2WD clunking sound but not in 4WD

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AK ID

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Greetings...

I recently purchased a 83 K20 that had been sitting for about 3-4 years. Previous owner is a neighbor/friend and he daily drove it until he bought a new truck when this one got parked. He says he doesn't remember it having any problems before.

Anyway, I got it started from its resting place and drove it up and down his driveway as a test drive and left it parked it in his driveway. I dont remember it making any sound or if it was in 4wd or 2WD when i did the test drive (driveway was snow covered).

Later that day had a friend come with me and we started it again and drove it home. That is when the sound was first noticed. It makes a "soft clunk" from the front end when it's in 2WD but the sound goes away when in 4WD. We couldn't figure it out and a storm was blowing in so we just left it in 4WD and drove it home about 2 miles. It has the auto hubs with the 4x4 decal where the hub would be.

When its in 4WD, there is no funny sound and its defiantly in 4WD as you can feel it crabbing when turning. The problem comes when it's shifted into 2WD. It has a soft clunk sound from the "front driveline area" about every 8 feet of distance traveled (kind of hard to drive and hang your head down to see what's happening by yourself) that doesn't go away until it's shifted back into 4WD. I've tried the shift into 2WD and back up 10-15 feet trick but that doesn't seem to make the sound go away. It makes the sound going forward and reverse. Once it's shifted back into 4WD, the sound goes away and drives just fine.

I have not checked any fluids. All I've down is crawled under and inspected the linkage which appears fine. The transfer case also seems like it moves fine between 2H, 4H or 4Lo range too.

My guess is its the auto hubs are sticking (no idea when they were last serviced if ever)

Do you think it's the auto hubs and they need switched out to some Warn manual hubs? If so, is there a different hub for the 3/4 ton vs the 1/2 ton?
 

bucket

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I had an auto hub years ago that was lazy to engage in cold weather. I tried cleaning and lubing (lightly) and it didn't help. After a couple years, it started randomly trying to engage in warm weather, when in 2wd. It made some funny clunking noises when it did it.

In short, yes, it could be a sticking auto hub. I'd suspect just one, not both. It would also be worth checking for slop in the front drive shaft too, of course.
 

PrairieDrifter

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Check front axle shaft u joints visually. Maybe put a little pressure on with a prybar to see any movement.

Also wouldn't be a bad idea to pop diff covers off to inspect and should change fluid anyways.
 

xm20k

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Sounds like the hub/hubs as the front drive shaft spins in 2wd as well as the differential.
 

xm20k

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jcperformance

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Yeah that definitely sounds like the auto hubs not fully disengaging
That “every few feet clunk” in 2WD but smooth in 4WD is classic—one hub is partially engaged, so parts of the front driveline are loading/unloading as it rolls.
 

Craig Nedrow

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Manual Warn hubs are hard to beat, what I would do, though not exactly a cheap date. I use almost no lube in my hubs, as they can stick in cold weather. There are several styles, 1/2 turn, (lighter duty?) and the 7/8 turn. I've had both, never broke either.
 

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