Transmission leak (persistent)

[MihuAMG]

Hello guys,happy to be part of this forum,lots of knowledge and very helpful threads.Im a happy owner of few c36 AMG left equipped with a 722.328 transmission.Its been few years since I started to experience the failure of reverse and multiple oil leaks.Been looking for some time after either a low mileage used transmission or rebuild mine.I ended up founding a very low mileage good trans 46k miles and pull the trigger.Even though it was a low mileage trans I decided to change all external seals (o rings vacuum modulator etc) all parts genuine from Mercedes including oil pump seals and also removed 7springs from the reverse piston.

Long story short im experiencing oil leak coming from the driver side middle pan bolt and rear bolts of the pan,imo rear bolts get wet from the starting point leak and its just trickling.I changed the oil pan with a new one from dealer(horrible quality) none of the ears was straight,went through 2 pan gaskets already,did use a torque wrench for every bolt in the transmission...and leak it’s still there. One of the test ports aluminum washer wasn’t sealing properly i did change that too (I thought that’s the culprit) but leak is still there. I ended up cutting down the transmission ears all around when i saw how crooked they were to make sure oil pan gasket seats even all around still leaking.

Now idk could the neutral switch shaft seal to leak even though I changed that too when trans was out,straight forward job took off the seal and tapped new one with a deep socket all the way down,didn’t seem to leave room for doubts,other than that any inputs are very welcome since im running out of what could cause this leak.I personally the way it looks im still blaming the oil pan gasket.Thank you

 

[gsxr]

It's not likely to be the pan gasket, if the pan was straight and an OE gasket was used, and bolts torqued to spec. You should not cut off the ears of the pan, if you did so, can you post a photo of exactly what you cut? The small vertical tabs at the corners are for location/alignment and have nothing to do with sealing.

You must pinpoint the exact source of the leak. Do this by cleaning the area 100% clean and dry, and packing clean paper towel 'diapers' everywhere. Use tie wire to hold them in place if needed. Test drive until you see the leak on the paper towels which should tell you where the leak is, and/or is not, coming from.

If the pan was leaking, everything above the pan would be 100% dry... very unlikely unless the pan is warped or damaged, or if an aftermarket gasket was used, or massively over-torqued.

 

[MihuAMG]

Appreciate your quick reply! Pic attached. Aren’t the bolts holes the ones that help to align the oil pan to the transmission? Im going to stuffing some paper towels above the pan see if im getting any surprises but if there are then neutral switch shaft seal would be at fault which I have no idea what could have been gone wrong. Ill keep you posted though.

 

[gsxr]

Uh-oh. If I'm seeing that correctly, you may have ruined the pan. Those ears aren't just decorative, they also provide some limiting resistance to the bolt torque, to keep the gasket from crushing. It's normal for the ears to not be perfectly level but they shouldn't be drastically tweaked either.

If you had only trimmed the small vertical portion at the very top that wouldn't matter, but I think you cut through the lower vertical and eliminated the horizontal section, which is bad. It will probably never seal correctly. On the bright side, a new OE pan is only ~$65. I like to torque to 5Nm first, then go to 8Nm, then go over the bolts a third time again at 8Nm. Avoid aftermarket pans & gaskets, btw.

1990-1996 Mercedes-Benz Trans Pan 126-270-10-12 | MB OEM Parts

1990-1996 Mercedes-Benz part # 126-270-10-12 - Trans Pan

www.mboemparts.com

 

[MihuAMG]

Got it bummer! So even if torque down to 8nm after i cut the ears off gasket might got crushed? Reason i cut them is when i put the pan with the gasket on a flat glass table those ears wouldn’t let the gasket sealing even all around and after going under the car 10 times already lol i got kinda fed up but still the problem didn’t solve.But if that’s the case at that moment i was still having the leak coming from the test port pressure which i was not aware of.So now after putting new aluminum washer and still leaking you think that putting a new pan and gasket would fix the leak?! Obviously im going to double check paper towels too and hopefully above gasket everything is dry...not going to be home till next week though

 

[gsxr]

Yeah, the ears are misleading, you care about the gasket sealing surface being flat - not the ears. Keep checking above the pan gasket and when you are certain it's all dry, and there's still a leak from the pan gasket, I'd replace the pan+gasket one last time. That *should* take care of it.

Make sure to check both sides, btw... sometimes fluid can move around from one side to the other, depending on where exactly you are seeing fluid. The 722.3 is generally a PITA to get completely dry.

 

[Duh_Vinci]

Make sure to check both sides, btw... sometimes fluid can move around from one side to the other, depending on where exactly you are seeing fluid. The 722.3 is generally a PITA to get completely dry.

Ain't that the truth, and the small leaks can be challenging to find... I originally had a small leak, couldn't figure out where it was coming from, particularly after a fresh fluid change with proper torque and gaskets etc Leaking at B1 cover. Easy repair? | Transmission and Driveline Ended up being B1 sealing ring, I really had to get in there with a mirror just to see the weep. @MihuAMG yours seem to be a pan itself, a lot easier to replace than B1!!!

Uh-oh. If I'm seeing that correctly, you may have ruined the pan.

Nothing can bypass the "eagle eye"?

Regards,
D

 

[MihuAMG]

Yes very annoying especially when its all clean and freshen up.Been dealing with that too on the old trans,changing the B1 o ring on the car,i was almost at the point of dropping the trans in order to put the cover back but my ambition was stronger and ended up putting it back without taking trans out.Good idea with the mirror going to get one and check if everything above pan is dry.Id be actually happy if this persistent leak it’s caused by the pan(I damaged) .Ill keep you posted.

 

[MihuAMG]

Ok guys,so here are some updates photos with some paper towels rolled up and squeezed on the trans leak point.The middle of the pan area seem to be the culprit.Don’t recall yet leak above the pan(neutral switch shaft seal) looked with a mirror and seems dry right at the shaft.The white paper towel completely dry and everything else pictures speaks themselves .Pan gasket seem to be good,I didn’t crushed it or it does not seem to be crushed.

 

[MihuAMG]

Took off neutral switch and no signs of leak at the shaft.Changed the pan along with new gasket torque everything to specs.

 

[MihuAMG]

Ok new update.Saga continues,small leak still present now on the passenger side rear corner.Since there is also the kick down solenoid,can this solenoid leak through the bolt all the way out? Area where is attached to the transmission (crush washer) looks dry but the solenoid right at the bolt looks a bit wet like small drops coming out right where the bolt meets the solenoid.

 

[gsxr]

There are 3 soft O-rings for the solenoid, plus the aluminium crush washer. Have the soft O-rings been replaced? Those would cause a leak out the end by the hex head.

You can stuff paper towels below the magnet/solenoid after cleaning, this would pinpoint the source (eliminate the pan or anything below the solenoid).

 

[MihuAMG]

They have not ,here’s a pic

 

[gsxr]

Usually new O-rings works, but in some cases the other 2 components might need replacement.

From the W124performance website:

 

[MihuAMG]

Yeah going to replace the whole thing.Do you know by any chance torque specs for this bolt?

 

[gsxr]

Yep, in the FSM...

https://www.w124performance.com/docs/mb/transmission/trans_722_kickdown_R+R.pdf

 

[MihuAMG]

Hey guys! Another quick update,id say a bit more conclusive but also need some thoughts...still inclining to think it’s the gasket pan that’s leaking.Now the pan completely dry,whats left wet are the pan bolts.Attached some pics

 

[MihuAMG]

Ive insert some paper towels around rear pan ears in between pan and trans,also to double check kick down bolt isn’t leaking which ive also changed,ive wrapped the head hex in paper towel also.

 

[gsxr]

That's a different used pan, correct? And a new OE gasket? If the pan is straight and torqued properly, I would still be really surprised if it's the pan leaking. Use cans of Brakleen to get everything 100% dry before paper toweling again, then check frequently.

 

[MihuAMG]

Its the pan from my old used trans that was on the car,yes. Yes i did uses a whole can of brake cleaner all around before putting paper towels. Also im wondering (I know proper spec is ideal for tightening it up) if a bit less or a bit more would help sealing better this type of gaskets?! (obviously id say probably applying more torque but i incline to think that maybe a bit less torque would balance the sealing better,idk)

 

[MihuAMG]

Ok,so after I cleaned everything and put paper towels on rear corners and kick down bolt(drove 5miles),driver side middle and rear bolt gets wet,kick down bolt dry,and source seem to be driver side middle of the pan/gasket.What am I doing wrong? What could be at fault?

 

[gsxr]

Ok,so after I cleaned everything and put paper towels on rear corners and kick down bolt(drove 5miles),driver side middle and rear bolt gets wet,kick down bolt dry,and source seem to be driver side middle of the pan/gasket.What am I doing wrong? What could be at fault?

Is the pan/gasket edge completely dry ahead of the bolt on the driver side? Sometimes the fluid runs along the edge from a different location. If it's bone dry everywhere except that one bolt head, it's gotta be the pan or gasket.

What brand gaskets are you using? Any chance the pan is tweaked somehow near that one bolt?

 

[MihuAMG]

Everything above gasket its dry,leak starts at the middle bolt driver side from what I could see and seeping towards rear left than rear right bolt,genuine gasket from dealership. What adds up to this frustrating leak is that i have an E55 also and changed trans oil every year using same gasket for three years and its not leaking. What’s interesting,is that even with the two other pans the one with trans came and the one I bought new from dealer leak seem to have the same pattern.Just before i had that aluminum washer that wasn’t sealing right at the pressure port between vac modulator and neutral switch.

 

[gsxr]

The OE/Genuine gasket can be re-used several times as long as it's undamaged and not hardened. I'm at a loss to explain the leak as you describe it. I'm assuming you have checked around that area with a dental mirror and bright lights and confirmed it's dry everywhere except at the bolt.

If it were my car, I'd try a new OE pan next...

 

[MihuAMG]

I wouldn’t mind get another oe pan if id know that would fix it but I guess that’s a mystery at this point.The way the previous new genuine pan looked (quality wise) id rather get a good dry used one from junkyard.Also if pan/gasket is leaking let’s say torque wise(too low) ,would the leak stop increasing torque or once the gasket leaks and gets wet in between surfaces needs to be taken off ?

 

[gsxr]

If not torqued to spec, then yes, tightening to spec could slow or stop the leak.

I was assuming you are using a torque wrench at 8Nm final torque.

 

[MihuAMG]

I do but willing to go past that at this point .Is dye a good idea?

 

[gsxr]

I haven't used dye outside of AC refrigerant, but it might not hurt... make sure it's compatible with ATF etc...

 

[MihuAMG]

So now i retorqued the pan at 7Nm went for a spin and only the right rear bolt its wet.Should i retorque at 6nm or torque this one more?!

 

[gsxr]

I'd go over all six bolts at 8Nm (maybe 9Nm max) and see if there's any change. Don't loosen the bolts first.

 

[MihuAMG]

OK so I guess we finally have a “winner “.I hurried when I looked over the neutral switch but I think the seal shaft is leaking or where is that oil coming from?

 

[gsxr]

Yup - looks like it. And that seal is NOT fun to replace with the trans in the car. Did you install a new OE seal, or was it aftermarket? Were you confident the seal was fully seated / even / straight / etc?

 

[MihuAMG]

Too confident about it,absolutely a genuine seal but unfortunately mistakes can be made,especially when you wanna make sure everything goes through more than how it should (seal was fully seated but tapped it in beyond its sealing point and broke the seating area of the seal,pic attached).Its already off and put back on a new one,now flushed. Indeed not a fun job almost like you have to get ready the trans to come off.

 

[MihuAMG]

Finally enjoying the life of a 722.3 with no present leaks and hopefully long time from now.Appreciate all your inputs guys and thank you for following my thread!

 

[gsxr]

Congrats! Glad you got it sorted out.