5hundo

Hey guys.

So, it looks like the rear main seal has gone kaput on our ML320CDI. We're probably just going to fix it because the auto market isn't really great for buyers at the moment. It's getting better but still...

I was trying to think of other things that we could do while the trans is off the car, which got me thinking about the possibility of putting a new trans in while they have the old one out. It's got 200K miles on it, so I'm thinking it would make sense. The only thing is that trying to find another transmission outside of the dealer network is complicated. Are there any good sources for rebuilt transmissions for the CDI/Bluetec?

Also, what else should I think about doing while the transmission is out? I was thinking about possibly rebuilding the transfer case, since that seems to be an issue on some cars. Honestly though, I haven't noticed ours slipping.

Anything else?

5hundo

...or would it be enough to replace any serviceable seals while the transmission is out?

kcmgt

This is a late reply. Those V-6 Diesel’s are notorious for the oil cooler seals leaking. The way they leak makes it look like the rear main is leaking. Yours may be different but the rest of us have done updated oil cooler seals.

5hundo

Thanks for the reply!

So, I've replaced the oil cooler seals (and flap motor) myself once. That's not to say that they haven't started leaking again (I'm not technically a professional mechanic) but two independent mechanics have now told me that it is, in fact, the rear main seal. I might order a cheap borescope and see if I can find any leaks myself. The shop we're having it fixed at couldn't do the job until April, so I have a little time.

In the eventuality that is is the main seal, what should I do when the transmission is out? I thought about just replacing it but that is cost prohibitive.

kcmgt

I think you are on the right track with a remote camera. You will find plenty of other uses for it anyway. I have a DEPSTECH from Amazon. You might try adding some dye to the oil and use a black light too (not much cost there). Combining this with the camera should tell you what you need to know. Out of the three I own, one is on its second set of oil cooler seals. The 722.9 transmissions are very robust and there really isn’t anything to replace inside the bell housing. Any “shift issues” are typically in the valve body and clean fluid and filter are your friend there. It is accessible by dropping the trans pan. I prescribe to old school Mercedes logic and do all of mine @30k intervals (book says 39k). You are correct, that’s a pricey transmission but rarely ever replaced.

5hundo

Ok. That's good to know. There's no shaft seals, that I could replace while its out? I was trying to view a schematic or something but its hard to tell.

Yeah, we have serviced it a few times already but we will make it a point to continue doing so.