4r70w speedometer off


Registered User
97 thunderbird lx just had transmission rebuilt and it works great except speedometer is 10mph off if you seeing 80mph your actually going about 70 now what's odd is this wasn't the case prior to the rebuild same harness same speedometer gear same transmission just rebuilt all connections are clean and tight there no "jumping" speed like it doesn't bounce its a smooth transition just 10mph off anyone got any suggestions on why or how to correct?
The gear was the first thing that came to mind. Did a shop do the rebuild? Change the tire size recently?

Yeah a shop did rebuild I pulled and installed trans but shop did the actual rebuild tire size hasn't changed I pulled the wiring harness and all sensors related off the trans before I dropped it off just to be certain I had the right ones when reinstalling so I know nothing was accidentally switched during rebuild only thing I can think of is something internally got changed in the trans that now requires a different tooth gear but I dunno which gear to get it's 10mp fast so if your doing 50mph by the instrument cluster your really going 40mph but the output speed sensor is correct live data shows correct speed... Working with the rebuilder to come up with a solution
Can you verify that the gear is the correct one in there, that the shop didn't put a different one in.

Did they rebuild your original trans though? I thought you bought a exchange 1 from a rebuilder just before Thanksgiving & it didn't work, so you bought another replacement from another company?
No the only exchange was the one just before Thanksgiving that didn't work had the one I pulled out when I put the exchange in... I had it rebuilt so the original got rebuilt I've only had one exchange and it didn't work
I agree, especially with it being a non S/C or XR-7.
Not sure how many different possibilities for a regular car
Yeah that's the only thing I can come up with going to contact them today and see what they've come up with the guy does great work I've known them my whole life but just like most southerner they do thing at there own speed haha
Poking around on TCCoA and the 4R had a 7 tooth and an 8 tooth output shaft. The T-Bird has the 7 tooth, so is it possible the shop put in an 8 tooth shaft. That will throw the speedo off.

Or check with the shop that did the rebuild. They either swapped the shaft or didn't give you your orig trans back
Too late & too much work to change shafts now I think?
You need to pull the speedo gear and see what color it is or how many teeth it has, then find the next higher tooth gear. For example if you currently have a purple 21 tooth you will need a white 23 tooth. Just went thru the same issue when switching from AOD to 4r70w.
See this link for speedo gear calculator.

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I know it's a white gear now I've got 3 of them 1 on the car 2 off I'll cheat and count one of the ones that's off