So i just got my car back, its a 66 coupe 289 with a C6 transmission and a 9" rear end..........The guy that was working on it he said that he couldn't get the speedometer gears to balance out with the gears from the cable on the transmission, so now it is around 30 mph above what it should be...


Any suggestions?

 

We need some info.

What is your:

Rearend gear ratio?
Tire Size?
Any idea what your drive gear tooth count is in the tranny?
What driven gear do you have currently on the speedo cable?

The calculation for what driven gear you need is:

((# of drive teeth) x (axle ratio) x (tire rev per mile))/1000 = # of driven teeth

 

30mph off at what speed ?
showing 60 when driving 30? showing 90 when driving 60? this should always be a percentage to how quick you're driving. as otherwise your tach would show 30 while stopped (and I'd recommend to bend the needle) ;-)
use Cowboys calculation to get an idea.

 

does the needle rest at 0 or at 30?

if not yes u need to bend the needle so it rests at 0

 

i actually meant that as a joke :-) i don't think his needle rests at 30

 

Was the C6 stock in a 66 coupe, or was it a replacement tranny for a C4?

HAHA. Loaded topic question, 1sick66. All the replies apply.

CP

 

I did the opposite of that to my gas gauge needle and I never run out of gas anymore. I've saved a lot of money.

CP

 

You are a genius! And all this time, I was just buying more gas.

 

I found 59 threads on speedometers, so the real answer should be there somewhere. https://mustangforums.com/forum/sear...earchid=456033

Yes, I said 59 threads. LOL. This problem comes up monthly.

CP

 

...I always noticed I had more gas when making constant Left turns. But after a while it became a real problem with making my destination. So I'm going to try the new mod tonight!