4wd auto question

[toddious]

how exactly does the 4wd auto position work on my truck? i was reading on howstuffworks.com about differentials, and it said for most all wheel drive cars, they use a differential between the front and rear to send the torque out as needed. i don't believe that thats my setup however, so what exactly happens in 4auto to send power from the rear to the front as needed? and then when in 4low, does it basically kick in some kind of locker between the front and rear diffs? thanks, todd.

 

[JackC]

2wheel hi -2 rear wheels only
4 wheel auto - there are 2 speed sensors on the transfer case. The computer compares the outputs of the sensors 50 times a second. When there is a difference it starts to apply a clutch inside the transfer case that engages the front wheel drive till the sensors indicate the speeds are equal.
The switch also engages a coupler(vacuum operated) on the front axle to provide power to the front wheels.
4 wheel low --transfer case is locked in the engaged position, and a lower gear is engaged in the transfer case. Do not use 4 wheel low on dry pavement. To engage 4 wheel low the truck has to be STOPPED AND IN NEUTRAL.
Your gas mileage will suffer in 4 wheel auto since the axles and front differential are engaged, even though the transfer case is not.
4 wheel high can be selected at any speed.
If I screwed up anything here someone please correct me.

 

[Mbrooks420]

I think only the 95's had the vacuum disconect on the front axles. The 96 may have also. The cv's are always turning. I wouldn't select 4high over 50, and never when the wheels are slipping. Take it easy on these t-cases. The Torque on Demand clutch won't take a lot of abuse before it won't lock up fully, and will start slipping.

 

[pjm]

Think the description by JackC is for the ControlTrac system. 96 was the last year you had the option of switching to 2wd. Later years made Control Trac 4wd auto mode the default with no 2wd option. You can drive highway speeds and dry pavement with 4wd auto - it's different from 4Hi. But no driving on dry pavement with 4wdLow.

But I thought Limited's came with the AWD transfer case which is different from Control Trac? AWD uses a chain driven transfer case and a viscous clutch setup and is always on...

 

[toddious]

it says "control trac" on my rear tailgate.....

 

[dman726749]

only v8's had awd

 

[BuffaloXplorer]

Within this master subject, my controltrac system has had trouble engaging the 4auto while moving. I had a rebuild done last april and worked fine until recently. Is this likely a vacuum issue? Here's the symptoms:

At times it'll engage at speed, while other times it takes a complete stop, and still at other times it takes a shut-down/restart of the engine. I've noticed that during the last snow, the 4wd light had shut off completely while still switched to 4Auto, but it still felt like it was engaged.

Ideas?

 

[Mbrooks420]

FYI All Explorer T-cases are chain driven.

 

[pjm]

Thanks for the info guys, learn something new every day on this forum.

BuffaloXplorer,
Did your rebuild include new front and rear speed sensors? If not, that's one of the first places I'd look. Your symptoms sound similar to what I had before I replaced mine. Probably want to check your vacuum disco hose and make sure it's in one piece and tightly connected. Then I think it's the control module you want to check.