Auto gearbox idler thrust bearing on W202

[rx6180]

I remember now what I was going to post on here back in March before my computer began to lose its marbles. In February I took my 1999 C200 to an independant auto transmission specialist because at 110,000 miles I thought it needed a fluid change which had never previously been done. Of course according to MB the trans is sealed for life. Two hours after dropping the car off I got a phone call telling me that there were aluminium particles in the sump fluid, which the mechanic was adamant was related to a thrust bearing wearing its way through an aluminium idler gear. He told me that it was a "well known fault" and that a new part had been designed to get around this, a needle roller thrust bearing with ears that fit into recesses on a new idler gear so that the bearing cannot spin independently. I was invited to go and see the metallic elements in the sump for myself (which I did) and was offered the option of having the trans refilled so I could get rid of the car, or having the job done, which would involve a trans strip down. I was told that left as it was the trans WOULD fail and that normally the cars were brought in on a trailer with seized transmission rather than driven in like mine.

I do have some issues with the price I paid as I opted to go 'cash in hand' to keep costs low, but the goal posts did move once or twice. However, I have little doubt the 60 odd-year-old mechanic was up front about the technical aspects of the job. I saw an exploded idler gear from another MB gearbox and he had one of the new design thrust bearings in stock when I went to view the deposits in my sump, and I am convinced the non-exploded but worn idler gear I saw when I collected the car was from my trans. I was going to take it with me, since I was getting no official paperwork for the job but darn it, I forgot.

The point is, if a new design of bearing was needed to prevent it wearing its way through the aluminium idler gear, how many cars have suffered or are suffering from this potentially disabling and expensive ailment? My car was driving perfectly normally. Apparently it would have continued to do so until the needle rollers fell out of the old bearing, due to it running eccentrically on its worn mounting face, and the needles would have jammed in the gear teeth. While my car was in for repair, I tried in vain to find anything out on the internet about this 'well known' design fault in the trans, and the only reference I found to it was on this very forum, with one member describing the sequence of events on the day his transmission failed in his 1990s E Class car, which he put down to the "Well known idler gear thrust bearing failure". I just don't understand why I can't find out more about this, or why windscreen wiper mechanisms are a highlighted weakness on 1993-2001 C Class cars but not automatic gearboxes with the 722.6 transmission! I'm satisfied with the standard of workmanship for my trans rebuild, if not the price, and satisfied that it DID need doing and would have failed sooner or later if I'd have carried on driving it with no maintenance to the trans as per MBs recommendations.

 

[television]

All boxes have some sediment in the bottom, what we do not know is if this bearing wears to a certain point and then stops,,it is not a common or listed fault

 

[rx6180]

Yeah, well, the guy did say that where he gets his idler gears from he was told it is only his company that buys them! I can't deny that I did have some alarm bells ringing in my head but I was insistent that I wanted to see the old parts that had been removed from my trans. I know that the wear pattern on the gear I was shown couldn't be faked by machining so unless it was from another car (which isn't impossible but I was satisfied that it wasn't at the time) then there was the potential for trouble ahead. Of course, what isn't known is how long it would have taken.