HOW-TO: Removing & Replacing 722.3 transmission (W124/M104)

[gerryvz]

One reason why I take a lot of photos when I do jobs. Which translate somehow, in to "HOW-TO" articles.

 

[nickguy]

Mystery solved. The oxidation I noticed was due to the ground strap. When actually working on the car it became obvious that JC220 was actually right. Not because of nuts but the longer bolts are for the aluminum oil pan. Imagine the design is to provide a bit more thread on the aluminum to provide more clamping style. So the 2 bottom bolts are the long ones.

 

[nickguy]

Completed my install. I would not have been able to do it without this brilliant thread. Thank you Gerry! Decided halfway through to make a video of the install. Posting here. Hopefully someone finds it useful like I found this thread useful.

 

[Unavita]

Well, tonight in the shop it was just 15 minutes or so to do some inspections of the underside of the car, since the transmission is out. I took some observations and photographs that you all should be interested to see. Glad I did this as I am getting ready to make my AutohauZ and parts.com parts orders tonight, and there are a few new parts I need to tack onto my p.com order....

First off is a good look at the flex disc. I'm going to remove it entirely from the car to inspect it closely, but here's a good close-up shot. From what I can see, there is no abnormal wear that would require its immediate replacement. However, I have one on my parts order and I'm going to replace it out of hand, because it's a consumable ("wear") part that will require replacement sooner or later. And it's MUCH easier to do it now, since I have extremely easy access to it....
View attachment 24894


Next is a view of the evaporator condensation drain tubes, located on either side of the transmission tunnel above the bell housing. These are the foam hoses with coiled wire inside. The 126 uses one of these hoses, too. The first one, on the driver's side, looked pretty good (first photo below), but it crumbled to dust when I touched the end of the hose portion. You can see from the second one that the only thing left of the end of it, is coiled wire, LOL!! So, automatic replacement. This is done from INSIDE the car, but you poke the ends of the hoses through the floor and into the transmission tunnel. Inexpensive but a good thing to do.
View attachment 24896 View attachment 24899

I'll bet your hoses on most of your .036s are close to or just as bad as these. Probably a couple hundred dollars of labor out of that $5K deferred labor bill that I'm always harping that EVERY .036 has. Even Dave's cars.

Next, it was time to look at the two-way water drain that channels water from the blower motor area under the windshield, down underneath the car into the bell housing area. This is sort of a "Y" shaped water collector.
View attachment 24900


You can see that the end of the collector on the right-hand (passenger) side is cracked off, and another chunk is in danger of cracking. So, automatic replacement time. Both of the ends were mildly clogged up with leaves and other dust/dirt, so I cleaned them out with a screwdriver. Then I just decided to pull the whole assembly off and order a new one.
View attachment 24907 View attachment 24904 View attachment 24902


Then, I checked out the oil pressure sender, which I just recently replaced around the time I did the top-end rebuild. You can see it clearly in the photo below, along with its electrical connector. Just below it in the photo, you can also see the crankshaft position sensor's black connector. I decided to replace the crank position sensor (it's a ~$55 part) as it is difficult to get to when the transmission is in the car, and an extremely simple one-bolt replacement now.
View attachment 24915


Then I looked backward to check the oxygen sensor. It looks quite original to the car, and since the car has 203,200 miles on the odometer, and I have a brand-new factory MB replacement O2 sensor, I'm going to replace it as well. It will NEVER be as accessible as it currently is, staring me right in the face...
View attachment 24916


From there, I inspected the steering box. Again, in plain view and extremely accessible from this vantage point. I have never seen a drier steering box in my life, so this is one sleeping dog that I'm going to let "lie."
View attachment 24910


Lastly, I looked straight upward to check out the flywheel and rear crankshaft seal, for any leakage or weeping. The area under the seal (actually a good portion of the entire rear of the engine block around and above the seal) was slightly damp and oil/dirt coated, but I did not see any active leakage from the large seal. Nevertheless, I'm going to pull the flywheel off (you can see that it is held on by eight XZN bolts) and replace this rather large seal. Just because if it ever DOES leak, the transmission has to come off to replace it, and it's an 8-10 hour job that I don't want to do again, any time soon. So 30 minutes of extra labor now, before I install the new transmission, is probably well spent doing this job.

Here are a couple of views of the flywheel and crank seal area.
View attachment 24912 View attachment 24908


I sincerely hope you enjoyed this little visual inspection tour of the underside of the car and transmission tunnel.

Cheers,
Gerry

Now that is has been 10 years Gerry, how did the Sun transmission hold up?

 

[gerryvz]

Now that is has been 10 years Gerry, how did the Sun transmission hold up?

It was just fine for the couple of years that I had the car after replacing the transmission. But I sold the car to a forum member, who sold the car to another forum member, who I think sold the car to yet another forum member, so I haven’t tracked things explicitly for some years now.

But I was happy with the Sun Valley rebuild. It did work fine out of the box.

 

[Seangbadee]

Lastly, I looked straight upward to check out the flywheel and rear crankshaft seal, for any leakage or weeping. The area under the seal (actually a good portion of the entire rear of the engine block around and above the seal) was slightly damp and oil/dirt coated, but I did not see any active leakage from the large seal. Nevertheless, I'm going to pull the flywheel off (you can see that it is held on by eight XZN bolts) and replace this rather large seal. Just because if it ever DOES leak, the transmission has to come off to replace it, and it's an 8-10 hour job that I don't want to do again, any time soon. So 30 minutes of extra labor now, before I install the new transmission, is probably well spent doing this job.

Here are a couple of views of the flywheel and crank seal area.
View attachment 24912 View attachment 24908

Does anyone know where I can find the XZN bolts? @gsxr mentioned that even with thread locker or anaerobic sealant they might still leak, and recommended the newer microencapsulated ones instead—any leads?

 

[gsxr]

Does anyone know where I can find the XZN bolts? @gsxr mentioned that even with thread locker or anaerobic sealant they might still leak, and recommended the newer microencapsulated ones instead—any leads?

EPC shows the original number was A0019909112 (see below), which appears to have been superceded to 008-990-05-04, $8.50/each MSRP.

HOWEVER! Google photos of the new part number show these bolts DO NOT have any sealant applied to the threads, so there's no point in buying them.

I would use anaerobic sealant on the old bolts after cleaning / degreasing them. Make sure the female threads in the crankshaft are completely clean and dry. You can apply Brakleen to the threads in the crank with a Q-tip until the Q-tip remains clean. The anaerobic sealant should work. I wouldn't use LocTite or other threadlock.

 

[Seangbadee]

EPC shows the original number was A0019909112 (see below), which appears to have been superceded to 008-990-05-04, $8.50/each MSRP.

HOWEVER! Google photos of the new part number show these bolts DO NOT have any sealant applied to the threads, so there's no point in buying them.

I would use anaerobic sealant on the old bolts after cleaning / degreasing them. Make sure the female threads in the crankshaft are completely clean and dry. You can apply Brakleen to the threads in the crank with a Q-tip until the Q-tip remains clean. The anaerobic sealant should work. I wouldn't use LocTite or other threadlock.



View attachment 217584 View attachment 217583

Great advice. Thanks.

 

[Seangbadee]

Great advice. Thanks.

Appreciate the pointers — I’ll clean everything thoroughly and go with anaerobic sealant as suggested, skipping the Loctite.

 

[Seangbadee]

Appreciate the pointers — I’ll clean everything thoroughly and go with anaerobic sealant as suggested, skipping the Loctite.

Gerry’s “How-To” write-up on removing the 722.3 transmission—along with the detailed photos—was exactly the motivation I needed to begin the job. At first glance, it seemed like a fairly straightforward process. But once I got started, I quickly realized it was more involved than expected.
Since I’m working solo on this project, safety—not speed—has remained my top priority throughout. To ensure stability, I put together a makeshift cradle to support the engine block, while resting the transmission securely on a scissor-style transmission jack I picked up from Harbor Freight.
With this setup, I was able to carefully shift the engine and transmission forward just enough to gain valuable clearance. That extra space made it much easier to access the top three 17mm bell housing bolts—including the notoriously difficult top starter bolt. With the added room, removing those bolts turned out to be far more manageable than anticipated.
After the bolts were out, I returned the engine and transmission to their original position. From there, separating the transmission from the engine block went smoothly.
P.S. I should mention that I'm currently working with the short block only—the cylinder head hasn’t been installed yet.

 

[Seangbadee]

Gerry’s “How-To” write-up on removing the 722.3 transmission—along with the detailed photos—was exactly the motivation I needed to begin the job. At first glance, it seemed like a fairly straightforward process. But once I got started, I quickly realized it was more involved than expected.
Since I’m working solo on this project, safety—not speed—has remained my top priority throughout. To ensure stability, I put together a makeshift cradle to support the engine block, while resting the transmission securely on a scissor-style transmission jack I picked up from Harbor Freight.
With this setup, I was able to carefully shift the engine and transmission forward just enough to gain valuable clearance. That extra space made it much easier to access the top three 17mm bell housing bolts—including the notoriously difficult top starter bolt. With the added room, removing those bolts turned out to be far more manageable than anticipated.
After the bolts were out, I returned the engine and transmission to their original position. From there, separating the transmission from the engine block went smoothly.
P.S. I should mention that I'm currently working with the short block only—the cylinder head hasn’t been installed yet.

EPC shows the original number was A0019909112 (see below), which appears to have been superceded to 008-990-05-04, $8.50/each MSRP.

HOWEVER! Google photos of the new part number show these bolts DO NOT have any sealant applied to the threads, so there's no point in buying them.

I would use anaerobic sealant on the old bolts after cleaning / degreasing them. Make sure the female threads in the crankshaft are completely clean and dry. You can apply Brakleen to the threads in the crank with a Q-tip until the Q-tip remains clean. The anaerobic sealant should work. I wouldn't use LocTite or other threadlock.



View attachment 217584 View attachment 217583

I originally thought I was chasing an oil leak from the right rear corner of the cylinder head gasket. After closer inspection, I found that oil was leaking from both the cylinder head area and the rear of the oil pan.
To remove the lower timing cover, I used the flywheel locking tool. During the process, I stripped a thread on the underside of the rear main seal cover.
After removing the flywheel and prepping the new rear main seal and cover for installation, I inspected the flywheel bolts.
The measurements are as follows:

• Shaft diameter of the used bolts: 8.28 mm
• Factory specification for new bolts: 8.5 mm
• Shaft length of used bolts: 22.34 mm
• Factory unstretched length: 22.0 mm
• Maximum allowable stretched length: 22.5 mm.

https://www.w124performance.com/service/w124CD1/Program/Engine/104/03-4100.pdf

The reduction in diameter indicates that the bolts have stretched beyond their original size, which may suggest permanent deformation. The length is slightly above the original but within the maximum allowed limit.
The end cover is sealed to the crankcase with sealant, per the manual. Would this be anaerobic sealant?

https://www.w124performance.com/service/w124CD1/Program/Engine/104/03-3270.pdf

I am looking for guidance on whether these bolts should be replaced or can be safely reused given these measurements.

 

[gsxr]

The end cover is sealed to the crankcase with sealant, per the manual. Would this be anaerobic sealant?

I'm not sure - @gerryvz, did you mess with the rear main seal cover?

https://www.w124performance.com/service/w124CD1/Program/Engine/104/03-3270.pdf

I am looking for guidance on whether these bolts should be replaced or can be safely reused given these measurements.

I believe those will be fine to re-use.

 

[Seangbadee]

I'm not sure - @gerryvz, did you mess with the rear main seal cover?

@gerryvz used MB black sealant

 

[IslandMon]

@gerryvz used MB black sealant

+1