Transmission Life Expectancy - PeachParts Mercedes-Benz Forum

Ron in SC · #1 12-13-2004, 05:27 PM

Have the transmissions used in the ML been used long enough to have a record as to how long they will last. With my older Mercedes cars and thoses of my friends I found that if the transmission lasted between 125k miles and 175K miles we did pretty good. Any less miles we were dissappointed and with any more we were quite happy.

Gilly · #2 12-13-2004, 08:04 PM

I personally know of a E300D with a 722.6 that at the last point I knew had gone 275,000 miles without so much as a fluid change (that everyone insists has to be done). It is the same type of trans as the ML.
Gilly

Ron in SC · #3 12-14-2004, 09:13 AM

That's certainly encouraging news. Do you think an E300D would put any less stress or more for that matter on the gearbox than an ML?

Gilly · #4 12-14-2004, 09:02 PM

I don't think it would be much different, unless you are an aggresive driver. The vehicle being discussed was owned by a salesman who put the first few hundred thousand on it and did maintenance only per MB literature (maintenance book/FSS, no more, no less), the guy REALLY piles on the mileage.
Gilly

RickT · #5 12-15-2004, 02:07 AM

I have seen some posts about the transmissions on the ML 320 going out early. I had 30,000 of VERY easy driving mixed equally between city and highway and mine needed to be rebuilt at 30,000. On the other end of the spectrum I have also seen posts of MLs in the 100,000 + miles and still going strong. To get this many miles in a few years likely means highway miles, which are probably easier on the vehicle.

I also recall seeing somthing about the specs on the transmissions were different for the ML 320 vs. the ML 500.

Gilly · #6 12-15-2004, 04:38 AM

So there's your answer, somewhere around 30,000 to 300,000 miles. Depending.
Yes the V6 and V8 transmissions are rated at different torque inputs. Internally they are known as the "small NAG" and "large NAG" transmissions.
Somewhere I have a spec sheet that lists the different torque ratings between the 2. The smaller one is for 4 and 6 cylinder engines (incl diesel, this is for the 722.6, not sure about the CDI, I think that's the new transmission) and the large one is for the 8 and 12 cylinders.
Gilly

jfreezn · #7 12-15-2004, 11:00 AM

A Chandler dealer's SA was reviewing my 98 ML320s service history and when he noted 123,000 miles he suggested I start saving up for a new transmission as he felt 125,000 was about the average. $5000 plus for a dealer replacement.

I immediately changed the ATF to Mobil 1 (not factory fluid) and am now at 131,000 miles. My 79 300SD, which slipped for years, is now shifting as good as new and has 261,000 miles with only a new accumulator. Also on Mobil 1 ATF.

It should be noted that when a dealer declares a transmission dead, it is the only expedient thing they can do to minimize come-backs. The first failure could be as simple as a gear selection solenoid failure, easily replaced, but probably the first in a chain of failures that the dealer would wish to avoid.

Just my opinion, YMMV.

Jim

Gilly · #8 12-15-2004, 08:30 PM

Don't be surprised when the tranny IS smeared at 125,000 miles since you're not running the factory fluid.......
Gilly

jfreezn · #9 12-17-2004, 11:10 AM

Quote:

Originally Posted by Gilly

Don't be surprised when the tranny IS smeared at 125,000 miles since you're not running the factory fluid.......
Gilly

Gilly,

I am well aware of MB stance on transmission maintenance: They say don't EVER change the fluid, it is good for life! But if you do, you have to use our fluid. Well, given the mostly negative results of their directions, I'll take my chances with Mobil 1 ATF.

Personally, I expect any automatic trans to last more than 125,000 miles.

Regards,

Jim

Litton · #10 12-17-2004, 02:30 PM

I will admit to being totally mistified by this whole transmission thing. To me, sealed for "life" means it's sealed and should never fail as long as it is driven withing the stated parameters. Now I am seeing experts telling us that a "newer" MB will only get ~125,000 miles on a tranny. That seems awfully short. My '90 420SEL had 197,000 and was in great shape, my '72 280 SEL 4.5 has 176,000 and the tranny is tight as a drum......hell, my '87 Chevy Blazer has 190,000 and it spends much of its life bashing through the Arizona mountains and deserts.

The key (at least I thought) was to change tranny oil every year. Now MB is saying never change the oil, and Oh Yeah, it will run for life but life seems to mean ~125,000 miles. If you do change oil use MB....if not it will fail. I'm sorry folks, but there seems like a disconnect here.......I must be missing something 'cause this makes no sense.

Gilly · #11 12-17-2004, 03:09 PM

Quote:

I must be missing something 'cause this makes no sense.

Yeah you're missing something. You're "missing" all the thousands and thousands of 722.6's that are running around with the original factory fluid (never been changed) that are doing JUST fine. ALL you hear about are the small minority that fail, and failures that are not attributed at ALL to the fact the fluid had never been changed. You coulda changed the damn fluid every 10,000 miles if you wanted to, and they STILL would have failed. Can't make anyone believe that though........

Gilly

smk_texas · #12 12-17-2004, 05:44 PM

Replaced one at 123,500......guess it was a mis daignosis on the dealers part....would not give the code printout (original report)......I wrote to MB also they said they couldnt anything......I think it was the low range motor all along and that was done for free after 5 months because transmission was acting up again with the new one also.....so a low range motor was put on for free......because once before when the transmission did not shift a low range motor was replaced......all its life the same dealer had done all service including oil changes....

BenzRepair · #13 12-18-2004, 08:41 PM

Bought a '99 ML430 with a bad transmission so I could educate myself on fault diagnosis and rebuild techniques; instead I got schooled on how many parts in that propulsion unit have been updated and are no longer useable when putting it back together again. The transmission itself tossed the entire planetary gearset (all three -- love auction cars, everyone has to drive it to make sure it's bad), and I originally thought it was the typical mercedes planetary failure where the center bushing that links the front shaft with the back shaft wears excessively and fails, pinching the bearing surface and shattering the bearing, causing catastrophic failure as the individual hardened steel needle bearings are fed through the planetaries (the update replaces the bronze bushing with a roller bearing, requiring the purchase of the front shaft and tail shaft assembly.

The sungear assembly is updated (main sungear almost always fails, and requires purchase of entire sungear assembly); the rear planetaries are updated; the bearings in much of the transmission are updated (requiring replacement of MUCH more expensive componants). But I'm a trooper, and even though I could have bought a completely rebuilt tranny for the price I paid for the parts ($2700 wholesale), I learned quite a bit. For example, there are not many good sources for used parts, because so many things were updated, and WHEN these transmissions fail, they like to toss the planetary gears. Also, the failure in earlier transmissions is due to to poor designing on Mercedes part (later transmissions are much more durable); the earlier transmissions ('00 and earlier 722.6) require fluid changes, and given the weakness of the center bushing, about 50-60K on the fluid changes seems about right (given that the tranny weakness is on a transmission already past that service period on an older vehicle anyway, I don't like my odds, particularly on the higher-output engines). I'm sure the newer tranny's are more durable (I can attest to that... mine is updated, and the transmission design IS more durable).

Which brings me to why the transmission failed in the first place... the front sungear to rear planetary bearing failed (the bearing was updated as well, but still has a weakness in the planetary design with that bearing, IMO). Bearing failed and little needle bearings greeted the planetary; they did NOT get along at all. That torrington still needs designed IMHO (I'm full of it tonight). I'll update (no pun intended) as I get time, but runs great now.

Mechanically, the internal difference in the transmission regarding the torque output I believe is such: lower torque outputs have a 3-wheel planetary drive, and higher output tranny's utilize a 4-wheel gearset.

Litton · #14 12-20-2004, 09:14 AM

BenzRepair.....that was an extremely informative post. For those of us that have lower mileage vehicles (my '98 just turned 80K) the question of changing fluid is is still a confushing issue, should we or should we not? And if we do will it really by us anything. Then there is the fluid issue. I suspect that the MB fluid is a synthetic and the change to a commercial grade (i.e. Mobile One may not be to our benifit.

You think that the 50K change interval may prolong our tranny life, and if the cause of premature failure is mechanical wear, that make a lot of sense. Granted, we are not going to reverse damage, but it should give some benifit.

What are the early symptoms these tranny's exhibit once they start down to slippery road to failure? With all the mods MB has made over the years, it would seem like we have two options: 1) Drive it till it fails completly and replace it with a quality rebuilt, or 2) Get it fixed as soon as it starts displaying the early symptoms.

RickT · #15 12-20-2004, 03:14 PM

My dealer told me that the cost was $300 for the transmission oil change. Compare that to $3,000 for a rebuild. To me the answer is simple, change the oil every 4 years or 100,000 miles (just like you do with the spark plugs). Even if it does nothing, it certainly won't hurt.

As for symptoms, a few are:
- shifting points are off
- sticks in a gear for a prolonged period
- sliping