Hi all,
I'm getting the diff in my trav rebuilt with a new 3.9 gear set.
It is a 1970 1098 model and had a 4.22 diff. The tyres are 175/75x14 fitted to slighty widened rims
With the change in diff ratio, what tpm value speedo should i upgrade to ?
cheers
Moray
3.9 diff speedo tpm
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mike.perry
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Re: 3.9 diff speedo tpm
Before you change the speedo, check the accuracy of the original with a sat nav. I am still using the original 1408 speedo on a 3.9 diff and 175/80 x 13 tyres and it is spot on.
There is a table of speedos on the Series MM website, http://seriesmm.mmoc.org.uk car ident.
There is a table of speedos on the Series MM website, http://seriesmm.mmoc.org.uk car ident.
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IslipMinor
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Re: 3.9 diff speedo tpm
For a 3.9 diff and 175/75x14 tyres the theoretical tpm is 1246, but Minor speedos are notoriously optimisitc, so you could well get away with a higher tpm head. Although the speed may be indicated in the right order of magnitude with a 'wrong' head, I would expect the odometer to be very inaccurate, as these are directly linked to the head gearing and tpm. The speed indication has a slightly more vague connection with reality!!
Richard
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mike.perry
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Re: 3.9 diff speedo tpm
Can you swap the milometers between speedos to get accurate speeds and distances?
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IslipMinor
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Re: 3.9 diff speedo tpm
Mike,
Yes, so long as the basic layout, i.e. tenths, trip etc. is the same. I did this with our original 948 head with no tenths/trip, for the Toyota 5-spd + 3.9 diff, and needed 995 tpm. There is an early, Series II?, speedo head with the same layout of 3 warning lights and no tenths/trip, which is 1000 tpm and the odometer is absolutely spot on with no changes made at all. The speedo part I did have to get recalibrated, as I have a kph face that reads 0-120 (courtesy of this messageboard), but with mph speedo internals. Again after the recalibration it is spot with the GPS.
We do the Euroclassic run of 1000+ miles across Europe most years and it is all tulip navigation, using intervals between points in towns often of less than a mile, so we have an interesting job to do!! Having a very accurate odometer means that we can use the cumulative distance from each start to know where we are (just don't go wrong as the recalc takes for ever!!) - seems to work well.
Yes, so long as the basic layout, i.e. tenths, trip etc. is the same. I did this with our original 948 head with no tenths/trip, for the Toyota 5-spd + 3.9 diff, and needed 995 tpm. There is an early, Series II?, speedo head with the same layout of 3 warning lights and no tenths/trip, which is 1000 tpm and the odometer is absolutely spot on with no changes made at all. The speedo part I did have to get recalibrated, as I have a kph face that reads 0-120 (courtesy of this messageboard), but with mph speedo internals. Again after the recalibration it is spot with the GPS.
We do the Euroclassic run of 1000+ miles across Europe most years and it is all tulip navigation, using intervals between points in towns often of less than a mile, so we have an interesting job to do!! Having a very accurate odometer means that we can use the cumulative distance from each start to know where we are (just don't go wrong as the recalc takes for ever!!) - seems to work well.
Richard