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Transmission output shaft seal


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The bike in question is DW's 2004 R1150R Rockster, with almost 60k miles. It's been "weeping" a little oil which drips from the boot between swingarm and FD for a while, but the leak is worse over the last month. Looking up inside the swingarm, I can see that there's oil a long way up there. So I'm pretty sure the leak is from the transmission output shaft seal. Last couple of times the bike has been to the shop, we were told the trans output shaft seal would need to be replaced eventually. And with November upon us, if the bike sits for a while it's not such a big deal.


Now my Clymer says to split the transmission case to drive out the old seal from the inside. As does my R1100 factory manual (5-speed, I know, but still!). Has anyone ever replaced the output shaft seal without taking the transmission case apart? How, and how hard was it?

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I've done it on my 1100 with the cases split. I don't think I've heard of anyone who changed the seal without splitting the case. I'm sitting here with the old seals in my hand. I guess it is possible that you could get a couple of screws into the output shaft seal and pull it out. I can't remember how much clearance there is to the bearing.

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If you can manage to remove the seal, then you can replace it from the outside. The BMW service manual calls for replacement from the outside of the case, it must be possible. I think I would screw some sheet metal screws into it and try to pull it out.


Make sure you drain your tranny oil first




Also, make sure you measure the depth of the original seal (I like to use a cut off Popsicle stick and mark the depth with a pen/marker). Remove the old seal, lube the new seals inner and outer race with a little grease, and drive it to the same depth as the original. Finding a suitable driver might be a bear as well, or you could look into picking up BMW Tool No. 23 4 620 (the proper driver for that seal)

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what do you mean split the case? you have to remove the trans and take it apart to do this?
Yes, I split the cases to do all the seals at once, and to check the shifter forks at 60K miles, because I was also doing the clutch at that time. I had a leak on the input shaft at the back.


Also, make sure that you get the lips of the seal facing the correct way when you install the new seal. I think the lips face in (if I remember correctly).

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I think there’s some variations in tranny cases; on some series the rear seal can be replaced from the outside, on others not. Anton Largiader or Seth would be better able to provide the specifics on this though.

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  • 1 month later...

To answer my original question: Yes, one can replace the transmission output seal without disassembling the transmission. Here's how it went....


The suggestion from Don at Bob's BMW was to use some dental picks to pry under the seal, and pull it out. That would avoid any risk of damaging the bearing by drilling into (and thru!) the seal. But every pick I have was too flimsy - it bent WAY before the seal moved. So I ended up drilling a couple of 1/16th holes in the seal, and putting in a couple of wood screws. One was too close to the edge, and just pulled out. I clamped vise-grips on the other, pried a little, and out she came!




With the seal out, I could see the bearing was a sealed one. I wiped up all the oil in there, along with any metal bits from drilling.




Interestingly, the new seal is different from the old one. When DW went to get the part, it wasn't in stock, which is unusual for Bob's BMW. But they were purging their stock of the old part, and making sure we got the new one. New on the left, old on the right.




I used a small PVC pipe fitting as a drift. It was the right size for the job, and the plastic is less likely to damage the seal. It's actually what I bought as a tool to install a swingarm bearing on my airhead - does that mean it's a BMW special tool?



The easy part is tapping the new seal home. Job done!




All in all, not too bad a job. The hardest part was drilling the seal to put the screws in. The hole I thought was centered in the metal part of the seal was actually too close to the inner edge, and tore out. The one I thought was too close to the outer edge was just right. So that was an important lesson.


Coupla' other notes. I pulled the trans out to work on my workbench. The bike is overdue for a spline lube anyway (nearly 60k miles!) so I wasn't going to go to this point and not do the lube too. Working on the bench was much, much easier that it would have been to work on the trans in the bike.


Bike reassembly is underway!!!

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