TH400 Speedometer Gear Housing

[damnyankee36]

On a TH400 I am determining what combination of gears to calibrate the speedometer. I see on transmissioncenter.net that there are two housings for the driven gear. A 34-39 tooth and a 40-45. (Mine is a 36-39 for some reason).


I installed a 34T and it worked for a few miles then became intermittent and finally stopped altogether. An inspection of the gears show everything to be in order. The speedometer will operate with a drill, too.

I think I am going to answer my own question because I am guessing the housing gear shaft hole must be offset differently depending on the tooth count. Since I went to a 34T it must be slightly smaller than the minimum 36 that's on the adapter.

What's weird is that on the smaller driven gears you see on TH350's and manual units the tooth count range is fairly large without an appreciable change in diameter.

Am I thinking this correctly?

[RustyPile]

To coin a phrase from a famous movie: "You have two, maybe three choices".... If you have already calculated the drive/driven gear combination needed, simply obtain a 34 - 39 gear housing.. Second choice would be increase the drive gear by one tooth count.. recalculate the needed driven gear tooth count.. Obtain the proper housing for that gear..

Here is the TCI speedometer gear information site that I use..

https://www.tciauto.com/speedometer-gear-calculator#400