T5 speedo gear question

[nachodog2]

My t5 has been in my truck for about 2 1/2 months now and is the best thing i've done to the truck so far. My speedometer runs a little fast (55 on speedo is actually 45 63 is 50 80 is 65 and so on) what size gear should i install in the tranny to correct this? The gear for the cable i mean.

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[jocko]

Nacho, it depends on your rear end/tire size AND # of teeth on the speedo drive gear (not, the driven gear) in the trans (can be 6, 7, or 8 teeth on the drive gear). You'll need to determine the number of teeth on your speedo drive gear (i.e. the gear you won't be changing) and then you can choose the correct driven gear (the one you will be changing, i.e. the one that comes out with the speedo gear housing) from the chart below (based on your rear end gear ratio). Here's a guide, but it is based on 26" tires diameter - but it's a start. Once you know what you have, you can see what changes might help. My guess is (based on the fact that your actual speed is slower than what you're seeing on the speedo) is that your tires are smaller diameter than stock - so this chart may be just about right for you because 26" is a little shorter than stock I believe. You might be able to determine drive gear tooth count by color - or mark one of the teeth sticking into the speedo housing bore (with the speedo gear housing removed) and then rotate the o/p shaft and count (sorry, I don't have a color cross-ref).

Speedo Gear Chart - reference to choose the correct "driven" gear that goes in the speedo gear housing (#'s below, i.e. 18, 20, etc, are the tooth counts on the driven gears) - in other words, look in the line for your rear end ratio - then look in the column for your drive gear - the corresponding # is the # of teeth on the driven gear you want to have for a correctly reading speedo. if your tires are much different than 26" diameter, then you may need to go up/down one tooth on the driven gear to make it more accurate.

Axle Ratio - 6Tooth / 7Tooth / 8Tooth (Drive Gears)
2.73 - NA / NA / 18
3.08 - NA / 18 / 20
3.27 - NA / 19 / 21
3.55 - 17 / 20 / 22
3.73 - 18 / 21 / 23
4.10 - 19 / 22 / 24
4.30 - 21 / 23 / 25
4.56 - 23 / 24 / NA

Calculated driven gears are based on normal 26" tires and the formula listed below:
Driven Gear Teeth = Drive gear teeth x axle ratio x tire revs/mile

Another option is to just buy 3 or so driven gears (if you have spare change lying around, and you may do some more swaps in the future..., you could have a stash on hand) and swap them until your speedo matches your gps speed....

Here's a good resource for the parts: http://www.thegearbox.org/catalog/it...32/3532466.htm
Here's ref data (including the above chart): http://www.thegearbox.org/catalog/it...32/3532517.htm
Here's another good resource, but most parts are listed as out of stock: http://www.transmissioncenter.net/sp...___va.htm#Misc. Gears

Note that if you have a hard time finding a T5-specific speedo gear, you can install a TH350 speedo gear housing and use the more readily available TH350 speedo gears.

By the way, a T5 or TH350 speedo gear housing should only cost about $6 from any local trans shop.

[Blue_71]

I know this is an old post, but something i discovered in case anyone who finds this through google (as did I); a TH350 driven gear will work, with a th350 housing. However, a TH350 drive gear will not. I was trying to convert a electronic t5 to mechanical, and ordered the 8 tooth gear off of that website from my work. the inside diameter is too big for the t5 output shaft.