Transmission repair or replacement - Mercedes-Benz Forum
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post #1 of 34 (permalink) Old 05-08-2019, 04:21 PM Thread Starter
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Transmission repair or replacement

First of all, I'm pretty sure I killed my transmission. It's a 2008 ML320 with about 175K miles on it.

Over the course of trying to get rid of drivetrain noise, I have replaced the front wheel bearings, rebuilt the front differential, and, recently rebuilt the transfer case.

While removing the transfer case, I removed the girdle that supports the tail of the transmission, and I was stupid enough to support the transmission with a decent sized board on a jack under the oil pan. I was concerned that this seemed to be dent the pan, but after everything was back together it looked OK, so didn't do anything more about it.

A few weeks and a few hundred miles later, the transmission started shifting badly and slipping. Pretty sure what happened was that the deformation of the pan blocked proper oil flow and damaged the transmission.

I took it to the shop that does my regular service work, and they installed a new pan and serviced the tranny. That helped things. Got rid of the hard shift when coming to a stop, but the slipping in first and second came back pretty quickly as soon as things were warmed up. They reported that the old fluid was quite burnt.

At this point, I'm thinking I either need a new transmission, to repair this one, or to replace it with a used one.

I really like my car, but I don't have much budget for stuff like this.

The shop came back with $5300 for a new transmission.

Looks like I can get a (theoretically good) used one for about $1100 including shipping. From what I've learned, I would then need to send out the TCM to be revirginized or made VIN agnostic so it could be used in my car.

I've never rebuilt a transmission before, but I've rebuilt engines, steering racks, the aforementioned transfer case... I wouldn't mind taking a stab at rebuilding the transmission, but I'm wondering how likely that is to be successful. How likely is it that the restriction from the pan caused damage that's reasonably repairable, like needing new frictions? Maybe steels? Bands? Looks like OE part rebuild kits start around $500.

Neither CEL nor ECU codes have shown up for this. As far as the control modules are concerned, everything's fine. So, no sticking solenoids as far as can be told.

What about getting a used one and switching my TCM into it? Is the TCM married to the valve body as well as the ECU, or just to the ECU? How much is involved in swapping the TCM and/or valve body?

Thanks for any ideas and help!
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post #2 of 34 (permalink) Old 05-09-2019, 02:35 AM
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M/B decided that the Trans. Control Unit is a Theft Relevant Part and can only be installed by a dealer or certain repair shops that they designate.

In other words they have cornered the market with this part and you cannot buy one.

Then after installation there is an adaptation that must be performed, step #10 in the PDF. So, even if you install a used transmission or the ECU, it must be adapted by M/B, and they won't do it.
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File Type: pdf R&I Trans. Electrohydraulic Control Unit #2..pdf (130.6 KB, 15 views)
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post #3 of 34 (permalink) Old 05-09-2019, 04:16 AM Thread Starter
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Thanks. Yes, that's what I understood.

However, places like Circuit Board Medics can "revirginize" a used TCM so it can be installed in a different car.

Then there's the question of whether I could swap my TCM into the used transmission. I don't think there's anything wrong with it. I am less sure about the valve body.
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post #4 of 34 (permalink) Old 05-09-2019, 05:22 AM
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Only revirginize with a guarantee. Good luck.
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post #5 of 34 (permalink) Old 05-09-2019, 05:24 AM Thread Starter
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OK. Does anyone else know whether it's likely that my transmission is repairable or whether I can swap my TCM into a used transmission?
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post #6 of 34 (permalink) Old 05-09-2019, 05:27 AM
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The 722.9 rebuild is well documented on youtube. Impossible to know in advance what was damaged, but I would replace the thrust bearings and torque converter while in there, in addition to the “soft” parts.
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post #7 of 34 (permalink) Old 05-09-2019, 05:56 AM Thread Starter
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Thanks. What about steels or pistons?

Although I'm still thinking it's probably not coincidence that it failed not long after my pan incident, is 175K miles a reasonable lifespan for one of these transmissions?

If it is wear of frictions, etc, and I replace all those, any ideas on the lifespan of the valve body? I'd hate to rebuild it only to have something else fail soon... but I'd love to actually go through an AT rebuild.
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post #8 of 34 (permalink) Old 05-09-2019, 08:26 PM
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You must have really dented the pan. The only thing I can figure is that the dent choked the filter and shut off fluid supply. For $1100, I'd buy the used one, swap out your conductor plate, and get ti back on the road.

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post #9 of 34 (permalink) Old 05-10-2019, 04:11 AM Thread Starter
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Originally Posted by rudeney View Post
You must have really dented the pan. The only thing I can figure is that the dent choked the filter and shut off fluid supply. For $1100, I'd buy the used one, swap out your conductor plate, and get ti back on the road.
Thanks. That's what I was hoping to hear: that the TCM could be swapped from one valve body to another and everything would be happy.
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post #10 of 34 (permalink) Old 05-10-2019, 10:39 AM
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Look on Hollander exchange. You may be able to source one for a little cheaper. Looks like 700.00 to 1200.00 depending on mileage. They also have them sorted between gas and diesel 722.906 and 722.902 respectively. Good luck.


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