4 wheel "clunk"

patpro · May 14, 2006

I have a 2000 Yukon XL and the "service 4 wheel drive" light has been coming on for the last 2 weeks or so. Also, the 4 wheel/2 wheel indicator lights do not light. I was on the beach (in sand) while in 4 wheel drive yesterday and noted a heavy "clunk" coming from the drivers side front. The "service 4 wheel drive" light was on and the "clunk" was erratic, meaning not continuous but occassional. I got under the truck this morning and noted that i could jiggle the front drivers side axle which to me indicates the CV joint is in need of repair. My questions are as follows; 1. Will the bad CV joint cause the "service 4 wheel drive" light to come on? 2. does this affect the indicator lights (4 wheel high, 4 wheel low, etc?, the lights do come on occassionally but do not stay lighted. )

Thanks for any help

ChevyTech007 · May 14, 2006

I would say you have two separate problems. Sounds like you are going to need a CV joint. It would probably be easier to replace the whole axle. You need to have it scanned for codes. Most probable cause of the lights in the switch acting up and no 4X4 is the dash switch. It usually sets a code.

patpro · May 19, 2006

Well....i put in the new front drivers side axle (with new CV joints) and decided to test it in 4 wheel drive. I put it in 4 wheel high and turned the steering wheel almost to the stops, rolled the vehicle forward and backwards and heard the same "clunk". When i change back to 2 wheel high without returning the steering wheel back to straight ahead there is the same "clunk" when it shifts out of 4 wheel drive (truck even "jumps" a little like the entire 4 wheel drive powertrain was being binded). It even seemed to be having a hard time going into and out of 4 wheel hi/low.

To further muddy the water, while on the beach in sand last week, I now remember it would make the "clunk" some while driving straight ahead. It seems i may just be forcing the noise when i turn the steering wheel to the stops and rolling.

Today i checked the front differential fluid level and the transfer case fluid level and both were fine. I even climbed out of the truck and looked at the transfer case and front propellar shaft (from the transfer case to the front differential) while my son made it "clunk" as described above, but could not tell exactly where it was coming from.

There are no codes coming up except for the "check 4 wheel drive" light comes on regularly.

I have not checked the front propellar shaft for play yet nor have i tested any of the other components.

My thoughts:

1. Is it really getting into 4 wheel high/low completely or is there something that might be limiting this from happening?? If it is limiting it from being in 4 wheel drive, are the "clunks" related to the system going into and out of 4 wheel??

2. Since my "check 4 wheel drive" light now comes on regularily ( normally after 15 minutes of driving or so) should i be looking at any of the other components of the system?

Again, thanks for the previous post you made and hope this will be descriptive enough for you to help.

skills4lou · May 19, 2006

I had a Sonoma with a mysterious clunk somewhere in the front. Finally narrowed it down to a bushing for the torsion bar on the driver's side. Total price for the part was about $15, dealer diagnosis and repair was another $50 or so.

As for the 4WD lights/switch: that why I really like having a real lever on the floor. There's a LOT of people who've had to replace that switch, so I'd start there. I guess it's easier to pay for a new switch than a new t-case! One other thing to look at is the "prop shaft" as you called it. There's a splined connection that may be worn out, but you'll have to remove the shaft and disassemble it to inspect. A simple push/pull won't always show how much the splines are worn down. While you have it out you might as well put new u-joints in if the splines are still good, otherwise go buy an entire new shaft. Last time I price one it was around $180 I think.