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Old 07-30-2012, 10:30 PM
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Default 4WD system demo w/ and w/o Locking Diff

Thinking back to my '84 Jeep CJ7 4WD, '87 Ford Bronco XLT (full size) 4WD and other non-GM 4x4 trucks and their "4-wheel drive" systems and wondering if any of them had a locking rear differential or similar like my '99 GMC Suburban (GM option code / RPO G80 has been "co-opted")

This video demonstrates the limited capability of 4WD truck systems (without computer assisted individual brake application or e-diffs) with open or limited slip 4WD systems:



Was surprised at the above video that 4WD trucks (not getting into sedan world and "all-wheel drive") without brake assist, when engaged in 4WD, would get stuck on the hill with the rollers.

Yes, I know that we've come a long way since "then" with "brake assist" or "traction control" and "e-diffs" but was still surprised that 4WD trucks that didn't have an Eaton locking diff (or similar) would have such a hard time.


Inside the Eaton G80 Diff:



Of course, aftermarket air lockers (diff) would be optimal for serious 4WD / off-roading but that is an add-on post purchase, not a factory option.

Range Rover / Land Rover solved this a long time ago with 4-wheel drive AND the ability to lock the diffs from lever/switch inside the cabin.

Just exploring.
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Old 07-31-2012, 07:41 AM
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Interesting.

So do the older Jeeps, trucks, 4wds with locking front hubs have the same issue? For example, if you have locking front hubs like Warn, Mile Marker, or even factory, are they locking you into 4wd? Or are they locking the differential like the Eaton? If locking the differential I assume the front end would then be able to pull the rear end up the hill.

Jeep has had electronic locking diffs as an option since the first Rubicon came out in the TJ model line. And I know Nissan had some as an option in the Frontier. I'm also pretty sure Jeep and Ford had them as factory options on other vehicles but I don't know what dates they started. (I just didn't want people to think Range Rover was the only company with electronic lockers from the factor.)
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Old 07-31-2012, 07:54 AM
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AFAIK, on my 2001 Suburban, in 4W LOW (need to be stopped to engage), it locks both the front & rear axles as well as the tranfer case. I would guess it would have no problem dealing with the rollers. Though not sure how well it would do in 2WD, although it does have an locking rear axle; it takes a certain amount of wheel spin to engage it (not electronic).
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Old 07-31-2012, 08:22 AM
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Dont confuse hubs with a differential.

LS in my 4wd chebby, agree 100% on the lack of traction in slick conditions. The video is a little deceptive though. I have yet to find a boat ramp or icy road with only one side that's slick. My truck will never see off road use, fingers crossed.
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Old 07-31-2012, 08:46 AM
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Quote:
Originally Posted by Jase007 View Post
This video demonstrates the limited capability of ... open ... 4WD systems:
^ I think that boils it down. 4wd w/ no LSD will do exactly like they say. If you get slip on one front AND one rear wheel you aren't going anywhere.

My f350 has the lsd option and I can confirm it will drive all rear wheels in the snow (even in the rain in 2wd.) Its a clutch type though and is known to wear out. I think wongers @ 100k was toast and I think someone else here replaced theirs too well before that. All clutch types need clutch disc replacement eventually. The eaton is no different.

I thought most everything had brake assist nowadays. It basically comes 'free' w/ ABS and a little extra programming.
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Old 07-31-2012, 09:06 AM
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My 2002 F-350 had the rear limited slip clutches shot when I bought it at around 70,000 miles. Replaced entire rear diff with a Torsen type Eaton Truetrac. http://www.filthymotorsports.com/Det...ettruetrac.htm

This was strongly recommended by Randy's Ring and Pinion for my use. Street use only, primarily concerned with snow/plowing. Nice thing is that it doesn't have clutches to wear out. Although, if I get one rear wheel in the air, or one rear wheel which has absolutely zero traction, then the rear will supply zero driving force to the ground. I am extremely happy the performance in the snow and rain. The thing is amazing. Now, if it ever snows again ...

As to an automatic locker that truly locks the rear, I've been told that these things are a bit scary for unexperienced drivers, as it takes a short while to lock up, and all of a sudden, you can have the rear break out on you going around the corner in the rain.
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Old 07-31-2012, 09:12 AM
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Quote:
Originally Posted by Jase007 View Post
Range Rover / Land Rover solved this a long time ago with 4-wheel drive AND the ability to lock the diffs from lever/switch inside the cabin.
Not a truck, but the old 1st gen Audi Quattros from the mid 80's had this feature as well. From switches on the dash, you could lock the center diff, and then also lock the rear diff. Those cars were amazing in the snow, could climb any icy covered hill.

The 2nd gen quattros went to a torsen center diff. Rear diff was still manual lock, but was electronically controlled to auto-unlock above ~15 mph.
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Old 07-31-2012, 09:31 AM
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Quote:
Originally Posted by Fairfax 944 View Post
Torsen type...
Although, if I get one rear wheel in the air, or one rear wheel which has absolutely zero traction, then the rear will supply zero driving force to the ground.
Left foot brake. IIRC, the hmmwvs also have torsen diffs since wear is less of an issue. Its SOP to left foot brake. The torque multiplier from the helicals will more deliver considerably more torque than the brakes are using to the other 'good' wheel.
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Old 07-31-2012, 08:05 PM
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I am impressed my meek little Ridgeline has a fully locking rear diff, selectable from the dash, and automatically transfers torque to the rear diff when the front wheels slip.

I had a 99 LRover - LR had removed the ability to lock the center diff and had removed the lever from the cockpit. Left it with open diffs and tried to employ ABS hub friction to transfer traction to the wheel with the most traction. Result was less than impressive, but it did work mostly, but only at low speeds. With all the oil leaking out of that Buick engine, all wheel drive was mandatory

With open diffs, as mentioned, cheating with your brake pedal can get some torque transferred away from the spinning wheel, though I have had little actual success when I had to do this with my old bronco and jeeps.
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Old 07-31-2012, 08:27 PM
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Quote:
Originally Posted by Spike View Post
With open diffs, as mentioned, cheating with your brake pedal ...
No, w/ open diffs it doesn't work. They have an even 1:1 transfer ratio and any transferred torque is eaten by the opposing brake. It takes a torsen/quaife TBD which are typ ~5:1 for the trick to work.
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