I have recently found that my speedometer reads about 15mph too slow. at 65mph it trads about 55. My car is an 82 pont T/A.

When i originally bought the car it had 14 inch rims on it. I put on the stcok 15 inch version of those rims. would that change result in the off readings im getting?. I would imagine it would effect it some but 15mph off seems a bit much to me.

But if the rim swap is the problem then what options do i have to make the speedometer read accurately?

Thanks,
James

 

Do you have the stock rear end on the car?

 

Also, have you or a previous owner replaced the transmission lately?

 

The rim size alone won't affect the accuracy of the speedometer, but if you changed the overall tire height it could.

 

I'm running 255/60 15's on the rear and the speedo reads low

 

Mine didnt work, but i knew with my new axle it would be wrong anyway.
Got a new cable [after cruise control removal] and still nothing, anyway removing the end of the gearbox to swap it is dead easy,
and i got Bowtie Overdrives to calculate the correct gears needed.
Working fine now, and reads spot on.

 

Theirs a tech article on the tgo main page about the speedo gears. It even lists what gears you need for each rearend and their part numbers too!

 

Thanks for all the responses. I myself havent changed the rear end or tranny. But im like the 800 kabillionth owner on the car too. Somone probably changed teh gear ratios in the rear end or tranny at some point. Ill have to look into the tech artical with all the gear ratios. I wasnt aware there was one. Hopefully it will tell me how many spines i need to make this work.

Thanks again