What's new

How bad will undergeared rig be?

Lil'John

Former #278
Joined
May 20, 2020
Member Number
488
Messages
1,056
Loc
Walking to the Rubicon
I'm trying to find out how bad undergeared axles will be for my rig.

Drivetrain is an unknown HP turbo 5.3L LS, 4l80e, Blackbox doubler(2.7 gears), and LC "splitcase"(2.3 gears) Tires will be 43" x14.5" swampers. Axles currently are KP Dana 60s with rear D60 but I'm leaning toward a change(Tundra center with SD60 outers). Intended use is Rubicon with driving from Georgetown and maybe some freeway driving(50/80)

How bad will 4.30:1 gears be with the 43s?

I'm trying to be a cheap bastard and $400 for gears alone make me cringe a little bit. An ARB or other selectable locker will be installed so cost of install is already out of the equation. A "side" benefit I'm looking for is common third member for three rigs.
 
Not a very close comparison but I ran 4.88s and 42s for years in a fullsize ford with a 302/C6/1356 manual valve body combo. It ran down the road just fine and gearing was plenty low for the wheeling here. You'll have the advantage of way more power and and the extra 2.3 case too. I trailered for longer trips but that was mostly for the breakage factor and not because I couldn't drive it to the trail.

Ford.JPG
 
That might be a bit slugish on the highway but thats plenty of gear for mild crawling.
The slugish freeway is something I could live with especially if I keep it out of OD ;)

One of my previous experiences on the Rubicon was with a SM465, 2.0:1 transfercase, 4.1:1 axles, and 35" tires. I wanted it to be a little bit lower. Are you thinking the new combo is going to be a worse experience?:confused:
 
We will ALL h8 you for bangin and clangin thru the trail, not to mention the need for high speed runs due to no grunt...:laughing:
Can you drive that shit like that?
Would you want to be in front or behind it?
Yes? Then ok.
No? Then fukkit.:flipoff2:
 
The slugish freeway is something I could live with especially if I keep it out of OD ;)

One of my previous experiences on the Rubicon was with a SM465, 2.0:1 transfercase, 4.1:1 axles, and 35" tires. I wanted it to be a little bit lower. Are you thinking the new combo is going to be a worse experience?:confused:

No because torqconverter + doubler.

Get a 2k tc WITH lock up and youll be fine.
 
Should be fine, your first gear is lower than mine (c6) and I can street drive mine on 42's with 4.88's and a turbo'd 351w. You won't be using overdrive much or getting anything that resembles nice gas mileage, but it should work.
 
I currently have a 4500lbs buggy with a 5.3/th400/3.0 atlas/5.13 gears on 43sx.

38:1 crawl ratio and I love it. Took me a few tries and some work from the TC guy to get the converter like I wanted.

I know your vehicle will be turboed, but the low end torque will be very similar and the engine will believe similarly.

You crawl ratio will be 66:1, you'll be fine on the trail. Its going to suck major ass on the street though.
 
Your overall crawl ratio is plenty low for an automatic, but the thing no one has mentioned is that your drive shafts are really going to be hating life with all your reduction upstream and a pretty high effective axle ratio. Also worth considering, especially if you are running pretty soft springs, is that you are going to get some pretty bad torque twist which is going to make it want to pick up a front tire on steep climbs and compromise your stability.
 
Your overall crawl ratio is plenty low for an automatic, but the thing no one has mentioned is that your drive shafts are really going to be hating life with all your reduction upstream and a pretty high effective axle ratio. Also worth considering, especially if you are running pretty soft springs, is that you are going to get some pretty bad torque twist which is going to make it want to pick up a front tire on steep climbs and compromise your stability.

The driveshafts are probably the one thing I'm "least" worried about. They are going to be "older" Land Cruiser ones that are beefy. I forget the size but back in the day, I had a shop think they were one ton pickup version:homer:

Good point on the springs. In my case, I will be linked front/rear with appropriate coilover springs.
 
The driveshafts are probably the one thing I'm "least" worried about. They are going to be "older" Land Cruiser ones that are beefy. I forget the size but back in the day, I had a shop think they were one ton pickup version:homer:

Good point on the springs. In my case, I will be linked front/rear with appropriate coilover springs.

I am not familiar with Land Cruiser joints, but for a point of reference, my cousin wheels with 39.5" tires and 4.10 gears and has taken out a few 1330 and 1350 joints and transfer case yokes. He is running a stock EFI 460, and his rig probably weighs between 5,000-6,000Lbs. My old beater rig had 38" tires and 4.10 gears, and I never killed a driveshaft since I am a pretty conservative driver, but the torque twist was definitely real.

This isn't the best video since it just looks like the rig didn't have any flex, but it was lifting the driver's front and "locking" up the suspension under power where other rigs with lower axle gearing weren't having this issue:
 
Top Back Refresh