TH350 speedometer drive 2WD

[Vitamin C]

Can someone tell me what the small square unit is that is installed between the factory speedo cable and TH350 transmission? It is on the tailshaft of the TH350 and looks to be some kind of reduction unit, the cable threads into it and it threads into the transmission. I am converting from the TH350 to a TH400 and was wondering what this is, and does it need to be used on the TH400 transmission?

 

[Matt69olds]

It’s a ratio adapter used to fine tune the speedo.

Certain tire size/gear ratio combinations require speedo gears that don’t exist. The ratio adapter can fine tune the speedo.

If you clean all the crud off the adapter you will find the ratio. Some overdrive the speedo (if it reads slow) or slows the cable down if it reads fast.

Speedometer repair shops use to custom make those adapters. Not to many speedo shops around anymore.

 

[Vitamin C]

OK, i understand now. So if i can get the correct speedo gear for the TH400 i may not need the ratio adapter.

 

[Matt69olds]

Read this:

TCI Auto Speedometer Gear Calculator - TCI® Auto

Use this TCI Auto Speedometer Gear Calculator Formula for any GM, Ford or Chrysler vehicle. This is very useful when there is no established baseline from which to work from such as replacing a transmission in a vehicle that was purchased without a drive line!

www.tciauto.com

You can use this to figure out what gears you need.