Rear gear options

[Ziegelsteinfaust]

My rcsb 73 C10 has 4.88 gears, and a Detroit locker.

Since I am giving the truck to my dad. I need to swap gear ratios.

Would 3.23's be too low with a C10 backed by a TH700R4 with 30" tall street tires?

[RustyPile]

Naaaa!! Don't change a thing.. Give it to your Dad like it is so he can take it racing sometimes.

[Dead Parrot]

online RPM calculators are your friend.
At 70mph, engine RPMs are:
3.23 = 1772
3.73 = 2047
4.10 = 2250
4.88 = 2678

Unless that motor is some kind of special low end powerhouse, 3.73 or 4.10 is probably a better choice.

Or just leave it as is.

[LS short box]

I'd go 3.73's.

[truckster]

If your dad is a conservative driver 3.23 would be just fine. If he wants a little more pull, I'd agree on the 3.73.

[kwmech]

3.23s may have a tendency to make the trans hunt between 3 and 4 especially with the lock-up convertor. With a 30'' tire I would personally go with the 4.10s. Cruising at 21-2200 rpm is actually ideal. No mention of the engine build

[Ziegelsteinfaust]

The engine will be a bolt on gen2 LT1 from a B body.

Or about 300hp/375tq crank

[dennislbrooks]

I run 3.73s in my BB 402 and 700R4 with 265/70R17 tires - 67 Chevy 4WD - 14 bolt. I would not change it but it does hunt between 3 and 4 at about 37-38 mph with light throttle like in a 35 mph zone- same with my other 2. Even with a small block I like the 3.73s behind a 700R4 - my 59 GMC 4WD (215/85R16)- 12 bolt, and my 42 Chevy 29 inch tires 10 bolt.

For 60 mph cruisin I like the 3.73s. But since you are making a switch 4.10s as kwmech says above may help the hunting problem.

[LS short box]

On my LS swaps with 4L60E's I delay the 4th gear and lock up until 45 mph. I know its done thru the ECM.
Can the the 700 be "programmed" mechanically to do the same? Just asking.

[dennislbrooks]

The tension on the TV cable will adjust shifts. There may be other ways. My 700R4 under moderate throttle shifts into 4th about 47 mph and lockup nearly immediately afterwards.

I am talking when you have slowed down for a 35 mph then just remain with a light pedal to maintain something close to 35. If I creep up to 38-39 mph under the light throttle it shifts up to 4. A little less like 36,7 back to 3. Yes I could move the shifter out of OD to D.