Hi Guys: I have gone to 2356015 all around and will need a new speedo for the shorter rear t ires.How do I figure the correct gear for this combo? does GM still sell gears for a TH400? 3:73 gears. Thanks for the info Ken
I can't tell you how to figure the gears, but a guy on ebay who sells the gears probably can. His name is Brian Hoffman and his email address is: bcamarors@att.net UticaGeoff
Kenny, I don't know if GM still sells them, but I see that they are available from NPD for reasonable prices. I would think other restoration places would have them as well. Several years ago, I was able to get them at my local transmission shop, in stock nonetheless.
Yes you can still get speedometer gears. The problem is going to be that they don't make a big enough DRIVEN gear for your combination. To calculate what you need, use this formula, http://www.tciauto.com/tc/speedometer-gear-calculator The three things you need to know are, 1) Tire height in inches, in your case, P235/60R-15 are 26.1" tall 2) Rear gear, in your case 3.73 3) Number of teeth on the DRIVE gear. The DRIVE gear is on the output shaft of the transmission and is visible when you remove the Speedo gear Sleeve. The most common DRIVE gears are 16, 17, or 18 teeth. Even if you had the smallest DRIVE gear, the DRIVEN gear needed calculates to 46. The biggest gear made is 45. That means you will need some sort of speedometer cable adapter. You should be able to find one here, http://www.partshp.com/speedometer_gears.htm
