A synopsis, hoping it helps someone.

BorgWarner makes the transfer case. The older version was 4409; the 4Matic version is called "Magna Steyr".

The original BorgWarner transfer case chain was the HV-091. It was discontinued in 2019 and replaced with the HV523, which is "quieter". I did not realize noise was a problem.

Most BorgWarner transfer case chains for 4Matic are listed as HV-091. An Ebay seller told me the HV-091 does not exist anymore - no more old stock - but the HV523 is sold as HV-091. Perhaps the public has not received the memo.

The 523 or 091 chains are sold "for the Mercedes M", which does not mean ML but either stands for Magna or Matic (for M = 4M = 4Matic, get it?).

I bought an Amazon Warehouse "091" chain and fortunately measured it; someone had substituted a different chain. So beware; when you get the chain, inspect it carefully against specs. Break out your caliper.

1.50" Wide: This is a "nominal" measurement, per BorgWarner, so the measurement may not be exact, and it is not clear to me where you take this measurement.
3/8" Pitch: This is the distance from tooth to tooth.
42 Links: The total number of teeth is twice this number; you may see "84 pitches".
Rocker pin design: This means the pins that hold it together have oblong, not round, heads. Mine had round head pins.

The 091, and probably the 523, has three colored outer links at one point in the chain.

The chain I received had "Morse" stamped in alternating links; this indicates legitimacy, as it refers to BorgWarner Morse. I do not know if the 523 is Morse also.

There are aftermarket chains available, for a discount of about 1/3 the $125 price. Given the amount of labor involved, it is not a risk I am interested in for the sake of about $40.

Max Blast and expl0rer felt that the chain should not be replaced without replacing the sprockets. This does not seem right to me; the issue with the chain is typically that it stretches long enough that it flaps around and eventually rides up on top of a tooth; I guess it then quickly stretches a lot and starts flapping like crazy. I don't see sprocket wear in there except maybe the tops of the sprocket teeth. The problem is not that the timing chain wears but that it stretches. BorgWarner could have put opposing tensioners in there, but I guess that would be a hill too steep. There are kits available that include the two sprockets, the chain, and the plastic guide, but they are >$500.

The plastic guide inside the case can get damaged by a stretched chain. I believe this is because the chain is stretched and slapping around, hitting the guide.

You could probably check the chain for slack by poking a finger (not steel; maybe aluminum?) inside either the drain or fill hole in the transfer case. But how much slack is a problem? BorgWarner does not give a spec that I recall.

BorgWarner recommends replacing the chain at 60k miles. This of course varies tremendously based on the amount of torque the chain is made to endure. Thanks, Vater, for letting us know - and not allowing for anything short of replacing the whole transfer case. Incidentally, MB now sells rebuilt transfer cases for the newer models. Ain't cheap, though.

Replacing the chain is about a four hour job, according to a guy on the x166 forum. To me it seems obvious as a preventive maintenance item.

 

This is what I used for my 08 ML350. You don't need to change anything else. Slack in the chain can be determined by turning the rear driveshaft back and forth and comparing the freeplay to a known good chain or a lower mileage vehicle. After replacement my driveshaft would turn slightly less than the diameter of one of the retaining bolts, approx 3/8" of movement. Prior to replacement 3/4" @ 182k miles. I could also feel the driveline slack when on/off the gas

 

Hey, that's the Ebay guy that schooled me on 091 vs. 523. I figured he was kinda sketchy because he shows a 091 box. But you are confident you got a BorgWarner chain?

One thing I am not clear on: How do you get the new chain on the sprocket? The links are closed on the outside; do you pull off the sprocket? Both sprockets? Is there enough slack to clear the sprocket teeth?

Thanks for the info on driveshaft play. I may check mine out. I'm assuming you have to have a drive wheel off the ground (and parking brake off).

 

Based on this video, it looks like both sprockets can be removed pretty easily and that's how you get the chain on and off.

 

Great information. I'm not sure if you are saying that chain stretch is different than "wear", but the elongation of the holes the pins go through/wear on the pins are the source of chain stretch - the links themselves don't get longer. Whether the sprockets need to be replaced or not would depend on how much wear they have experienced as a result of a chain that no longer meshes properly with the teeth on the sprockets. I'd guess they have experienced wear that will wear a new chain out more rapidly if the chain has gotten to the point of skipping, but that's just a SWAG.

 

They could just be speculating, too. They might be thinking about motorcycle or bicycle drive chains. Both the teeth and chain links are shaped differently. This transfer case chain has nearly perpendicular teeth. It is more efficient but I guess it has to be kept clean.

To your point, which may be the same as theirs, if the chain is stretched, the leading edge of the sprocket takes all the load momentarily before handing it off to the next tooth. Ideally the sprocket teeth all pull together - though that may never be realized in practice. The chain has to be a little too long for the sprocket, otherwise it would be an over-tight fit when it is first installed. I dunno, this is new territory for me.

One thing that might actually stretch on the chain is the outer side of the link frame that goes around the pin. It might stretch outward. But you are right, the links themselves probably do not stretch. Certainly that is not the weakest link, har har.

 

Bingo! Thanks.

 

The shape of this chain and interference is slightly different than a single row chain, which the conventional wisdom of replacing all wear surfaces (sprocket, cog and chain) definitely applies to in the basic transfer case (non hi/low range)

but the same mechanism applies - a worn and micro pitted sprocket will accelerate the wear of a new chain just by its surface roughness, vice a new sprocket with a heat treated surface. To what degree, we don’t have data on.

glad to see pointed out that chain stretch is a function of trunnion wear.

​​​​​(except when cast in prefabulated amulite, surmounted by a malleable logarithmic casing in such a way that the two spurving bearings are in a direct line with the pentametric fan.)

 

don't forget the triumvariate oxygenate reaction

 

Seriously, though, it's in the realm of *who the hell knows*, amirite? We have MB implying that somehow the transfer case is a lifetime part, and if not, it should be replaced even though it costs more than the vehicle is worth. On the other hand, we have the manufacturer of the transfer case saying the chain should be replaced every 60k miles.

Somewhere in between, I dunno, the transfer case gears seem to cost about $200 each, which is nuts.

Micro pitting of gear tooth faces is the demise of many a warship. Just ask the captain of the Titanic.

I can't say what to advise. I'm on 187k miles and have no noise on shifting from R to D or back, let alone at full torque, But there are various clanking noises, maybe CV joint play, during various operations, and I really would like to not get into a terrible minimal torque allowed situation, so ... take a few hours and change the timing chain for the fun of it? Why not?

 

im at 217k with the hi/low transfer case and looots of driveline slack, prime suspect is the chain. No slippage or chatter.

 

I wonder how long a transfer case would last with regular fluid changes? I’m ashamed to say mine didn’t get one until it was well into the 100K mile range since it wasn’t on the MB maintenance schedule and it almost made it to 200k. I’d bet the vast majority of them still have the original fluid in them.

 

Hey, so part number for an EORP chain in the two speed transfer case is hv-098/hv-518 then?

There was a YouTube video of a guy in Norway changing and refurbishing his GL500 2speed transfer case but that seems to have been pulled off of YouTube I cannot find it.

I’m gonna give this a shot without the sprockets.

 

I haven't cracked the xfer case open. @ just over 101k miles/168k km currently I have no indication the case or chain are a problem. I have the 2 speed case like Max.

If the sprockets are showing any visible wear at all, I would replace them, just by the same logic you're not willing to save $40 and put a lower quality chain. Id rather once "under the car" than twice or more for the same parts/job. I know it's a little hard to justify adding 400 to the bill now, but if you were to do the same job again to replace the sprockets and another chain later plus the 4 hrs, you've doubled your expense and then some. I count hours spent under the car as expense. Add scraped knuckles and the chance that the next failure could be at a very inopportune time. As much as I enjoy tinkering with the car, I'd rather drive it for 4 hrs than be under it.

On the other hand I like experiments amd not afraid to tests some things. But a 4 hr job done twice would not be my preference.

 

What's the worst that happens? You see wear, you reassemble with a new chain, etc. Then go hunt for sprockets. Based on a cursory search, they are ecks-pen-sive. And you don't want Chinesium steel in there; assuming it wears, those metal particles would probably wreak havoc on your new chain. If it isn't slipping now, I would just do the chain.

If you figure out who makes the transfer case, and what model it is, it shouldn't be too hard to back-figure what chain it needs.

Transfer cases are weird. No one seems to make their own.

 

I believe the main reason transmission fluid gets problematic is because of the clutches. And thermal breakdown. Neither of those apply to the inside of the transfer case.

MB doesn't specify a service interval because they buy the transfer cases intact, and the transfer case is expected to last outside the warranty period, so who cares, amirite?

 

Yeah I’ve come off my previous position because it is such a wide chain and sprocket, Contrary to a narrow single roller motorcycle chain and cog.

I’m also investigating whether or not just getting a DD 295 box off of a Land Rover of the same vintage would work… Magna Steyr manufactured these for MB and land rover; All parts appear to be interchangeable between the two cars,the cases appear to be visually identical as well as having the same ratios in clutch packages.

Low mileage box swapped in for $250-450 while one rebuilds the MB branded one, or sells it.

 

The motorcycle chain is also out in the dirt. Thus the greatest wear would be on the exposed surfaces - the chain's rollers and the sprocket teeth. Those exposed surfaces also lose lubricant. I bet the pins do not wear much inside the bushings.

Properly sized spur gears (which is what the transfer case chain and gear are, effectively) normally simply don't wear out. The shape of the teeth is such that the metal faces only press against each other and then release. If the chain starts skipping, that wears the parts mighty quick, of course.

On the Land Rover TC, I would only be concerned that the input and output shaft splines might be different.

 

Could be, but chains wear which creates gunk and makes the fluid somewhat abrasive which contributes to more wear. Also as they wear they "stretch" (they really just get longer due to wear of the pins and plates) which causes wear on the gears since the pitch of the chain no longer matches the pitch of the gears, which creates even more gunk and also causes even more wear. I'd guess an xfer case would last longer with regular fluid changes (mine was pretty nasty when I finally drained it) and maybe a chain replacement at some point, but nearly 200K isn't a bad duty cycle.

Eric

 

Wait, does the EORP xfer case have clutches in it? It has to, to switch between high and low, right?

That would also contribute to wear. Clutch material is horribly abrasive ... which is part of why it is so important to refresh your transmission fluid.

 

It does

 

I just stumbled across this thread as I wrap up changing the transfer case chain on my 2009 ML550, and I'm a bit worried by the original post. I actually just put the cover on this morning and am letting the RTV dry overnight before putting the fluid in and test driving it.

I got the BorgWarner 091 chain (at least according to the Amazon listing title), but the chain came in a plastic bag without even a BorgWaner logo so likely it's aftermarket. I should've returned it but I was in a hurry.

It seemed to fit perfectly, and a lot of comments said it fit similar year vehicles so I thought I was fine other than it likely being an aftermarket chain.

Here's the one I got:

I guess I'll cross my fingers tomorrow when I finally test drive it.

 

It will probably work fine, and it is anybody's guess whether the steel is good. All the aftermarket parts seem to exhibit the same spread of characteristics: They range from honest copies to junk copies wildly overpriced. At the top of the range would be parts that last about as long as OEM, while the bottom is junk that will fail in a short time. We see that with compressors, with some failing at 10-20k miles; no word on non AMK compressors that last a respectable amount of time. Some suspension components are seemingly doomed from the start, while others (knocks wood ... Delphi) are solid. Transfer case chains are very simple; you just need uniform links and reasonable tolerances in the manufacture, along with good steel. Chinese steel is hit-or-miss, and the manufacturing is hit-or-miss also, as they are prone to not maintaining the machinery and replacing the stamping dies frequently enough.

I would suggest, pour out the fluid after 10k miles and stir it with a magnet. If you see any shavings, you had better replace the chain pronto. This is just my guess based on the known potential shortcomings.

 

Here is a vendor selling the HV523 transfer case chain, taking pains to assure it is genuine BorgWarner. Curious, the price is not very high, making me think the fakers are cleaning up.

https://www.transmissionpartsdistrib...164-gl-hv-091/

 

I paid way too much thinking it was a real BorgWarner ($130), so hopefully it's at least a decent quality. It sounds quiet so far, so fingers crossed.

That's a great idea about draining the fluid after 10K miles to look for metal shavings. I'll do that when this thing hits 250K or so.

I bookmarked the link Eric sent as well, just in case I have to do it again.

Now that I've done the job once, I think next time will only take me about 2-3 hours, and that's on my back with a floor jack. It's much easier to do on the car than removing it if you're only doing the chain, at least on my ML550. I just unbolted the rear driveshaft where it connects to the transfer case, dropped the center bearing to give me some play to move the driveshaft out of the way, pulled the cover off, swapped the chain, cleaned everything up and put it back together. I didn't have the right tool for the Mercedes silicon and my thumb was turning blue trying to push it through with the plastic piece they give you, so I wound up using Permatex Ultra Grey, so hopefully that holds up.

Thanks guys....