diff and speed question

[mmjosh]

hi there i have a 4.5 diff in my 54 split screen morris with a standard speedo ill the reading of the speedo be inacurate with this diff.

[mike.perry]

Yes, you need a speedo with a 1504 TPM

[mmjosh]

where can i get one of them from as i might be running it with the 1098cc engine and box soon

[mike.perry]

There were dozens of them at last year's national rally. Probably loads of them on the shelf in people's garages (except mine)
There is a table listing most speedos on the Series MM website, car ident.

[mmjosh]

are they the same as the original speedo's

[mmjosh]

also mike i hav the gold dash not the centre speedo

[PSL184]

Engine and box won't make any difference to your speedo reading. I would suggest you check your speedo against a sat nav before you bother to change speedo as you will no doubt be running on 145 or 155 tyres now which are bigger than your car would of had when new so the speedo will be inaccurate even if you did fit the correct one for your diff ratio. Call me if you want a further explanation.....

[mmjosh]

so how would i make the speedo reading to be correct

[mike.perry]

Sorry, forgot about the early dash, you want a speedo for a Series MM with a 1600 tpm. Your speedo should have a 1000tpm.
Again you can probably pick one up at the nat. rally, usually the whole inst panel.

[mmjosh]

i have a trip metre speedo

[PSL184]

Shouldn't the tpm come down with a lower ratio axle....??

[mike.perry]

I also have a trip speedo, originally from a Morris Oxford Series MO but it still has a 1600 tpm which is the important bit when using a 4.55 axle. What tpm is on your speedo?

[mmjosh]

yes its a 1600 and heres a picture[frame][/frame]

[bmcecosse]

Well - it should be 'near enough' accurate with the 4.55 final drive. As pointed out earlier - should be 1504 for a 4.55 final drive, but 1600 is as near as you will get.

[mike.perry]

That is the same as mine, it should be fine. Does the trip meter still work and have you got the cable that zeros the trip meter? To fit my cable I had to drill through the bottom of the panel next to the steering wheel bracket.
I have just boxed mine up to send away to have the trip meter cable repaired and to check the calibration, it is about 4mph too fast at 60mph

[mike.perry]

Well - it should be 'near enough' accurate with the 4.55 final drive. As pointed out earlier - should be 1504 for a 4.55 final drive, but 1600 is as near as you will get.

I think that the drive cog gearing is different on the MM and S11 which is why the tpm figures don't match up.

[bmcecosse]

Drive cog - in the gearbox Mike ?

[mike.perry]

The cog on the end of the speedo cable. I need to check the teeth on the MM/S11 & 948/1098 boxes.