Leaking transmission front seal

[500AMM]

Upon purchase of my '92 it had an oil seepage from the transmission, just a few drops on the floor over time and it was hard to see where it came from. It didn't bother me too much, but it has developed over years and I suspect a bad front seal. The oil drains out from the bottom of the bellhousing below the torque converter (TQ), and it's not many potential leak points in there besides from that front seal and the TQ itself.

I have to fix this and supposed it is the front seal, the transmission has to come out to remove the torque converter to get access to the seal. I haven't done this before so I have a couple of questiones:
- can this seal be replaced from the outside, like the crank seals?
- does the TQ just slide off the pinion?

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[gerryvz]

Hi Arnt,

This thread with a similar variant of the 722.3 may help you. You have to remove the torque converter to get to the front seal, but it can be replaced at that point.

The torque converter just slides onto the shaft, yea. But you have to be very careful with lining everything up.

It actually makes sense to do a complete exterior reseal while the transmission is out of the car. It’s only a couple of hours of labor to do this as long as you have the parts. They are all available.

The HOW-TO on removal pertains to a six cylinder model but is about 98% applicable to the 722.3 as used in the V-8 models of the 124. Definitely the process is the same, but access to the bolts is slightly different due to bell housing design and how closely packed things are under the V-8 hood.

HOW-TO: Removing & Replacing 722.3 transmission (W124/M104) | "HOW-TO" Tutorial Articles

Well, as I'd mentioned on another thread, last Sunday my wife's 1995 E320 wagon transmission died, with 203,200 miles on the odometer. It died suddenly, losing all four forward gears. Reverse worked fine. This is the classic 722.3 "B2 piston failure" that is very common to the 722.3...

www.500eboard.co

 

[500AMM]

Many thanks Gerry!

I've scrolled through the HOW-TOs and various related threads, and they will definitely be helpful! Yes, I have to sort out as much as possible while in there, both post and preventive maintenance. The car has approx 160 kkm, where 110 kkm is after the 6.0 conversion, but due to aging all rubber & seals, bushings, flex discs etc.. will be done. Should be a nice deduction from the well known GVZ $5000 deferred maintenance list.
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[gsxr]

I have to fix this and supposed it is the front seal, the transmission has to come out to remove the torque converter to get access to the seal. I havent done this before so I have a couple of questiones:
- can this seal be replaced from the outside, like the crank seals?

There are TWO seals which can cause this leak. One is the TC (torque converter) radial seal, and yes this can be replaced from the outside without taking anything else apart. The other is the large-diameter O-ring which goes around the outside diameter of the pump. To replace this, you need to remove the primary pump, AND take it apart, which requires buying or fabricating special tools to compress the springs. While apart, it's generally advised to reduce the spring count from 20 to either 16 or 15 (evenly spaced), to help with reverse piston engagement/wear. With the pump out you can inspect/replace the reverse clutches and K1 clutch pack.

- does the TQ just slide off the pinion?.

Yes. However, it's important to carefully measure the TC depth before removing, assuming it did not shift during removal. This is step 24 in the FSM/WIS doc, job 27-600 (link). The document shows ~30mm depth but I vaguely recall the actual depth is more. I need to find my notes on this. When installing the TC, it is absolutely critical the converter is fully seated, and this can take repeated efforts to get the primary pump engagement tangs aligned with the TC notches. If the TC is not fully seated, it will destroy the front pump ($$$) if you use the bellhousing bolts to force the transmission to pull up against the engine. The trans should pull up to the engine by hand, while the converter spins freely... if not, something is wrong.

With the transmission removed, don't just replace the TC seal and front pump O-ring. Replace EVERY external seal and O-ring, including the selector shaft seal, output shaft seal & O-ring, and speed sensor plastic cup O-ring. Don't damage the plastic cup though, that part is NLA. Search the forum, I believe this has been discussed in detail in the past. Cost for the seals is minimal, and the labor is relatively easy with the transmission out of the car.

Documents: Index of /docs/mb/transmission
Photos: Index of /images/W124_transmission

 

[500AMM]

Yes. However, its important to carefully measure the TC depth before removing, assuming it did not shift during removal. This is step 24 in the FSM/WIS doc, job 27-600 (link). The document shows ~30mm depth but I vaguely recall the actual depth is more. I need to find my notes on this. When installing the TC, it is absolutely critical the converter is fully seated, or it will destroy the front pump if you use the bellhousing bolts to force the transmission to pull up against the engine. The trans should pull up to the engine by hand, while the converted spins freely... if not, something is wrong.

Thanks Dave! It will be a great job with a lot of technical reading and high attention to details. How do I know if the TQ is shifting during removal?

 

[gsxr]

Thanks Dave! It will be a great job with a lot of technical reading and high attention to details. How do I know if the TQ is shifting during removal?

Arnt, after unbolting the TQ from the flex plate, it will push back towards the transmission slightly - maybe 10mm? This is the fully-seated position. When jockeying the transmission around during removal, the TQ could shift. Once the trans is separated from the engine and lowered on your transmission jack, try to use wire & wood blocks to force it to stay fully back, until you can measure the depth anyway. The TQ is HEAVY, btw.

Forgot to mention for the top 2 bellhousing bolts, do not try to remove these from below the car with long extensions. Remove the throttle linkage from the back of the intake manifold, and remove those 2 bolts from above - way way way easier. Might also need to pull the plastic air intake grille assembly to make room for tools.

 

[500AMM]

Thanks again - very useful advices!
It will be some time until I take on the job, have to prepare with more tools & equipment first, maybe install a 2-post lift as well. Another issue is the winter & low temps and the cost for heating up the garage, the power prices are insane over here now due to the ongoing stupid war.