I have a question that I hope someone will help me with. My speedometer is of about 5 to 7 MPH off. I have the original tires and rims on my 71 Toronado but I have changed out the differential from a 3.08 to a 3.21. I see in my service manual that on the transmission that there is a speedometer assy, what part do I change out to correct the speedometer? Ther looks to be several different gears in there and also where do you get replacements.

 

Can anyone help.

 

The speedo cable is driven by a set of gears in the trans. The gears MUST match the final drive ratio and the tire diameter. I don't know if TH425 speedo gears are the same as those for a TH400. On the TH425, the speedo drive gear is part of the governor assembly, and the speedo driven gear uses a holder similar to those on the RWD transmissions. If you can't get a correct speedo gear, you can get a speedo ratio adapter that will accommodate the different ratio. There are numerous vendors who will custom make these. Try Google.

 

I will look for a vendor now. Thanks Roy

 

Call these guys - it can be more complicated than you initially think:

http://www.transmissioncenter.net/sp..._____va.htm#gm

- Eric

 

I will do that. Thank you