Speedo correction...help

[TenorPlayinGuy]

I have an 87 mustang with 2:73 rear gears and the speedo reads about 15mph off... the reason being becaus ei have a 4cyl tranny from an 86 turbo coupe... so wha ti need to know is what speedo gear should i be using? to counter the t-birds 6tooth to the 7tooth used by v8 trannies... i cant remember what i put in there... but i have numerous spares including a 20, 21, and 23 tooth gear. so which would give me the closest fix (for the time bieng of coarse)

 

[jrichker]

See http://www.hanlonmotorsports.com/t5speedo.asp for help

 

[TenorPlayinGuy]

so i would have to change the drive gear it self... doh well... guess i could live with this for the time bieng

 

[Asha'man]

No, just change the driven gear. You should need an 18 tooth, it's what I'm running. My tranny is from an '87 TC and I have stock 3.73's. $7 at the Ford dealer.

Ash

 

[87gtconv]

No, just change the driven gear. You should need an 18 tooth, it's what I'm running. My tranny is from an '87 TC and I have stock 3.73's. $7 at the Ford dealer.Ash

but he says he only has 2.73 not 3.73 rear gears so he cant use the 18 tooth gear. He needs like a 13 and they dont make that. So he needs to either change rear gears or needs change speedo drive gear to a 7 tooth one!

 

[84blkstang]

so how far off would this make the speedo?

 

[Asha'man]

Whoops, I guess I saw 3.73 instead of 2.73 in the original post. Pay no mind, citizens.

Ash

 

[TenorPlayinGuy]

my speedo when running along side someone on the freeway is about 15-20 mph off...

 

[TenorPlayinGuy]

im at 57 when they are at 75
or something like that

 

[TenorPlayinGuy]

my speedo to be correct... or more correct for anymatter... is to change the tranny gear to an 8tooth... and the drive gear to a 17tooth... now all i have to do is drop the tranny and pull off the tail housing... oh what fun...

 

[Michael Yount]

Well, the other approach would be to pull the 2.73's our and put 3.73's in -- that'd make the speedo much closer, and the car would be much more fun to drive. 'Course, it's gonna cost a bit more....

The drive gear swap isn't complex, just takes time. You'll need the correct size drift to punch out the pin that holds the shifter rod onto the shifter shaft. And once that comes apart, be sure to catch the spring/ball assembly that's underneath it. Suggestion - there's a spring clip that holds the gear on the shaft - do not re-use it. Replace it with a new one. The one time I re-used, it came off allowing 1) the drive gear to slide on the shaft, 2) chewed up my driven gear, 3) made me go fishing around inside the case with a magnet (through the fluid drain hole) to find the retaining clip that had gone floating around inside the tranny. Just lucky it didn't get itself wedged someplace where it could do more damage.