Leaking manual 4-speed gearbox

[mille]

We have had three Pagodas and all of them have had a leaking (manual) gearbox. Our current 230 SL from 1964 is a 4-speed which functions perfect without any noises or other problems. But it leaks and we have to check the oil level often to be sure not to run dry. Are we just unlucky or do you also have this problem? And what to do about it apart from dismantling it and fit new gaskets? What about Bardahl's products, which claims that their transmission oil with additives will stop leaks? As the 4-speed box uses ATF oil, I wonder if it is safe to use a product such as Bardahls?

Thank you in advance for any comments or suggestions - it is much appreciated.

Cheers

/Finn  

1964 MB 230 SL 4-speed manual Euro silver metallic with black interior

[Naj ✝︎]

Hello, Finn

I've had this problem too.
I think I was over filling by jacking the car on the right hand side.
The leak was usually from the rear seal.
Once I let the level drop just below the filler plug (when level), it seems to stay there.

naj

68 280SL

[waqas]

I can sympathize... my pagoda and 111 coupe both have the same issue!
However, I'm not sure whether the leak is in the front or back... the oil always seems to drip from the bell-housing (lowest point before the droplets are forced to break-free!)  I reckon a good cleaning might help pin-point the source.

This begs the question: if the manual transmission is to be removed, does the extra effort involved in disconnecting the engine still justify removing both together? (or is it still easier to crawl underneath and remove just the transmission?)

WAQAS in Austin, Texas

[ja17]

Hello Finn,

The bad news is that it is usually a front or rear seal leaking. The good news is that these seals are so high up on the gearbox that the fluid level never gets very low unless left unchecked for a very long period of time or miles. As long as  you do not mind the mess on your garage floor and check the level every once in a while you should be ok.

The leaking is worst after topping off the gear box then quickly tappers off to a slightly lower level.

The fluid should be filled level with the side filler plug opening.

Joe Alexander
Blacklick, Ohio

[jeffc280sl]

Thought some graphics might help explain potential leak locations.



Download Attachment: Trans Gaskets.jpg
15.94 KB

There are three paper gaskets and two main oils seals in the transmission.  

The bell housing is mounted directly against the transmission case without any gasket.  The area between the case and the bell housing is a potential area for leaks.  If this seam leaks fluid will come from this area and collect on the outside of the bell housing.Surprised MB did not provide a gasket here.  Maybe they know more than I and the metal to metal contact is so precise as to not need a gasket to prevent leaks.

Oil seal 1 is mounted in the front cover and it seals the shaft to prevent leaks into the bell housing and clutch area.  The bearings in the transmission are open so ps fluid flows freely through the bearings along the shaft, to the oil seal and then returns to the case.  It this seal leaks you will have a fluid leak showing up inside the bell housing.  Likewise if gasket 2 fails (it is located between the front cover and bell housing) (the bell housing is not shown)fluid will again leak on the inside of the bell housing.

On the rear transmission cover you have gasket 4 and seal 5.  A leak could occur from either area.

Then there is gasket 3 which is on top.  Unlikely leak location because of the fluid level.  There are 2 other oil seals not shown in the graphic.  One seal is located in the top cover plate and prevents leaks along the main shifter shaft.  The other seal is located in the speedo cable shaft.  

It may be possible to replace the rear cover seals and gasket with the transmission still on the car.  Maybe others can tell us if that is true.

Jeff C.
1970 280SL 4-speed

[Benz Dr.]

If you just want to fix the trans then only remove the trans. Complete engine removal takes about 6 - 7 hours if everthing comes apart easily. Add another 2 or 3 hours if it doesn't.
You can remove the trans in about 3 - 4 hours in most cases.

Dan Caron's
 SL Barn
benzbarn@ebtech.net
 slbarn.mbz.org
  1 877 661 6061

[mille]

Thank you guys for your advise. I wonder why MB specify ATF in the manual box? Morgan +8 owners (like me   )with 5-speed boxes installed are also instructed to use ATF, but many does not do it as it increase leaking.Several Morgan owners claims that the only reason why the Rover factory specified ATF was to ensure a smooth gear shift while cold. Consequently many +8 owners use 20W/50 engine oil, apparently without problems. What is the experts view here, could we use say 20W/50 oil in a Pagoda 4 or 5 speed manual box?

/Finn  

Sadly no Pagoda at the moment, but a 1974 Morgan +8  

[jeffc280sl]

Finn,

I don't have experience with any other transmissions so I shouldn't  offer an opinion on using motor oil or additives.  I would recommend buying a spare transmission from the era and rebuilding it.  MB made over 500,000 W110 and many many W111.  I suspect most had 4 speed manual transmissions.  It's a not that hard a job and it is worth it to have no leaks.  I have 50 or more pictures that I could share with you to help and many others on this site can help with advice.

Jeff C.
1970 280SL 4-speed