My 1965 Mustang coupe has a rebuilt automatic transmission. The speedometer is fast, at 35 mph it reads 45 and at 65 mph it reads 77. The rear differential tag has this info, ---2---80---5DD---911---
What does this tag info mean?
Is it true that I need this info to change the gears at the transmission speedometer cable connection?
How do I determine my transmission type?
Thanks
gene lee

 

are your tires stock size? youll need to adjust your speedo gear on the tranny to compensate... the gears are cheap...they are matched to what ever the rear gear ratio is in your differential.

 

I think you'll need to step down in the speedo gear size. The gear has between 16-24ish teeth. You probably have a 19 or 20, just take it out of the tranny and count the teeth, count them a few times to get an accurate count. If you have a 20 tooth gear then goto your speed shop and pick up a 19 or 18 etc. Don't for get to lube it a little with some 80-90 oil before you put it back in and when the gear is off, I drop a drop of lube into the speedo cable as well.

I use my iphone GPS and my wifes iphone in the passenger seat to get an accurate reading and then look at my speed on the speedo. I try to get on a straight section of highway going 60 or 70mph for like 5 minutes. There are better methods for sure, like measuring distance off and marking the car (you can google them or someone will likely post a better way).

Changing your tire size, rear diff gears or tranny will mess up your speedo reading.

James

 

Thanks for your help, I will take that apart now to see the gear.
But I would still like my other questions answered, the tag info on the rear end and how do I determine my automatic transmission type.
thanks
gene

 

I found this, but what you have doesn't match the plate he has

http://www.woodyg.com/fairlane/finfo/fordrears.html


Your transmission should be a C4 unless someone has put a later model AOD in.

 

Holy crap, thats a cool refrence site! I just dumped that into my favorites. Thanks for posting that.

James