Help with my suburban please
 

I've never had a big 4wd before. I understand a little about what happens to engage the front drive system, but obviously not enough.

Something is wrong, or bad, or wearing out, or about to let go in the drivetrain system of my '96 GMC Suburban. I don't know what it is...

I can hear and feel a vibration, I really think two parts that should be coupled or uncoupled are grinding on each other. The first time I heard this noise, I took off in the rain and the rear wheel started spinning. Then this awful grinding noise. It sounded like it was coming from the transmission. The sound changed pitch with wheel speed, not engine or trans speed. I got to a place where I could stop and at least give a visible inspection for something hanging down or out of wack. When I slowed to a stop, I heard a clunk and the grinding noise stopped. After driving some more, it felt like it went in and out of manual shift on the fly 4wd just fine.

Today, it happened again. Then when I came to a stop, I felt the same clunk and it stopped.


Have you guys ever heard of anything like this? I'm outta my league. Thanks.

I just sold my 94 z-71 but once I got it serviced and had the rearend fluid drained and replaced and afterwards it did just as you discribed your rear. I had a limited slip rear that was doing all kinds of crazy slipping and grabbing because their replacement gear oil didnt have the limited slip additive .... I added some and the problem went away after 100 miles.

Had 4x4 burb and the rear axle locked up. Had the fluid replaced and the rear end cleaned out and it was ok after that.

If it's in the front drive there are a few possibilities. The switch can go bad if it's electronic shift, it will do a lot of weird things. The actuator motor can also go bad, it thinks it's in the wrong position and tries to correct it. The front axle is vacuum actuated but that shouldn't be a problem here. If it fails the front axle just won't engage even though the transfer case is in 4WD. Is it electric shift or manual? Does the service 4WD light come on?

Mine is screwed up right now. It goes into 4WD ok but the light comes on after about 1/8 mile. I think the forward output shaft sensor isn't working so it thinks it's not spinning.

The 4wd is lever-operated manual shift. There is a lever on the tranny hump. It isn't coming from the rear end, I am almost certain of that.

Is your transfer case chain driven. Could need a new chain. Also do you have manual or automatic hubs ?

I don't know if the front shaft is chain driven. It very well could be, and the racket it makes sounds like it could be a slipping chain. It is a 4L60E trans, and there is no front hub locking mechanism...so I guess they're always locked, and the front running gear is always supposed to be somewhat engaged. It has IFS and half-shafts or CV shafts or whatever. Visual inspection showed no wear or damage to the boots, and there was no real visible leaks where the t-case or front ring/pinion may have dumped its juice.

I believe the sound is coming from front drive system, possibly where it mates to the tranny. That makes me, ignorant as I am, think possibly drive chain...or whatever else couples with front shaft with the tranny.

I know it isn't the infamous use of the wrong posi or g80 gov-lock gear oil or lube, it has open carriers front and rear.

The front hubs are always locked and the axles are always spinning. Like I said there is a vacuum operated mechanism in the front differential that engages the front differential to the front driveshaft. I believe the transfer case is gear driven, could be wrong. Make certain the 4WD lever is all the way to 2WD and lube the linkage. It may be hanging up part way between 2WD and 4WD.

what's it do in reverse ?

I am going to take a real good look tomorrow, pull off both front wheels and calipers/rotors, do a complete thorough inspection of everything underneath, and see what I can find.

It won't stay in 4wd right now. The lever stays in 4HI, but the light on the manual shift cover plate blinks. It is supposed to stay on, and I'm pretty sure that when it blinks, something is wrong.

This is the noise. It is in 2 hi during the clip, he is outside right now on jackstands still. I pulled the front wheels. It looks to me like I can get the noise to stop by disconnecting everything necessary to keep the ring/pinion from spinning. Can I remove the CV shafts and the driveshaft?

I just made this video...driver side forward/backward, then same on passenger side.

http://s812.photobucket.com/albums/z...nt=4wdburb.mp4

Do you know what that racket is?

Hi there Jake, I own a 1995 lifted suburban as well. I haven't had that particular problem, but I do know these trucks inside out now.

There are a couple things you can do to try and isolate the problem. First off, when you had the front of the truck jacked up and spun that hub did the other side turn the opposite direction or was it stationary? In two wheel drive each wheel should spin freely without effecting the other. On the passenger side of the front differential is an electric actuator that slides a collar over the inner and outer shaft to engage the right wheel.

I can't see what's spinning and what's stationary in the video. If your drive shaft is not turning and your other wheel is turning in the opposite direction then the coupler is engaged when it shouldn't be or it's stuck. The noise could either be from a stripped collar on the coupler or something in the front spider gears.

Just listened to your video again. What happens when you put the front in 4wd? does the actuator engage the front differential? It almost sounds like the collar is partially or is up against the splines on one side so when you spin the cv the splines are clicking against it.

Thanks for the advice. I didn't take notice as to whether the other side spun when I turned one either of the hubs. It has open carriers, no G80 locker or G86 posi units...in case that makes a difference. When the manual 4wd is placed in 4hi, the sound is gone. The 4wd indicator light blinks, but the grinding noise goes away. This makes me think that it is the actuator, like Hank initially suggested.

That is my gut feeling, after having a little more understanding of the mechanicals. I think the actuator isn't disengaging the front drive when shifted back into 2wd. Isn't there a fork in there too?
I think this is a schematic of the front drive system in my 'burb.
http://www.compnine.com/largeimg/970519TC06-060.gif

All of the part numbers are listed here:

A friend told me to pull the front driveshaft and see if that makes the noise stop. I'm feeling like it will still grind, because its the CV shafts that are making it grind. Someone else told me that I should pull the actuator and see if the noise goes away. I'm not sure what that will accomplish or prove.

If I pull the front shaft, will I lose fluid from the t-case or front diff? I am clueless, and really want to try and fix this, or at least buy myself some time to figure out how I'm going to get the $ to fix it right.

I believe it's the actuator as well. Especially if your 4wd indicator light is acting up. You could have a worn out return spring causing the collar to partially disengage and making all that noise.

First thing I would do next is Jack up the front passenger side and try and spin the tire. With the actuator in normal 2wd mode you should be able to spin the tire since the collar would be disengaging the outer axle from the inner. If the tire spins and the noise is present then you definitely have a problem with your actuator or collar retraction. Make sure when you are turning the tire that the drive shaft is not turning. If the drive shaft is turning then your actuator is engaged when it shouldn't be.

Here's a pretty good picture of the front diff I tore down. You can see the actuator fork and collar gear in this pic.

http://www.allenitllc.com/suburban/apart_2.jpg

I have the actuator off. It doesn't seem to be making its full stroke. There are guide slots in the female tube of the portion that sits inside the diff. They are an inch long, which makes me thnk that the actuator shold have an inch or travel to dis/engage 4wd. It is stuck at halfway. Is this right? The truck was in 2wd when I shut it off last. The actuator is at the "top" of its stroke and only protruding from the female tube about 1/2". the guide slots suggest that it should be coming out another 1/2" or so.


This actuator is the same one used on more or less ALL GM 4wd trucks from '97 to '06, including 1500, 2500, and 3500. Wouldn't you know that ain't a GD junkyard in town that has one. Figures.
Anyways, it seems like it is hung up, halfway in its travel. All the pictures of new ones I'm seeing online show the actuator "button" parked all the way in or in other words...completely retracted. I'm guessing that is the 2wd position, and that it actuates to engage 4wd.

With the thing off, I can look in the hole and see the end of the rod that it pushes. When I reached in there and pushed it, everything locked up...driveshaft, and the other wheel. When I let it back out, everything disengaged.

I'm tempted to remove the actuating button and its guts, then put the rest of the unit back in the diff, and see if it runs right.

I cut the "button" off, and threaded the housing back in nice and tight. Test drive says he is back in action, in 2wd. No grinding noise, in forward or reverse.

Good deal Jake, glad you got it running. You don't need 4WD very often so now at least you can drive it.

I got your Private, but could not replay Jake. It says you have exceeded your storage capacity.

Sorry I was at work. Sounds like you got it taken care of for the time being until you can get a replacement. Usually when the go bad they will not engage at all. I've run into that problem out on the trails and just pulled the actuator and I carry a socket that fits in there perfectly so when I screw in the faulty actuator it engages my 4wd for me. LOL

You can pick up the actuator at any local checker or autozone store. They tend to fail often, especially when they get submerged under water. =)

Thanks man. I was looking for an opinion about modifying my broken one....and just wound up doing it.

Mine got real wet, I think that is what fried it. I drove down a good mile of road that had 3-4" of water on the pass side, and after that day is when it started acting up.


Your advice helped me figure out what was wrong. Thanks a million.

For the time being, I'm okay. Hopefully once I get the new actuator, I'll see that nothing else got torn up while it was hung up.