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violinr 11-26-2009 08:44 PM

450sl transmission rear seal failure
Any ideas as to why my auto tranny seal has twice blown out?
Neither time was it over filled, or being mistreated,,,correct seal for the transmission....last night coming back from the mechanic's it blew approx. 5 miles from the shop when it down shifted from 3rd to mechanic is stumped,,,and so am I...any thoughts would be appreciated!

Werner W 11-26-2009 09:10 PM

Did you check your VIN with the classic center to find out if you need a left handed seal or a right handed seal?

Just kidding......:):o

violinr 11-26-2009 09:17 PM

Ha-ha!.....we even used adhesive to help insure it's staying in....still blew out as if under too much pressure.

Gurunutkins 11-27-2009 10:56 AM

1 Attachment(s)
Werner is probably not joking :)
I just replaced both rear axles on my 450sl and the seals on both were handed unless you can get the upgraded part. the actual shaft itself has small threads machined into it to return oil from between the seal and the bearing back through the bearing. if you use the wrong one it actually pumps oil into the space. I bought new upgraded shafts without the thread so it didnt matter which seal I used. Here is the relevant bit out of the 107 bible. EPC seems to be down at the moment so I cant check it for the transmission seal but if you have an older car with the treads on the shaft (and I cant check for now) you may have a problem if using an aftermarket seal (right size number or not)

violinr 11-28-2009 07:31 PM

:)Thanks!,,,,after doing a very long search, I have found that there are 2 different seals for the 722.004 transmission,,,one is smooth and and one is handed...the one that blew out first was smooth and the one I replaced it with was also smooth,,,so,,,,I'am going to order the handed seal (both are the same size) and see if that fixes the problem...I would have never known as 95% of the parts houses carry the smooth one only.

Gurunutkins 11-28-2009 07:48 PM

hope that is the problem - simple fix. please let us know if it works:)

Werner W 11-29-2009 08:39 AM

:DGeese I thought I was joking. Well hopefully my joke put you on to the solution to your problem. GOD works in mysterious ways. :pleased:
Good luck!

violinr 12-12-2009 11:42 AM

WE replaced with the other (handed seal)...It blew while still on the lift!...
I'am going to try and find a good transmission ...anyone close by have one?

Jack M 12-12-2009 12:25 PM

Dare I say the "D" word ?

violinr 12-12-2009 12:30 PM

My mechanic as well as myself have already said several "choice words"...

Gurunutkins 12-12-2009 01:11 PM

I really thought that might be it - I would be onto choice words by now as well.
good luck and if you disassemble it let us know what the problem was - there just should not be that much pressure at the seal.
good luck

Jack M 12-12-2009 02:08 PM

No, the "D" word I meant, the one no one on the forum says with a smile. DEALER!

Might be a better choice before a Transmission replacement?

Jack M 12-12-2009 02:34 PM

HI Again, Now to be serious.what did you have done at your mechanic before the seal leaked or blew out.? The transmission has an internal pump that moves the fluid along and out to the trans cooler which is part of the radiator. None of these can bring pressure up to that level unless you have gotten air into the lines which does compress and can build up pressure. I think that you might want to look in other places before you do another seal. Best of luck J.

violinr 12-13-2009 09:02 PM

the seals that have blown is all that I have had him look at other than make sure the vent part was venting / no bent lines....probably cheaper to just put in a good used tranny...and then tear the old one down and repair/rebuild for a spare.

cth350 12-14-2009 12:00 AM

there are specs posted in the TDM for governor pressure and the like. Check those, if nothing else to eliminate any concern for the transmission internals.

On the mechanical front, are you sure the tailshaft diameter is correct? Perhaps it's scored or out of round?

There's a fellow in the vintage and parts for sale areas actively discussing rebuilding a transmission. He has a spare that he's been pulling parts from. See if you can get his spare tail shaft. Or at least, get him to mike it and compare the numbers to yours.


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