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Axle ratio of USA TR4A


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I have been trying my axle ratio by turning the wheel and counting the prop shaft revs, it seems to be a 2.1 ratio ie 1 turn of the wheel turns the shaft 2.1 times. All references discuss 3.7 or 4.1. This is a non overdrive US import can anyone shed some light on this please. I suppose it would have a very good freeway speed.

Or am I doing something stupid

Cheers

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There's a factor of two to be taken into account if you just jack up one wheel. So your diff appears to be 4.1

+1 - unless you've got a LSD fitted

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If you want to know you have to take the back plate off and count the teeth in the crown wheel: if there are 37 it will be 3.7:1 if 41 it will be 4.1

you will need a new gasket when you put the back plate on

Hope this helps

Michael

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Thanks all its been established as a 3.7:1

Life is one big learning curve

Paul J

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Was there a different ratio for US cars ?

Not normally only TR250 and TR6 for US market got 3.7 instead of 3.45

Stuart.

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Going back to my post 6 above, how do you make it a 3.7 diff Paul? If you measured 2.1 turns of the prop shaft for 1 turn of a rear wheel, then assuming you only jacked up one wheel that makes it a 4.2 ratio (most likely 4.1).

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I followed another thread that turns the wheel and count the turns of the prop shaft which made it quite different, have also counted the crown wheel teeth which has 37 teeth. Michael H suggested this method, open to other suggestions.

Slightly confused

PaulJ

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Now I'm confused too. In your first post I read it that you turned the wheel once and the propshaft turned 2.1 times which approximates to a 4.1 ratio. If it turned 1.85 times then it would be a 3.7. So I guess you miscounted?

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Really need to get to the bottom of this, reason being I want to purchase the correct speedo, both wheels are off the ground, two full turns of one wheel will turn the prop shaft slightly less than 4 turns, is this the correct method or is counting the teeth more accurate.

Lock the opposing wheel, turn the prop shaft 2 full turns and the wheel turns 1.1 turns.

Edited by Paul J
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See Section E2 of the Technicalities CD for the article which I wrote for TR Action #29 (a very long time ago!).

This explains how to determine the axle ratio without the need to remove the diff. cover.

Ian Cornish

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Lock the opposing wheel and turn the wheel 1 turn and the shaft turns approx 1.8 turns so Pete I think will settle for the 3.7. If it's wrong then I will have a poorly calibrated speedo. Unless Stuart can advise otherwise.

Thanks

Paul

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Hi Ian how do I obtain this cd

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Yes apologies I wasn't very clear with my procedure, the opposing wheel was indeed off the ground but the brake was stuck on. Today I have been removing the rear wings so had to remove the wheel, in doing so I also removed the hub and released the brake adjuster. The wheel now turns, so to carry out the last test I had to lock it off. Hopefully the last test was conclusive and proves that it's a 3.7. If as Stuart says they were all 3.45 then I will need to get my new speedo calibrated to suit.

The Crown wheel number of teeth has not been questioned.

 

On a brighter note I received my dating certificate from the Heritage Centre today and all is with the car as it left the factory on 10th Oct 1966 (nothing else remarkable happened that day with the exception of the Dominican Republic adopted its constitution) with the exception of the wire wheels that have gone astray. All numbers match.

Thanks again

Paul

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Thanks Mike, another lesson learned today.

Paul

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4.1 is actually a very rare fitment although I believe all the 1991cc cars supplied to Japan had them. Nearly all TR4/4A`s are 3.7.

Stuart

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Stuart referred to 4-cylinder cars, TR2-4A, for which the 3.7 final drive was standard both sides of The Atlantic . . . .

 

TR5PI and TR6PI ran 165 tyres and a 3.45 diff, whereas the less powerful carburettored TR250 and TR6 (N.America) ran larger diameter 185 tyres and the lower 3.7 ratio . . . .

 

Cheers

 

Alec

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PaulJ - a few years ago, each existing member received the Technicalities CD and, subsequently, all new members received one as part of the Joining Pack.

if you haven't got the CD, call Jo in the office.

Ian Cornish

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Was there a different ratio for US cars ?

 

Not normally only TR250 and TR6 for US market got 3.7 instead of 3.45

 

Nearly all TR4/4As are 3.7.

 

Thanks, Stuart, but aren't you contradicting yourself here ?

 

Anthony

OK OK just because I missed a comma out! I was answering one question and supplying some other information for reference ....sheesh!

Stuart.

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Thanks everyone and yes Ian I have received my cd just not observant enough when opening my post. Going to take the afternoon off from the TR give it a rest, my wife thinks I'll need to be surgically removed.

Cheers

Paul J

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