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Spitfire 1500 diff in GT6?


Roger K
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3.63 :1   its the best of the bunch

remember the higher the ratio the more torque you have to transmit for the same performance as a lower ratio 

just part of the reason 3,27 dont last .............always on the loud pedal 

in general  bigger diameter pinion needs  a thinner crown wheel or diff case to accommodate  the off set  from the pinion 

Pete

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6 hours ago, Roger K said:

Pity it's not the Mustang speedo as I just change the plastic gear in the gearbox to recalibrate!  Oh well, hello Speedycables...

Thanks for the advice, all

Not sure if there are different gears available for the d type. There certainly are for the J type. 

Yes, 3.63 is strong. I broke 3 x 3.27 diffs in as many years in my 2.5 vitesse, but the 3.63 ran for 10 years, then 2 years in a 150bhp spitfire, and after a reseal now resides in a Belgian MK3 Spitfire. 

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see   https://www.overdrive-repairs.co.uk/buy-spares.php?cat=D Type Spare Parts List

they only show 15t Triumph  16t MGB 

then if more teeth you may need to change the bearing mount ,as bigger diameter will change its mesh with the worm

( easy on our  old truck gearboxes the drive housing was an eccentric you just turn it to suit the pinion size)

 

to get the TPM     my days  you mark tyre with a chalk line on the side wall   you add a card needle to the cable inner drive 

under the dash, 

mark the road 52,8ft   align tyre mark and push /drive the 52ft carefully and count the turns of the inner cable needle    multiply by 100  and thats the TPM for the speedo 

bear in  mind it must read fast  it must not read slow the old spec was 10% + 4mph  

so a speedo could read at 60 true  + 10% +4  read 70 in the car 

Pete

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That, Pete, is pretty much how Speedycables ask you to check what calibration you want.  Not quite as complex, though, they just ask for a chalk mark on the tyre and a card pointer and disc on the cable, and count how many turns of the pointer for a set number of rotations of the tyre.  They do the maths, otherwise just as you say.

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7 hours ago, Gully said:

When I had my 3.27 ratio diff replaced with a 3.63 I got Speedy Cables to recalibrate my speedo to 1075 TPM, which appears to be spot on against the Sat Nav.

Gully

Do you find the ratios OK for motorway driving as well as twisty bits with the 3.63 and o/d?  What would you be able to do for a couple of hours on a French autoroute - 75-80?

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i use 52.8ft as the maths is ....simpluze  Ha 

easy with the rolling road for my tacho calibration set up  in the factory    to get the tyre rolling circumference and gearbox TPM    you could always take the car to a Tachograph centre and ask if the have a car speedo drive adaptor that fits 

Pete

 

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Well, on one of those RBRRs we arrived at Bristol, after an enthusiastic drive through Wales with a few other cars (Stag, PI, Spitfire, and possibly a Sprint) and one of the other drivers described mine as "the very fast GT6". I do prefer the more relaxed cruising with the 3.63 but it's not quite as spirited on windy roads.

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guess to sum it up with a higher ratio diff  any spirit will  need  3rd gear more 

if triumph got their  gear ratios right 3rd OD could be a split shift but they didnt and 3rd OD and 4th  are  about the same

redesign by moving a few teeth around might have given us 6 ratio's  but  no you get just 5  

pete  

 

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22 hours ago, Roger K said:

Do you find the ratios OK for motorway driving as well as twisty bits with the 3.63 and o/d?  What would you be able to do for a couple of hours on a French autoroute - 75-80?

It's great - I do quite a few motorway / A-road journeys in mine and it's fine. I found with the original 3.27 diff I was rarely using the overdrive unless I was cruising, but now I find flicking in and out of OD in 3rd is really useful on twisty roads! I've not driven a 3.89 ratio diff car (the standard UK market Mk3 with OD), but I'd guess it would be a bit revvy cruising on motorways. I see 3000RPM (or just under) at 70.

Gully

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22 hours ago, Roger K said:

That, Pete, is pretty much how Speedycables ask you to check what calibration you want.  Not quite as complex, though, they just ask for a chalk mark on the tyre and a card pointer and disc on the cable, and count how many turns of the pointer for a set number of rotations of the tyre.  They do the maths, otherwise just as you say.

Or if you know the TPM for the 3.89 ratio diff and also for the 3.27 diff (it's written on the different speedos) you can interpolate what you need for the 3.63 - which is what I did to get the 1075 TPM. I gave that info to Speedy Cables, they worked to that and it's correct.

Gully

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8 minutes ago, Gully said:

Or if you know the TPM for the 3.89 ratio diff and also for the 3.27 diff (it's written on the different speedos) you can interpolate what you need for the 3.63 - which is what I did to get the 1075 TPM. I gave that info to Speedy Cables, they worked to that and it's correct.

Gully

That's fine - I'll get Andy on it for me!

Thanks

Roger

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