It isn't that no one has done a T5 before. It's that there is a speedometer/odometer that is calibrated for a certain number of revolutions of the cable per mile. That can't be changed. The combination of a 2.79 rear axle with a .76 OD ratio (= 2.09 effective ratio) is virtually off the charts (I hope the engine has tons of low-end torque!). I really doubt there is a combination of drive/driven gears that will work out. Hence the cable adapter. Taking the tailhousing off a T5 multiple times to play with different gear combinations isn't any fun, in fact I suspect it can't be done with the trans in the truck (depends on rear mount design).

 

I don't think anyone here was trying to say it has never been done before, but that we will be here to help him when he figures out his combination. I think that it will be a close one considering the tall rear end gears but I do think he will be able to find something.

 

Ross let's play devils advocate
# Drive Teeth x Axle Ratio x Tire Rev. per Mile / 1000 = # Driven Teeth

assume he has the standard 7 tooth (they added 8 tooth in 91, and 6 is so rare I hadn't heard of it till I dug yesterday)

we know the axle (2.79)

lets assume he doesn't low rider and goes with stock size tires (28.4" - same as the 6.00x16, which would be 225/70/16 in a modern 6" rim) those get 733 rev per mi - note a dozen people are gonna post different rev per mi figures for that size, believe it or not you can't be perfect, different mfg list different rev per mi figures for the exact same size, lump it folks this isn't perfection this is getting close enough (and when you buy new tires and switch brands do you change out your gear?)

and speedometer calibration - lets assume 1000 since virtually every speedo heard of want that.


7 * 2.79 * 733 / 1000 = 14.31549

so *IF* big asterisks if here folks if he goes with a typical good looking tire size and *IF* he has a 7 tooth drive gear and *IF* his calibration is 1000, then a 14 tooth gear would do it.

All that aside I agree with Ross, you got too high (high ratio, low numerical) a rear end figure - swap that thing out for a 3.50 otherwise you'll hate it. I'm sooo not fond of 3.00, can't imagine seriously driving around on a 2.xx.

lets show the math for a 3.50

7 * 3.50 * 733 / 1000 = 17.9585

an 18 tooth would be perfect - much closer than off by 30% of a whole tooth we had with the other numbers

 

Just a point of reference for people with the stock trannies... I bought a driven gear 2 teeth different to correct for my 3.50 9" (for the stock LD 3-sp). It made no difference! Despite 10% fewer teeth, it read the same. I pulled it out and there were obvious signs of "distress" on the gear teeth after maybe 20 miles. These are metal teeth, unlike the later models' plastic gears. I investigated as best I could from the parts CD, and figured out on the stock trannies there is no going up or down more than 1 tooth on the driven; to get more of a change, you need to change both. Which brings up this note on Jegs' site for Ford plastic driven gears for C4/C6:
"This is a retrofit gear to allow the speedometer to function with 3.73 and 4.10 rear end gears. Since the gear tooth pitch is slightly different than OE, the service life of this gear is limited to less than 25,000 miles."

Another reason to consider the adapter.

 

sounds like you are referring to the 23 tooth driven gear?

 

As far as the warning, that was for a 23T gear. But it applies to many non-standard combinations of drive/driven gears. Worm gears have a fixed pitch.