Transfer Case Drive Chain HV-091 Mercedes ML350 4MATIC

Replacement drive chain for the Magna single-speed 4MATIC transfer case bolted to the back of the 722.6 and 722.9 automatics in Mercedes M, GL and R Class trucks. It is the HV-091 chain, sold under Mercedes part numbers A2512800800 and A2512800900. Measured specs are 1.50 inch width, 3/8 inch pitch, 42 links, rocker pin construction.

This chain is the single most common failure inside that case. It carries every bit of front axle torque from the input sprocket to the front output sprocket, it runs in a small amount of fluid that most owners never change, and it stretches. A stretched chain announces itself as a whine or growl that tracks road speed rather than engine rpm, a clunk from under the floor when you get on and off the throttle, and a driveline shudder that people usually blame on the transmission or the drive shaft flex disc first. Pull the fill plug and you will typically find dark fluid with metallic fuzz in it. Once the chain has enough slack it starts riding up the sprocket teeth, and at that point you are buying sprockets and a case instead of a chain.

On the bench the case has to come off the transmission and be split at the seam. The input shaft, front output shaft and chain lift out together as one assembly, so do not try to peel the old chain off inside the housing. Inspect both sprockets for hooked or ridged teeth before the new chain goes in, because a fresh chain on worn sprockets will be noisy again in short order. Note the chain orientation as it comes out, clean the mating faces completely, reseal the halves, torque the perimeter bolts, and refill the case to the fill plug with the fluid Mercedes specifies for it.

Fitment covers ML Class W163 from 2003 up and W164 from 2005 up, including ML320, ML350, ML450, ML500, ML550, ML55 AMG and ML63 AMG; GL Class X164 2006 to 2012 in GL320, GL350, GL450 and GL550; and R Class W251 R320, R350 and R550 from 2007 to 2011. It fits the Magna single-speed case only. It does not fit non-US GL models equipped with the two-speed Off-Road Pro package transfer case, so confirm which case is under the truck before ordering.