Speedo gear

[Chris Greenley]

Any one got a Th350 with a 342 rear end whats the drive and driven gear yall using with a 15 in tire
I see where a 8 drive gear and a 21 works for the 14in tire thanks

 

[Twisted_Metal]

It's not the rim size... It's the tire diameter which figures into the calculation.
What size tire?

Here's a speedometer gear calculator to figure out what you need.

TCI Speedometer Gear Calculator (tciauto.com)

 

[Chevyforever]

My 1980 Z28 has the 3.42 rear gearing w/ a TH350,15 " wheels and 225/70r15 tires. Drive gear is orange 8 tooth and driven gear is dark gray 44 tooth.

 

[Chris Greenley]

My 1980 Z28 has the 3.42 rear gearing w/ a TH350,15 " wheels and 225/70r15 tires. Drive gear is orange 8 tooth and driven gear is dark gray 44 tooth.

Is your speedometer spot on now and thanks so much for your input its very appreciated

 

[Chevyforever]

Yes, my speedo is spot on. I am original owner and car has just shy of 50,000 miles (80000 km's)

 

[Chris Greenley]

Yes, my speedo is spot on. I am original owner and car has just shy of 50,000 miles (80000 km's)

Beautiful car is that a current pic looks like it needs some more miles with smiles. Just ordered the speedo gears that worked for you. Thanks you
CHEVYFOREVER

 

[Gary S]

I hope everybody here is aware that the Chevy TH350 used two different kinds of speedometer gears. The earlier ones used the small gears. Some of the later ones used the larger style gears like the BOP trannys.

 

[Chris Greenley]

My 1980 Z28 has the 3.42 rear gearing w/ a TH350,15 " wheels and 225/70r15 tires. Drive gear is orange 8 tooth and driven gear is dark gray 44 tooth.

Is that 44 tooth driven gear for a BOP transmission

 

[Chevyforever]

My car was built with a Chevy TH350, it had the BOP extension housing since new. BOP housings take larger gears and 2 inch sleeves. "Chevy" hsg is orange in the picture while the natural alum hsg is my OE "BOP" unit. As you can see the gear size difference is obvious.
You can physically swap BOP and Chevy TH350 extension housings of the same length. BOP TH350 sleeves and the driven and drive gears are larger with different tooth counts than Chevy TH350 gears, so any housing swap requires changing all three parts.

 

[Chris Greenley]

My car was built with a Chevy TH350, it had the BOP extension housing since new. BOP housings take larger gears and 2 inch sleeves. "Chevy" hsg is orange in the picture while the natural alum hsg is my OE "BOP" unit. As you can see the gear size difference is obvious.
You can physically swap BOP and Chevy TH350 extension housings of the same length. BOP TH350 sleeves and the driven and drive gears are larger with different tooth counts than Chevy TH350 gears, so any housing swap requires changing all three parts.

Thanks so much I had no clue
That's some good information