Oil leak drive shaft boot

Got a oil leak from the drive shaft boot on my 95 RT. What would be the cause of that? Appreciate your inputs!

I'd suggest cleaning everything up and blowing a bit of baby powder in the area. Then after a minutes of riding or at the end of a ride, get down there and see where the leak is coming from. Likely the boot clamps are loose. Or maybe the boot has a small hole in it.

The rubber doesnt last forever. Stretch it in a few places and look for cracks. Also check the clamps. Make sure it isnt leaking down from the clutch throw out arm also.

As was said above the rubber does not last forever however on my airheads I've found it lasts one heck of a long time. What does happen on my bikes is eventually (a season or two) oil begins to seep under the clamped area. Tightening them a bit (don't go nuts here...) will stop it temporarily but the real fix is to undo the clamps, clean the rubber boot especially under the clamped area as best as you can. Clean the mating surface on the rear of the tranny and the shaft housing side as well. Install the boot again and this usually solves the problem for a long time again. Over tightening the clamps is often what causes the leak as it compresses the rubber too much and distorts it. As the rubber ages, dries and hardens a bit leaks begin and these ones typically don't go away until you get a fresh rubber boot and replace the old squished one.

YMMV of course.

oil leak

Thanks for feedback took boot off cracks in bottom, time for replacement.

I highly recommend getting the improved version of the boot! It has an inner groove that holds it in place while you tighten the clamps plus its more flexible. Max BMW has them on their parts fiche. I have on on my 81 RT

The boot exists for dirt/dust shielding. It is NOT for oil retention. You have a leaking seal at rear of transmission.

lkchris said:

The boot exists for dirt/dust shielding. It is NOT for oil retention. You have a leaking seal at rear of transmission.

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On this model, is it a dry driveshaft housing or one with gear oil in the swingarm? I lost track. If not a dry swingarm then the boot also protects against leakage of the bouncing, swirling oil.

PGlaves said:

On this model, is it a dry driveshaft housing or one with gear oil in the swingarm? I lost track. If not a dry swingarm then the boot also protects against leakage of the bouncing, swirling oil.

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There is oil in the housing.

If there's oil in the housing, the problem is a leaking seal. Could be transmission or rear drive, actually.

http://www.realoem.com/bmw/enUS/showparts?id=0469-USA-06-1995-2478-BMW-R_100_RT&diagId=33_0609

http://www.realoem.com/bmw/enUS/showparts?id=0469-USA-06-1995-2478-BMW-R_100_RT&diagId=33_0642

Back to my Post #8. I don't really want to go out to the shop tonight to dig out my Airhead manuals. So, I will repeat with greater clarity:

Does a 1995 R100RT have a dry driveshaft housing?

or

Does a 1995 R100RT have a driveshaft housing that contains a specified quantity of gear oil like most of the older Airheads?

I notice from the fiche picture Kent linked to that there is a fill plug shown in the final drive where the swingarm bolts to the final drive, but fiche drawings are not the final answer.

PGlaves said:

Back to my Post #8. I don't really want to go out to the shop tonight to dig out my Airhead manuals. So, I will repeat with greater clarity:

Does a 1995 R100RT have a dry driveshaft housing?

or

Does a 1995 R100RT have a driveshaft housing that contains a specified quantity of gear oil like most of the older Airheads?

I notice from the fiche picture Kent linked to that there is a fill plug shown in the final drive where the swingarm bolts to the final drive, but fiche drawings are not the final answer.

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Paul, read pose 9, it is a wet drive shaft. There are fill and drain plugs to change that oil. So, a leaking boot is most likely the fault, not the transmission seal.

Wayne

toooldtocare said:

Paul, read pose 9, it is a wet drive shaft. There are fill and drain plugs to change that oil. So, a leaking boot is most likely the fault, not the transmission seal.

Wayne

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Wayne, I did read post #9 but apparently Kent didn't when he wrote post #10 so I felt I needed to be more specific in order to allay any confusion.

Kent thinks the single-side setup is not wet as were the earlier models.

Just looking at the photo should indicate that were the new driveshaft housing wet, oil could be present at the swingarm pivots, as they are incorporated in the driveshaft housing, unlike earlier models. The fiche shows only sealed bearings there, no seals.

I think I can say with some confidence that it's pretty rare in the automotive world to find a rubber boot/bellows fastened with hose clamps intended to retain liquid oil. Grease, yes, oil no.

Full discolosure: no actual hands on experience with these models. I could be surprised. Still, the problem is a leaking seal somewhere, not the boot because it's not an oil seal.

Thanks Paul for clearing the confusion. My airheads have included an 1974 R90S, 78 R100RS Motorsport, 87 R80RT (mono-shock), 88 R100RS (mono-shock), and a 95 R100RT (mono-shock). I've done all the wrenching on these bikes since I bought my first one in 1986. I sold my last airhead a few years ago when I let the Motorsport go, although I am looking at another 95 R100RT. I currently ride a Triumph Bonneville, the closest thing (in my opinion) that you can get to a modern airhead.

The R90S had a final drive/driveshaft seal failure allowing oil to migrate from the drive shaft into the final drive. This caused oil to come out the breather in the final drive. This is the normal symptom when that seal goes bad, the oil migrates from the driveshaft into the final drive.

The R80 had a final drive failure that required removing the final drive to replace the bearings and seals. The symptom on that was oil leaking out the final drive onto the brake shoes. I also did a clutch job, and a couple spline lubes on it.

The 78 RS had a clutch failure due to a rear seal leaking in the engine, I removed the transmission, clutch and flywheel, and replaced the engine seal, oil pump seal, and clutch. The 88 R100RS was mostly trouble-free, but I did rebuild the top-end and replace the pushrod seals, plus a couple of clutch spline lubes which required the removal of the transmission. The 95 RT got its splines lubed a couple of times, other than that it was trouble-free.

The drive shafts on these bikes contain oil. While the bike is not loaded the driveshaft sits low in the back and the oil in the drive shaft flows back to the end near the final drive. However, when ridden it sits almost level, allowing the oil to sling around all the way to the front boot. When I have removed the drive shaft to do spline lubes, or other work, there is always a bit of oil in the boot. There is no seal in the front of the driveshaft housing, so it is only natural that oil could/would migrate into the boot.

I guess the seal could be bad in the transmission, if there is one. I've never had a transmission apart, so I don't know. But, I think that would allow the drive shaft to fill up with oil. The easiest way to test this is to either drain the drive shaft and measure the oil, or take a short cut and stick a small screwdriver down the fill port of the drive shaft housing and touch the drive shaft inside. Remove the screw driver and see how much oil is there. When I've done this to see how much is there, it is usually just on the very tip of the screwdriver.

Before I would pull the transmission or final drive to replace the seals, I would install a new boot and clamps. Note the boot is not round, but a bit egg shaped. A 95 RT is more than 20 years old and that boot is not in the best location for a trouble free life, everything will eventually wear out and require a little maintenance.

On another note, there is no oil in the swing-arm pivots. They are part of the housing, but they are not opened to the driveshaft. They require their own periodic maintenance from time to time, a bit of grease.

Wayne

lkchris said:

The boot exists for dirt/dust shielding. It is NOT for oil retention. You have a leaking seal at rear of transmission.

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I guess the oil in the driveshaft housing that is there from the factory isn't supposed to be there?

SCBuckeye said:

I guess the oil in the driveshaft housing that is there from the factory isn't supposed to be there?

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Yeah, and they have been doing it that for decades. You think they would get it right, some day. Oh, I forgot, they stopped putting oil in the driveshaft when they stopped making the airhead.

I am "reviving" this old thread as I came across it doing a search on oil dripping off the rubber boot on my 1972 R 75/5.
I don't have any experience on this and just started looking for some advice as I had the bike on my lift and was running it to sync the carbs so it was running for awhile (with fans in front of cylinders). I had noticed previously that there was a bit of oil around the boot and on the center stand (from blow back from the boot, I presume), but this is the first time that I noticed a fair amount of dripping.... I think, because the oil was hot and I had never seen the undercarriage when the bike had ever been at those temperatures.

I am wondering if a '72 /5 model has a similar set up as the model discussed in this post, as one of the posts said this was similar on all airheads. I am hoping that it just needs a new boot, or possibly loose clamps(haven't checked that yet).

Thanks for any advice.

2wheeljunkie said:

I am "reviving" this old thread as I came across it doing a search on oil dripping off the rubber boot on my 1972 R 75/5.
I don't have any experience on this and just started looking for some advice as I had the bike on my lift and was running it to sync the carbs so it was running for awhile (with fans in front of cylinders). I had noticed previously that there was a bit of oil around the boot and on the center stand (from blow back from the boot, I presume), but this is the first time that I noticed a fair amount of dripping.... I think, because the oil was hot and I had never seen the undercarriage when the bike had ever been at those temperatures.

I am wondering if a '72 /5 model has a similar set up as the model discussed in this post, as one of the posts said this was similar on all airheads. I am hoping that it just needs a new boot, or possibly loose clamps(haven't checked that yet).

Thanks for any advice.

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Under normal conditions the gear oil at the end of the drive shaft where it connects to the rear drive stays there and the boot at the swing arm pivot only has to keep dirt out and oil mist in. However, there is almost always some oil which collects in the bottom pleats of that boot over time from the oil mist. So, if you drive shaft boot is failing, then there's your leak.

I would start by cleaning the boot and then going over it with a flashlight and my fingers to see if I could find any damage, wear, or tears. Finding none, then check the hose clamp tightness. If they are very loose, then tighten and test ride. However, those clamps tend to stay put, so if they are ok then I would pull back the end attached to the transmission and look for signs of gear oil coming through the transmission vent hole (drilled into the face of the gear box cover behind the output shaft flange). You might need to rotate the drive shaft flange to see that hole. This may not be a conclusive inspection, in which case I would also check the transmission oil level. It's kind of hard to over fill, but it can get water contamination because of a failed speedometer cable boot and water can make the gear oil foam which might cause some to pass into the drive shaft housing.

Having said all that, your most likely problem is an bad drive shaft boot. Unless you have changed it or know that someone else did, then it's 50 years old and even the good German rubber of the day doesn't last forever.

GREGFEELER said:

Under normal conditions the gear oil at the end of the drive shaft where it connects to the rear drive stays there and the boot at the swing arm pivot only has to keep dirt out and oil mist in. However, there is almost always some oil which collects in the bottom pleats of that boot over time from the oil mist. So, if you drive shaft boot is failing, then there's your leak.

I would start by cleaning the boot and then going over it with a flashlight and my fingers to see if I could find any damage, wear, or tears. Finding none, then check the hose clamp tightness. If they are very loose, then tighten and test ride. However, those clamps tend to stay put, so if they are ok then I would pull back the end attached to the transmission and look for signs of gear oil coming through the transmission vent hole (drilled into the face of the gear box cover behind the output shaft flange). You might need to rotate the drive shaft flange to see that hole. This may not be a conclusive inspection, in which case I would also check the transmission oil level. It's kind of hard to over fill, but it can get water contamination because of a failed speedometer cable boot and water can make the gear oil foam which might cause some to pass into the drive shaft housing.

Having said all that, your most likely problem is an bad drive shaft boot. Unless you have changed it or know that someone else did, then it's 50 years old and even the good German rubber of the day doesn't last forever.

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Thanks for the info. I am not sure of the age of the boot as the bike was redone a few years ago by the previous owner and I'm not sure if that boot was changed or not. I have a box of original parts that were replaced and I don't recall seeing that boot....but it could have been so dirty and worn that it just got tossed. I will look closer at the boot now that I know about the oil mist and oil collection inside the boot. From what I have seen blown back on the center stand and surrounding area it does not look like a major amount of oil, so I don't think I have a big problem.