Rear Main Seal leaking? - BMW Luxury Touring Community
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post #1 of 8 Old Oct 17th, 2018, 9:20 am Thread Starter
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Rear Main Seal leaking?

Yes I know there's lots of threads talking about drilling weep holes, but that sure sounds like a temporary solution. Before I tear into the transmission I want to make sure I'm going after the right parts. I've got a 99 LT which I bought new, and it currently has about 70,000 miles on it. Late last year I noticed the slow oil drips on the floor. A month ago I starting having trouble shifting gears. This past weekend , riding "up north" as we say in Michigan, shifting when the engine was cold became very difficult. Then I experienced a lot of clutch slippage, especially during heavy torque/acceleration. I'm thinking the rear seal is leaking oil and is now spewing it onto the clutch plates. As a winter project I'm ready to replace the seal and most likely the clutch plates which are now 19 years old. My questions to you are, am I chasing after the right problem, and what else should I be doing while I'm in there?

I've watched Kirk's videos on how to do this, and I've got the Clymer manual.

I'd sure appreciate any suggestions that would keep me from having my very nice dealer perform this very expensive fix.

Charlie
99 K1200LT
85 R80RT
81 R100RS (Sold it 4/10)
03 Moto Guzzi V11 LeMans
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post #2 of 8 Old Oct 17th, 2018, 9:57 am
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Re: Rear Main Seal leaking?

Charlie, drilling the weep holes is not a remedy but an indicator. Depending on the mating of the surfaces of the engine and transmission, significant oil can collect in the bellhousing so drilling a small hole there can give you an earlier warning of a leak beginning. Same with the weep hole on the slave cylinder except in that case, it allows any oil leaking another path besides heading down the pushrod tube and into the clutch. The purpose of the weep holes is not preventative but informative of an issue before you get to a point where the bike is not rideable somewhere far from home.

The difficult shifting is not going to be caused by the clutch so taking a look at the shift linkages, cleaning, lubricating and making sure everything is tight may help there. The bellcrank is held in place with a hex bolt and nut and can come lose preventing full motion from being transferred through the linkage making shifting difficult.

The seals inside the bellhousing area should be on your list of things while you are in there.
Main rear seal.
Trans input shaft seal.
19X4 O-ring preferably Viton. PM me before you go in and I will send you one.
The slave seal and slave cylinder. Seal depth is critical.

You can also do the transmission output seal while you have the swing arm off but that depth is also critical or it will leak.
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Gordon
Sugar Hill, GA
2001 K1200LTI – Champagne (current ride) Lazy Susan
1998 R1100RT – Never should have sold it
1974 Yamaha TX 750 Twin. Omni Phase Balanced


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post #3 of 8 Old Oct 17th, 2018, 10:08 am Thread Starter
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Re: Rear Main Seal leaking?

Gordon,

Thanks for the quick and helpful reply. I'm seeking the hands-on help from my GM engineer son-in-law on this project so at this point I'm just trying to gather as much research as I can.

Charlie
99 K1200LT
85 R80RT
81 R100RS (Sold it 4/10)
03 Moto Guzzi V11 LeMans
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post #4 of 8 Old Oct 17th, 2018, 1:15 pm
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Re: Rear Main Seal leaking?

A good read for how to do it all is located here plus there are a few other articles in that same area.

John
2009 K1300GT Red Rocket
2009 R1200GS (Gone)
2005 K1200LT Ocean Blue Blue Wizard 110 K and counting...
2006 Bushtec Turbo+2 Spell
2004 330 Ci Convertable
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Have ridden a Motorcycle in all 48
But lack DE, MA, RI and CT with the 2005 LT

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post #5 of 8 Old Oct 17th, 2018, 1:55 pm
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Re: Rear Main Seal leaking?

Hi Charlie , sounds like the "O" ring went bad . They get hard and crack , $2 part & a lot of work.. The one in my friends 2000 K1200LT down in Oxford 2000 went bad last year & I put one in a lady friends sidecar K1100LT rig last year too. Of course it takes the clutch out as a side with it.

Probably a O ring , & a 11 21 1 460 696 COMPRESSION RING ,rear seal along with a clutch disk & a new clutch slave cylinder .

To me , if a gear box seal isn't leaking I don't mess with it. I have heard of more that one that I will just change something wile I'm there & didn't get it in correct . They got the bonus of redoing to to fix something they broke.

Patric Blackman
2002 K1200LT/Hannigan2+2
2010 R1200GSA ...1987 Helix...
AMA Charter Lifemember
37 Year Member of both BMWMOA & BMWRA

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post #6 of 8 Old Oct 17th, 2018, 2:30 pm Thread Starter
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Re: Rear Main Seal leaking?

I can't thank you enough for this exceptional manual. Incredibly helpful. Years ago my son-and-I jointly purchased a motorcycle hydraulic lift which we installed in his stand-along one-car garage. Yeah, it's a man cave for sure. Between us we have I think eight bikes, including three Ducatis one of which is going through a complete engine rebuild at the moment. Your manual will be an enormous aid when we tackle the main seal replacement. Thanks again. Much appreciated.

Charlie
99 K1200LT
85 R80RT
81 R100RS (Sold it 4/10)
03 Moto Guzzi V11 LeMans
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post #7 of 8 Old Dec 7th, 2018, 11:25 am Thread Starter
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Re: Rear Main Seal leaking?

Just as a followup to my service issues, I realized this was beyond both my skills and tool collection so I took the bike to the dealer. I'm fortunate that the same tech who's been working on my BMWs since 1985 fixed my 99 KLT. Here's what he wound up doing: Install new rear main seal, new clutch assembly and associated gaskets, install new slave cylinder, bleed clutch, replace transmission seals, two bearings; replace input drive shaft; replace transmission gear oil.

While I was focusing on the rear main seal, he found additional problems once he removed the trans. I for sure would never have spotted those.

Next spring when I uncover the bike I'll be ready to roll. As much as I hated writing that check, the alternative was worse.
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Charlie
99 K1200LT
85 R80RT
81 R100RS (Sold it 4/10)
03 Moto Guzzi V11 LeMans
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post #8 of 8 Old Dec 7th, 2018, 11:46 am
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Re: Rear Main Seal leaking?

Quote:
Originally Posted by BMWCharlie View Post
Just as a followup to my service issues, I realized this was beyond both my skills and tool collection so I took the bike to the dealer. I'm fortunate that the same tech who's been working on my BMWs since 1985 fixed my 99 KLT. Here's what he wound up doing: Install new rear main seal, new clutch assembly and associated gaskets, install new slave cylinder, bleed clutch, replace transmission seals, two bearings; replace input drive shaft; replace transmission gear oil.

While I was focusing on the rear main seal, he found additional problems once he removed the trans. I for sure would never have spotted those.

Next spring when I uncover the bike I'll be ready to roll. As much as I hated writing that check, the alternative was worse.
Yes, there are a bunch of things to check while it is apart as you really don't want to do this type of thing more than once every 100K+ miles depending on how hard you are on the clutch. I am sure that was a sizeable check based on that list but if you trust the dealer and he didn't pad the services, you should be good to go when the ice melts.

Gordon
Sugar Hill, GA
2001 K1200LTI – Champagne (current ride) Lazy Susan
1998 R1100RT – Never should have sold it
1974 Yamaha TX 750 Twin. Omni Phase Balanced


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