I converted my car to a T400 many moons ago and now would like to make the spedo read correct. The original rear gears were 3:08 and now are 4:10 the tires are 28" tall. What combination of gears will work? Thanks Rick
We'll need one more piece of the puzzle...we need to know how many teeth there are on the drive gear (on the trans output shaft). Usually the only way to know is to count, meaning you'll have to pull the driven gear sleeve out so you can look inside. Devon
www.tciauto.com has a great little tech section on this, and have all the parts you will need for less $$ than your local GM parts counter.
I finally got the trans to shift where I want it (5000 rpm wot) now I will have to go to the other side and see if I can count the teeth. Thanks Rick
OK guys I finally got the count on the teeth of the gear in the transmission. 18 teeth on the shaft and 38 on the housing gear. Here are the specs on the car the tranny is a t400 BC, 4:10 rear gears 275/60-15 tires. Right now at about 25 the registers 35mph. What do I need to do to get this to read right? TIA Rick
you have to "slow" the cable down. that means a bigger driven gear. the housings for those gears are meant to hold only a certain set of gears. for example one might be able to use 35, 36, 37 + 38 toothed gears, above that there is a different housing. the housings are marked with the #'s on them. if you have a good and patient gm parts guy he should be able to help you out. i think i run a 44 tooth driven gears in my camaro with your exact set up. it can be trial and error. good luck.
Rick, I did some calculations with the details you've given, I think the size of your drive gear is going to mess things up. With your 18 tooth drive gear, 4.10:1 rear gears and 28" tires, the numbers say you need 53 teeth on the driven gear. The problem is that the max I think you can get is 45. If you switch the drive gear to the 15 tooth version (p/n 8629547) you can use a 44 tooth driven gear, p/n 9780470). Someone else want to check my math? Devon
Devon thanks for the info. I will have to change my housing in order to go to a 45 tooth gear, the one I have will go to 39. Do you know where to find one of them? TIA Rick
Rick, TCI sells them , but what I've read here at v8buick is that they're made of plastic. You can get a new aluminum part from GM, but I think you should try your local trans shops first. They may have the gears you need as well. I still think someone else should verify my calculations before you start buying parts! Devon
I have 1 spare TH400 and the original TH350 for the car, the 400 has the same gears as the one in the car but the 350 had a 44 tooth. Now to get a 15 tooth for the shaft. If I did it right on the TCI page if I put the 44 with the 18 it would be correct if I had 3:42. That way I will be ready when I change rear gears. Thanks Rick
