johny Posted September 7, 2020 Report Share Posted September 7, 2020 Sorry well covered topic but I cant find a definitive answer on what my options are to correct the speedo reading when putting a 3.63 diff in my non-OD 2L Vitesse. Is there a chance of changing the gearbox speedo drive and if so how do I identify the gears I need? Thanks Link to comment Share on other sites More sharing options...
Pete Lewis Posted September 7, 2020 Report Share Posted September 7, 2020 triumph did not do many alternative speedo pinions they just specified different TPM speedos big saloon /TR boxes have some alternatives but not much for the small chassis gearbox if the speedo is fitted mark 52.8 ft on the road accurately push car this distance , fit a card needle to the speedo cable inner and count the turns it makes multiply this count by 100 and you have the TPM you need to get another speedo or get it recalibrated Link to comment Share on other sites More sharing options...
NonMember Posted September 7, 2020 Report Share Posted September 7, 2020 When we put a 3.63 in a Herald, my brother got a circle of card just larger than the speedo and marked the correct speed points on it. The error on a Vitesse will only be about 5% which is way less than the misreading I've seen on most of my old Triumphs (although, bizarrely, the GT6 appears spot on once corrected for the diff change, which is what led me to "have a look" and discover that it had a 4.11 diff fitted for many years). Link to comment Share on other sites More sharing options...
johny Posted September 7, 2020 Author Report Share Posted September 7, 2020 Thanks, I make it just over 7% increase which with the 165/80 13 tyres I like to use will be a bit too much error for comfort.... As Pete says calibration would sort both out in one hit. Link to comment Share on other sites More sharing options...
Nigel Clark Posted September 8, 2020 Report Share Posted September 8, 2020 If it was just the switch to a 3.63 diff, I wouldn't bother changing the speedo. As has been said, the effect of this one change is well within the (in)accuracy of the speedo anyway. However, with larger tyres giving a greater rolling radius and higher gearing, added to the 3.63 diff, turns per mile may have changed by more than 10%, so recalibration is the sensible option in my opinion. Nigel Link to comment Share on other sites More sharing options...
Prince Brainier of Meccano Posted September 23, 2020 Report Share Posted September 23, 2020 sat nav for accuracy and speedo for indication? Assuming you'd have such witchcraft in a proper car. Link to comment Share on other sites More sharing options...
Iain T Posted September 23, 2020 Report Share Posted September 23, 2020 You can have a gearbox corrector made to your spec from Speedograph Richfield. I had a right angle adaptor made for my T9 box, I think it was around £80-90. This way you can leave your speedo as original. Iain Link to comment Share on other sites More sharing options...
johny Posted September 23, 2020 Author Report Share Posted September 23, 2020 Thanks Iain, I'll have a look into it👍 Link to comment Share on other sites More sharing options...
Gully Posted September 25, 2020 Report Share Posted September 25, 2020 When I changed the diff in my GT6 from a 3.27 to 3.63 I had the 1152TPM speedo recalibrated by Speedy Cables to 1075TPM - with 175/70R13 tyres (very close to 155/80R13), it's spot on my sat nav reading. Gully Link to comment Share on other sites More sharing options...
johny Posted September 25, 2020 Author Report Share Posted September 25, 2020 Gully does it include the mileage/trip reading as well or is that hoping for a bit too much? Also your reading must have been miles out beforehand as my speedo is 1152 and thats standard for a 3.89 diff! Link to comment Share on other sites More sharing options...
DVD3500 Posted February 19, 2021 Report Share Posted February 19, 2021 I found a battery powered GPS speedometer that you can set on the dash. Supposed to be very accurate. It is "technically" a radar trap indicator devices that you download all known traps into it, supposedly legal and all but the upshot is it tracks your speed... We have a lot of 30 kmh zones here and my speedo bobs up and down so I am not sure how accurate it is... I have not bought the device yet but my plan is to use it instead of getting the speed recalibrated... Link to comment Share on other sites More sharing options...
Pete Lewis Posted February 19, 2021 Report Share Posted February 19, 2021 if the error is reasonably linear a small move of the needle may give you all you need to stay within the tolerances of speedo's they must not read slow but read fast used to be 10% + 4mph when i ran a tacho centre in the factory ( the only truck factory to get UK approval ) all long gone so that spec may be a bit historic and havnt looked at Construction and use Rules for some years Pete Link to comment Share on other sites More sharing options...
PeteH Posted February 19, 2021 Report Share Posted February 19, 2021 The nearest I can find online appears to be in the region of -0 to +10%+2.4mph current, before prosecution for exeeding any precribed limit?. Which would suggest that Pete was near enough correct. 30mph would equate to 35.4 under those limitations Link to comment Share on other sites More sharing options...
Pete Lewis Posted February 19, 2021 Report Share Posted February 19, 2021 i remember on the rollers 60 could read 70 and its ok Ford always used the top end so MPG looked better but distances were longer In the Hunter torquay was 212 miles in FiL Cortina it was 225 miles doesnt matter when were all electric we wont get that far anyway Pete 1 Link to comment Share on other sites More sharing options...
JohnD Posted February 19, 2021 Report Share Posted February 19, 2021 A Vitesse came with the 4.11 diff, which is 16mph/1000rpm, while a 3.63 diff is 18mph/1000 (Both in top gear - direct drive - and assuming no great change in the rolling wheel circumference). That is a 12.5% difference, so you might not be within the allowance for speedo error, that is usually 10% on speed cameras. Pete is correct (of course!) about how Triumph and all UK manufacturers matched their transmisison and speedos. Somewhere like Speedy Cables can rebulid a speedo to suit a different gearing, But I believe that US makers fitted diferent cogged speedo drive pinions to the gear box, so that a modifier could choose a different cog if the gearing was changed. John Link to comment Share on other sites More sharing options...
PeteH Posted February 19, 2021 Report Share Posted February 19, 2021 1 hour ago, Pete Lewis said: doesnt matter when were all electric we wont get that far anyway There is currently a thread on a facebook site generating a Huge amount of "opinion" on that subject. "Range" being the "BIG" objection to moving to E-V`s followed by Charging times and Grid capacity. I suspect that eventually all MPH will become GPS generated. Not that it will effect "our" cars unless or until some genius come up with a "conversion"?. Current issue of P-C is focused on "electric conversions" to Classics. Pete Link to comment Share on other sites More sharing options...
Pete Lewis Posted February 19, 2021 Report Share Posted February 19, 2021 on commer gearboxes the speedo drive was an eccentric housing so with a vast aray of transmisions and tyres you had a whole range of pinions and a fixed 5 start worm so bigger or smaller pinions you just rotated the eccentric to give the right mesh and kept a fits all speedo , but a dozen pinions not rocket science then they invented electronic units you just flip the switches to set /match the gearbox output (W) Pete Link to comment Share on other sites More sharing options...
Guppy916 Posted February 23, 2021 Report Share Posted February 23, 2021 Best talk to Andy at speedy cables he is very helpfull they recalibrated my speedo have a look here https://speedycables.com/speedometer-calibration/ and dont be put off it is so simple to do Link to comment Share on other sites More sharing options...
Clive Posted February 23, 2021 Report Share Posted February 23, 2021 On 19/02/2021 at 13:16, JohnD said: But I believe that US makers fitted diferent cogged speedo drive pinions to the gear box, so that a modifier could choose a different cog if the gearing was changed. John The later boxes and J type OD used different speedo drives in the gearbox. The speedos are all the same TPM (1000?) Same system used in other makers gearboxes. Match the speedo drive to the diff. Link to comment Share on other sites More sharing options...
Pete Lewis Posted February 23, 2021 Report Share Posted February 23, 2021 just playing with a speedo where the oddometer rolls are not indexing and quite surprised to find the drive worm is loose on the main shaft no wonder its failed but a simple solution will be spa glue , it would need a drag to pull it off and being plastic thats going to wreck it if it wont stick its off to speedy or JDO as another repairer www.jdmo1.co worth pencilling in your little black book Pete Link to comment Share on other sites More sharing options...
Colin Lindsay Posted February 23, 2021 Report Share Posted February 23, 2021 1 hour ago, Pete Lewis said: if it wont stick its off to speedy or JDO as another repairer www.jdmo1.co worth pencilling in your little black book Pete I'd just fit a different speedo, probably much cheaper... or cannibalise another one. Herald ones are two a penny online. Link to comment Share on other sites More sharing options...
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