What is my gear ratio?

[LONGTOM]

Just joined and have a question I need help with. This really is a two part question. I have a 1979 K10 full time 4x4x with 342 gears. 10 bolt front and 12 bolt rear. The truck came with 700x15" tires when new but I now have 35x12.50s on it. I was wondering what my gear ratio is now? Second part of the question. It had a 350 with a turbo 350 in it and I was very pleased. The engine blocked cracked and we just finished a swap from a 1983 with a 350 and a 4 speed automatic that had lock outs. We changed the hubs also so I now have two wheel drive for the road. Problem is the 4 speed auto and my gear/tire combo just don't work. It won't shift into drive until about 50 mph and only shifts into overdrive if you are doing over 70. I know I need lower gears but how low?

 

[HotRodPC]

Changing Tire size does NOT change your gear ratio.

As far as shift points, you likely now have a 700r4 so have you adjusted the TV cable properly? That 700r4 with a lower first gear should work just fine if the TV cable is adjusted properly. DO MAKE SURE it's adjusted properly, you may be killing that transmission and not know it. Critical on a 700r4 that the TV cable is adjust properly since it regulates fluid pressure. Not enough fluid pressure to compress clutch packs tight enough, you're slipping the clutches and burning them up.

However, with 35in tires, that 700r4 isn't likely to live a good long life.

 

[LONGTOM]

I understand that I still have 342 gear ratio. Maybe I should have stated it differently. The bigger tires didn't change the gear ratio itself but wouldn't the taller tires make it drive like it had 308s or even less power wise? Maybe I got it all wrong in my head. As far as the trans goes, I am not sure what it is. The guy who did the swap didn't say but I think you are right about the 700r4. I know he had a lot of trouble with the cable and that may well be where my problem lies. My old 350 turbo broke the park ears off and my transfer case was starting to get a little chain slap so that is why we swapped the whole package. Been thinking about having my old set up rebuilt and putting it back in. At least I would know what I had and how it should run with them.