Been doing some research on 4R70W transmissions and have a couple questions. I've seen that 96-97 and prior versions have the 7 tooth speedo gear output shaft for a mechanical speedometer. Also, that the 98 and later cases are better built. I can get both versions at the local pull-a-part for $75 plus tax plus a $25 core charge. I can also get the 7 tooth shaft for $60-ish. So...

Can all of the later 4R70W trannies be retrofitted with the (correct length) 7 tooth shaft, or just ones set up for mechanical speedometer output (i.e. the 8 tooth versions)? It will help me in identifying donor vehicles to know this.

Are there any hard parts besides the 7 tooth output shaft that I would want to carry forward to a later year tranny? If not it would be easier to just get the shaft itself. Otherwise I might consider getting two transmissions.

I want to use the stock speedometer in my '77 F100 with a 3.27 or 3.55 rear end, and while I know there are mechanical drivers to run the speedo off the VSS they cost close to $400. I expect any pull-a-part transmission will need a complete tear down and rebuild, so replacing the later version output shaft for the 7 tooth version while it's apart make the most sense, as long as I know which ones will accept it.

Thanks!

 

You could just get the later model transmission and install the 7 tooth shaft, I cant think of any reason why you shouldn't be able to.

Just make sure its a 4r70w shaft and not a AOD shaft.

 

Thanks, I think that makes the most sense. Appreciate your help.

Travis