Clunk and Bump while in 4WD HI

[bdc]

I was out with the wife today slow riding on some pretty steep logging and gas well roads in my 09. Twice, on seperate occasions, while going UP a pretty good incline in 4WD HI,, I noted a clunk and felt a slight bump under my feet coming (seemingly) from the front end area. Hubs were locked in correctly before I started and I was not doing any aggressive driving. Got back on the highway after unlocking hubs and out of 4WD and no problems.

So, I was wondering, does this sound like the 4WD is not catching correctly or staying in 4WD, or about to blow up? This is my first 4WD and my first diesel, so any help (in not too technical terms) would be appreciated. Even, "get yourself to a good mechanic", may be appropriate instruction....

thanks

 

[Cucvnut]

Check the front shaft U Joints. and T case mount

 

[WARWAG]

Get yourself a good mechanic. Sometimes is better to just pay to have someone do the work for you. If you dont have the tools but want to learn then go ahead and start. A great place to learn if you have the time is to take a local college course in automotive repair. This would be a great place to take your Rig and get her back into shape while learning all about her! The class will have all of the tools on hand with a teacher who is versed in all types of automotive repair. Pick up all of the manuals you can find for your rig and treat them as long lost treasures found again. I like to get cd versions as well if I can find them and print the section I am currently working on. These I have with me when Im all greasey and dont mind getting them dirty. Keep the manuals as clean as possible for the future generations.

 

[WARWAG]

WE all have the occasional "CLUNK" or worse. I have noticed one myself and am not sure what it is, yet. Sometimes an individual component has a strange way about her and thats just how they are. (just like women) I have never owned a rig with a NP208 T case before. I am told that sometimes they Clunk. Next time it happens I will be going under her to see what the he11 it is. Of course when I get home the "Clunk" is gone and I cant replicate it. Your clunk sounds like something different. Keep us posted on what you find with plenty of pics!

 

[DokWatson]

The NP208 is a chain driven transfer case. A 25 year old chain is probably a little stretched. You are most likely experiencing 'chain jump' which is a common sign of a chain driven transfer case on the road to failure.

 

[Iceman3005]

Yup mine clunks from time to time. sometimes will even jump and hit the floor, I have bad trans/transfer case mount bushings.

 

[mistaken1]

...... A great place to learn if you have the time is to take a local college course in automotive repair. This would be a great place to take your Rig and get her back into shape while learning all about her! The class will have all of the tools on hand with a teacher who is versed in all types of automotive repair. ......

What a great idea! It bears repeating. (wish I had thought of it)

 

[wallew]

plus the YOKES move up and back (not much but they do move) and THAT can cause a clunk.

WORSE is to have a yoke that has chipped or missing 'teeth' so it CAN REALLY MAKE NOISE. My M1028A2 had drive shaft problems and in the process of getting it fixed they found the yoke to the front of the rear drive shaft was really messed up. Several chipped and three missing teeth. I was surprised it was still functioning at all when they showed me what they replaced. One of those jaw dropping moments.

But it just 'vibrated' at about 65 mph indicated.

So there are SEVERAL possibilities. I'm not sure suggesting a mechanic to fix these trucks. As long as it's tranny or other NON-ELECTRICAL stuff, maybe.

But these trucks are unique. They are NOT your normal Chevy K5/10 truck. Several of the parts are completely different. The front axles from the spindle out ARE different on the M1009's than on any other Blazer I've worked on. SO be aware.

 

[Cucvnut]

put the truck in 4x4 get under the truck (with it not running) and try to move the front drive shaft up and down.

 

[kassim503]

I would lock it into 4x4 and drive it around a little bit to make sure all of the hubs are engaged and everything, and shoot a line of spray paint across the tires to u joints, front yoke to tcase yoke to rear driveshaft yoke, and romp it until it clunks a little. Whatever is slipping should show a difference in markings.

Had a similar clunk and found it was a bad passenger side hub, which took over two years of hard beatings to go from a occasional to a continous clunkey clunky clack