TH350 to 700R4 speedometer questions

[Guest zthang43]

Haven't posted in a while, the Z's been just sitting in the garage, but now I've gotten hold of a factory rebuilt 700R4 from a 89 Caddy with a 350 Chevy motor. I'll be pulling the TH350 out and swapping this in. I'm not sure what to do about the speedo though. The 700R4 I got has the early style electronic speedo, where it is gear driven but still electronic. Can I use the speedo bullet from my TH350? Or, do I need to go to the wrecking yard and find a cable driven speedo bullet for the 700R4?

Also, for those of you who have done this, what speedo gears should be used for my 3.54 rear end and 245/60R15 tires (about 26.5 inches tall?).

Thanks for any input.

[dmanzo57]

You can get new speedo gears from your local Chevy dealer. The following web page has info on

what gears are available and how to figure out which gears you need...

 

http://www.tciauto.com/tech_info/speedo_gears.htm

 

The Datsun speedo uses 1024 revs per mile vs. 1001, so make that change when you do the math.

 

The gears run about $30 to $40.

 

Don

 

           # Drive Teeth X Axle Ratio X Tire Rev. per Mile 
       --------------------------------------   = # Driven Teeth 
                            1024 


Use the following formula to calculate the Tire Rev. per Mile for the above formula. 

                                            20168 
Tire Rev. per Mile =  ---------------------- 
                                     Tire Diameter (inches)