Speedometer setup help needed

[PCP71Demon]

Hey All,
Had a new transmission put in my 71 Demon, upgrading from a 904 transmission to the 727.
My speedometer is now out about 10 MPH high at 40 MPH.
So, thinking either the internal speedometer gear of the transmission is a different tooth count or the car shop that changed out the transmission did not convert the speedometer gear over to the new 727.
So, how do i figure out the correct gear teeth count needed ?
Driveline is a 340 with extras, 3200 stall 727 with shift kit, 3:91 rear end and P275/60R15's on the back.
Any help would be appreciated.
Thanks Mike

 

[Professor Fate]

First step is a stop back at the transmission shop that did your install. You paid them for a job, they need to make it right. It's probably just a 5 minute job for them, provided they still have your old gear.

 

[Locomotion]

The shop probably just disconnected the speedometer cable when swapping transmissions. The "should" have several old ones if the do trans rebuilds. But if you can't get the old, original gear back, here is a chart to figure which gear/pinion is needed.

There are several similar charts on the net. Some vary a little bit.

 

[PCP71Demon]

The shop probably just disconnected the speedometer cable when swapping transmissions. The "should" have several old ones if the do trans rebuilds. But if you can't get the old, original gear back, here is a chart to figure which gear/pinion is needed.

There are several similar charts on the net. Some vary a little bit.

View attachment 1715560094

Locomotion, Thankyou very much for all the info and chart. Helps a lot. Appreciated! Stopped back at the tranny shop and they don't have one (37 tooth) in stock, but will look to sorce one for me. Thanks

 

[PCP71Demon]

First step is a stop back at the transmission shop that did your install. You paid them for a job, they need to make it right. It's probably just a 5 minute job for them, provided they still have your old gear.

Thanks to everyone for your help and direction. Stopped back at tranny shop and they don't have the needed 37 tooth gear in stock....but are going to source me one. Thanks to all for input and responses.