Speed

[Jason67F-250]

Hello all I was wondering why when I swapped my tranny from 67 with a tranny from a 76 why my speedometer reads differently Exp. speedo reads 90 mph but I'm only doing maybe 60 mph.

[craftsman]

Because the tranny that you put in has a different number of drive teeth for the speedo in it.
What tranny did you swap in and what did you have?
If you put a c6 in the speedo drive gear is mechined onto the out put shaft, you will have to change the gear on the end of the speedo cable.

[Jason67F-250]

I installed a c6.

[Jason67F-250]

so I wouldn't use the same out put gear from the c6?

[fordman]

what tranny did you take out? a c4? or fmx? maybe you can use just the plastic gear from your old trans to put in the c6. im not sure it will fit but its matched to your rear end gears. or you can just buy a new gear for a c6. you should need the same number of teeth as your old trans had on the gear.

[FORDification]

What everyone's saying here is that the donor truck's rearend was apparently geared different than the one on your current truck. You can easily fix that by changing the speedo gear on the end of the cable. There's a lot of online info about how to figure out what speedometer gears you need when changing axle ratios. Here's a couple:

http://www.boss302.com/speedo.htm

http://www.tciauto.com/Products/TechInf ... _gears.asp