Loud Clunk 4H to 2WD

New ‘22 OR with 8600 miles. I switched into 4H yesterday just to get the oils flowing in the transfer case. I was going about 35-40 when I switched out and I heard and felt a loud clunk. I attempted it a few more times and got the same result. All attempts were made driving in a straight line at low speeds.

I don’t live in an area where I can drive the recommended 10 miles a month in four-wheel-drive. So when I can on straight roads, I switch it in the four high, just to keep the parts lubricated as best I can. The truck never used to act like this, but it has been a while since I’ve switched into four high and driven for a substantial amount.

Should I have any concerns here?

 

Let off the gas when switching, meaning be coasting.

 

You might also check the transfer case fluid level. Not unheard of to come low from the factory.

 

It will make a clunk if there is some bind up in the drivetrain. For example, on snowy days when I forget to put it in 2wd before entering my underground garage, it lets out a loud clunk.

 

This happens in my truck if I'm trying to outsmart the computers. The transfer case tries to synchronize the gears before engaging and disengaging 4x4. It takes your current speed and accelerator position into account. I've noticed the clunk happen if I try to coast when engaging/disengaging 4x4. It doesn't happen though if I just maintain current pressure on the accelerator and not change anything up until it engages/disengages.

 

Not exactly. The ecu will not allow the shift into 4HI over a certain speed, but it has no control over synchronizing anything. That duty is handled by a boring old synchronizer ring that's been handing these duties since long before ecu's were involved. Ideally you want as little load on the drivetrain as possible. Fully off throttle is actually decent engine braking load so that's not ideal. Very slight throttle so you're not accelerating or decelerating results in the smoothest shifts in and out of 4HI.

 

Sometimes it happens, other times it does not. It is more likely to make some noise if the drivetrain is in a bind. The noise usually isn't a problem.

A note about the "10 miles/month in 4X4". Nothing says 10 miles all at the same time. And if you skip a month occasionally it isn't going to blow up. It is when you don't use it for 6 months to a year that problems come up. BTDT years ago with a 4X4 Jeep Cherokee my wife drove. I rarely drove it and 4X4 didn't get used much. Once when needed it wouldn't engage. It was a simple matter of disassembling the hubs, cleaning and re-lubing. Since then, I've made it a point to get some time in 4X4 and I've had no other problems.

In theory operating in 4X4 on a straight road shouldn't damage anything. And for short distances sometimes you've got to do what you've got to do. But 10 miles/month on pavement is slowly causing damage to the drivetrain. You probably won't have a catastrophic failure, but in a few years will start to see premature parts failure if this is done on a regular basis. Lots of people drive way too much in 4X4 on pavement. Why I won't purchase a used 4X4.

During some parts of the year I may get in 200-300 miles some months. Other times of the year I may only be able to get in 2-3 miles and I may have to skip a month. But it gets used regularly.

I simply won't drive on dry hard pavement in 4X4. I've had to pay to have transfer cases rebuilt in the past. The risk may be small, but it still isn't worth the reward. I need to drive 1-2 miles at a time on dirt or gravel roads at least once a month. I always engage 4X4 at that time. It isn't 10 miles, but is better than nothing and has been working.

 

I am coasting every time I try it. It seemed to be getting better today the more I drove in 4H. Still a noticeable jarring feeling albeit slight.

 

But what binding? I have the wheels completely straight.

 

Thanks for making sense of what’s happening in the case. I’ll give this a try.

 

I live in D.C. I don’t have a choice unless I want to drive 2 hours west every month to the mountains. I agree, it’s not ideal.

 

Gears meshing will almost always give you a little clunk. Under load, like accelerating, will give a bigger clunk. Been driving part time 4wd so long I don't pay it much attention but I tried it after reading your post and mine does it too. Perfectly normal.

 

Thanks for the peace of mind.

 

My 21 is a bit clunky. The transfer case itself shifting is pretty smooth, which is what happens first. Then, the ADD engages, and the light on the dash goes solid. Any clunking I have happens during the ADD portion.

The clunk is a matter of meshing the front right wheel’s speed with the front diff (since the front diff is now spinning from the transfer case engaging).

I regeared and it got worse due to higher driveline speeds, so I adjusted my max speed by a percentage. Stock is around 60 mph, with 5.29s and stock tires I won’t do it above about 45 mph. Neutral throttle helps for sure.

 

I get told neutral throttle is good, then I get told to apply slight acceleration to counteract the force of engine braking with neutral throttle.

 

Ive found that applying very slight pressure to the accelerator gives the smoothest transition to 4 wheel drive. Any other time I get varying degrees of clunk when switching to 4Hi except when completely stopped.

 

I get mine into 4wd every time it rains

 

You're also hearing from manual transmission and automatic transmission owners. Manual transmissions if left in gear are going to engine brake significantly. For a manual, neutral throttle in gear will be best. Just maintaining speed as lightly as possible will be the most smooth.

With an auto, no throttle ends up engine braking a little bit but not much. In an automatic, probably best to let off the throttle.