speedometer

[Guest]

Hi;

I have a 59 OD that needs a drive and driven gear. I am trying to calculate what I need but I'm having a problem finding out how many revolutions/mile on the speedometer.
Anyone know?

thanks

[JohnG]

Bill, you're referring to the gears in the transmission? (as opposed to the gears involved in the speedometer)

John

[tbird430]

Yes. He needs the one on the transmission shaft (inside tailhousing), and the one on the end of the speedometer cable. Good luck is all I can honestly say.

[Guest]

Hi;

What I have currenty is a bad drive gear(7 tooth) and a 18 tooth driven. What I was trying to find out is how many revolutions of the cable input to the speedomenter per mile. There are some variations, but 1000 rev/mile seems to be more common. Knowing this lets me look for the right gears.

thanks

[byersmtrco]

Give me your final drv ratio and your tire size and I'll get you the corr tooth count (18T does not sound right)

[Guest]

Thanks BYERSMTRCO.
The tooth count I come up with is a 20 tooth driven (cable) gear for 3.73 rear end with 14" tires. But that assumes that the odometer needs "1000 revolution per mile" to clicck up a mile.
I am trying to confirm that ratio because it effects the readings.

[tbird430]

I see that only 1 new replacement driven gear is even available now for our original 1958-60 cruise-o-matic trannys. Even if u find out which combo of drive/driven gear teeth u need, how on earth are u going to find a proper set?

I hope I didn't burst ur bubble any, but u may never have the right combo in there when u do figure this tooth count out...

[Guest]

Hey tbird430;

Surprisingly enough, I have found all the gears for the T-85 transmission. Something I thought was impossible. My best source to date is Northwest Transmission. They are looking for the gears. (drive and driven). The driven gear shouldn't be that hard since they are plastic. There are a couple of places on the net that deal in the plastic gears. The drive gear on the OD shaft is metal and may be problematic.

thanks

[tbird430]

That's good news, I will have to add them to my Tbird Roladex for future reference.

That's right I forgot about the drive gear which slid onto my 430cid cruise-o-matic trans shaft was steel also...

[byersmtrco]

A J code car "should have" a 2.91 rear end ratio.
W/14's I'd try a 17T. If it reads to fast, go to 18. (the smaller the driven gear, the faster the speedometer will read.

[Guest]

Thanks BYERSMTRCO.
It got mixed up somewhere along the line.

I have a 59 convt with a 3 speed Borg T-85, a Borg R-11 Overdrive (cable) on a 352 with 3.73 rear gears and 14" Kelsey repro. wheels.