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04-13-2007, 08:28 AM
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#1
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Rivet Master
Currently Looking...
Pittsfield
, Maine
Join Date: Oct 2003
Posts: 1,108
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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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Cracker
2003 GMC 3500 D/A, CC, LB, 4x4 and 2000 Airstream Excella 30. WBCCI 7074
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04-13-2007, 08:46 AM
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#2
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Rivet Master
2009 27' FB Flying Cloud
1982 31' International
1991 35' Airstream 350
Jay
, Oklahoma
Join Date: Oct 2006
Posts: 1,706
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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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Jeff & Cindy
'09 27FB Flying Cloud;'82 31 International
'91 350 LE MH; '21 Interstate 24GT
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04-13-2007, 09:31 AM
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#3
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Retired.
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, At Large
Join Date: Jun 2003
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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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Meddle not in the affairs of dragons, for you are crunchy, and taste good with ketchup.
Terry
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04-13-2007, 09:45 AM
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#4
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Rivet Master
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Pittsfield
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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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Cracker
2003 GMC 3500 D/A, CC, LB, 4x4 and 2000 Airstream Excella 30. WBCCI 7074
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04-13-2007, 09:53 AM
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#5
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Retired.
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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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Meddle not in the affairs of dragons, for you are crunchy, and taste good with ketchup.
Terry
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04-13-2007, 10:10 AM
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#6
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Rivet Master
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Pittsfield
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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.
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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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Cracker
2003 GMC 3500 D/A, CC, LB, 4x4 and 2000 Airstream Excella 30. WBCCI 7074
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04-13-2007, 11:00 AM
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#7
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More than one rivet loose
Currently Looking...
Los Alamos
, New Mexico
Join Date: Feb 2006
Posts: 3,756
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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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Michelle TAC MT-0
Sarah, Snowball
Looking for a 1962 Flying Cloud
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04-13-2007, 11:02 AM
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#8
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More than one rivet loose
Currently Looking...
Los Alamos
, New Mexico
Join Date: Feb 2006
Posts: 3,756
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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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Michelle TAC MT-0
Sarah, Snowball
Looking for a 1962 Flying Cloud
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04-13-2007, 11:28 AM
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#9
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Retired.
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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.
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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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Meddle not in the affairs of dragons, for you are crunchy, and taste good with ketchup.
Terry
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04-13-2007, 11:30 AM
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#10
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Retired.
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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.
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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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Meddle not in the affairs of dragons, for you are crunchy, and taste good with ketchup.
Terry
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04-13-2007, 11:45 AM
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#11
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_
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, .
Join Date: Dec 2004
Posts: 8,812
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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
2air'
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all of the true things that i am about to tell you are shameless lies. l.b.j.
we are here on earth to fart around. don't let anybody tell you any different. k.v.
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04-13-2007, 12:33 PM
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#12
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Aluminut
2004 25' Safari
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, Illinois
Join Date: Feb 2003
Posts: 10,477
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All I know is that the MPG still blows either way towing.
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04-13-2007, 02:34 PM
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#13
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Rivet Master
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Pittsfield
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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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Cracker
2003 GMC 3500 D/A, CC, LB, 4x4 and 2000 Airstream Excella 30. WBCCI 7074
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04-13-2007, 03:06 PM
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#14
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Rivet Master
Elgin
, Texas
Join Date: Jan 2004
Posts: 800
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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.
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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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04-13-2007, 03:21 PM
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#15
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Rivet Master
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Pittsfield
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Quote:
Originally Posted by coriolis1
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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Nope - I haven't done that and, for the record, the truck was just recently realigned by a very reputable commercial truck shop. They're the ones who pointed out that the "cupping" problem is common with the 3500 4 x 4 trucks.
__________________
Cracker
2003 GMC 3500 D/A, CC, LB, 4x4 and 2000 Airstream Excella 30. WBCCI 7074
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04-13-2007, 08:13 PM
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#16
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4 Rivet Member
1964 17' Bambi II
Santa Cruz
, California
Join Date: Feb 2006
Posts: 319
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Some Basics...
The TRANSFER CASE behind the transmission is what engages/dis-engages the front drive shaft that supplies power to the front axle and also changes the gear ratio, i.e. 2WD,4WD-HI RANGE,4WD-LO RANGE.
The DIFFERENTIALS, front or rear,allow the axle shafts to turn at different speeds to allow the wheels to turn at different speeds while cornering. Example; when making a left turn, the right side wheels must be able to turn faster than the left side wheels.
The LOCKING HUBS, whether AUTOMATIC or MANUAL allow the wheels to rotate freely from the axles they are attached to, reducing drag and wear on the front axle.
BTW, preloading (cranking up) the torsion bars is a BAD idea, it prevents the suspension from moving through out it's full range of motion, resulting in a harsher ride. There are other ways to lift a vehicle.
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Mark
1964 17' Bambi II
2005 Dodge 2500 PowerWagon -5.7 Hemi
WBCCI #4207
AIR #11485
"you don't need a weatherman to know which way the wind blows" ~bob dylan
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04-13-2007, 09:08 PM
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#17
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More than one rivet loose
Currently Looking...
Los Alamos
, New Mexico
Join Date: Feb 2006
Posts: 3,756
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Duh! Forgot about that one. The little switch makes me forget about all te workings.
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Michelle TAC MT-0
Sarah, Snowball
Looking for a 1962 Flying Cloud
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04-13-2007, 10:40 PM
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#18
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Rivet Master
2005 25' Safari
Salem
, Oregon
Join Date: Mar 2006
Posts: 8,376
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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.
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Hi, Yes you do have Auto and Manual settings on the hubs, In Auto mode the hubs are vacuum controlled to engage and dissengage them. This also works in conjunction with the transfer case as you shift in and out of 4X4 modes engages and dissengages the front differential at the same time. So, out of 4X4 with hubs on Auto, Your front drive shaft has no power to it and the front wheels are free wheeling.
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Bob 2005 Safari 25-B
"Le Petit Chateau Argent" Small Silver Castle
2000 Navigator / 2014 F-150 Eco-Boost / Equal-i-zer / P-3
YAMAHA 2400 / AIR #12144
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04-13-2007, 10:56 PM
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#19
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Rivet Master
2005 25' Safari
Salem
, Oregon
Join Date: Mar 2006
Posts: 8,376
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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.
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Hi, whether you have four wheel drive or all wheel drive you have a front and rear differential; And in some all wheel drive vehicles there is a third differential in the transfer case. As front and rear differentials have spider gears to allow one axle to turn at a different rate than the opposite side, the third differential in the transfer case also has spider gears to allow one drive shaft to turn at a different rate than the other one.
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Bob 2005 Safari 25-B
"Le Petit Chateau Argent" Small Silver Castle
2000 Navigator / 2014 F-150 Eco-Boost / Equal-i-zer / P-3
YAMAHA 2400 / AIR #12144
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04-13-2007, 11:55 PM
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#20
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4 Rivet Member
Currently Looking...
Yakima
, Washington
Join Date: Sep 2006
Posts: 381
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You guys sure made this MORE complicated than it need be. Ford 3/4 , 1 ton, etc. have either auto lock or manual get out in the mud hubs that work the same way as they did 40 years ago. A transfer case the engages the from diveshaft that goes to the front differential that drives the axels. GM has a system more akin to a front wheet drive car. They are not as truck like as the Ford system. But they have more moveing parts and boots to replace over the years. Half tons are different. ...But I am only talking about trucks..not half tons. Ford has the same system of transfer case,,,front differential and manual hubs availible as they have since they came out with 4X4 in the 50's. AND ITS THE STRONGEST BY THE WAY....BUT ITS OLD SCHOOL. The auto lock hubs tend to fail if dirty....manual never fail.....but you have to get dirty. Its up to you.
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