Speedometer is not correct after transmission replacement. Any Ideas?

[1986.5supra_kid]

So i have a 1986.5 supra, that had a r154 from a 87 turbo that was mated to a 3.91:1 and the speedo was dead on. Well know i have a Newly rebuilt trans from a 89 turbo. The speedo is off by 7mph. so i swapped the plastic speedo gear from the pre89 into the 89built transmission. its still off. my next idea is that the actual worm gear in trans is a different pitch.

Any ideas

 

[1986.5supra_kid]

The left is from 89+ r154

Some other pictures

 

[Dirgle]

So i have a 1986.5 supra, that had a r154 from a 87 turbo that was mated to a 3.91:1 and the speedo was dead on. Well know i have a Newly rebuilt trans from a 89 turbo. The speedo is off by 7mph. so i swapped the plastic speedo gear from the pre89 into the 89built transmission. its still off. my next idea is that the actual worm gear in trans is a different pitch.

Any ideas

Your next idea would be the correct one.

 

[suprasick]

You also could adjust the gauge.

 

[IndigoMKII]

I wonder if the numbers stamped on the top are the degree in pitch of the teeth then the number of teeth on a 360 degree. Such as 10 degree pitch with 32 teeth as opposed to 11 degree pitch with 33 teeth.

You would honestly have to changed both trans/speedo gear to maintain it from transmission to transmission.

http://www.cygnusx1.net/Supra/Library/EPC/291210/catalog.aspx?F=3305&P=1 you would want 33481 over to the far right then pick from the selection of years on http://www.cygnusx1.net/Supra/Library/EPC/291210/part.aspx?S=33481

 

[1986.5supra_kid]

I've got a 89+ cluster to try out. I'm going to try current speedo gear setup then return the 89+ speedo gear if its still off.

My 3.91 and or CV axles have a lot of play to. In first gear I get a clang and bang sound when I poke the gas and let off.

So next thought is changing out for a good or (rebuilt) 3.73

 

[1986.5supra_kid]

Pre89


This is 89+

 

[1986.5supra_kid]

After looking at gauge clusters more I figured out that if I swap them that the speedo will be even further off because it is currently reads fast. Ex. GPS says 70mph and the speedometer reads 77mph

 

[Dirgle]

Wouldn't make a difference anyways. The later model speedo is scaled to a wider speed range. But for both speedo's ~17.1 RPM's = 1MPH. So both would read 77mph at a GPS 70mph. The issue is in your speedometer gearing. Both the drive and driven gears need to be changed to get the correct speed. And since both gears are no longer avaliable that I know of(if someone knows of a source please let me know as I need a set), your next best option is do do your diff swap.

 

[1986.5supra_kid]

I always wanted a 3.73