Clunk when shifting between drive and reverse, or vice versa

Bulldogger

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My ride sometimes clunks, sometimes doesn't. I'm not familiar with the cause of this, and wonder if it's something I can address outside of a trans rebuild. (Please don't say it's a trans rebuild, oh please.)
My ride is a stock 1987 M998 with 6.2L NA and standard drivetrain. All fluids are at correct levels, and the noise persists after performing the standard lube order and greasing.

I appreciate your ideas and suggestions.

Bulldogger
 

Bulldogger

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They looked OK, and I greased their zerks, those that had them. It occurred to me I could replace them and know they're good for sure.

I don't mind doing that.

Bulldogger
 

Dock Rocker

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In my experience a clunk when going into gear is usually attributed to drive line slop.

Take it to a shop that specializes in drivelines and let them check your U-joints and yokes/driveshafts.


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erasedhammer

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My ride sometimes clunks, sometimes doesn't. I'm not familiar with the cause of this, and wonder if it's something I can address outside of a trans rebuild. (Please don't say it's a trans rebuild, oh please.)
My ride is a stock 1987 M998 with 6.2L NA and standard drivetrain. All fluids are at correct levels, and the noise persists after performing the standard lube order and greasing.

I appreciate your ideas and suggestions.

Bulldogger
Normal. Every time I shift into D or R from a stop it clunks into gear. Ive replaced my engine, transmission and transfer case. As well as each driveshaft twice, the diffs rebuilt, half shafts replaced, hubs replaced.... clunk still there.
 

Bulldogger

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The idle speed seems normal, but this is my first diesel. I don’t have a tach.

The clunk is towards the front.

I think I’ll replace th u-joints since they could be 30+ years old anyway.
And I’ll take a harder look at the carrier bearing.
I seem to recall being able to wiggle the rear drive shaft (propellor) back and forth a bit when I was under there doing the lube order.

I was worried it might be trans wear, but it sounds like hypochondria

Thanks gents.

Bdgr
 

Action

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Normal. Every time I shift into D or R from a stop it clunks into gear. Ive replaced my engine, transmission and transfer case. As well as each driveshaft twice, the diffs rebuilt, half shafts replaced, hubs replaced.... clunk still there.
So, it only happens once each time you drive? Unless you have to back out of a parking spot. I hope you didn't replace all those things because of the clunk. Find another humvee owner near you and see if they will take you for a comparison ride.
I would wager a guess that it is just driveline slack being taken up when you change directions.
 

dhaumann69166

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Mine clunks a little when you put it in drive or reverse from neutral. It also clunks when you go from forward to reverse or vise versa. If you are going down hill and drop it to first you can hear a little clunk. I have checked all U joints, diffs and anything else I could think of and can’t find a bit of slack.
 

suzukovich

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The idle speed seems normal, but this is my first diesel. I don’t have a tach.

The clunk is towards the front.

I think I’ll replace th u-joints since they could be 30+ years old anyway.
And I’ll take a harder look at the carrier bearing.
I seem to recall being able to wiggle the rear drive shaft (propellor) back and forth a bit when I was under there doing the lube order.

I was worried it might be trans wear, but it sounds like hypochondria

Thanks gents.

Bdgr
That's the front driveshaft engaging the differential. The Humvee is full time 4 wheel drive. I get that too every so often. As long as the U joints are tight and greased it shouldn't be an issue. Nothing wrong with the idea of changing them out. But I from the school if it not broken don't fix it. Having spare parts on hand is always a good thing.

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EladB

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One other possibility. I had an old station wagon once that would clunk when shifting into drive from reverse (or the other way around, I don't remember for certain). We thought it was U-joints or whatever too. Nope. Turned out to be a broken motor mount. The steel parts were intact but the rubber was gone. Under certain conditions the engine would actually pivot up on the good mount a couple of inches from torque. When you shifted, it would plop back down into place with a clunk. Found it because we had the hood up doing something and noticed the engine moving when I shifted.

I agree that in 90 out of 10 cases it's probably slop in the driveline somewhere... but if you can't find that, maybe look for slop in the mounts.
 

erasedhammer

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So, it only happens once each time you drive? Unless you have to back out of a parking spot. I hope you didn't replace all those things because of the clunk. Find another humvee owner near you and see if they will take you for a comparison ride.
I would wager a guess that it is just driveline slack being taken up when you change directions.
All upgrades. 6.5T 4l80 242 t case, 2.56 gears. New driveshafts for 4l80, half shafts break over time... I've managed to take out a few hubs...
 

Bulldogger

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The prize goes to those who urged me to check the u-joints. It turns out it's a little bit of everything. The front most u-joint was in active decline, slapping back and forth maybe 15 degrees back and forth. Ready to fail. Glad we spotted it. I noticed the carrier bearing was clunky too. Once off, I realized the bearing is rotating OK, but the mount was loose, even though the bolts were tight. I attribute this to the rubber mount around the bearing shrinking. I decided to not bother trying to shim and replace it instead. I have a new one on the way from an eBay seller in GA, along with a bearing separator kit ordered from Amazon (I never heard of one before last night, only bearing pullers). While staring at the front assembly, I decided to replace all the u-joints, not just the one that is clearly bad. The mid and front rear joint seemed OK when I pulled them, but there is no reason to re-use them when I have good Spicer replacements in hand.

Incidentally, for anyone looking, Hummer Knowledge Base reveals the u-joint is a Spicer 5-213X. It is available fairly widely, though I found less common at typical auto parts stores when searching. NAPA has them at a decent price, but I was surprised to see them on Amazon Prime of all places at less than $20 each. I bought 4, one-day shipping included free, thinking I only for sure needed one. I'll finish the front propellor shaft and make a mental note to buy a few more to do the u-joints on the rear next time I'm under the backside for another reason. They are tight still, but just as old I'm sure. Tip: wire brush and wipe clean the yokes before trying to reinstall new u-joints, so debris isn't being splashed over everything while getting the new joints in.

Incidentally, the TM didn't give me a lot of help on how to remove the front propellor shaft, so here's how I did it for those interested: loosen and remove front and rear u-joints bolts and straps and unbolt the carrier bearing. Then, unbolt the steering sway bar and rotate it as far downward as possible. You can then remove the front propellor shaft OVER the sway bar straight outta the front of the vehicle. I couldn't find any way to remove the shaft by bending it at the center joint and going under the sway bar, but once the sway bar was unbolted and rotated down I could pull the whole mess straight forward. Going back in will be annoying in the reverse direction, but should be totally do-able.

Bulldogger
 
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