R100RT Drivetrain Chatter

So I’ve scoured the forums and the net trying to help figure out the issue on my new to me 1979 R100RT. I’ve read about rattles, slipping clutch, input splines, throwout bearings etc. I’ve not read an article here that really sounds (pun intended) like mine.

Problem: Under load the drivetrain seems to chatter and make an unpleasant noise. It happens when the load on the engine is increased, e.g. shifting to higher gear or driving up an incline.

I purchased the bike in this shape, I assumed it would be the final drive splines or the driving dog but they are in great shape and believe the owner previous to seller I purchased from did take care of a lot of the known pitfalls on these airheads.

Link to video of noise: https://youtu.be/S-oVzTiAmKI

Rear tire was low in video. Was just doing some testing. I’ve since inflated.

Things I’ve tried:

1) Lubed input splines on transmission
2) Checked final drive splines as well as driving dog
3) Changed transmission oil, no large shavings present.
4) Input splines look fine with little wear
5) Clutch splines look good.

After lubing input splines and reassembling the problem still persisted.

Here are picture of clutch splines and transmission input splines.



Should clutch plate have a hole in it?



Flywheel


Clutch parts


The clutch cable is maxed out at the lever, I’m wondering if this is a clutch replacement job or if possible it could be related to transmission which looks to be in great shape (new seals etc...)

Thanks so much to everyone who has some input.

Welcome to the forum! I can safely say that I've never heard a sound like that? It would be good to hear more such as sitting in the driveway on center stand going through the gears. So, after the 4 second video and you shifted into 2nd, what happened besides the pfffft noise? Could you continue to accelerate? If you stop accelerating in gear and just maintain speed, does it still make the sound? Kinda strange that the sound happened shifting into 2nd...if there was some kind of drivetrain issue, it should be there the whole time.

From 1000 miles away, the clutch parts and splines look OK. You didn't say how many miles were on the old parts. It's hard to tell from the pictures, but the pressure plate with the small hole in the center looks as if that hole is pretty big, like it's worn too large. The hole on my pressure plate which had 100K miles on it was maybe 3mm in diameter. Yours looks much bigger, but it could be the way the light comes through it. If that hole is worn bigger, that might explain the problems with the clutch adjustment disappearing.

For the proper clutch cable adjustment, follow what Tom Cutter has on his website:

http://www.rubberchickenracinggarag...d Clutch Cable Replacement and Adjustment.pdf

As I said, strange sound. Almost sounds like it's engine related as in a head gasket leak or something.

Let us know what you find!

I’d have a look at the spring in the driveshaft damper. Unfortunately, that requires removing the driveshaft and that process requires some special tools. You can see a typical damper setup in this diagram:

https://www.realoem.com/bmw/enUS/showparts?id=0399-USA-04-1979-2474-BMW-R_100_RT&diagId=33_1655

I’d also recommend shifting at a much higher rpm; boxers don’t like to be lugged.

Best,
DeVern

20774 said:

Welcome to the forum! I can safely say that I've never heard a sound like that? It would be good to hear more such as sitting in the driveway on center stand going through the gears. So, after the 4 second video and you shifted into 2nd, what happened besides the pfffft noise? Could you continue to accelerate? If you stop accelerating in gear and just maintain speed, does it still make the sound? Kinda strange that the sound happened shifting into 2nd...if there was some kind of drivetrain issue, it should be there the whole time.

From 1000 miles away, the clutch parts and splines look OK. You didn't say how many miles were on the old parts. It's hard to tell from the pictures, but the pressure plate with the small hole in the center looks as if that hole is pretty big, like it's worn too large. The hole on my pressure plate which had 100K miles on it was maybe 3mm in diameter. Yours looks much bigger, but it could be the way the light comes through it. If that hole is worn bigger, that might explain the problems with the clutch adjustment disappearing.

For the proper clutch cable adjustment, follow what Tom Cutter has on his website:

http://www.rubberchickenracinggarag...d Clutch Cable Replacement and Adjustment.pdf

As I said, strange sound. Almost sounds like it's engine related as in a head gasket leak or something.

Let us know what you find!

Click to expand...

Thanks for the response. It is strange indeed. When the noise occurs there is a loss in acceleration and forward momentum. The sound originates from directly beneath me (clutch, transmission). The sound is directly felt in the bikes forward motion if that makes sense. The bike itself jitters forwarded.

There have been times where it doesn’t happen in shift into second but will do it when transitioning to third. All of my testing has been done as slower speeds which you noted.. I did not want to experience anything catastrophic running at a high rpm. Also trying to keep repair bill down.

Thanks again for looking.


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GTRider said:

I’d have a look at the spring in the driveshaft damper. Unfortunately, that requires removing the driveshaft and that process requires some special tools. You can see a typical damper setup in this diagram:

https://www.realoem.com/bmw/enUS/showparts?id=0399-USA-04-1979-2474-BMW-R_100_RT&diagId=33_1655

I’d also recommend shifting at a much higher rpm; boxers don’t like to be lugged.

Best,
DeVern

Click to expand...

DeVern the sound appears to come from a more forward location, transmission or clutch. Also there is a stutter in the actual momentum of the bike in unison with the noise. I will keep your advice in mind if push comes to shove. Thanks for chiming in.


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GTRider said:

I’d have a look at the spring in the driveshaft damper.

Click to expand...

Matt Parkhouse wrote a couple of articles in ON in 2015 and 2016 which were about putting the damper from a post 1980 cush shaft into a pre 1980 driveshaft. From that, I take it that the OP's 1979 bike wouldn't have that arrangement.

That said, Snowbum posted on a different forum that this appeared in 1979. He referenced this page:

https://bmwmotorcycletech.info/models.htm

but there's no specific mention of a year.

As usual, Brook has documentation on this. On this page, a little ways down, he shows the cushion setup and entitles it as "1981+ Drive Shaft Torsional Shock Absorption Assembly".

https://brook.reams.me/bmw-motorcyc...-index/33-bmw-1983-r100rs-remove-drive-shaft/

20774 said:

Matt Parkhouse wrote a couple of articles in ON in 2015 and 2016 which were about putting the damper from a post 1980 cush shaft into a pre 1980 driveshaft. From that, I take it that the OP's 1979 bike wouldn't have that arrangement.

That said, Snowbum posted on a different forum that this appeared in 1979. He referenced this page:

https://bmwmotorcycletech.info/models.htm

but there's no specific mention of a year.

As usual, Brook has documentation on this. On this page, a little ways down, he shows the cushion setup and entitles it as "1981+ Drive Shaft Torsional Shock Absorption Assembly".

https://brook.reams.me/bmw-motorcyc...-index/33-bmw-1983-r100rs-remove-drive-shaft/

Click to expand...

I will give that link a read. Would the driveshaft damper cause issues with forward motion? The noise comes along with loss of momentum and force.


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I think that the damper only softens the clunk from the transmission to the final drive. Certainly if it were broken and/or misaligned there could be issues. I would drain the driveshaft fluid and see what it looks like. Refill about is 100-150cc. But since your bike IMO doesn't have this full damper assembly, that's not it.

A badly misadjusted clutch could easily hamper forward motion. It's been reported that owners might notice a rise in RPM in say 5th gear but the bike doesn't perceptibly speed up...that would be the high gear over powering the pressure of the clutch. What was the thickness of the fiber disk? Specs say that the service limit is 4.5mm thick.

20774 said:

I think that the damper only softens the clunk from the transmission to the final drive. Certainly if it were broken and/or misaligned there could be issues. I would drain the driveshaft fluid and see what it looks like. Refill about is 100-150cc. But since your bike IMO doesn't have this full damper assembly, that's not it.

A badly misadjusted clutch could easily hamper forward motion. It's been reported that owners might notice a rise in RPM in say 5th gear but the bike doesn't perceptibly speed up...that would be the high gear over powering the pressure of the clutch. What was the thickness of the fiber disk? Specs say that the service limit is 4.5mm thick.

Click to expand...

Yeah it’s a ‘79 and I agree that it is likely not that. Also sounds appears to be much further up in the drivetrain.

What’s odd is normal clutch slippage as far as I know doesn’t necessarily make noise, maybe some smell and a loss in acceleration. This one is bizarre given the noise. I will take a look at the specs this afternoon and let you know what I measure at. The hole in the pressure plate looks abnormal as well, to me that is maybe it’s normal. I’m really leaning towards clutch issue, also possibly the throwout assembly is not working as expected and sticking?

Was really hoping someone had experienced this before. I do appreciate all your input.


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Can't say as anyone has had this specific issue in this particular way. All you can do is go through each element, measuring/resetting, and work your way out until something makes sense.

How many miles on the parts/bike?

Warped pressure ring and plate can cause chatter and slipping however...

Transmission output splines look fine as do the clutch plate hub splines - like new. Clutch plate rivets look seated solidly and friction material seems adequate. No image of the pressure ring contact surface (big heavy cast/machined part). Pressure plate looks a bit rough but I've seen worse that didn't make that kind of noise. Diaphragm spring looks fine. thrust rod tip and pocket in the pressure plate look normal. I don't think the noise is coming from the clutch assembly nor does it look to have been out of adjustment at any recent time. Your recorded noise reminded me a little of loose drive shaft bolts but you'd have noticed that pulling the box. ???

20774 said:

Can't say as anyone has had this specific issue in this particular way. All you can do is go through each element, measuring/resetting, and work your way out until something makes sense.

How many miles on the parts/bike?

Click to expand...

I do not know of exact mileage to be honest. I am going to work through it thanks.


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Na Cl K9 said:

Transmission output splines look fine as do the clutch plate hub splines - like new. Clutch plate rivets look seated solidly and friction material seems adequate. No image of the pressure ring contact surface (big heavy cast/machined part). Pressure plate looks a bit rough but I've seen worse that didn't make that kind of noise. Diaphragm spring looks fine. thrust rod tip and pocket in the pressure plate look normal. I don't think the noise is coming from the clutch assembly nor does it look to have been out of adjustment at any recent time. Your recorded noise reminded me a little of loose drive shaft bolts but you'd have noticed that pulling the box. ???

Click to expand...

Na Cl,

Here is a picture of plate.


Also the clutch measures a little over 5mm


Driveshaft was secured tightly during testing. If it’s not from within the clutch assembly the only other possibility being something within the transmission? But I can’t think what would cause it to vary which gear it occurs in.


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So I drained the transmission to check for shavings. I recently did a change on it during my testing, there was some at that time. But I don’t know timeframe on when it was last done so I chalked it up to accumulation over time.

So it appears to have some fresh shavings. I’m guessing this is going to be a transmission issue as I cleaned up shavings on plug prior. Looks to be fresh.

Fresh shavings


Shavings floating around in gear oil
https://youtu.be/F-6Bjvm726A


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It sounds like a broken ear on the drive gear in the transmission. I had the same thing happen on a 84 r100rt. Going down the highway in fifth gear same noise and reduce speed. Had to drive home in 3rd gear, and take it easy on power. Look ln Max bmw parts and you can see the drive gear with the ears. I saved my broken one but can’t find it, only the yoke. From what I have read, the angle on the torsional yoke was changed from 17 degrees to 15, to stop ears breaking. Maybe drain transmission and fish with magnet to find broken ear? I do not think it will go through drain hole.

drost said:

It sounds like a broken ear on the drive gear in the transmission. I had the same thing happen on a 84 r100rt. Going down the highway in fifth gear same noise and reduce speed. Had to drive home in 3rd gear, and take it easy on power. Look ln Max bmw parts and you can see the drive gear with the ears. I saved my broken one but can’t find it, only the yoke. From what I have read, the angle on the torsional yoke was changed from 17 degrees to 15, to stop ears breaking. Maybe drain transmission and fish with magnet to find broken ear? I do not think it will go through drain hole.

Click to expand...

It’s funny you say this. Looking at the input shaft online I noticed that mechanism and it seems very likely that’s the case as the sound matches the spacing on that shaft, frequency less than if it was 30-40 splines stripping. Also would explain why it does it under loads great enough to compress spring and not in every gear.

Thanks for the input and feedback. I’m going to crack the case and have a look.


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When you split the transmission be careful to keep shims in same order. It was in 1996 when I did mine. I do remember I had to remove one bearing from shaft, and had to use a press to compress spring to remove retainer clip. I reused all my bearings, no wear. I never checked for shim adjustment because the only thing I changed that would affect shim adjustment was the gasket. I probably measure gaskets to confirm... it was a long time ago. Good luck, and let us all know how things turn out.

The clutch looks pretty awful but it's not the problem. If you are losing forward drive, then I'd say it is likely the input shaft coupler. Are you?

Yes, clutch disc and pressure ring look fine BTW. A beat up spring dampened “thrust adapter“... ?! That puts a face on the culprit alright. Interesting failure. The bits on your magnetic drain plug don’t look like bearing material.

drost said:

When you split the transmission be careful to keep shims in same order. It was in 1996 when I did mine. I do remember I had to remove one bearing from shaft, and had to use a press to compress spring to remove retainer clip. I reused all my bearings, no wear. I never checked for shim adjustment because the only thing I changed that would affect shim adjustment was the gasket. I probably measure gaskets to confirm... it was a long time ago. Good luck, and let us all know how things turn out.

Click to expand...

Thanks I will do. Will need to order tool to remove output shaft properly, puller I have is a little too big as well.

Thanks to everyone for their input and help!!


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