Hey guys, I've been reading past threads on speedo gears, and I figured I would just recruit some help to make sure I've got it straight. I have a green drive gear, large speedo housing (35-40) with an off-white driven gear (not sure if the color has faded or what). The car was a 350-2, pretty sure I have 2.56 gears in the rear. I have a posi and 3.73 gears to install and want to get the speedo set up now since I have the trans out of the car. From what I have figured, I will have to replace my drive gear and driven gear. If the gear colors have remained the same, that would mean the green drive gear is a 9 tooth drive gear. The only thing is it looks like it has a heck of alot more teeth than that. That being said, I have run the calculator on TCI's website, and it appears with 3.73 gears, and 28" rear tires, I wouldn't be able to use the green (9 tooth) gear. I would prefer to keep the same housing for my speedo since I am assuming it would be tough to track down the housing for the higher driven gear. Suggestions for what I should change to for a drive gear/driven gear combo?
Craig, Before you do anything, count the teeth on the DRIVE gear. Take the sleeve out and rotate the drive shaft with the transmission in neutral. Mark one of the teeth with paint and do it several times to make sure you get it right.
Hey Larry, I counted a few times and came up with 18 teeth, with the calculator, it said the gear was not available. With the next lowest (17 tooth drive gear) it is also unavailable, and with the next on the available parts list at a 10 tooth drive gear, it gives me a 26..
Yes, I'm afraid you may need to change to a Chevy tail housing with the smaller tailhousing sleeve. That way, you could use a much smaller drive gear and driven gear combination. I've never done this, but maybe get the tailhousing off a junk transmission. A 8 tooth Drive gear, and a 21 tooth Driven gear would work for your 3.73's and 28" tire.
It's a THM350. The only differences should be bell housing patterns and calibration. Hopefully, the tail housings are the same length as the BOP, but I'm not positive.
Thanks for all of the advice Larry, I have a chevy style tail housing ($40 with a new seal and bushing, and a front pump seal) in my hands and the speedo gears should arrive any day now. :beer
