juhu
- Thread starter frank
- Start date
1999 gmc 4wd pick up has a rumbling noise in the front drivers side@ 40-50 MPH
SO FAR I HAVE CHANGED FRONT WHEEL BEARING,UPPER AND LOWER BALL JOINTS
ALL 4 TIRES BALANCED U JOINT REPLACED IN DRIVE SHAFT ALSO HAD DRIVE SHAFT
BALANCED.
SO FAR I HAVE CHANGED FRONT WHEEL BEARING,UPPER AND LOWER BALL JOINTS
ALL 4 TIRES BALANCED U JOINT REPLACED IN DRIVE SHAFT ALSO HAD DRIVE SHAFT
BALANCED.
Molson02536
New member
In the full size, the front actuator is electric, not vacuum.
When in 4wd mode, a switch on top of the transfer case conducts 12 volts out to the actuator. Wire #50 (brown) is the 12v feed, and it conducts to the light blue wire (#900) to the actuator.
When shifted out of 4wd, the switch opens up and no voltage goes to the actuator.
Check voltage at the connector for the front actuator (at the front differential - it looks like a large bullet that threads into the front diff.) If it has 12 volts, the actuator is the problem. If it does not have 12 volts, check the transfer case switch and the power feed to the transfer case.
I'll assume it is the actuator, if the plug to the actuator is getting 12 volts when in 4wd.
The way this actuator works, is it is a sealed chamber that gets heated by voltage. When it heats, the pin in the end swells and pushes a shift fork in the front differential. The shift fork engages a spline on the passenger side of the differential, and boom! you have 4WD.
GM offered an upgrade to this actuator that is a motor instead of a heated device. However, it requires a small harness addition, a spacer, and a new actuator. It is about a $150 to $200 option.
Good luck. The actuator is usually the problem 90% of time but recheck all of the wire harness just to maker sure there is no short before replacing any parts. The actuator may not be fully engaged or disengaged and the fork to the spline may be what is causing the grinding.
88-UP C/K ACTUATOR UPGRADE
VEHICLE SERVICED: 1994 CHEVROLET FULL SIZE
PURPOSE: IMPROVE AXLE CONNECT ENGAGEMENT TIME AND
COMPONENT RELIABILITY.
SYMPTOMS: NO FRONT DRIVE AXLE ENGAGEMENT WHEN SHIFTED
INTO 4X4.
Obtain the following GM part numbers:
(1) 26060073 Actuator
(1) 88959465 Harness/Spacer Kit
When in 4wd mode, a switch on top of the transfer case conducts 12 volts out to the actuator. Wire #50 (brown) is the 12v feed, and it conducts to the light blue wire (#900) to the actuator.
When shifted out of 4wd, the switch opens up and no voltage goes to the actuator.
Check voltage at the connector for the front actuator (at the front differential - it looks like a large bullet that threads into the front diff.) If it has 12 volts, the actuator is the problem. If it does not have 12 volts, check the transfer case switch and the power feed to the transfer case.
I'll assume it is the actuator, if the plug to the actuator is getting 12 volts when in 4wd.
The way this actuator works, is it is a sealed chamber that gets heated by voltage. When it heats, the pin in the end swells and pushes a shift fork in the front differential. The shift fork engages a spline on the passenger side of the differential, and boom! you have 4WD.
GM offered an upgrade to this actuator that is a motor instead of a heated device. However, it requires a small harness addition, a spacer, and a new actuator. It is about a $150 to $200 option.
Good luck. The actuator is usually the problem 90% of time but recheck all of the wire harness just to maker sure there is no short before replacing any parts. The actuator may not be fully engaged or disengaged and the fork to the spline may be what is causing the grinding.
88-UP C/K ACTUATOR UPGRADE
VEHICLE SERVICED: 1994 CHEVROLET FULL SIZE
PURPOSE: IMPROVE AXLE CONNECT ENGAGEMENT TIME AND
COMPONENT RELIABILITY.
SYMPTOMS: NO FRONT DRIVE AXLE ENGAGEMENT WHEN SHIFTED
INTO 4X4.
Obtain the following GM part numbers:
(1) 26060073 Actuator
(1) 88959465 Harness/Spacer Kit
Molson02536
New member
Nope, you should not be getting any Voltage to the actuator at the front differential in the 2wd mode. Look for a short at the switch on top of the transfer case or replace.
You were right, it was a broken wire on top of the actuator. Had a hard time to find it at first. I hauled the actuator right out of the housing, plugged the wires in and moved the wires at the connector and that's where a wire was broke.
Thank you very much for your help! Greatly appreciated!
Thank you very much for your help! Greatly appreciated!
Molson02536
New member
Welcome friend and keep me posted. Always like good news or any news at that. Good luck and hope everything is good. 