Mechanics

4 WHEEL DRIVE PROBLEM - FRONT AXLE NOT ENGAG

1994 GMC Yukon

Transmission problem
1994 GMC Yukon V8 Four Wheel Drive Automatic 150000 miles

I have no lights coming on indicating that 4H or 4L are engaged. I pulled actuator. Shifted w/ key on. Actuator worked! Shifted back to 2H actuator popped backed in - it worked! What else could be the problem? Could actuator just be old and weak? How come the lights on the floor shifter don't come on? Could this have something to do with it? Why would actuator work but no lights? More importantly. How come I can't get my front axle engaged for 4 wheel drive? Thanks for your help!
Avatar
Bigspan
December 19, 2008.



These are thermal actuated and have a two pin connector. When they get cold they don't like to work. You put in a solenoid type napa pt #fwd32 and get the 5 pin harness for it too.

Racefan966
Dec 20, 2008.
I was out working on it today, It is 16 deg in ny. We took the actuator off again. We tried it while it was hanging from the wire harness. 4H popped the actuator out. Put in 2H and the actuator popped in. It seems to work fine. I even put pressure on it and put it in 4H and it pushed my hand. When we activate the actuator it sounds almost motorized.
My point is. The actuator appears to work fine. Question: Can an actuator be old and not strong enough to apply enough pressure to lock the axles in?

While working on it today (In the snow).I checked all wire connections in and around actuator and transfer case and they all seemed fine(No corrosion)
I checked if transfer case worked by putting in 4H and the front driveshaft did in fact turn!

So. In closing. My problem seems to be. Still. Front axles not locking in 4H and front axle light on floor board shifter still does not light up when in 4H.

I am at the end of my rope with this thing. Surely someone can help me figure it out. Thanks for your time

Tiny
Bigspan
Dec 20, 2008.
You need to replace it I sell so many of these things it isn't funny. You did look in the hole to see that nothing was broken inside right. The two wire ones are thermal and the metal around it is cold so it isn't going out all the way this is why it is not engaging. It is -2 here in Idaho so you have it warm LOL.

Racefan966
Dec 20, 2008.
Ok. Now.I took your advice.I replaced the actuator. Sealed the threads and filled with gear oil. I still have no 4 wheel drive. The light on the floor shifter does not light up on the front axle. I replaced bulb there. I checked new actuator prior to installation. It worked fine. From what I can tell. Inside the housing of differential nothing is broken. 4 wheel low works on rear axle thats is. Front axle in both 4L and 4H is definitely not engaged. When I punch it in the snow only the rear tires are spinning. What would suggest at this point. Oh.I really do appreciate the time you are spending with me on this situation. Unfortunately I don't have alot of money so I am trying to make this repair myself. It is adding up already with the actuator purchase, however, I know I wont need one of them at this point. Thanks for the gratitude you gave me! I now can appreciate the 16 deg. I have as compared to the neg. Temps. LOL.

Thanks again for your time.

Tiny
Bigspan
Dec 21, 2008.
Wow that usually fixes them. Now do you know if the front drive line is engaged or not? There could be a problem with the shift shaft or the shift fork but that would not be very cheap to fix. That actuator is what turns the light on by closing the switch to indicate that you are in 4x4. I wonder if they are not engaging far enough to lock the front axle. Now this is going to sound really crazy to ask but is the A/C heater fuse good? It sounds nuts but this is the 4x4 fuse too. Have you checked the transfer case switch yet?
Ok the t-case switch is on the left top side of t-case near the shifter area. You will need a test light for this ok. Connect the test light to ground and probe the brown wire (with key on engine off) your test light should light up. If it don't light you need to check the fuse or fix that wire as it is broken or shorted. If it does light up then you need to probe the light blue wire and put it into 4x4 again key on engine off your test light should light up if not replace the t-case switch. If it does light up then get back to me and we go further to check the 4x4 relay ok. Thanks and let me know how it goes.

Racefan966
Dec 21, 2008.
Thanks for the reply.I assume the axle is engaged.I looked underneath while my son moved the vehicle slowly and the front driveshaft was turning. We pulled every fuse and visually inspected them. All good. A/C and heater work fine. I have not checked the transfer case switch.I assumed if the front driveshaft was turning it was providing power to the front differential and it was working. Am I wrong for assuming this? This may seem like a stupid question however I have to ask. When I punch it in the snow. The front tire(s) should spin like the rear is that correct? Is the driveline considered engaged if the front driveshaft is turning while in 4 wheel drive? Another note. We did try to shim the actuator thinking it was not pushing far enough to engage the axles however the actuator bottomed out in the closed (2H) position before the threads would contact. The shim we used was 3/4" thick.
Thanks again

Tiny
Bigspan
Dec 22, 2008.
DO NOT SHIM as this can do damage and if you shim there is only one way to shim and that would make it not be able to engage this is why the actuator extends when you put in 4x4. Now never assume anything as vehicles can act different then you think it should. Now if you jack up the front end and have the 4x4 button pushed and turn the wheels by hand the does the front drive line spin? If so then your transfer case may not be locking in. I would check the transfer case switch as I have instructed and if all that checks out ok. Then you need to check the linkage for proper adjustment so one step at a time here. Let me what you find.

Racefan966
Dec 22, 2008.
Thanks for the good point. Fortunately the actuator would not go in with the shim! I am going to jack up the front end now and will get back to you. Thanks again

Tiny
Bigspan
Dec 22, 2008.
Thanks for the good point. Fortunately the actuator would not go in with the shim! I am going to jack up the front end now and will get back to you. Thanks again[/quote: e099a9dec4]

Ok. Here we go. We jacked up the front end w/ both tires off the ground. In 2H tires spun freely. In 4H tires still turned but a bit sluggishly at first then spun freely again. Driveshaft does not spin when we turn tires. Does that mean transfer case is not locking in? When we move the vehicle slowly and I look underneath and the shifter is in 4H position the driveshaft does turn. However it is not turning while we have it on the jack in 4H. What should be our next step? I am going out now to use the test light on the transfer case. Thanks. Will check back later

Ok.I am back before you are so I will add to my last comment.

We just went out and checked the transfer case switch as you suggested. I found no power at that location as well as far as I could trace it into the transmission. Both wires were dead in both 4H and 2H. I hope this is a big discovery in terms of the problem at hand. Can you tell me where the power source is for this switch. Can I jump a connection over to the same hot wire as the actuator? Thanks again for your patience in this matter. If this finally works out I will make it worth your time the best I can.

Tiny
Bigspan
Dec 22, 2008.
Ok so we have determined that the t-case is engaging this is good this means we need to move to having no power as it should have. You have checked the 25 amp fuse for the 4x4 in the fuse block correct I beleive you said you did. So now we need to figure out why there is no power to that brown wire at the t-case switch connector.
Now there is a convenience center located under the the left side of the instrument panel it has a pink and white wire going into it and a brown wire coming out of it. Yes the brown wire goes to the t-case switch. The pink and white wire is the power to the convience center with the test light connected to a good ground you need to probe this wire and turn key on engine off and see if it lights up. If this pink and white wire has no power then the fuse that it leads to is no good.
Now if all this is ok then you need to put the truck in 4wd and attach the test light to a good ground and probe the light blue wire at the t-case switch and turn key on engine off it should light up if not then t-case switch is bad. The t-case connector must be hooked to the switch as you do this test.
As for the fused you need to check they are location 213 to better explain you have relays on the bottom of it right now the third row up and the from left to right the first three fuses are you 4x4 and rear defroster fuses if equiped if need be use a multi meter set on ohms and check for continuity. Get back to me as to what you find ok.

Racefan966
Dec 22, 2008.
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