0.82. First is 3.61 i think, and could stand to be a bit higher even with the 3.54.

I always thought the 3.55 was the option and 3.77 standard, at least in the federal four speeds. I checked the November 1972 Motor Trend road test for the Plus 2S 130 (four speed) "Two for the Road - Twin Cam Europa and Plus 2" and it lists 3.55 as standard and 3.77 as optional. :?:

I also recall we did not get five speeds in Canada, but can certainly be corrected.

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PostPost by: billwill » Fri Jul 17, 2015 12:14 pm

I always thought that 3.77 was standard in the UK.

Back in the 90's when I aquired a spare diff complete, I had it refurbished and changed to 3.55 and that is what has been in my car since. (my used 3.77 diff complete with Lotus rear casing is available to buy)

It's better for motorway cruising.. There were few or none motorways when the Elans were designed.
Last edited by billwill on Fri Jul 17, 2015 2:23 pm, edited 1 time in total.
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PostPost by: denicholls2 » Fri Jul 17, 2015 1:26 pm

As an owner of a 4-speed Europa, it makes perfect sense to me that 3.55 might have been standard in the U.S. market even if not in Europe. In the sixties, the U.S. had a vast network of interstate highways and lots of distance between places to get to in most parts, 70 mph typical speed limits with a couple of states unlimited. Most highways much less congested than the Autobahns. And out west, sometimes over 200 miles between filling stations.

Spend a few hours at highway speeds with your ears less than a foot ahead of a Weber 45 and you'll get a keen appreciation for tall highway gearing even though it sounds great when you start it up. Granted, these aren't Lotus roads and the family Chevrolet will traverse them as fast and with greater comfort. But people with places to go made a lot of use of them.
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