2002 Suburban Front Axle Issue When In 4WD

Zep86

Member
Hello folks.
I recently acquired a 2002 Suburban and I am having issues with it in 4WD. In 2wd it drives like a dream, however when I put it in 4WD it binds rather rapidly and makes a clunking sound from the front. It is less frequent when in moving in a straight line, however even with a slight amount of turn it binds and "clunks" in the front...either direction. I put it back into 2WD, all is dandy.

I don't want to rule out CV joints, but something about this doesn't feel right, especially when it takes just a small amount of turn to get it to bind and "clank" enough where it can be felt in the vehicle. All my tests have been at very low speeds, but the impact still seems rather aggressive.

If anyone has any ideas, please let me know. Thanks.
 
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azswiss

Well-Known Member
Sounds like a CV. A couple more questions:
1) How many miles?
2) Any idea if the CV's were ever replaced? How do the boots look?
3) Has the front been raised (torquing the torsion keys)? Check to see if the CV's are level or slope down from the diff to the knuckle. The greater the slope the greater the wear on the CV's.
 
OP
Z

Zep86

Member
Sounds like a CV. A couple more questions:
1) How many miles?
2) Any idea if the CV's were ever replaced? How do the boots look?
3) Has the front been raised (torquing the torsion keys)? Check to see if the CV's are level or slope down from the diff to the knuckle. The greater the slope the greater the wear on the CV's.
85k...
The CVs look original. The suspension has never been touched in order to change geometry.
 
OP
Z

Zep86

Member
Hmmm. You might also want to check the U-joints on the front drive shaft.
I just went back out and put it back into auto 4wd, again. This time it did make the same noise as it does it 4wd. After straightening the wheel, it will pop once or twice and stop, yet once a turn begins it starts popping.

This happens in both left and right turns.
 

azswiss

Well-Known Member
Turning exercises the following elements of the front drive system: CV joints, front diff, front drive shaft u-joints. How do the CV's & U-joints feel when you shake them? Any wobble or play? Trying to rule out the simple stuff before having to get into the diff (internals).
 
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Zep86

Member
Turning exercises the following elements of the front drive system: CV joints, front diff, front drive shaft u-joints. How do the CV's & U-joints feel when you shake them? Any wobble or play? Trying to rule out the simple stuff before having to get into the diff (internals).
There was nothing out of the ordinary. I checked CVs and looked at the U joint. It seems normal. I did put it in 4hi and checked the passenger side while jacked up and it doesn't spin beyond a few degrees either way...nothing that didn't worry me; however, while moving the wheel a little each way I could hear a something moving inside the TC due to 4wd being engaged...but I am not sure how normal that is with these vehicles.

I have a bad feeling that it's probably going to be the diff.
 

northcreek

Well-Known Member
Assuming that the tires/rims are the same front to back. A long shot but, it's possible that the front or rear diff was changed out and the ratios do not match.
 
OP
Z

Zep86

Member
Assuming that the tires/rims are the same front to back. A long shot but, it's possible that the front or rear diff was changed out and the ratios do not match.

I see the logic, but I knew the previous owner and he wouldn't have done that. Age got to him and he didn't think he needed 4wd anymore, so he never had it fixed.
 

northcreek

Well-Known Member
I see the logic, but I knew the previous owner and he wouldn't have done that. Age got to him and he didn't think he needed 4wd anymore, so he never had it fixed.
Okay, then I think that I would drain the front diff fluid and check it for metal.
 

azswiss

Well-Known Member
A simple test of the diff would be to get both front wheels off the ground and spin one while securing the front drive shaft (either with an assistant or by having it in 4wd). As you spin one of the wheels listen/feel for the clunking. From there you could check the fluid for proper level and state.

Edit: northcreek is right. Rather than check the level, drain it and look for metal
 
OP
Z

Zep86

Member
It was awfully sparkly inside the front diff.

The fluid did have some small chunks in it and had a metallic sheen.

I believe the culprit has been isolated. Thank you folks. Now off to find a diff.
 

northcreek

Well-Known Member
Make sure that you source the correct ratio replacement and good luck with the fix.
If I can I make a guess, I'll say that it's the spider gears.
 
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OP
Z

Zep86

Member
So, I went down the rabbit hole a little further.
The loud clunk is made in both 4wd and 4Auto.
The noise doesn’t happen if the truck is in a straight line.

Today I put the TC in neutral and heard a whirring sound as if something was moving or engaging. The trans was in neutral too. The increment lessens (goes faster) when I press accelerator.

Does the tail shaft still spin even in neutral? The sound isn’t made in gear in 2wd or 4wd. Does the front axle impact the transfer case when in 4Auto?

thank you all for your help so far.
 

azswiss

Well-Known Member
Does the tail shaft still spin even in neutral?
Yes; the rear drive shaft turns if the vehicle is moving.
Does the front axle impact the transfer case when in 4Auto?
Yes. The difference between 4Auto & 4Hi is that the transfer case allows for slippage (speed differential) between the front & rear shafts in 4 Auto & no slippage in 4Hi (& 2HI).
 

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