Sheryl Crow may have been onto something when she said “A Change Would Do You Good”. Although the song did mention “Mercedes rule”, I doubt my interpretation has anything in common with hers. No, what I am referring to is your car’s transmission fluid.
If you want to skip the long explanation and get right to the point, just go right to the last paragraph. If you want to know why I recommend a transmission service then read on.
In 1996 Mercedes-Benz debuted a new 5 speed automatic transmission labeled the “722.6”. This transmission has provided great service for many Mercedes-Benz owners, but it does have one serious fault. The fault I am speaking of is the decision by Mercedes to not recommend a fluid and filter replacement interval. All earlier Mercedes-Benz transmissions were recommended to have the fluid and filter changed every 30,000 miles.
I am going to try to explain the very basics of how an automatic transmission works so you can understand why this fluid must be replaced. The transmission is a series of shafts attached to gears which engage and disengage to allow the engine to remain in its most optimal rpm range over a wide range of vehicle speeds. The engagement and disengagement of these gears is done by applying clutches with hydraulic pressure. The clutches are stacked and alternate from a steel disk to a disk made up of friction material. As the hydraulic pressure squeezes the stack of disks together, they turn or hold the gear they are attached to.
Here is why the fluid and filter need to be replaced. Every time those stacks of clutch disks are applied or released, some of the friction material is rubbed off of the friction disks. That friction material is suspended in the fluid and causes friction in areas of the transmission that it is not supposed to.
So you say “Brian…isn’t that what the filter is for?” Well, yes but it can only trap so much friction material before it gets stopped up. Have you ever forgotten to replace the dust filter for the intake of your home air conditioning unit? Of course you have. Remember what it looked like? It was completely stopped up and probably in the shape of a bowl from being sucked into the intake. Your electric bill was probably higher that month because the air conditioner fan was working so much harder.
Another reason the fluid needs to be replaced is that it gets extremely hot. The normal operating temperature of the transmission is about 100 degrees Celsius. If it were water it would be boiling and that is just the normal operating temperature. It can get much hotter in stop and go traffic. The fluid used in this transmission is very high quality, but it still breaks down in that extreme heat.
As I have already mentioned, all of the earlier Mercedes-Benz transmissions were to be serviced every 30,000 miles. The fluid in the 722.6 is much better than the Dextron III in the older transmissions, so it is definitely good for longer than the 30,000 mile interval for the older transmissions but not the “lifetime” of the car. I don’t know about you but I expect to get at least 250,000 miles out of any Benz, and I don’t want to have to replace the transmission.
I recommend replacing the fluid and filter in this transmission every 60,000 miles. It is the best $259.00 you will spend. The alternative could be a $5000.00 repair.