Paul J Posted November 26, 2015 Report Share Posted November 26, 2015 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 Quote Link to post Share on other sites
peejay4A Posted November 26, 2015 Report Share Posted November 26, 2015 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. Quote Link to post Share on other sites
Chilliman Posted November 27, 2015 Report Share Posted November 27, 2015 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 Quote Link to post Share on other sites
MichaelH Posted November 27, 2015 Report Share Posted November 27, 2015 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 Quote Link to post Share on other sites
Paul J Posted November 27, 2015 Author Report Share Posted November 27, 2015 Thanks all its been established as a 3.7:1 Life is one big learning curve Paul J Quote Link to post Share on other sites
peejay4A Posted November 27, 2015 Report Share Posted November 27, 2015 3.7? Quote Link to post Share on other sites
Superaquarama Posted November 28, 2015 Report Share Posted November 28, 2015 Was there a different ratio for US cars ? Quote Link to post Share on other sites
stuart Posted November 28, 2015 Report Share Posted November 28, 2015 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. Quote Link to post Share on other sites
peejay4A Posted November 28, 2015 Report Share Posted November 28, 2015 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). Quote Link to post Share on other sites
Paul J Posted November 28, 2015 Author Report Share Posted November 28, 2015 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 Quote Link to post Share on other sites
peejay4A Posted November 28, 2015 Report Share Posted November 28, 2015 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? Quote Link to post Share on other sites
Paul J Posted November 28, 2015 Author Report Share Posted November 28, 2015 (edited) 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 November 28, 2015 by Paul J Quote Link to post Share on other sites
ianc Posted November 28, 2015 Report Share Posted November 28, 2015 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 Quote Link to post Share on other sites
Paul J Posted November 28, 2015 Author Report Share Posted November 28, 2015 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 Quote Link to post Share on other sites
Paul J Posted November 28, 2015 Author Report Share Posted November 28, 2015 Hi Ian how do I obtain this cd Quote Link to post Share on other sites
peejay4A Posted November 28, 2015 Report Share Posted November 28, 2015 I did say that I'd assumed only one wheel was raised. It's definitely 3.7 then. Quote Link to post Share on other sites
Paul J Posted November 28, 2015 Author Report Share Posted November 28, 2015 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 Quote Link to post Share on other sites
mike3md Posted November 28, 2015 Report Share Posted November 28, 2015 Paul, I think Stuart was speaking of TR250 and TR6 for the 3.45:1 Pretty sure all TR4s and TR4As were 3.7:1, although 4.1:1 was an option if overdrive was fitted - as stated in "Original Triumph TR" by Bill Piggott. Mike Quote Link to post Share on other sites
Paul J Posted November 28, 2015 Author Report Share Posted November 28, 2015 Thanks Mike, another lesson learned today. Paul Quote Link to post Share on other sites
stuart Posted November 28, 2015 Report Share Posted November 28, 2015 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 Quote Link to post Share on other sites
Superaquarama Posted November 28, 2015 Report Share Posted November 28, 2015 (edited) 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 Edited November 28, 2015 by Superaquarama Quote Link to post Share on other sites
Alec Pringle Posted November 29, 2015 Report Share Posted November 29, 2015 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 Quote Link to post Share on other sites
ianc Posted November 29, 2015 Report Share Posted November 29, 2015 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 Quote Link to post Share on other sites
stuart Posted November 29, 2015 Report Share Posted November 29, 2015 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. Quote Link to post Share on other sites
Paul J Posted November 29, 2015 Author Report Share Posted November 29, 2015 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 Quote Link to post Share on other sites
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