Transfer case

I have a 2018 2500 with the Cummins diesel and the shift on the fly transfer case. What is the model of this transfer case? Is it chain or gear driven? If chain how hard is it to change the chain. I feel slack somewhere in the drivetrain but haven’t gotten under the truck to check things out. I’m pretty sure it’s not the u joints because I don’t have any vibration and no rust coming out of the caps.

It's chain driven gears went away long ago.. That said you should only feel that slack in 4x4 if it were the t case as the rear side of things is directly driven..
The best way to test to see if it's a chain is to put it in 4x4 and Floor it. Make it be under extreme load it will start to make a popping sound and that's the chain slipping on the sprockets.

I thought all power was driven through the transfer case.
I do understand about the noise and popping. I had that problem once before on a Chevrolet.

It is but in 2wd it's only transmitting straight through the transmission. Anything turning in the t case while in 2wd is just the film strength of oil allowing it to frewheel or if you're moving the front driveshaft back feeding into the t case. I'd start by checking mounts and u joints. Do you have a one or two piece driveshaft?

I suggest you get under the truck and check it out before jumping to conclusions and going down a rabbit hole. Typically these trucks have a little play in the rear differential so you may want to check that first.

I’m just thinking and getting ideas from people, as I said I haven’t checked anything out yet.
I’ve only had the truck for two months.
If I remember correctly it is a two piece driveshaft.
I’m definitely not going to just start throwing parts at the truck. The parts prices for these heavy duty trucks are too costly for that.

I'd have someone hold the brakes and shift it from Forward to reverse and see if you see anything or can pinpoint the location of the sound.

Runaround said:

If I remember correctly it is a two piece driveshaft.

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It should be a single piece driveshaft...

This truck is the crew cab, long bed.

There's no one shaft which goes through the transmission and also through to the rear driveshaft...it all goes through the transfer case which is a separate unit and contains planetary gearsets and lots of gears...and a chain. The chain only connects to the front, so if there's more slop in 4x4 it's probably not the chain. There's a coupling between the trans and the xfer, either on an input gear (internally splined). Looks kind of like THIS.

There are a LOT of places where 'slop' can come from. For one, splines could be weak on the driveshaft, or driveshafts. That's usually the first place to check b/c it's very common. Could be the transmission/transfer case coupling is worn. Could be the diff's a little worn, or axle splines, or front driveshaft splines. Yeah it could be the chain too. Those chains are pretty robust. Everyone points to chains. The ones I've checked even after a ton of miles weren't really very worn. But you never know. More than likely it's probably a little accumulated wear on several or all of the load-bearing surfaces. But the only way to know for sure is to get it off the ground and check each sub-system one by one.

It's pretty easy to remove and split the transfer case too, if you're mechanically inclined. Then you can inspect the chain and check for excess 'slop' too on the individual component.

Good luck, Hope it helps.

Runaround said:

I’m just thinking and getting ideas from people, as I said I haven’t checked anything out yet.
I’ve only had the truck for two months.
If I remember correctly it is a two piece driveshaft.
I’m definitely not going to just start throwing parts at the truck. The parts prices for these heavy duty trucks are too costly for that.

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As you have already seen, the causes of slack are many and varied and they haven't all been covered either. If you crawl under the truck and do some very basic diagnostic work, right down the steps and the results, it will be a whole ton easier for us to give you quality advice.

Let us know what you find and we can try to help.

Runaround said:

I thought all power was driven through the transfer case.
I do understand about the noise and popping. I had that problem once before on a Chevrolet.

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There have already been replies to this. But as mentioned an issue with the chain should only be obvious when in 4wd. All the power goes through the transfer case, but when in 2wd the chain is not doing anything. The only thing the chain does is transfer power to the front driveshaft, so in 2wd it is not really even connected to the power.

What's the miles on this truck? How many of them were towing miles? Was it light-duty towing, or rough-service towing?

When you say "Slack" in the driveline ...are you talking it goes "Ca-Chunk Ca-Chunk" when you blip the gas? Or is it minimal? Some slack is normal as miles accumulate, and ya feel it more on a responsive engine. But it's hard to gauge w/o driving it. In general slack is pretty normal on a higher mile rig, and almost expected after a lot of towing miles. There are so many variables. You're talking a tk going on 6yrs old now.

Thanks for the replies. I will try to get under it in a couple of weeks after I get off of these 7-12 hour days.

I guess if it were me, I'd probably do the following in this particular order:

1) Raise one wheel at a time with a floor jack and rock each wheel back/fourth and feel (by hand) what level of freeplay there is. There will be some, of course, but take note of how much. If you can...Ideally come up with a way to lock the pinion 'solid' ..maybe tying down a chain vise-grips on the DS onto something solid so the driveshaft isn't moving AT ALL. Then you get a greater sense of what's going on with the diffs and axle splines as you rock each wheel. Repeat the same process for the front. Pay special attention to the joints and front diff outer axle joints for excess movement.

2) Get under it...(wheels on ground, but axle wind-up released)...and shake the driveshafts vigorously ...like you mean it! Feel for any freeplay up down sideways. Pay special attention to the U-joints at the pinion, and any center bearing at the rear driveshafts (if yours is split), and front driveshaft splines and CV. Then rotate the driveshafts by hand and observe movement.

3) Remove the driveshafts at the pinion ends (wheels on ground), one at a time. Rest the loose end of the driveshafts on a bucket or something (don't let the U-joint caps fall on the ground!! ...tape them). Then rotate the differential pinions back/fourth.

Rotate the removed driveshaft (vehicle in 4x4, tranny in "Park") and feel for excess back/fourth slack. Esp the rear driveshaft. Test the splines where they enter the transfer case output shaft. There will be some slack, but how much? Try to quantify if you can. Look for any side-to-side movement in the driveshaft joints. You may need to hook at chain vise-grips to get a little extra leverage to use more back-forth turning torque. Grab the front driveshaft and rear driveshaft at the transfer case ends and counter-rotate with your hands. How much slack do you feel? Look for excess freeplay on all these 'tests'.

4) Support the rear end on jackstands in the air, then rotate the pinion by hand feeling for smoothness ...or bearing roughness. Never hurts to check. At this point I would lift up/down on each wheel to check the wheel bearings for any slop. Or use a 2x4 under the tires if you have oversized tires on it (they're pretty heavy). Now's the time to check them. Same with front only you want to rock in/out with your hands at the 6:00-12:00 positions on the tire/s.

5) You can repeat the tests for 2WD too if you want.

6) Pull a U-joint cap off the rear DS U-joint and inspect the trunion/s for fluting. Now is a good time to do that. Add a daub of like-grease if they look dry. Replace if you see any fluting. Otherwise put it all back together and let us know what you discovered.


That's pretty much it. If I missed something, I'm sure other forum members will fill in the gaps.