Holy dog p*ss ... 4LO ?!
I was thinking to myself, high 15's ? ... Wow! ... Then I read you're running in 4LO ...
I'll try to put this in perspective with our trucks (1500 series)... The driveline in the 1500 avalanche (rear half) is good for about say 400-450 lb ft of (motor output) torque give or take (in a straight line; equal traction under each tire) depending on who you talk to it varies ... Now that's full-on torque; from a dead stop ... That's the worst case scenario... Once you're in motion things aren't as stressed ... The truck is designed with it also in mind that you will shock load the driveline a bit too... As long as you're not doing neutral drops, it will take it ... Now I wouldn't go hammering it to the floor from a stop with a 5,000# trailer out back though...
Now enter 4LO ...
When you are locking the driveline in 4LO or 4HI, the torque split is 50/50 ... This means that the rear driveline and front driveline share the torque the motor is making ... No biggie to the driveline now right?
Not totally... The transfer case in 4LO in the 1500 av has a reduction gear ratio of 2.72:1 ... This takes your front and rear diff to a 10.14:1 ratio presuming you have 3.73 gears ... Now, that's a down and dirty ratio (any time you increase drive ratios through gearing, torque multiplies... assuming there is input torque ...
) ... Things start spinning really fast really quick within that T case ... Remember also, the T case input is taking all that output torque from the tranny... Now reduced to 2.73:1, the whole driveline spins faster sooner under great/er torque multiplication ... Everything has to happen perfectly ... Traction, parts alignment, tire height, etc...
Climbing hills at say 3,000 RPM in 4LO in first gear has some serious torque multiplication but you are not coming out of first gear... the inertia of the truck and the driveline is much less, and if something binds, and even if the tires don't
slip all that much, you have less chance of breaking something... Things are happening at a slower speed all around ... Runnning an avalanche down the 1/8th mile on a paved track while going through the gears is IMO the ultimate test of it's driveline ... If it didn't break, it's worthy ... I'm not trying to pound it into anyone, but it is testamant to the precision and strength of our trucks 4x4 system...
Now to comment on "other settings" ...
It's one thing to run balls out in autotrac where there is slippage... (not too bad as long as it's not all the time... I would change the fluid after a hard night at the track though...)... It is also another thing to run in 4HI at a track (worse than running in autotrac I'm guessing because there's no slippage if something binds but at least you're running 1:1) ... But running in 4LO through a reduction of 2.72:1 on an aluminum T case in a 6,000+ pound truck, well I already said it...
You're riding on the odds if you do it ...I wouldn't do it in my truck ...
Now if your truck held together and it's not making funny noises from the driveline, you are probably fine... Maybe even better than fine... Because it possibly passed the ultimate QC and endurance test... Like a rock they say ... !!!
11H
*** I got a little nuts on the details, but I thought some may be interested in more than: "be careful" ... If I mis-spoke something, please provide corrections ... Sometimes I know what I'm trying to say, but don't say it right ... LOL