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Old 04-13-2007, 09:28 AM   #1
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4 WD Question

Because so many of us use modern 4 WD vehicles for towing this question might be of general interest. Back in the early 4 WD days we equipped our vehicles with "Warn" hubs to isolate the front-wheel drive mechanism and cut down on drag. That was due to the fact that the transfer case simply hard-connected the entire front-wheel drive mechanism to the tranny. I know that, somewhere along the way, the "automatic-type" Warn hubs were developed - or at least they could be activated without getting out in the mud! My question is, "Do the modern systems still disconnect at the wheel hub - or simply at the tranny?" I know that, with a true full-time 4 WD system, there is another form of clutch or differential that permits movement between the front and rear wheels. I believe that the GM system - as found in the suburbans - utilizes another differential, whereas Subaru uses a viscous coupling. Maybe one of the "gearheads" out there can provide an answer.
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Old 04-13-2007, 09:46 AM   #2
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To my knowledge, the GM product uses a system similar to a front wheel drive. CV joints and independent front suspension, not the old U-joint solid axle style. The front wheel drive is then disconnected at the differential, not the hub.
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Old 04-13-2007, 10:31 AM   #3
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Newer Fords have auto-engage hubs. They engage when the drive axle starts to spin, and disengage when the torque is released.
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Old 04-13-2007, 10:45 AM   #4
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Is the GM system similar to Ford? If so, it would mean that the entire front wheel drive mechanism is disengaged when out of 4 WD - and thereby not creating any drag. That makes the most sense but I wasn't sure how it all worked.
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Old 04-13-2007, 10:53 AM   #5
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It's different. The axle shafts are still connected, but the diff is disengaged. So, there is still some drag.
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Old 04-13-2007, 11:10 AM   #6
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Quote:
Originally Posted by overlander63
It's different. The axle shafts are still connected, but the diff is disengaged. So, there is still some drag.
Ah-hah! I wonder if this has anything to do with why the late model GM 3500 4 x 4 duallies tend to cup their tires on the outside tread??? If the axle attached to the wheel is just the least little bit bent - or bends due to flexing under side loading - it could, IMHO, be the cause of the cupping. See my other post where I was questioning if anyone else had experienced this problem. I would guess that a standard spindle axle setup is far more rigid.
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Old 04-13-2007, 12:00 PM   #7
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On my F-250 I have auto /engage setting on the hub. I cycle them at aleast once a week..
I was under the impression that just the hubs released and the power was still going to the front drive shaft at all times.
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Old 04-13-2007, 12:02 PM   #8
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If the hubs did not release it would make going around corners on hard surfaces nearly impossible. There is no front differential in the Ford Trucks.
All time four wheel drive is a different animal.
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Old 04-13-2007, 12:28 PM   #9
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Quote:
Originally Posted by thecatsandi
If the hubs did not release it would make going around corners on hard surfaces nearly impossible. There is no front differential in the Ford Trucks.
All time four wheel drive is a different animal.
Michelle, are you sure about this? Power is usually transmitted through a propeller shaft to a pinion gear in the differential housing, then to a ring gear, with differences in load distributed via spider gears to the axle shafts.
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Old 04-13-2007, 12:30 PM   #10
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Quote:
Originally Posted by thecatsandi
On my F-250 I have auto /engage setting on the hub. I cycle them at aleast once a week..
I was under the impression that just the hubs released and the power was still going to the front drive shaft at all times.
I think your truck has an electronic shifter that disengages the front driveshaft when operating in 2wd. Looks kind of like a power window motor.
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Old 04-13-2007, 12:45 PM   #11
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lets go 4 wheelin'!

neither ford or ge'em make 4wd systems...

but they do buy components and systems from other vendors.

so discussions of what is under there and how it works first need to specify...

which system? and which differental and which connection...

here's what i have and like...

The ONLY Official TORSEN Home Page!

the faqs and images and other details are specific to torsen differntials BUT...

help us understand how the other designs work too...

IF ya need some math this is the long quoted original paper...

http://www.torsen.com/files/Traction...ol_Article.pdf

and a condensed version...

Torsen differential white paper

for a more general understanding go here...

Howstuffworks "How Differentials Work"

or here...

AutoZine Technical School - Traction

and this is a good site on the 'abc' of 4wd. check the section on basics....

http://www.4x4abc.com/

cheers
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Old 04-13-2007, 01:33 PM   #12
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All I know is that the MPG still blows either way towing.
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Old 04-13-2007, 03:34 PM   #13
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Forget my comments about "bent axle" or "flexing" made in post #6. I had forgotten the universal or CV joints in the equation. There may still be something to the idea of a bearing-supported spindle being more flexible (i.e. -tire "cupping"), as opposed to the old "king pin and fixed spindle" - but, again, I had rather defer to the gearheads! I like the idea of the whole front end drive mechanism being idle when disengaged, as Terry suggested - but we seem to be coming up with different descriptions of "wha-hoppens."
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Old 04-13-2007, 04:06 PM   #14
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Quote:
Originally Posted by Cracker
Ah-hah! I wonder if this has anything to do with why the late model GM 3500 4 x 4 duallies tend to cup their tires on the outside tread??? If the axle attached to the wheel is just the least little bit bent - or bends due to flexing under side loading - it could, IMHO, be the cause of the cupping. See my other post where I was questioning if anyone else had experienced this problem. I would guess that a standard spindle axle setup is far more rigid.
This could also be caused by cranking the torsion arms in order to raise the front end of the truck. Doing this and then not having the front end realigned will cause premature wear on the outer tire edges.
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