Rear gear options
 

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?

Re: Rear gear options
 

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

Re: Rear gear options
 

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.

Re: Rear gear options
 

I'd go 3.73's.

Re: Rear gear options
 

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.

Re: Rear gear options
 

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

Re: Rear gear options
 

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

Or about 300hp/375tq crank

Re: Rear gear options
 

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.

Re: Rear gear options
 

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.

Re: Rear gear options
 

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.