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‘83 R100CS weird clunking noise while coasting  

Stefanos Tran
(@admiralpepega)
Eminent Member Expired Membership

I have this strange issue when i am coasting in 1st or 2nd gear, i will feel, NOT HEAR, clunking on my feet. It happens only while coasting. Its hard to explain. So I tried to do some diagnosing. Could it be the transmission? I put the bike on the stand and spinned the rear wheel slowly and could not feel any notchiness. It spinned smoothly. But when i rocked the rear wheel back and forth, there was some clunking/freeplay. Then I realized how I was able the weird clunking noise. If I am on 2nd gear coasting with no throttle and then wack the throttle, I will feel that clunk.

What do you guys think is the problem? I hope its not expensive.

Maybe its loose drive shaft bolts? I checked the bolts by hand and they dont seem loose.

Quote
Topic starter Posted : 07/10/2020 21:38
Richard Whatley
(@wobbly)
Member Moderator

It could be any part of the drive train, from the gearbox out to the rear wheel bearings. I'd start by peeling the swing arm boot back and then running tests to see if it's forward or to the rear of the U-joint that's under to boot. Or the U-joint itself or loose output flange bolts.

Don't think I'd ride it any further either, until you do that.

[color=blue]Don't hide 'em, Ride 'em !!
#15150[/color]

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Posted : 07/10/2020 22:40
Stefanos Tran
(@admiralpepega)
Eminent Member Expired Membership

Thanks will do. When u get going its perfectly normal. Its really hard to detect but something does not feel right.

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Topic starter Posted : 07/10/2020 22:47
Richard Whatley
(@wobbly)
Member Moderator

Thanks will do. When u get going its perfectly normal. Its really hard to detect but something does not feel right.

There are many issues, that, when you get the RPM up or start rolling fast enough happen so many times per second that they seem to go away. But they have simply smoothed out due to speed. Damage is still being done.

You are saying the noise varies by road speed. That means it's definitely in the wheels or final drive.

How many miles are on the bike ?
How often do you maintenance the drive train ?
Is there any perceptible looseness in the wheel bearings ?
When was the last time the wheel bearings were lubed ?
Are the brake rotors tight and the brakes don't "jump" at low speeds ?
Remember: Do not rule out the front wheel !!

I have every encouragement that the issue will reveal itself to slow, careful, logical, systematic scrutiny. A stethoscope could be an invaluable aid when the bike is on the lift and the wheels are being turned very slowly.

[color=blue]Don't hide 'em, Ride 'em !!
#15150[/color]

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Posted : 07/11/2020 08:35
Scot Marburger
(@8166)
Member Moderator

When you put the bike on the center stand and moved the back wheel with the transmission in 1st gear, how much free play did you feel? I just did that on my '93 R100GS, and got somewhere between 1/2"-1". When I put it in 2nd gear, the amount increased. I suspect that in higher gears, it would be even more.

What we're feeling, I think, are the gear dogs moving relative to each other, and that movement is perfectly normal. If, as you describe, you're "coasting" in 2nd gear, which I interpret to mean going along under constant throttle opening, then "wack" open the throttle, all you're doing is taking up the free play in a particularly violent manner, one that is not good for your transmission.

However, starting sometime in 1984, BMW started leaving off the output shaft circlip, and the best test for that is to pull the rubber boot off the transmission , push it backward far enough to remove the drive shaft bolts, and separate the drive shaft input flange from the transmission output flange. At that point, with the transmission in neutral, you'll be able to rotate the transmission output flange. If you feel anything but buttery smooth rotation, chances are good that 5th gear has shifted on the output shaft and is busily destroying bearings. You can also drain the transmission gear oil and look for deposits on the magnetic drain plug. There will always be some, but they should have the consistency of flour, and you should not be able to feel any texture when you put some between your fingers and rub.

So do those two tests and let us know what you find. Also tell us how long you've had the bike, and how many miles are on it. And how many miles since the last spline lube. If the answer to that last question is more than 25K, you're due for a spline lube, and the drive shaft has to be disconnected to do it anyway.

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Posted : 07/11/2020 16:34
john stirling
(@arni)
Trusted Member Expired Membership

I have this strange issue when i am coasting in 1st or 2nd gear, i will feel, NOT HEAR, clunking on my feet. It happens only while coasting. Its hard to explain. So I tried to do some diagnosing. Could it be the transmission? I put the bike on the stand and spinned the rear wheel slowly and could not feel any notchiness. It spinned smoothly. But when i rocked the rear wheel back and forth, there was some clunking/freeplay. Then I realized how I was able the weird clunking noise. If I am on 2nd gear coasting with no throttle and then wack the throttle, I will feel that clunk.

What do you guys think is the problem? I hope its not expensive.

Maybe its loose drive shaft bolts? I checked the bolts by hand and they dont seem loose.

so by "coasting" you mean coasting in gear. throttle closed and clutch engaged?

you posted a sentence that makes no sense. Did you leave out the word "reproduce"?

drive train problems tend to be costly once the damage is done. Catching loose bolt before damage is done, not so much. So hope for a loose bolt.

You do not disconnect the driveshaft from the transmission to lube the transmission input splines unless the plan is to remove the transmission. For a simple clean and lube the transmission, swing arm and possibly subframe are move rearward as a unit about 1 1/2 inches. That is enough clearance for the work.

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Posted : 07/12/2020 15:30
Scot Marburger
(@8166)
Member Moderator

You do not disconnect the driveshaft from the transmission to lube the transmission input splines unless the plan is to remove the transmission. For a simple clean and lube the transmission, swing arm and possibly subframe are move rearward as a unit about 1 1/2 inches. That is enough clearance for the work.

Maybe that's how YOU do it, but the small amount of additional effort needed to remove four engine/transmission and four drive shaft bolts lets you see the back of the engine, all of the transmission splines, all of the clutch splines, and check for leaks from the oil pump cover. Be a shame to do a half way job of cleaning those parts, especially the splines. You can't do that by moving the engine/transmission only 1 1/2" apart.

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Posted : 07/12/2020 16:15
john stirling
(@arni)
Trusted Member Expired Membership

You do not disconnect the driveshaft from the transmission to lube the transmission input splines unless the plan is to remove the transmission. For a simple clean and lube the transmission, swing arm and possibly subframe are move rearward as a unit about 1 1/2 inches. That is enough clearance for the work.

Maybe that's how YOU do it, but the small amount of additional effort needed to remove four engine/transmission and four drive shaft bolts lets you see the back of the engine, all of the transmission splines, all of the clutch splines, and check for leaks from the oil pump cover. Be a shame to do a half way job of cleaning those parts, especially the splines. You can't do that by moving the engine/transmission only 1 1/2" apart.

I'm slightly confused (not an uncommon condition). Removing the transmission to engine block bolts is not additional effort. The splines cannot be accessed any other way.

But if one goes through the considerable effort to disconnect the driveshaft (and dealing with the four special bolts inside that boot and getting the boot on and off and needing a special tool, etc, is one of the more PITA jobs on the bike) what is gained? Are you removing the transmission altogether? it cannot be moved back much, the driveshaft and a frame crossmember are in the way.

I can completely clean and lube the tranny input shaft in a 1 1/2" gap. el toothbrush. I cannot do anything with the clutch disk splines but unless they are rusty they need nothing. In the event of rust the disk must be removed and very carefully dry brushed with a bore brush. I can inspect for how much crud is on the inside of the bell housing. The oil pump cover seal is a static seal and lasts a very long time although requires replacement if the cover is removed. the rear main seals are the leakers and will throw oil around the bell housing. This mixes with clutch dust to make a nice anti-corrosive coating. unless there is so much oil it washes the dirt off I ignore it. i used to own an old Land Rover. Those things are an education in oil leaks.

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Posted : 07/13/2020 22:07
Richard Whatley
(@wobbly)
Member Moderator

Let's get back to the OP's issue.

[color=blue]Don't hide 'em, Ride 'em !!
#15150[/color]

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Posted : 07/14/2020 08:29
Stefanos Tran
(@admiralpepega)
Eminent Member Expired Membership

I have 50K miles on the bike. I change all the fluids religiously if not WAY too often.

I have been able to identify the clunkiness that I feel on the right foot peg when I am in 2nd gear at 1k RPM. I have checked driveshaft bolts and they were properly torqued. I have checked for any notchiness in transmission by spinning rear wheel and listening for any weird noises coming from tranny. Nothing.

Does anyone know what the heck I am talking about?

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Topic starter Posted : 07/29/2020 03:05
Richard Whatley
(@wobbly)
Member Moderator

One time at the Honda dealership I had a K5 750cc 4-cylinder which had a distinct gearbox bearing whine. It was there. I heard it. And it was indeed loud. But all the bearings tested good. That same week, another of the same model bike came in with a blown out gearbox. But that bike had straight pipes. I took both engines apart and swapped the entire contents of both gearboxes. That was the only way to make both owners happy in the minimal amount of time allotted by Honda warranty. It worked.

Some noises are simply like that. Obvious to the rider, but nearly impossible to locate without mass parts replacement.

Your issue will be very hard to diagnose without video... which you will obviously be very challenged to make. My only suggestion at this point is to find an Airhead mechanic near you and let him ride the bike.

[color=blue]Don't hide 'em, Ride 'em !!
#15150[/color]

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Posted : 07/29/2020 09:10
john stirling
(@arni)
Trusted Member Expired Membership

I would check the rest of the drive line. With a big screw driver and working through the timeing hole check for play in the clutch carrier/flywheel. Pry gently for and aft as well as pushing inward. Should be no play. Then pull the rear wheel and check the spline hub in the wheel for play and the splines on the rear drive for play.

As the 'noise' is felt more than heard I would do a nuts 'n' bolts check of every bolt from the cylinders back. Pay close attention to bolts transmission>block, footpegs and all of subframe and shocks. These can give weird noises if loose that are difficult to track down.

If you take it to a mechanic they will test ride it and really put it through its paces. Every gear, rpm and speed, clutch in and out in all, trailing throttle, blipped throttle, etc. It creates a comprehensive picture in the mechanic mind. Your presentation here has not created this in my mind.

Before spending a lot on a mechanic (a desperate resort for an airhead owner unless you are dealing with something that has gears inside) consider other forums. Some have hundreds of participants, many with extensive knowledge as well as some mechanics from well respected shops. Larger shot of finding someone that had the same r similar problem as well as gathering more troubleshooting steps. These cost nothing but the better your initial presentation the better your results. On ADVRider.com (olds cool>airhead forum) stick around, big crowd and things move very fast. I know little of the facebook group.

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Posted : 07/30/2020 05:36
Stefanos Tran
(@admiralpepega)
Eminent Member Expired Membership

Hey guys. I just wanted to update on my issue. It turned out to be a bad output flange bearing. I had the transmission rebuilt with new bearings and my issue has been resolved.

 

Thanks guys

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Topic starter Posted : 10/13/2020 08:04
Richard Whatley
(@wobbly)
Member Moderator

@admiralpepega

That's great news ! Congrats !

Now to the root cause. Was rust pitting evident on one portion of the output bearing race ? Had this bike been in long-term storage or spent a winter outdoors ?

I ask because standard ball bearings can collect a small amount of condensate at the bottom-most portion of the outside race during poor storage conditions. The race develops a localized rust spot, the rust causes pitting, the pitting causes bearing noise far in excess of what one would ever expect. If it goes untreated, the pitting can sometimes chew up the balls in the bearing too. 

[color=blue]Don't hide 'em, Ride 'em !!
#15150[/color]

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Posted : 10/14/2020 17:40
Stefanos Tran
(@admiralpepega)
Eminent Member Expired Membership

@wobbly

 

I didn't inspect the bearings myself. I just turned the output flange by hand and felt super notchy. That was enough reason for me to have it rebuilt by MAX Bmw. They did a great job at a great price. I had to supply the bearings myself since it'd be faster that way. 

 

I think the reason my transmission failed was because water got in through the speedometer rubber boot. When I replaced it, I found it was completely destroyed. 

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Topic starter Posted : 10/14/2020 21:06

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