Tooth count of speedometer driven gear in TH350?

[75ChevDrvr]

Does anyone happen to know or can you find out what the tooth count is for the speedometer driven gear in a TH350.  The truck it came from is a 1975 C10.  Even the tooth count for the drive gear would work.  I just need to figure this out because I can't find my old one.

Thanks!

[roundedline]

It really depends on your rearend ratio:
73-87.com/7387garage/driv...speedo.htm

Chris Lucas
www.73-87chevytrucks.com
www.captkaoscustoms.com
Project Su
Jimmy 2WD Project

[75ChevDrvr]

True...  It's 3.73 in my truck (stock from the factory).  I don't know what the original tire size was, but it came with 16" wheels.  I do know that I'm running slightly larger tires (265/75-R16) and the speedo always used to be off by a bit.  If I could figure out what the drive gear is, I could get the appropriate driven gear.  If I could figure out what the stock driven gear was, I could figure out what it should be.  

[VileZambonie]

chevelleengineer.home.com...speedo.htm

[75ChevDrvr]

I've got about four different sources with the same info on how to calculate the speedometer driven or drive gear now.  What I don't know is the tooth count of either one.  Can anyone help??

[DnStClr]

75, have you seen this site? You'll notice that the 3.73 ratio has a bunch of combinations- depending on  your tire size. Measure the tire diameter to get started. Lots of info. Hope it helps. BTW, isn't your drive gear still on the transmission output shaft?
www.transmissioncenter.net/speedometer_calibration_______va.htm

Don St.Clair
Culleoka Tn

Edited by: DnStClr at: 3/13/07 11:26 am

[123 pugsy]

What color is the drive gear? There is a lot of info about the gear colors and tooth count on the net.

[75ChevDrvr]

I hadn't thought about figuring it out by the color of the drive gear!  I forgot those were color coded too.  I kept trying to think about how I was going to count the teeth on it if I couldn't figure something else out.  I'm not sure where my driven gear or the housing went...

[75ChevDrvr]

I have seen that PATC site.  I even have a heavily built 700R4 Raptor trans that I put in my truck for a while.  I'm putting the TH350 back in instead so I can sell the truck and hang on to the 700R4 trans to either sell seperately or put in another project.  

[DnStClr]

Know whatcha mean. I bought a TH400 from them and it's sitting on my garage floor still on the pallet after 2 years! I rethought my plans and now want to put in an OD trans like you have.  

Don St.Clair
Culleoka Tn

[75ChevDrvr]

It's an impressive transmission, that's for sure.  It's somewhere between the top and second to top of their line.  I only ran it for about 3000 miles (about a year).  My truck is mostly a dirtbike hauler, so it doesn't see a ton of miles.  If you're interested, it's basically brand new.  I don't know what I'd have to do to ship it though.  I paid somewhere north of $2k for it, but I'd let it go for $1500.  

BTW...  The drive gear in my TH350 is green and I FOUND my driven gear!  It's red!  Thanks for the help though guys!  

[DnStClr]

I already have the 700R4. The Raptor you have is a good one tho!  

Don St.Clair
Culleoka Tn