Gear ratios

[Ziegelsteinfaust]

I am swapping rear ends in my truck going from 4.88 with a Detroit locker to a 3.08 open rear end.

The truck is a 73 C10 with a gen2 LT1 with a carb and full bolt ons. The transmission is a th700r4, and 31" street tires.

I am worried I may be going to far. Since I wanted 3.42, but they are rare to find on the budget I have to play with. Since I won't be able to do anything in the rear end for a year or switch tires. Partially to lower it further.

How do you expect it to be as a driver. Or am I just over thinking it.

[Keith Seymore]

I think that's way too far.

I do 3.73 with an overdrive trans and P235/75R15 tires. 3.42 with a non overdrive trans.

The combination of the overdrive, large tires and 3.08 is going to be a total dog, IMHO.

But - since you are locked in to the ratio and tires, may as well try it for a while and see if it works for you.

K

[bnorth]

I agree with the above. Since you are running big tires and already have a locker for the 4.xx+ gear ratio what if you just swapped to 4.10's in your existing diff? That shouldn't break the bank especially if you can sell the 3.08 diff and then you get to keep your locker as well.

[Ziegelsteinfaust]

Originally Posted by bnorth

I agree with the above. Since you are running big tires and already have a locker for the 4.xx+ gear ratio what if you just swapped to 4.10's in your existing diff? That shouldn't break the bank especially if you can sell the 3.08 diff and then you get to keep your locker as well.

I scored a G10 rear-end for $100 which also gets rid of the spacers.

My Dad who I am reinventing the truck for is 82, and in the beginning stages of Parkinsons. Plus when you back up or turn to tightly the truck slides sideways. Which he already hates.

Although it was great when I had to drag a stuck project car 200 foot in the dirt/sand of the high desert.

Tied into the fact to redo what I have is well over $1000 I don't have as it is.

I am mostly worried he will fall out of his van.

[AussieinNC]

Here is a link to an online calculator, using trans type, rear gear ratio and tire height...makes it simple

https://www.blocklayer.com/rpm-gear

Using your 3.08 gears, I get around 1590 rpm and 70 mph.....engine better have some deep torque curve for this to work ok....

Leave the 4.11 gears in it for a decent driver....