Hello,

I have 2002 Z71 Suburban. Over the course of the last couple of month I'd developed a very strange intermittant problem that no one can figure out apparently. So far the truck has been to a normal mechanic, and 2 transmission/driveline shops. They have all looked at me like I escaped from a mental institution and told me there is nothing wrong with the truck at least that they can find. The problem is as follows, Every once in a while for no apparent reason the truck makes a noise like you drive over the rumble strips on the side of the highway. it can last for 5-10 seconds and then most of the time everything is normal for 200-500-1000 miles. Truck drives smooth as silk. The last time this happened last week at the end of 500 mile trip I noticed that the the engine was working harder on the highway. Transmission shifted normal, I tried butting in neutral with no change. I also noticed when I got off the highway that the steering felt slightly weird almost like the truck was in 4wd. The noise is on the front driverside wheel. And there is little or no vibration, just mostly a noise. It sounds ominious. When it first started I had the typical whomp, whomp, whomp noise of a failing hub so I kinda figured that was the problem and changed it. But the problem came back. It's very strange becasue after parking the truck for a few minuted it generally goes back to normal which is why none of the shops can replicate the problem. Right now I'm driving the truck with the ATC and 4WD fuses out because I have a feeling that the TCCM is partially engaging 4WD uncommanded. Is there anything else I should be looking at? I'm 99% sure it's not torque converter shudder, and I've be assured that ujoints are tight and all fluids look good buy both transmission shops. This is really starting to annoy me so any help would be greatly appreciated.

My plan is to drive it on my next trip (500 miles) with the fuses out. If the problem does not present itself I'm going to change the TCCM and Shift motor. If it does present it self, I'm going to drive the truck off a cliff, Or just ignore it and drive it until something breaks. At this point being able to fix it and know the truck is good to go is my primary concern. If it takes out a Tcase or a diff or something at least I can fix it. Please Help!!

 

I can't offer much. you have done some good diagnosis. You have ruled out eng, and tcc by performing a neutral run up test. This leaves driveline as the most likely source.

the fuse pulling seems like a good idea. the tccm not only engages the front prop shaft but also the engages the front axles.



which tcase...3 button or autotrac?
what driving conditions does this occur at? speed?

assume you have tried making a tcase mode change to see if the noise stops?

all the tires are the same brand and size? I have seen newer gens make rumble noises in auto 4wd if the tires have differences in circumference. tire shop installed one tire with a smaller aspect ratio. the noise is gone in 2wd

 

Thanks Tech2!

It's the autotrac, and to this point I haven't had a hit of trouble. 217,000 Tranmission replaced at 194,000. Tires are new, not aggressive Goodyear Wrangler HP and are all the same size. It usually happens at higher (thsn I like to engage 4x4 speed) like 60-70 mph. I'll know more when I take it up to the cabin this week! If it doesn't do it I'm gonna start with the shift motor and see. Other wise I've afraid I've go a drive it until it breaks situation.. I was just gonna unplug the shift motor, but this could go on for weeks before I'm sure it gone, and don't want to leave that unsealed against weather and such so the fuses at least in my mind accomplish the same thing. your thoughs? I've got both the 4wd and ATC fuses out. No problem running long distances like that right?

 

no problem to drive with the fuses out.



have someone with a full function scan tool check for dtc in the tccm before you pull the fuses ,just to see if any logic errors are set.