RedeyesUK Posted May 7, 2006 Share Posted May 7, 2006 Hi there,I've been having a few problems recently with my rear axle, which has eventually led me to take the thing off the car for a strip down and service. However, I've now noticed something odd....Looking at the bottom of the diff casing, the number stamped on there is CT 254. Looking that up reveals this to be an early type automatic axle, with a 3.27:1 ratio, whereas my car is a 4-speed manual, and (I think) should have the 'CG' type axle, with the 3.63:1 ratio.Without getting into what it's doing on there in the first place (I truly don't want to know.... :-/ ), my question is this:What effect will I see if I swap the axle to the proper CG type, or even fitting a later 5-speed axle (As far as I can see, it's more or less interchangeable, and I plan to swap the box for a 5 speed in the near future anyway)? I know going one way will increase my top speed (I currently max out at [s]80[/s] er, I meant 70 ;) ) at the expense of acceleration, but I can't remember whether the higher numbers are better.Any ideas/recommendations?(And if you have a good axle to sell, I might be interested! ;) ) Link to comment Share on other sites More sharing options...
chris turner Posted May 7, 2006 Share Posted May 7, 2006 The car will be faster with the correct axle. If you are going to put a 5 speed axle on, the propshaft will need modifying so I would wait and do 5 speed gearbox and axle together. I have a 4 speed car for everyday use and prefer the lighter feel anmd nippier acceleration. Link to comment Share on other sites More sharing options...
Beans Posted May 7, 2006 Share Posted May 7, 2006 The car will be faster with the 3.9:1 ratio :PSorry Chris, had a 3.45:1 (5 speed axle) but ditched it for a 3.9:1.OK, top speed will be down ( in my case from 240 to 200 km/h) but than ultimate speed is totaly unimportant. Its accelaration and nimbleness that counts ;DRemember the rally cars ran ratios between 4,55:1 and 5,38:1. So what are you expecting from ie what will you be doing with your car? I'll help you a bit ;) A TR7 is not a high speed GT car ::) Link to comment Share on other sites More sharing options...
RedeyesUK Posted May 7, 2006 Author Share Posted May 7, 2006 [quote by=beans link=Blah.pl?b=tr78,m=1147007800,s=2 date=1147027940]. So what are you expecting from ie what will you be doing with your car? I'll help you a bit ;) A TR7 is not a high speed GT car ::)[/quote]heh, I'm well aware!As for the driving, I'm not looking for high top speeds, acceleration is where it's at. ;)But I do drive down to London fairly regularly, and 100 odd miles at 4500RPM doesn't exactly do wonders for fuel consumption - or my ears! Ultimately that's what the 5 speed conversion will be for. I can put up with a top end as it is, but I'd hate to go any lower really. Plus of course I'll be on the RBRR on October, so longer legs would be a bonus!Tricky decision, I know.... :-/:EDIT:I just had another thought. Having the wrong diff ratio is going to put my speedo out, isn't it? And if it is, which way? Am I going too fast or too slow?That changes things...... Link to comment Share on other sites More sharing options...
Beans Posted May 7, 2006 Share Posted May 7, 2006 Depnds which way you go.There are different speedodrive gears, depending on the 'box and final drive ratios.So depends on what you choose ::) Link to comment Share on other sites More sharing options...
RedeyesUK Posted May 7, 2006 Author Share Posted May 7, 2006 My head hurts..... :B Link to comment Share on other sites More sharing options...
Beans Posted May 7, 2006 Share Posted May 7, 2006 OK a bit off help than ... a 5 speed with a 3.9:1 rear drive ratio gives a cruising speed off about 70 mph @ 3500 rpm. Depends offcourse on the tyre sizeoh yes, with both 'boxes 4th gear has a 1:1 ratio Link to comment Share on other sites More sharing options...
RedeyesUK Posted May 7, 2006 Author Share Posted May 7, 2006 OK, that helps.....So if I fitted the correct axle, I'd get better acceleration, but at the cost of top speed, right?Except if my speedo is expecting to have a 3.63:1 ratio (which it probably is), then it'll be reading too slow? In which case I'm going faster than my speedo says I am? Oops..... Link to comment Share on other sites More sharing options...
chris turner Posted May 7, 2006 Share Posted May 7, 2006 Beans, when I said correct axle I meant for a 4 speed manual which is 3.63-1. The correct axle for a 5 speed car is 3.9-1. You shouldnt mix and matchRedeyes, if you live near Sheffield I will give you a 3.63-1 axle as I have a spare. Link to comment Share on other sites More sharing options...
RedeyesUK Posted May 7, 2006 Author Share Posted May 7, 2006 [quote by=chris_turner link=Blah.pl?b=tr78,m=1147007800,s=8 date=1147041550]Redeyes, if you live near Sheffield I will give you a 3.63-1 axle as I have a spare.[/quote]Hmmm, I might take you up on that. How much would you want for it? Link to comment Share on other sites More sharing options...
Beans Posted May 8, 2006 Share Posted May 8, 2006 [quote by=chris_turner link=Blah.pl?b=tr78,m=1147007800,s=8 date=1147041550]Beans, when I said correct axle I meant for a 4 speed manual which is 3.63-1. The correct axle for a 5 speed car is 3.9-1. You shouldnt mix and match[/quote]But than I didn't say he should ;DYou're right offcourse, always swap 'box and axle if you go from 4 to 5 speed 'box ;)But a 4 speed car is diffinitely not for longer highway useLater automatic TR7's (with the "5 -speed" rear axle) had a ratio of 3.08:1.The USA Fed cars from 80 onwards with axle no from CL1 and Non UK Solihull built cars had a 3.45:1 ratio. Gives 70 mph @ 3000 rpm, but imo a bit lustless performanceRedeysUK; for every 'box/diff ratio there is a different (coloured) speedo drive gear. I think someone like S&S can give you the correct one for a 3.63 diff. You probably need the black one (with 23 tooths) but I am not sure so better ask someone who knows ::) Link to comment Share on other sites More sharing options...
chris turner Posted May 8, 2006 Share Posted May 8, 2006 My 4 speed car is brilliant on the highway as it is fitted with the Coombes of Guildford overdrive conversion. Link to comment Share on other sites More sharing options...
Beans Posted May 8, 2006 Share Posted May 8, 2006 That's a very interesting conversion indeed :)But I will nevertheless stick to the 5 speed & Salisbury diff rear axle Link to comment Share on other sites More sharing options...
chris turner Posted May 8, 2006 Share Posted May 8, 2006 Definitely, the 5 speed is a better gearbox, the 4 speed and overdrive is a bit of a novelty. Link to comment Share on other sites More sharing options...
AdamSindrey Posted May 9, 2006 Share Posted May 9, 2006 Don't want to hijack this thread but I got an 1850 dolly with a 3.63 back axle. I've been told the diff is very weak and now my cars got a TR7 motor in it ;D (Do I get to join your gang now :P) isn't expected to last very long.... Are they the same differentials on tr7s and 1850s?Oh and as for ratios. I put a 4.11 on my car for well a laugh really. Accelerations better but it is totally useless for M ways. Link to comment Share on other sites More sharing options...
Beans Posted May 9, 2006 Share Posted May 9, 2006 [quote by=AdamSindrey link=Blah.pl?b=tr78,m=1147007800,s=14 date=1147180995] ... isn't expected to last very long.... Are they the same differentials on tr7s and 1850s?[/quote]Yes, and as a mate off my can confirm they are rather weak. Btw, his is under a standard Dolly 1850. He has all sorts off Dolly diff's lying around, rattling, rumbling, whining, you name it :P Link to comment Share on other sites More sharing options...
Paul S Posted May 9, 2006 Share Posted May 9, 2006 ...but not the diffs from the 5 speed TR7s, totally different axle (if you didn't know Adam)..I somehow still seem to have 2 1850 Dolly axles at the back of my flat...don't suppose anyone wants them (for free)?! ;) both 3.63 from memory.... Link to comment Share on other sites More sharing options...
Beans Posted May 9, 2006 Share Posted May 9, 2006 [quote by=Paul_S link=Blah.pl?b=tr78,m=1147007800,s=16 date=1147202578]...but not the diffs from the 5 speed TR7s....[/quote]But even they can make some noise if you abuse them long enough ::) Link to comment Share on other sites More sharing options...
RedeyesUK Posted May 11, 2006 Author Share Posted May 11, 2006 I've just come across this handy little site:http://www.mintylamb.co.uk/gearspeed/(Thanks James!)According to that, If I fit the correct diff, I'll lose roughly 10MPH off my top end - although if the chart is correct, my speedo has been lying to me by about 5% or so, so realistically it'll only appear to be 5MPH off the top end, but with better acceleration on the way up there.I can live with that! :)Now to get a new axle..... Link to comment Share on other sites More sharing options...
.thumb.jpeg.b15b81ef10abeea1c3039ae03c4a9f3a.jpeg)
Recommended Posts
Archived
This topic is now archived and is closed to further replies.