Running in 4 low, 2WD in a 4X4

[StephenA]

In upgrading my fwd axle from the thermal actuator to the stepper motor one, it occurred to me that it would be easy to install a switch which would turn off the actuator in 4x4 low, thereby allowing 2WD operation. When towing in the mountains on asphalt, there are a few occasions where the lower gearing would come in handy, but running on pavement in 4WD wears out the drive train & binds it up. My other 4WD vehicles all had cautions against running in 4WD without the hubs locked. Does this apply to the K2500, since the hubs are always locked and instead it's the transaxle that engages? If it is harmful, I'm wondering how much damage I may have done shifting into 4WD when I was unaware that the actuator was intermitant. Wally? Anyone?

[Uncle Wally]

Stephen,

Never thought of that one. I know the older gear driven t-cases had two shafts that controlled the case. One for 4x4 and the other high/low. You could run a twin stick setup and control it that way. I'm not sure that same idea can be done on these new ones. There is one control rod that moves the shift forks. The rest is all internal. I suppose you could use low with out the actuator engaged, but you would still be rotating everything up front, it just wouldn't be engaged. I have heard that axle designs are such that when power is applied to them they create they're own internal flow to keep things cool. I would check on that to make sure there will not be premature wear due to that. I think that was more for towing vehicles with a tow bar or dolly more than anything else.

In this case, I know enough to be dangerous. It seams like a neat idea though. Let me know what ya find out.

I wouldn't worry too much about wear at this point, as whatever damage is done is done. My old 90 had 253000 miles that were extremely hard, and I never had to touch the front end. I went through the trans and t-case once (the t-case was done because I had the trans out and it made sense to replace the bearings, chain and seals while it was out). I went through alot of front end parts, but never touched the axles or engine (350). I kinda wish I still had that ol truck!

Waldo

[ulhpilot]

Do it the easy way. Scrap the thermal actuator and install a cable operated Posi-Lok:
http://www.4x4posi-lok.com/
It allows the vehicle to be operated in 2wd/low range because without the front axle locked (by means of manual cable control), no power is being transferred to front wheels. Been running mine for about 6 years, no problems except the little boot that covers the actuator rod keeps tearing. Called them up and they send me a couple more. Handy as he** when you want 2WD and low range, no worries with driveline binding, but don't think you are going to run down the road in low, 25MPH is max in low range. GM IFS doesn't use 'hubs' per se, CAD has axle halves and CV joints to each wheel (spindle). Front axle is connected and disconnect in diff. When I get my new truck (someday), I'm going to do a IFS to Dana 60 axle swap on my current GM and them I'll have a 'real' 4X4 :)
Mick

[StephenA]

I checked out the posi-lok. It advertises the 2WD 4low usage. I think I'll put this in instead of the stepper motor. Thanks!

[StephenA]

Mick- was your posi-lok $170.. -or did you find a deal?

[ulhpilot]

When I bought mine back in '97 (anal me has receipts for everything I've bought for my truck), the Posi-Lok was distributed by a parts store in Missoula, MT and cost was $155. A quick check of on-line parts stores shows just about everyone sells them now, and $170.95 seems about the going price. Well worth it to get rid of the ill-designed thermal stuff. Plan on a good 2 to 3 hours to install. If I lived back in the woods and didn't drive on paved roads very often, I'd even consider the permanent set up they sell for $89. No cable, no linkage, just shift into 4 high/lo and go. The trade off is no 2wd lo and front axle is permanently locked.

[rjschoolcraft]

Again, why go backwards in technology? I would not waste the time or money on the cable.

The warnings for not running in 4wd on pavement are becuase of the binding due to slightly different tire sizes. However, at low speeds it is not that significant and there is very little risk of damage. I pulled my travel trailer up to the Whitney Portal campground just west of Lone Pine California this summer. That pull was so steep that I had to use 4-low to make the grade for about 7 of the 13 miles. I didn't get above 15 mph.

On the other hand, you don't really want to use low range in only 2wd for the primary reason that excessive torque will be delivered to the rear drive line. There is a big multiplication in low range and the engineers counted on a split of that huge torque to the front and rear to keep things within stress limits.... Sending all of that torque to the rear can overstress the driveline components. This is more risky than 4wd on dry pavement.

If you like the cable, though, I have a nice two-person, one-horse buggie that needs a little restoration work sitting down in my barn. Absolutely no electronics knowledge needed! ;)

[StephenA]

AHHH the light dawns... torque to the rear. Yep, now I remember. I was hoping the cable rig would save me some $$, but it's $70 more than the stepper motor update. If I want the 2WD low once in a gentle while, I can rig a switch to defeat the voltage to the actuator & just go easy on the rear end, I think.

[ulhpilot]

Always nice to use sarcasm to prove a point. You like buttons and switches, others like levers and linkages.
> you don't really want to use low range in only 2wd for the primary reason that excessive torque will be delivered to the rear drive line. <

Pay no attention to those twin stick transfer cases.

[StephenA]

ulhpilot- my sarcasm was aimed at myself... I realized I had forgotten something I knew a decade ago about torquing the rr end. At 52, I get dim-witted sometimes and forget stuff- oh well!
I really appreciate your post on the manual locker- it helped me understand the whole mechanism. I may end up getting one anyway, as the seller points out that it stays engaged when the ignition switch is off. I don't know if that's true of the stepper motor update. It's certainly not true about the thermal electric unit.
Thanks again!

[rjschoolcraft]

Well...

My dad has a 1948 Willys Jeep CJ2A with a "twin stick" (as you call it) transfer case. That transfer case would not allow the vehicle to be shifted into two wheel drive low range. He's had this vehicle since 1969 and just finished a body off restoration...I learned to drive in this vehicle before I was ten. In 1970, he installed a 1966 Buick V6 in it. He also had a 1967 International Scout four wheel drive. It also had a "twin stick" transfer case. It would allow the selection of two wheel drive low range; however, there was a large warning sticker on the dash that said not to operate the vehicle in two wheel drive low range as rear driveline damage could occur.

StephenA: I think that the stepper motor stays engaged when the key is off. I will check and find out. By the way, I think the sarcasm comment was directed at me.

ulhpilot: It's your vehicle. Do as you please. As far as levers and linkages go...I have owned a 1974 Jeep CJ5 and still own a 1972 Chevy K10 pickup (both have single lever transfer cases and manual lock-out hubs). I really liked both of these vehicles and drove the pickup back and forth to western Illinois once a week for nine months in 1998-1999. The Suburban gives me something neither of the other two could...the ability to pull one lever and instantly have four wheel drive without getting out of the truck. I don't view new technology as inherently bad.

[ 10-07-2003, 07:58 PM: Message edited by: ronniejoe ]