dodgy speedo (MA70)

[supra_cam]

I have a 7mge MA70 and the speedo reads more than it should, eg. 120k's when its actually doing 100 (tested this driving through one of those speedo checkers on the Hume Highway). I think it gets more innacurate the faster you go. I'm not too fussed but if its easy to fix I may as well do it. Anyone know what to do? It has 16inch wheels would this make much of a difference? cheers

[Negative Boost]

What were the stock wheels and tyre diameters? And what tyre size's do you have at the moment? Increasing overall rolling diameter will affect the speedo.

[wiso]

it sould be a few things causing it. a bit more info about the car please.

is it auto? is it manual?

if the car has had a diff change, maybe the same diff wasn't used. (there are 3.7, 3.9, 4.1, 4.3, 4.5 diff ratios available for the ma70)
if the car has had a gearbox change, the box may not have been a supra box. (ie getting a differant drive gear perhaps)

if its an auto and has the original 4.3 diff it should have a 21 tooth cog on the drive gear. not sure about the manual sorry.


when i first got mine on the road i had the original 4.3 diff, but the auto had been changed and i didn't change the cog, so i had a 19 tooth cog from a 3.9 diff in the box. at 100km my speedo read just about 120km also

to fix it i found my original box pulled the drive gear out and used the 21 teeth, was fine after that until i changed my wheels

[wiso]

What were the stock wheels and tyre diameters? And what tyre size's do you have at the moment? Increasing overall rolling diameter will affect the speedo.

not to that kind of exent, on 16" tyres you would need to have tyres as big if not bigger than the gurad to affect the speedo by 20%. original tyre size is 225/50 r16, my 18" rims with 40 profiles on afftect the speedo by about 4%. with my current config of tyres/diff/cog my speedo over reads by 5%

[Diz44zy]

My brother has the same problem when gearbox was change!

[supra_cam]

Tyres are 225/55. Its a manual and as far as I know its stock gearbox and diff, but I didn't get a great deal of info from the previous owner about it so I can't be sure.

[EldarO]

check engine number against engine number on chassis.

i know i change gearbox whenever i change the motor (so far anyway ).

but yeah, you've got either a gearbox with the wrong speedo drive for the diff, or the wrong diff for the speedo drive.

its a half-empty, half-full thing

Elmo.