1969oldsH

I am having troubles finding a speedometer gear for my TH-350 Trans. Currently reading 75-80 when im going 60-65.

Anyone know of a site with data to find the correct part?

w-30dreamin

Good question,I'll be changing my rear gear soon. Same combo,th350 with 3:42 gears.

I'll be watching your thread for info.

GAOldsman

I think this may shed a little light on the subject

stevengerard

there is a guy on ebay from Southwest Michigan that sells the correct driven gears and speedo gears, he can tell you what you need. There is a site though I'll try to find it'

DeltaPace77

Another place to try is transmissioncenter.org, as they sell just about any GM tranny gears.

1969oldsH

thank you all for the help on this. i have to figure out what my drive gear is right now and figure it out. thanks answered all of my questions.

DeltaPace77

Finding out the speedo drive gear size, should be easy as pulling out the driven gear housing, and checking gear color. Really depends on what axle you originally had vs the 3.42 now, as may need a new driven gear plug in housing as well. The Transmission Center site shows all of this. Note, the listed 700R4 parts are the same for non Chevy TH350's. I went from 2.41 axle on my car to 3.73's and had to change both gears when running a TH350. You'll need to pull the driveshaft, and unbolt the tailshaft housing to change the drive gear. When I switched to a 700R4, all gears were directly swapable. The 700R4 I used, had a Chevy bolt pattern, and needed an adapter plate to make it work.

Slomega

Thanks for the link (www.73-87.com) ...

VERY GOOD Site for references, especially with the Speedo Gear calculations and ratios!! ....

Transmissioncenter.org mentioned above was helpful too!

GAOldsman

No problem Dave, always my pleasure to help out.

Scot

ah64pilot

Best place I've dealt with is Performance Automatic Transmission Center (PATC). They have everything for the speedometer gear, housings included.

http://www.transmissioncenter.net/sp...n_______va.htm

hookem horns

I faced this same issue a year ago. Got an adaptor so I did not have to change both drive and driven gears. Within a couple of MPH on the GPS now.

https://classicoldsmobile.com/forums...o-adapter.html

brownbomber77

Old thread, yes. I'm trying to find if I can just stick a 43 tooth speedometer gear into the 18 tooth drive gear to make it read right with a 3.42 rear from 2.73. This is a '77 TH350.

1969w3155

Try here: http://www.speedometersolutions.com/

brownbomber77

Ah, there's a link I haven't seen yet. I visited most of the other sites other suggested on different forums. The TCI website and a couple others that sell trans parts. I'll give them a whirl. Thanks

olds 307 and 403

Supposedly there are 3 different housings, you need the correct one for the 43 tooth gear.