TR6 TR250/early TR6 v. late TR6 Different Speedo Ratio

[glemon]

I have done a little research but not conclusive, I have an J type (later type) overdrive on my TR250, the speedo reads low, like about 30 mph when I am doing 40 mph. Did the later TR6s have a different speedo ratio drive, if so maybe I can just take the working guts from a late 6 speedo and stuff in mine to make it work right?

I have looked at my parts manuals and books and the best I can figure out as an answer to the different ratio question is maybe, I see the speedo drive gear in the tranny/overdrive switched at some point.

 

[Gliderman8]

It might be easier to get a speed ratio adaptor... that's what I did after I installed a Toyota 5-speed. The male end of the adaptor attaches to the transmission, and the speedo cable attaches from the female end to the back of the speedo.
I paid about $80 locally for the adaptor.

 

[TR3driver]

Did the later TR6s have a different speedo ratio drive, if so maybe I can just take the working guts from a late 6 speedo and stuff in mine to make it work right?

Definitely different. Earlier TRs always used a speedo drive ratio of 5:2, and changed the calibration of the speedo head to account for changes in tire size, final drive ratio, etc. So the typical calibration for a US-spec TR6 (with 3.7 final drive) was around 1120 turns per mile.

But the later cars always used 1000 turns per mile, and changed the drive gears to accommodate tires & final drive ratio.

The speedo drive gears can be changed, but you'll probably have to remove and disassemble the OD to do so.

A ratio adapter is a good solution, if your speedo works well otherwise; or for about the same money, places like West Valley Instruments can repair and recalibrate your speedo to match your car.

 

[sail]

Whadda ya mean 80 officer. My speedometer said 60, honest.

 

[glemon]

Thanks, I have been looking at ratio adapters, will probably go that route.