Fried Chicken

New RMS is in and is sitting overnight. I'll know tomorrow if the new one leaks or not. I had to re-do the one on the M113 because it didn't sit right (inside lip folded out).

Not a job for noobs. While in there I replaced the crankshaft position sensor, as it's a ***** to reach otherwise.... like idk even how one would reach that.
There's a lot of hoses and **** to remove, re-installing everything is going to be a *****, although there aren't any brackets to contend with on the very top of the bellhousing, unlike the M113 with ABC.

The transmission fluid came out black, I'm not happy about that, but idk if there's anything to be done . I'm going to do a proper flush, and hopefully I can find the seal for the torque converter so I can change that out too.

Not a fun job, would not want to do this in a gargge, but hopefully I'll be done by tomorrow. Here are some pictures of the back of the engine that people in the future might want to use as reference.

Fried Chicken

Update: Everything got put back together and it looks like it went well. There are no obvious leaks anymore. The torque converter didn't have a drain so I pulled it out and manually drained it. I also blew pressurized air through the transmission cooling lines to get rid of whatever fluid is in those lines and the radiator.

This is not a job for the fainthearted. It's not that any particular step is difficult (mercedes are in fact, designed to be worked on), but requires full mental faculties and good habits of someone experienced with working on vehicles. There's a lot of stuff that needs to be moved away, including releasing various hardline pipes for the transmission cooling lines and ABC from their mounts. My recommendation is only releasing the bolts enough to free the clamp holders, otherwise it'll be a PITA to get those back in. Furthermore, I would not do this in a garage on jacks and/or without a proper transmission jack with tilting functions. Other tools you'll need are E-Torx sockets, a ~2-3ft. extension, and a wobble joint with some rigidity to remove/install the bellhousing bolts. You will find the above pictures useful (I certainly did)

Another recommendation is a genuine rear main seal. I mentioned having done the rear main seal on the M113 W220 twice. The first time I used a non-genuine unit. I don't believe it was inherently bad/faulty, but the tolerances made it thus that when slipping it on the crankshaft, the inner lip was too tight and folded over. I had to do that job again, and it rendered the car dangerous in the meantime; it was gushing so much oil out the back it flew onto the exhaust and started smoking. This isn't the first time I've found minute differences in tolerances between genuine mercedes parts and OEM/Aftermarket (The other time was the valve cover gasket on the M113 which leaked oil onto the alternator and fried it. Fortunately it had warranty, but saving $20 would have otherwise cost $300 + labor).

Mercedes recommends new flywheel bolts and torque converter bolts. When I called the local dealership, mercedes only had the flywheel bolts, so I re-used the torque converter bolts (there are 6). I used blue loctite. To remove the bolts you'll have to turn the engine. This requires you to disconnect and pull the radiator fan upwards. Then you can shove a 27mm socket onto the crank bolt at the front of the engine. Only turn clockwise (when looking at the engine from the front). Use a ratcheting wrench and not a breaker bar, since you're not going to get the fan fully out and you don't want to damage the fan by constantly shoving the socket up and out.

I already mentioned this, but it's worth repeating: now is the time to replace the crankshaft position sensor. It's the little black thing sticking into the inside of the engine bell-housing area. These have a tendency to fail and will cause the vehicle to not start when hot. It's a $30 part and I installed a Bosch unit (in fact I think I have an extra if you want to PM me, $20 + shipping).

Out of an abundance of caution, I unplugged the battery as I was told the starter (+) line is always hot and you will be unbolting the starter. If it strikes any ground, it would throw lots of sparks and cause general problems. I don't believe the mercedes documentation calls for disconnecting the battery, and nor did the starter move really at all during this procedure, although I had to shove it a little bit to get the flywheel off. Before lifting the transmission back into position, I threaded one of the longer bolts into it and pulled it into position so as to make threading the bolt with the bellhousing/transmission in place easier and prevent stripping/cross-threading. You don't have much access to the starter by hand as there is shielding in the way.

While I had the transmission drained and re-installed, I replaced the filter and transmission gasket once I had it back in the car. The bolts for the transmission drain pan are torqued to 8NM, and apparently there's an order/sequence they need to be tightened (Tried searching for it, couldn't find it. It's a picture someone posted on benzworld). I still stripped out one of the bolts, but it doesn't appear to be leaking. No harm no foul. Once I had the car on the ground, refilling through the dipstick tube took about 6 Liters. The fully drained transmission/torque converter takes 8 liters, so this about makes sense. Mercedes doesn't include a dipstick b/c they are dipsticks. I used a mixture of Febi Bilstein 29449 and Liqui-Moly 1600 ATF, b/c that's what was laying around. ATF fluidspecs are weird. There was the standard mercedes ATF 134, but I think that's deprecated and now there's MB 236.12 and 236.14. The 722.6 is an old transmission, so I think it'll take any of those three.

Anyway, here are some useful torque specs (they are pretty much the same for all 722.6/722.9 transmissions across all models):

Flex plate (flywheel) to Torque Converter Bolt (M10): 58NM
Crank Bolts: 45Nm + 90°
Bellhousing bolts (trans to engine): 38Nm

Trans mount to trans: 40Nm
Frame carrier: 40Nm
Flex disc bolts: 60Nm

I'll update if anything happens like the engine exploding or something. Anyone with further suggestions/comments are encouraged to share. I believe there's an additional step of programming/adaptation resets that I did not do. If anyone else knows, pls share.

Fried Chicken

The transmission drain plug torqued to 20 Nm

Fried Chicken

Just did an oil change and checked. She's bone. Dry.

brucewane

Thanks for posting this. I've got a minor leak in the lower rear engine area on mine, not sure if it's the oil pan or the rear main seal yet. It'll leave 8-10 drops of oil on my garage floor after a drive, so for now I just live with it by sliding a sheet of cardboard under it. It's not my daily driver, so it's not terribly inconvenient.

Have you ever swapped out the transmission of any other car? I've done a bunch in the past, DIY on a garage floor, Chevys, Toyotas, a Datsun truck, all RWD. Just wondering how it compares. I've spent a fair amount of time under my SL600 and it doesn't look like it'd be all that different from most other RWD cars. There's always trans cooler lines and exhaust various other stuff to get out of the way. ABC lines won't be a problem for me; I've converted to VVK coilovers and already removed some of the ABC lines, and any remaining in the way can be removed via wrench/bolt cutters/angle grinder/whatever and not reinstalled.

I did all those previous jobs in true shadetree mechanic style, just basic tools and a floor jack 'cause I was broke and specialty tools/jacks were a lot harder to come by 30-40 years ago. If I do it on the SL I'll buy one of the transmission jacks that Harbor Freight carries. And I've got a much, much bigger toolbox these days than I did back then with pretty much everything needed for MB work - torx drivers/sockets, ratcheting flex-head wrenches, triple-square bits, etc.

brucewane

I've also got a hot start problem, but it's weird - once the car's hot, on first try it'll crank for a long time and sometimes start, sometimes not, but then on the second try it starts right up like nothing's wrong at all. Cold, even after sitting for weeks, it always starts right up. I need to spend some time with it hooked up to my SDS to see if I can figure out what's going on, just haven't had time due to other projects.

Fried Chicken

I've done three before this one. Mercedes transmissions are relatively easy to do (actually Mercedes cars in general are pretty good to work on for what they are). The only thing that changes with the V12 is the amount of crap and the amount of care that needs to be taken because of all that. The only real "*****" part were the exhaust mounts welded to the exhausts, and anything that mounts along with the bellhousing bolts being in the way. I couldn't get my transmission to seat right when I realized by oil dipstick tube mount was wedged between the engine and the bellhousing. I have to stress good habits, including organization so you can keep track of all the nuts and bolts for all the crap, and also not forcing something if it won't go. For the hardline tubing, like I mentioned, you're going to want to loosen them, but all the bolts going forward from the transmission along the engine are accessible (again, Mercedes was thinking when they built this).

I said you want to do this with a proper lift and proper jack, but that's just because of all the crap you have to maneuver around. You don't want to damage anything removing or installing the transmission, and that's where a very good jack helps a ton. If you're patient and masochistic enough, you could do this on jacks and from the floor, but just be careful not to damage anything going in and out. Make sure you remove/loosen everything you can. My writeup will make more sense once you're actually underway doing the job. If this isn't your first transmission, you'll be fine. It took me 2 days to do, about.... 14 hours?

Sounds like a crankshaft position sensor. Allegedly they can be replaced from the top, but in practice I don't see how this is possible (see the first picture I posted). If it's leaking and not starting right, I'd go ahead and do it.

NHSl550

How did you replace the seal? Did you use the proper tool or just tap it in like most do?
I picked up all the parts to do mine last fall but havent done yet due to weather. (My lift is outside) Also got the seal tool. and a tranny jack.
MB also recommends replacing the plate that holds the seal. Did you change that or use the old one?

Fried Chicken

Didn't touch the plate that holds the seal, and didn't use the special tool, *did* use genuine Mercedes rear-main seals. The first Mercedes rear main seal I did was on the M113 and I had to do that twice. It reversed itself on startup and gushed fluid out. I used an aftermarket rear main seal, it resisted when going on and likely folded over. I used a tool, but not *the * tool. I'm not sure how important the tool is.

If you see leaking around the hosing, you might want to re-do the housing... but it's a gasket-maker/RTV job with all the caveats that brings with it (chiseling the **** off, expertly/artistically applying it, etc.)