4x4 Not Engaging

[RedLegRider]

Posted this over on the GM Tech forum. Maybe someone has an idea or a fix?

 

 

My truck is a '93 Silverado 4x4 with auto trans. This is the first 4x4 I have owned that didn't have a straight axle where I had to manually lock the hubs in.

Last weekend I was out in the desert and needed 4WD. After shifting into 4-high and waiting, the front drive indicator did NOT light up. Shifting into 4-low it didn't light up either. I gave them each a good minute after shifting in. Transfer case shifter goes in smooth and feels rock solid. I know the front wheels were not engaging because I was some what high centered and they weren't turning after shifting into 4WD and giving it throttle.

I have gone trough my Chilton manual but nothing in there on troubelshooting 4WD.

I checked fuse box thinking it may engage electrically?... I found one 25 amp fuse that says 4WD...checked continuity of the fuse and is good.

I also got under the truck and found the wires that leads up to the shifter and seperated the quick disconnect and plugged back together thinking this may have not been making good contact. Still nothing. I have not pulled the 4WD shifter cover yet.

I'm stuck on what to troubleshoot for next and would appreciate any ideas.

Thanks... Jon

[Matt_]

My memory may be faulty here... but for the 1993 isn't the front axle actuator vacuum controlled?

 

I faintly remember having a similar issue on an early 90s GM SUV and the issue was a cracked air line going to the front actuator.

 

Not 100% sure but its worth a look... make sure all the wires or hoses coming off the front diff are connected and in good shape.

[RedLegRider]

My memory may be faulty here... but for the 1993 isn't the front axle actuator vacuum controlled?

 

I faintly remember having a similar issue on an early 90s GM SUV and the issue was a cracked air line going to the front actuator.

 

Not 100% sure but its worth a look... make sure all the wires or hoses coming off the front diff are connected and in good shape.

 

 

 

Thanks, I appreciate any help.

Just checked and acuator is electrical. Checked both waterproof connectors and they are okay, no corrosion and no broken wires. Four wires in a cluster running up over the top of the tranny housing and will look to see how they run from there. Curious if there isn't some kind of switch in the floor shifter that makes the electrical connection...kind of like an ignition switch. I'll pull the cover off and check that too.

Electrical trouble shooting is my weak point.

[Matt_]

Check to see if you're getting 12v at the actuator. You can use a test light but i prefer a DVOM since a test light will go on with any voltage... you want to make sure that you have a constant 12 there.

[Chris]

your main thing is continuity

[RedLegRider]

Check to see if you're getting 12v at the actuator. You can use a test light but i prefer a DVOM since a test light will go on with any voltage... you want to make sure that you have a constant 12 there.

 

 

 

 

With ignition on... 12.2 volts at both connections with the shifter engaged. Now I'm beginning to think it may be the actuator itself.

[Matt_]

Check to see if you're getting 12v at the actuator. You can use a test light but i prefer a DVOM since a test light will go on with any voltage... you want to make sure that you have a constant 12 there.

 

 

 

 

With ignition on... 12.2 volts at both connections with the shifter engaged. Now I'm beginning to think it may be the actuator itself.

 

 

I'd consider that a good thing

 

I'd rather replace a $50 actuator that takes a few minutes to change out than troubleshoot an electrical circuit (i hate electrical circuits too... but will do what needs to be done to fix something).

 

You can try jumping 12V to the actuator to see if it engages just to be sure.

[RedLegRider]

Check to see if you're getting 12v at the actuator. You can use a test light but i prefer a DVOM since a test light will go on with any voltage... you want to make sure that you have a constant 12 there.

 

 

 

 

With ignition on... 12.2 volts at both connections with the shifter engaged. Now I'm beginning to think it may be the actuator itself.

 

 

I'd consider that a good thing

 

I'd rather replace a $50 actuator that takes a few minutes to change out than troubleshoot an electrical circuit (i hate electrical circuits too... but will do what needs to be done to fix something).

 

You can try jumping 12V to the actuator to see if it engages just to be sure.

 

 

 

 

 

Yeah, it is a good thing when you mention that.

 

Where the wires run into the housing, it resembles a giant spark plug. Looks to be threaded and just unscrews from the housing like a temp sending unit. A ten inch left handed adjustable wrench and a big hammer should get it out....

Of course my luck would be to replace the actuator and the problem is still there.

 

I have had very good luck with this truck. Had it almost fourteen years now and 120k miles and replaced a radiator, water pump and had the main drive line rebuilt... that's it. It has never left me stranded.

[RedLegRider]

Check to see if you're getting 12v at the actuator. You can use a test light but i prefer a DVOM since a test light will go on with any voltage... you want to make sure that you have a constant 12 there.

 

 

 

 

With ignition on... 12.2 volts at both connections with the shifter engaged. Now I'm beginning to think it may be the actuator itself.

 

 

I'd consider that a good thing

 

I'd rather replace a $50 actuator that takes a few minutes to change out than troubleshoot an electrical circuit (i hate electrical circuits too... but will do what needs to be done to fix something).

 

You can try jumping 12V to the actuator to see if it engages just to be sure.

 

 

 

 

 

 

Matt, thanks again for your help. It is greatly appreciated..... Jon

[shadetree25]

My 97 had the same problem. replaced the actuator and cured the problem. On the older models the actuator had a rubber tube filled with fluid. An electric heating element heated the fluid which expanded the plunger to engage the front axle. On the newer ones there is an electric motor that moves to engage it. They even had a recall in the late 90's for them.

[gleno97]

My 97 had the same problem. replaced the actuator and cured the problem. On the older models the actuator had a rubber tube filled with fluid. An electric heating element heated the fluid which expanded the plunger to engage the front axle. On the newer ones there is an electric motor that moves to engage it. They even had a recall in the late 90's for them.

 

My 95 suburban actuator went out while trying to get off of a frozen lake after a few days of ice fishing. It worked when we drove out on the ice but two days later when it was time to leave...it didn't work. Managed to rock the burb a few times when we got stuck and was very happy to be back on shore. Actuator was a cheap/easy fix and was back in 4X4 for the following weekends ice fishing trip.