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david, Heavy Duty Repair Mechanic
Category: Chevy
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Experience:  Certified Master Technician,Certified in diesel & gasoline engines
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99 gmc jimmy 4x4 not working changed vacuum actuator ...

Customer Question

99 gmc jimmy 4x4 not working changed vacuum actuator actuator cable. and dash switch. Still not working the lights on dash do blink and stay on. I did also unplug the vacuum lines from the switch on the firewall also and the service 4x4 light did come on. I did clear the code afterwards. transfer does engage but not the front axles. They do if vehicle is off the ground kind of. Got any other clues...
Submitted: 7 years ago.
Category: Chevy
Expert:  david replied 7 years ago.

thank you for your question hope this helps.

It's either one of 2 things.. It's either the v ac switch on the side of the transfer case, or the encoder motor...I would lean more towards the encoder motor.

there have been means owners with this same problem.

here is how i would go repairing this problem

1. Raise vehicle safely so that you have enough room to work under the drivers side. Always use jack stands or another suitable support for your vehicle.

2. Locate the encoder motor, it will be right next to the front drive shaft yoke on the transfer case. (You will notice a round plastic dust cover going sideways under the transmission)

3. Have an assistant press the 4x4 button so you can listen to see if the motor even moves or if it possibly shifts the transfer case into gear, or you may hear no sound at all, motor dead.

4. removed the front drive shaft for additional room. This thing is in there tight, little or no room to work. Remember to mark your drive shaft for proper re installation with a grease pen etc.

5. be careful so that your bearing caps don't fall off the U joints unless your gonna to replace them.

6. Use a 10mm wrench to loosen and remove the very top bolt holding in the encoder motor. Its way on top and hard to see. you should be able to remove the other two with a socket wrench. (3 in all)

7. To remove the motor pushed the encoder motor farthest away from the transfer case as possible but it still wouldn't come off, but almost. Then used a large screwdriver or pry bar and preyed it forward, VERY GENTLY. If you can remove the front yoke from the transfer case you should have no problems at all.

8. It pop's forward and out. Then have an assistant press the 4x4 button once more while your watching the gear inside the encoder motor. It was fidgeting back and forth so you knew immediately something in not right inside.

9. Remove the wiring harness with an 8mm socket and take the motor to the bench. (no sense in laying on the ground working on it)

10. Remove the torx screws that hold the case together and pried it apart, it is pretty gummed together and there are pry points. I would recommend using the pry points as the case isnt the strongest thing ever made.

11. Inside you will notice the gear coming off the motor was cracked in two but still in place, but no chance of it effectively engaging the transfer case.

graphic
Blue= Wiring Harness Connector

graphic
Blue= Torx case screws

graphic
Gear Assembly-Broken main gear

graphic
Broken Main Gear-How it is supposed to look.

i hope this helps you

Customer: replied 7 years ago.
I have checked to see if the transfer does kick in. When vehicle was off the ground and it does. Do you think this is still the problem?
Customer: replied 7 years ago.
Reply to david's Post: That is the same answer as last time and I sent in the first question that the transfer did kick in????
Customer: replied 7 years ago.
I am selling this truck I did change encoder motor no change thanks for trying

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