I finally installed the 8.5 rear. Its a 3.73 gear. Which is a huge upgrade from the 2.14 or 2.29 peg leg that was in there. How can I determine which spedo gear to install. I have a th350 and 14 in tires.

 

225 70 14

 

To calibrate the speedo their are two gears at the tranny. One is at the end of the speedo cable the other is on the drive shaft of the tranny. Depending on what rear gears and how tall tour tires are there are a number of combinations of gears to get you close. Try this.

http://www.tciauto.com/tc/speedometer-gear-calculator/

 

Yeah I've seen that. Its all greek to me to a point. i need someone to tell me which ones to buy.

 

You/we need to know what drive gear do you have now? How many teeth on it? After you know this, its pretty easy.

 

If you don't want to mess with the gears they sell an adapter that goes on the outside of the trans between the cable and housing. The spedo will be off by a percentage and can be checked with a GPS. Then all you have to do is order the adaptorby the percentage it's off by and it will correct for it. Can't remember the company but sure someone will chime in soon though for ya.

 

Year and model of the car would help. There are charts in the service manuals, depending on the transmission/rear end your car originally came with.

 

Its a 1980 Cutlass Supreme

 

The old rear was a 6AH rear = 2.29

 

Ok My speedo gear is a brown 18. Trying to peek in the side of the tranny while under the car and count the drive gear was really a PITA. It looked like a tan or neutral color 8 or 9. Per gps when im going 50 my speedo shows 70mph. Also my speedo housing is the small bullet shaped one. Will this work for a bigger gear and which gear or gears should I buy?

 

I would just call these guys and tell them what you have and they will tell you what is available to get you where you need to be.

http://www.transmissioncenter.net/sp...____va.htm#350