please help... 4wd issues. and more

[cfd641988]

Ok so I just bought this 1999 gmc yukon loaded up for $4500. Super clean truck no rust, rot, anything. Now that i have had it for a month or so though ive run into nothing but problems with it. The "security" system in the truck keeps stopping me from starting it. Ive got the fix for that coming in the mail. Plus some just weird electrical issues. My heated seat buzzes when you turn it on and the fan blower makes all sortsa noise when its on... like the fan blades hitting something. But the issue im trying to figure out now is the 4wd. I have checked the front actuator and its working properly but i have no 4 wheel drive. Where should i go from here? Is there any good way to tell whats going on without spending tons of money that isnt needed?. I really do love the truck i just wish the issues would go away because the 350 is a darn good motor and she pulls my trailer like a dream. I just need help getting these bugs worked out.....

Any help would be greatly appreciated. Thanks so much!!! And i do plan on putting how to's and stuff once i get working on her!!!

 

[muncie21]

How did you test your actuator to know that it's good?

 

[SunlitComet]

Can I assume you use the push button switch with 2hi,4hi,4lo and led lights? If so describe what happens in detail when you push 4hi.

I have factory diagnosis info on these but my attachments are always small and are probably not readable. I am trying to find a better way to embed them but for now I usually just fax them and just go step by step online.

---------- Post added at 01:29 PM ---------- Previous post was at 01:27 PM ----------

How did you test your actuator to know that it's good?

Aplly 12 volts to the actuator to see if it extends.

 

[cfd641988]

Ok. I took the actuator out of the front axle and pushed the 4 hi and the 4 low buttons. Both times the actuator extended and retracted as it should. Other than that i have nothing. This unit also has the auto 4 wheel which does not work. Im new with these and very unfamiliar to the 4wd systems.... It seems as though the buttons are working as they should. is there a way to tell the transfer case is working. I do know that when you press 4 lo it shifts because it foes into low. Idk. Im very confused! Thanks for your inpuut!

 

[cfd641988]

anyone?

 

[scottg918514]

transfer case. Still need that to be working to get 4wd to work. If actuator working, then I'd check that. When you put it in 4 LO do you hear a noticeable "clunk"? BTW how do you know the 4wd isn't working?

 

[longstand]

transfer case. Still need that to be working to get 4wd to work. If actuator working, then I'd check that. When you put it in 4 LO do you hear a noticeable "clunk"? BTW how do you know the 4wd isn't working?

I think if you switch to 4 wheel drive. and make a very tight TURN.and if you hear some weird squeal. then its working.

 

[SunlitComet]

Mine is the three button switch but the theory should be the same. As I recall for a front actuator to activate the t-case shift motor shifts the t-case therefore activating the front actuator thru a switch in the transfer case that responds to it being shifted. After the front actuator is engaged there should be another switch int the front axle to reply back that the system is engaged. Under your details if the Transfer Case Control Module does not see that response the switch light will continue to flash. Since your transfer case do shift to low check again on your status lights and report back. If you drive on dry payment with 4 lo and you drivetrain does not bind up while driving either something is wrong with the shift mechanism in the front axle or possibly you t-case chain or sprocket is damaged. Again what happens with that light?

 

[cfd641988]

The indicator light on the dash just switches over as normal in all modes(4hi,low, and automatic).... When turrning in tight corners on dry pavment the truck kinda jumps . (the front end is engaging). I found it wasnt working when i was trying to back up a small muddy hill and i started spinning and so i put it and four wheel drive. And it made no difference... No tire spin any gears? So how can i test the tranfer case control module, that shit mechanism? And there is a clunk when you put in 4 lo.... plus it seems to "lunge" a little bit. But still no output from the front tires.

 

[SunlitComet]

A few ideas. if it lunges under 4lo then the 4lo shift is complete. if the selected shift status light stays on then the front axle seems to lock from left to right and work. The same could be said of other selections. The front left axle I believe is always has a direct connection the the front driveshaft thru the differential. When the front actuator engages it locks locks the right front axle to the differential. the front drive shaft is locked the the rest of the system in the t-case.


I quick way to norrow the cause is get it to a shop put it in the air with some one inside. Put tranny into manual first gear. Put t-case in to 2hi verify rear wheel movement. In 4hi verify all 4 wheel at same speed and again in 4 low but tires should be slower in the same transmission gear and same engine rpm speed as 4 hi. if when engaged and tranny in park you can turn one front wheel and the other spins oppisite direction with front driveshaft still then front axle works correctly. If in any 4x4 setting rear wheels move but no movement on front driveshaft then the t-case is at fualt by either a broken locking mechanism, sprocket shifting fork or chain.

I can fax you all that i have on the system which is about 2 dozen pages just keep in mind that mine does not have 4wauto however the all the hardware should be the same should be the same internally. I think you will benefit from it.

Let me know.

---------- Post added at 03:28 PM ---------- Previous post was at 03:25 PM ----------

BTW when you said no wheel spin in any gear did you mean no high speed spin on any one wheel or no wheel movement at all and in what t-case selection?