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Mercedes torqued transmissions

Wednesday, October 29, 2014 - 07:00
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Mercedes 722.9 transmission is a two part case (Figure 1). The converter housing is made of die-cast aluminum. The main transmission case or housing is made of die-cast magnesium. This provides a reduced weight compared to aluminum by approximately 2.5kg/5.5lb. As a result, the bolts which screw into this magnesium case require them to be made of aluminum (Figure 2) since steel bolts would have a different expansion rate and corrosion concerns. Additionally, all aluminum bolts must be replaced if removed as they can stretch and when reused, could snap.  

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In-between the converter housing and main case there is an intermediate panel or gasket (Figure 3). This is made from an aluminum sheet with an Elastomer coating (a polymer with viscous and elastic characteristics) and can be reused if there are no signs of damage to the Elastomer coating.

This gasket extends out beyond the sealing surfaces of the converter and transmission housing to prevent water from settling on the transmission housing. Standing water (especially salt water) can corrode magnesium in as little as eight weeks.

When replacing the aluminum bolts with new, a specific torque procedure should be followed for the best results. The procedure is simple and easy but finding theinformation took some effort – thanks Eddie!

The bolt torque procedure for the Converter Housing to Case bolts is as follows:
Stage 1 - Tighten to 10 Nm (88.51 in-lbs)
Stage 2 - Turn an additional 90 degrees

Service information:
• A bolt and plate package can be purchased as a set - 600 0000 64 10 (figure 4)
• A package of housing to main case aluminum bolts - 140 990 46 01
• Main case to housing bolts (2 required) – 004 990 23 12
• The aluminum sheet coated with Elastomer - 220 277 16 14

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