4wd Again/Still

[JoulesWinfield]

Im still trying to figure out exactly what is going on with my 4wd.

Can someone tell me if you can engage 4wd when the engine is not running (ignition on of course)?
Can you hear the motor on the transfer when you hit the 4low button when the engine is not running?

Thanks

[laxman21]

Originally Posted by JoulesWinfield

Im still trying to figure out exactly what is going on with my 4wd.

Can someone tell me if you can engage 4wd when the engine is not running (ignition on of course)?
Can you hear the motor on the transfer when you hit the 4low button when the engine is not running?

Thanks

Yes. You can hear the motors work with the ignition turned to the on position.

[JoulesWinfield]

Originally Posted by laxman21

Yes. You can hear the motors work with the ignition turned to the on position.

Thats what I thought. I dont hear anything at all from under the truck .

I get no vacuum up front and I dont hear the motor . Anybody know if the vacuum switch in the t-case is in the sequence before the motor or after?

Its got to be one of the two that is bad. I just dont want to drop the case without a replacement part in hand.

[blazes9395]

You can engage the transfer case with the engine off, but not the front differential, as that needs vaccuum from the engine, and it has to be running. The vaccuum switch located on the transfer case is switched on when the transfer case engages. The actual movement of gearing inside the case is what controls the switch. If the transfer case is not going into 4hi, the switch will not be contacted and hence not switched to send vaccuum to lock the front diff.

[JoulesWinfield]

Originally Posted by blazes9395

You can engage the transfer case with the engine off, but not the front differential, as that needs vaccuum from the engine, and it has to be running. The vaccuum switch located on the transfer case is switched on when the transfer case engages. The actual movement of gearing inside the case is what controls the switch. If the transfer case is not going into 4hi, the switch will not be contacted and hence not switched to send vaccuum to lock the front diff.

Thanks for the reply. I found after some searching on the internet that it is a ball actuated switch (valve). So it would seem that my problem is in fact the motor.

When I pull the motor will I have to refil the t-case? I know for sure if I have to pull the yoke for the front drive shaft I do. How do you pull the yoke?

[blazes9395]

You won't loose oil when you pull the encoder motor out. I dont remember if you actualy have to pull the yoke out to get to the encoder motor. To pull the yoke you need a puller, but I dont remember if its necessary to pull it or not.

[JoulesWinfield]

Originally Posted by blazes9395

You won't loose oil when you pull the encoder motor out. I dont remember if you actualy have to pull the yoke out to get to the encoder motor. To pull the yoke you need a puller, but I dont remember if its necessary to pull it or not.

Im not sure if I have to pull the yoke or not. I was reading on another site where some people had to pull the yoke to get the motor out.
I guess I will have to try and find out which models or circumstances warrant pulling the yoke.

Thanks for the help.

[muddog321]

Remember that encoder motor is ONLY for 4Lo. Need the front axle coupler to engage first and if this is pre 99 you have a vac switch on top of the transfer case to control it - check the lines first. 99 up have an electric solenoid on the firewall to activaye/turn on the vac to the actuator.

[JoulesWinfield]

Originally Posted by muddog321

Remember that encoder motor is ONLY for 4Lo. Need the front axle coupler to engage first and if this is pre 99 you have a vac switch on top of the transfer case to control it - check the lines first. 99 up have an electric solenoid on the firewall to activate/turn on the vac to the actuator.

I appreciate the reply, but I think you are wrong. The GM description says that the front drive shaft is always coupled. It also says that the front diff actuator only couples the right shaft to the left. Based on that logic you always have torque delivered to the front left as well as the rear (right rear).

From the real description the encoder moter engages first, the vacuum switch on the t-case is a ball actuated valve that is mechanically driven by the inner mechanics of the t-case. This switch then delivers vacuum to the front diff actuator. In turn when the line has been evacuated the switch on the right inner wheel wheel trips and tells the tccm that the vehicle is in 4wd.

Do me a favor, go out to your 4wd and turn the ignition on but dont start it. Then hit 4 hi. If you hear something move, its electrical.

I dont know how GM has gotten away with this incorrect information for a 10 year production run, but alas, they have. Maybe it was New Venture that duped all of the engineers that decided to buy their transfer case.

[laxman21]

Originally Posted by JoulesWinfield

In turn when the line has been evacuated the switch on the right inner wheel wheel trips and tells the tccm that the vehicle is in 4wd.

Do me a favor, go out to your 4wd and turn the ignition on but dont start it. Then hit 4 hi. If you hear something move, its electrical.

The first part is wrong. There are no electrical lines from the from actuator and my truck said I was 4x4 when the switch on top of the t-case was bad and I got no vacuum.




It's electrical for sure. If you take the switch off and switch the case to 4x4 you can feel the bar/rod that moves to open and close the switch.

[JoulesWinfield]

Originally Posted by laxman21

The first part is wrong. There are no electrical lines from the from actuator and my truck said I was 4x4 when the switch on top of the t-case was bad and I got no vacuum.

It's electrical for sure. If you take the switch off and switch the case to 4x4 you can feel the bar/rod that moves to open and close the switch.

Im having a little trouble understanding what you are saying.
Regarding your first statement are you saying that the switch T'd off of the vacuum line to the diff actuator is not an electrical switch? And that the T-case vacuum switch said you were in 4wd while ther was no vacuum to the diff actuator?

Your second statement; are you saying that the T-case vacuum switch is electrical because with the switch removed you can feel the mechanical operator moving that should switch the Tcase vacuum switch?

Where would the electrical connection be on the T case vacuum switch?
Details Here

[laxman21]

Originally Posted by JoulesWinfield

Im having a little trouble understanding what you are saying.
Regarding your first statement are you saying that the switch T'd off of the vacuum line to the diff actuator is not an electrical switch? And that the T-case vacuum switch said you were in 4wd while ther was no vacuum to the diff actuator?

OK. The vacuum switch on the transfer case isn't electrical.


The motor inside the case is. The motor moves a rod that opens the ball valve on the switch to let the vacuum up to the front actuator.

Yes, it said I was in 4x4 when there was no vacuum to the front actuator.

Originally Posted by JoulesWinfield

Your second statement; are you saying that the T-case vacuum switch is electrical because with the switch removed you can feel the mechanical operator moving that should switch the Tcase vacuum switch?

Where would the electrical connection be on the T case vacuum switch?
Details Here

The motor in the case is electrical that opens the vacuum switch.

The picture is the switch. See the ball at the bottom? That is what the motor slides a rod across to open. It pushes it up to open it.

There is no electrical connection to the switch, just to the transfer case motor that is used to open the switch.


Do you have a push button 4x4? What year? How many buttons?

[JoulesWinfield]

laxman21, we are in total agreement. I was just having trouble understanding what you wrote before.

As for my truck it is a 1995 Blazer it only has three buttons. My op was short because I have several other post about my troubles I just wanted a little more information.

Thanks for the help.

I still thought you had to have the switch on the front diff, the vacuum switch on the inner fender and the encoder position before the 4wd light went on solid. If thats not the case I wonder what switches do what.

[laxman21]

Originally Posted by JoulesWinfield

laxman21, we are in total agreement. I was just having trouble understanding what you wrote before.

As for my truck it is a 1995 Blazer it only has three buttons. My op was short because I have several other post about my troubles I just wanted a little more information.

Thanks for the help.

I still thought you had to have the switch on the front diff, the vacuum switch on the inner fender and the encoder position before the 4wd light went on solid. If thats not the case I wonder what switches do what.

I only have one button with the top for 4 high and the bottom for 4 low, like a seesaw switch.

I dont know about yours, but that's the way it happened with mine last winter.


The front actuator pulls a wire that engages the front diff. Can't remember if there is any electrical connections comming out of there.

[BlazerLT]

Sounds like the encoder motor is seized.