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  #1  
Old 05-25-2015, 10:33 PM
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The case for not changing trans fluid

Maybe, at least on a 722.6. .

I've taken apart 2 722.6 trans that had high miles. ( 120 K range )

The 98 S320 trans was bought as a core with a broken center planet. ( thrust washer cage came apart and rollers broke gears.) The pan had metal bits but no fine shavings. Worn clutch material build up in the pan was nearly non existent. Filter was same date as trans build so I'd say the fluid was never changed. Clutches and steels were in excellent condition.

97 C230 bought as a working trans, filter was ~ 4 years newer than trans build. This one didn't have any metal bits and worn clutch material build up in the pan was nearly non existent. I haven't pulled the internals apart yet.

In both cases the fluid was brownish but translucent, still retaining a red color with no sign of being overheated / burnt.

In the past I've found some reference on the net that the fluid used in the 722.6 is designed to keep friction material in suspension so as the friction plates wear, the friction coefficient of the fluid rises to compensate. The down side I see is possible increased wear of sliding metal surfaces.

The 722.6 controller has a fluid life calculator and some other info as well that can be viewed using a MB scan tool. This makes me wonder if fluid life was used in shift calculations.

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  #2  
Old 05-26-2015, 10:04 AM
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I've seen too many failures under 120k that makes me suggest otherwise. funny mb changed their mind in 2008. and so it goes, chuck.
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  #3  
Old 05-26-2015, 01:14 PM
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Both my 00 C230 and 05 CDI have been running well, no issues.
195K on the C230, 187K on the CDI.

Not the original fluid in either, so maybe that helps...

Jim
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  #4  
Old 05-26-2015, 04:58 PM
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The trouble with making assumptions about the care and use/treatment of any used trans. is just that - a guess. Forensically speaking, when you open 'em up, all is clear - except how the car was driven.

I can make a case for the fact that some trans.' are destined to fail long before the 100K mark. The reason(s) why are unclear though. One would have to believe that either the trans. was faulty, it's associated system(s) failed, or, the hard use given those trans.

I can make a case that in service time and miles, changing the fluid/filter(s) was unnecessary, to a fine working trans.

Knock on wood, none of our (6) (most bought new) MB AT trans. have failed in up to nearly 500K miles of use on one. With well over 1 Mil miles collectively - no fails.

Have had super good luck with American-branded cars' AT trans. too - with the exception of a GM /FAIL @ 60K miles.
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  #5  
Old 05-27-2015, 07:44 AM
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If you look at it from a materials standpoint, you can make a case that a particular transmission is designed to execute X number of shifts for it's design life.

Factors modifying the X number would be, of course, how hard the shift was (light throttle, hard throttle) and the amount of torque transmitted (engine power). Fluid changes to remove the "fines" that accumulate from wear products would be beneficial, more so if the transmission is driven hard.

So, lifetime will vary considerably depending upon use and maintenance.

Obviously, the trans that is driven in town, under hard acceleration will have the lowest lifetime, probably independent of fluid changes. And a small engine car will tend to shift much more than a lazy big engine car, giving the big engine trans a better chance at a longer life (if not abused by excessive power application).

And the longest lived one, will be one that lives on the highway, accumulating hundreds of miles between shifts. Add in a light footed driver, and possibly unnecessary (premature) fluid changes and you have the recipe for potential high mileage.

My 91 300D belonged to my cousin Tim, and his use followed the above, The 300D currently has 301K on it, and the original trans is quite nice, firm, crisp with little or no lag into reverse. Likely good for many more miles.

Jim

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14 E250 BlueTEC black. 45k miles
95 E320 Cabriolet Emerald green 66k miles
94 E320 Cabriolet Emerald green 152k miles
85 300TD 4 spd man, euro bumpers and lights, 15" Pentas dark blue 274k miles
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