Mechanics

AUTOMATIC 4WD, WHERE'S ACTUATOR

1996 GMC Jimmy

Transmission problem
1996 GMC Jimmy 6 cyl Four Wheel Drive Automatic 217000 miles

My 4WD did work. I have no buttons to push, it did everything by itself. With vehicle on jack stands and in drive, rear tires turn and transfer to front diff. Shaft rotates. Front axles shafts don't turn. I can't find the actuator on the diff. Or transfer, and I didn't see anything under the battery using a mirror. The only thing I can find on the diff. Is the vent tube. The transfer has an electrical connector on the rear of the shaft but I believe this a speed sensor. The manual I have has show's an actuator on the diff, right side. I have nothing. No external cables connected to the diff. Or transfer that I can see or find. The backing plates on the front axles, brakes, have what I believe are speed sensors. Thanks
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Kaysickie
October 10, 2008.




Hi kaysickie,

Thank you for the donation.

I have some data which I hope can assist you in solving your problem.

DESCRIPTION & OPERATION
Front axle assembly on "T" Series models uses a 7 1/4" ring gear. Front axle assembly has an electric 4WD engage/disengage feature which allows shifting in or out of 4WD while vehicle is moving (under most conditions). The 4WD feature is shifted by a vacuum actuation system.


http://www.2carpros.com/forum/automotive_pictures/192750_VacumnActuating96GMC_1.jpg



The vacuum actuation system consists of a vacuum switch and vacuum actuator. Shift mechanism in transfer case triggers vacuum switch to apply engine vacuum to vacuum actuator after about a 3-second delay. The vacuum actuator, in turn, pulls on shift cable which pulls on shift fork in axle. This connects the right axle output shaft to the front axle differential. Torque is now available to front wheels.

Right side of axle assembly consists of a solid axle shaft which rides inside of a stationary axle tube. A short stub shaft with CV joint attached is bolted to right inner axle shaft flange. Left drive axle shaft consists of a flexible drive shaft using an inner tripod joint and outer CV joint. Left axle tripod joint housing is bolted to axle carrier output shaft drive flange. CV joint splined/threaded shaft on outer end of drive axle shaft slips through steering knuckle/hub assembly.


http://www.2carpros.com/forum/automotive_pictures/192750_LeftAxleShaft96GMC_1.jpg



Front axle assembly differential uses a conventional ring and pinion gear set to transmit driving force of engine to the front wheels. Ring and pinion gear set transfers driving force at a 90-degree angle from front drive shaft to drive axle shafts/CV joints.

Vacuum Actuation System Courtesy of GENERAL MOTORS CORP.

Page 1 of 1 DRIVE AXLE - FRONT -1996 GMC Jimmy 10/11/2006
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KHLow2008
Oct 11, 2008.
Sounds like the Jimmy has an AWD system. That was available as an option. It is the same system as the Bravada.
There is no front axle actuator or transfer case range selector. Inside the Borg Warner 4472 transfer case is a chain driven planetary gear set with a viscous coupler clutch to the front end. Since your front axle isn't getting power the likely problem is a failed ring gear or differential housing.

Tiny
SWilliams
Oct 18, 2008.

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