Best gear ratio for 8 inch lift and 40s?

[78k10bro]

I have a small block 350 and I’m about to swap a 14 bolt rear and Dana 44 front in. Im going to put an 8 inch lift and 40 in super swampers on it also but I’m wondering what the best gear ratio would be?

 

[nvrenuf]

What do you plan to do with it? Daily street, off road only, etc? Do you have an overdrive transmission?

 

[SquareRoot]

Welcome. Prepare yourself...

 

[78k10bro]

Daily driver and light off-road also I don’t know if I have an overdrive trans it’s a 4 speed manual

 

[SquareRoot]

You probably wont be seeing many highway miles with 40 inch swampers so you're gonna need some steep gears with a 350 and 4 speed. I would say 4:56 is best, 4:10 minimum. I have had both in my truck but I have OD with human size tires and the 4:56's work great for me.

 

[Strick]

Seems that most GM Dana 44HD's are 4.10 gear whereas the 10 bolt Corporate were 3.73 gear. The 4.10 will move the 40 Swampers by using the "Granny" in the SM465 but it will be very underpowered. I would consider 5.13 or 4.88 to be able to both drive the truck and use it without killing the clutch in your truck.

Strickland

 

[nvrenuf]

Daily driver and light off-road also I don’t know if I have an overdrive trans it’s a 4 speed manual

There's a 99.9% probability that you have a non overdrive SM465 (it will have a granny low first gear). There was an overdrive 4 spd available in the 80's but they are pretty rare.

I agree with @SquareRoot, 4.56 would probably be your best bet. I'm inclined to suggest deeper gears but I'm Mr Vegas in that aspect.

 

[78k10bro]

Yea i have a granny low first so probably not an overdrive. Thank you all for your input, what is the best place to get gears? Also if i went with 38s would that make much of a difference or would it be close to same as 40s?

 

[Strick]

Also if i went with 38s

The SM465 is going to help out with running the larger tires. A gear ratio of 4.56 and numerically lower (higher gear) will pull those tires without issue. I have 36's on a truck with an SM465 with 4.10 gears and pull trees with it on the farm. I recently had a CUCV with 37's and 4.56 gears and it was OK too until you really started serious off-roading. The gearing was great but the 150HP diesel in it wouldn't cut it on the low end.

Strickland

 

[Bextreme04]

Spicer has some good calculators that will help you get an idea of what everything will be doing. With 4.56 gears, 40" tires and your trans that has a 1:1 final drive ratio, you will be at 2500rpm in fourth gear at 65mph. with 38" tires that goes to 2650 rpm at 65mph.

 

[Bextreme04]

https://spicerparts.com/calculators/transmission-ratio-rpm-calculator

 

[85K304SPD]

That is 'lots of tire. Go with some big number gears. Upper 4's or lower 5's. Get some good axles too for the Dana 44. Get all the good steering stuff as well, to keep that thing on the road.

 

[SquareRoot]

Someone should mention reinforcing the frame/adding a stiffener brace at the steering box. Oh and the jeep steering shaft upgrade. And the possibility of creating driveline vibrations. Oh and.....

 

[78k10bro]

I’ve already fixed the crack and reinforced at the steering box so that won’t be an issue. I’m going to go with cross over steering and I have dual stabilizers on it already. I’ll look into spicer but I’m pretty sure I’m going to go with 4.56s, also what would be the best way to stop driveshaft vibration if it happens, lengthen the driveshaft? or could I run a spacer and tcase drop bracket kit? thankyou all for being so helpful to this young guy who’s just getting into these older trucks!

 

[AuroraGirl]

There's a 99.9% probability that you have a non overdrive SM465 (it will have a granny low first gear). There was an overdrive 4 spd available in the 80's but they are pretty rare.

I agree with @SquareRoot, 4.56 would probably be your best bet. I'm inclined to suggest deeper gears but I'm Mr Vegas in that aspect.

are you talking about the new process overdrive trans? @Keith Seymore has one of those I think,starts with an A or something I think