Transmission Oil Drain leak

[Rando]

Hi all, I have had a wierd problem creep up all of the sudden. I changed my tranny oil (synthetic BMW oil) about 7K miles ago and just recently developed a very slow leak out of the drain plug. I checked the torque and it is tight. I put in a new crush washer when I did the original change. Does the tranny have pressure relief system of some sort that may be plugged? I know that a similiar problem with the engine happens and the oil level sight glass will pop out. It only leaks when I have been running it for a while, not while it is just sitting. My tranny has 125K (miles) on it. Any insight would be greatly appreciated. Randy.

[AntonL]

It's a simple sealing interface. Plug, gasket, and base. It's not right - redo it.

[1fastjunebug]

Say Rando, had a similiar problem on my 96RS and after doing some research, established that sometime in 96 BMW changed from no crush washer 94+95+some96) to a crush washer on the drain plug. Find out which is yours. Once you have this out of the way and torqued the plug to the proper setting (BMW says 17ft/lb - I went to 20ft/b w/crush washer), try this - after plug is in and torqued properly, spay some (a lot) aerosol carb cleaner into the recess of the drain plug and on the drain plug to flush out ALL residual tranny fluid that you couldn't get out with a shop rag. Really give that little whole area plenty of juice. Absorb all the excess CC with shop rag/towell before it dries. Repeat until you are sure that all residual has been removed. By doing the above, what I thought was a slow weep actually turned out to be residual synthetic fluid on the plug, around the plug and everywhere you couldn't get the shop rag into and then after warming up, the residual becomes more viscous and consequently ran down the drain path looking for all the world like a leak/weep. In my case, by doing the above the weep/leak stopped. Hope this helps.

[MikeH]

Say Rando, had a similiar problem on my 96RS and after doing some research, established that sometime in 96 BMW changed from no crush washer 94+95+some96) to a crush washer on the drain plug.I think it was the other way round - The early bikes had crush washers on the transmission drain plug, but later bikes, from '96 onwards, did NOT have a washer fitted. On this type there is a shoulder machined on the end of the plug and the tightening torque is higher - 30 NM.

[Rando]

Thanks for the suggestions. I will drain the tranny and have a look. One more thing for the winter project list. Speaking of winter projects...

[1fastjunebug]

:rolleyes: Whatever the model year of change in either using or not using a crush washer on the transmission oil drain plug, judginf from the responses from the BMW tech.s that I have spoken to, they all - without exception - use a crush washer on all BMW's that they service - regardless of the plug type. Also, they caustiously admit that the only torque wrench that they use on the plugs are their forearms! But, all agree that even though BMW recommends 17 ft/lb, that this is a sizeable thread and 20 ft/lbs couldn't hurt. It worked for me! If you want to use 30nm, which converts to 22.126844 ft/lbs, this probably won't hurt one durn bit. As a point of reference, the plugs on my 95 & 96 RS,s and my 2000 RT are all the same and they look something like this. Starting from the magnetic tip that goes inside the transmission case, from there we move to threads on the shaft of the bolt, after the threads expire there is a constant OD smooth surface turned for a short bit. At the end of this smooth surface the shaft tapers outwards (bigger) into a shallow cone which expires into a flat which carries outwards to the full OD of the head of the bolt. If you the proper crush washer on the bolt, it will settle on the cone portion of the bolt and will not have a big enourh ID to sit flatly on the flat - it will be kind of "tilty". This is good as the cone was designed to center the washer under load and form a seat against the flat of the bolt and the flat on the case. The cone of the bolt also provides a form of interference fit between the bolt and the case and seems to act as either a primary or secondary sealing mechanism. If you do not have the type of plug alluded to above, disregard everything said, do some more research and let me know what you find out!

[1fastjunebug]

:rolleyes: Whatever the model year of change in either using or not using a crush washer on the transmission oil drain plug, judginf from the responses from the BMW tech.s that I have spoken to, they all - without exception - use a crush washer on all BMW's that they service - regardless of the plug type. Also, they caustiously admit that the only torque wrench that they use on the plugs are their forearms! But, all agree that even though BMW recommends 17 ft/lb, that this is a sizeable thread and 20 ft/lbs couldn't hurt. It worked for me! If you want to use 30nm, which converts to 22.126844 ft/lbs, this probably won't hurt one durn bit. As a point of reference, the plugs on my 95 & 96 RS,s and my 2000 RT are all the same and they look something like this. Starting from the magnetic tip that goes inside the transmission case, from there we move to threads on the shaft of the bolt, after the threads expire there is a constant OD smooth surface turned for a short bit. At the end of this smooth surface the shaft tapers outwards (bigger) into a shallow cone which expires into a flat which carries outwards to the full OD of the head of the bolt. If you put the proper crush washer on the bolt, it will settle on the cone portion of the bolt and will not have a big enourh ID to sit flatly on the flat - it will be kind of "tilty". This is good as the cone was designed to center the washer under load and form a seal against the flat of the bolt and the flat of the case. The cone of the bolt also provides a form of interference fit between the bolt and the case and seems to act as either a primary or secondary sealing mechanism. If you do not have the type of plug alluded to above, disregard everything said, do some more research and let me know what you find out!