Ok, I have looked everywhere. I even emailed Tremec support with no luck. I'll be swapping out my 86 F150's rearend soon for a nice new unit. But I'm going from a 2.47 gear to a 3.31. I know I'll need a new Driven gear for the Speedometer cable to correct my gauge. I need one more bit of information and I can't seem to find it anywhere. I hope someone here knows. I need to know the tooth count of the Drive gear in my transmission. It is the 3spd + 4th OD - The transmission shop called it a Tremec RTS. Anyone know?

Ed

 

I believe the transmission you have is a SROD if it hasnt been swapped, Could be wrong on that so could you get trans code off the sticker in the door jamb?

 

It's a B or maybe an 8. After 26 years it's a little faded.

 

SROD or variant. Just pull your existing driven gear. Since you are going to a 3.31 from a 2.47, you will need a larger driven gear.

You are going from 44 mph per 1000 rpm to 33 mph per 1000 rpm.

I would try 3 teeth larger than what you have, if you can get it.

If you have to change the drive gear, it would be a real question as to if that would be worth the effort.

All the driven gears are the same for years and years and years, so it should not be hard to find.

 

While you have the driven gear out, look in the hole and see if you have a removable drive gear, or it is machined into the output shaft. Removable isn't bad if you have to change it, machined in, tranny has to come apart to change it.

 

I seem to remember when I picked it up at the transmission shop it was a separate gear and it was ping I believe. It kind of glowed in that hole.

 

Teeth on DRIVEN (end of cable) & DRIVE (output shaft) speedometer gears based on rear axle ratio, trans type and tire size.

RUG SR-OD (Single Rail 4 Speed Overdrive) = 1978/83 E/F100/150 300/302 & 1978/79 E100/150 351W / Misc 1978/83 Passenger Cars.

RTS TS-OD (Top Shift 4 Speed Overdrive) = 1984/89 E/F150 300/302.

C3/C4/C5/C6/AOD: The is no part number for a DRIVE gear since it's made as part of the output shaft.

See examples:

 

THAT's IT! It's a 9 tooth, thanks I really appreciate that.