"Play" in drive shaft?

stanley

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Over the last couple of thousand miles, I'd noticed a knock develop when riding over bumps. This was felt through the footpegs... It felt like the centre stand was bouncing, or something was loose. All seemed in order, so I thought I'd investigate the shaft.

I've dropped the final drive out of the way to expose the rear uj. The shaft is free of corrosion and feels smooth to rotate. However, when I pull it back and forth (yes), there is a couple of mm of "in and out" play coming from the gearbox end. This play is accompanied by the familiar knock.

Should there be "in and out"play between the gearbox output and shaft?

Thanks in advance.

I recorded a video but not sure how to upload.

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Apart from general corrosion there are two ways there might develop an issue with the shaft drive. The front or rear U-joint bearing, or the splines where the shaft is split in order to make it extend/compress.

If the bearings are worn, there will be a noticeable 'clunk' whenever you change load direction to the shaft (accelerate or brake).

If the splines are lubricated with the wrong type of grease, or the grease dries out, the splines will eventually get stuck. This lack of ability to extend/retract puts an axial load to the gearbox, and will be noticed the most when the shaft swings beyond normal angles, such as spring compression/extension when hitting a bump.
Whenever you lower the bevel drive, the aft part of the shaft with the rear u-joint should stay put to the bevel gear, so if the splines - joint is the problem, you will know as you lower the bevel box. The required force to stretch/compress the shaft should be possible using two fingers only.

My 2c are on the splines.
The bearings rarely wears out, while the splines tend to dry out and the splines freeze up.
If you end up needing to lubricate the splines, I STRONGLY recommend the specified lubrication. A bit pricy, but the clearance in the splines are so marginal that if you use a lubrication that will dry out, there simply is not room for it, and they freeze up.

In order to make sure, the only way is to get the drive shaft out and inspect it.
 
Thanks for that,

I've pulled the shaft out. All splines look good. No real corrosion, no play in joints, etc.

Are you suggesting there should be movement at the joint indicated by the pencil?
I can't detect any movement there at all?

Thanks
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No, I don't think he is.. there should be no movement there.. but on your shaft from the gearbox, in the grove there should be a spring clip.. is it there or maybe its inside the shaft?
Did your drive shaft just come out easy, or did you have to pull it or lever it out somehow?

otherwise everything there looks in very good condition!!
 
Yep,
As theoneandonly mentioned, there is a steel retaining ring that suits inside the driveshaft and locates on the gearbox output shaft.
It's in place and doesn't appear to be worn. I've not removed it, but the groove on the gearbox output shaft appears to be wider (but not worn) than the steel ring. I imagine there will always be slight fore/aft movement here.

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I'm thinking that I reassemble with the proper moly-wotsit grease and see if there's an improvement.

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Do you get it on all bumps or just on light surface imperfections especially on a neutral throttle ? If yes mine and most other gs I’ve ridden have had that. There have been at least 3 threads on here about it
 
TBH when I lube my shaft :blush I do notice a change in the feel through the pegs.. in some respects its better, in others its worst. But lubing it so it can move easier will maybe enable it to bounce up and down on the clip a bit more? maybe this is what you are feeling?
 
It's on bigger hits. Ones that might make the centre stand bang if it had a spring missing. I'm very familiar with that feeling you describe though. I've noticed it on other bikes.
TBH... I'm not that bothered other than it has only recently developed this bang.

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Have you checked for any play in the shock movement or it’s bushings
 
Seems like my previous post needs a bit of elaboration.

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My explaination was based on experience with shaft drives where there was a C-clip at both ends, (red and yellow circle, and the shaft was split at the white circle, where there where 10 cm with splines inside, and these spline made the shaft stretch and compress.
There is still a need for this slight axial movement, but it seems like BMW now have dropped the splines in the middle (white circle) and also they have dropped the C-clip at the bevel end (Yellow circle), thus the axial movement is now moved back to the bevel box input shaft rater than to the dedicated splines splitting the shaft. On earlier models you had to split the shaft to get it out and in of the swing arm, while now there is room to pull the shaft out, thus no need to split the shaft. I apologize for this dis-information, not relevant to the LC-bikes. My bad, and it will happen again. :friday

Anyway, this leaves us with the need of axial movement between the rear u-joint and the bevel box input shaft (yellow circle), so that will be the area that needs attention, and the rear u-joint should slide freely on the input shaft.

As for the question regarding the blue circle, this is where the outer in inner part of the saft is bonded by vulcanisation in order to absorb shock in the shaft. It is bonded on a permanent basis and there should not be any movement what so ever.

If there are no visible wear on the u-joint bearings, lubricating the rear splines is the only action that can be done. While you also need to lubricate the forward splines (red circle), these are held to the gearbox output shaft by the C-clip locking itself into a groove in the shaft (Thus, you need some force to get the shaft loose from the gearbox) and there should be no axial movement during normal operation
 
Thanks for that detailed post... Very informative and makes sense.
I'll try and get the retaining ring out of the front section and make sure that it isn't worn (thus allowing axial movement at the gearbox end), then make certain I have good axial movement at the final drive end.

Spoonz, I'd thought it might be the shock too... But all seems good there. Funnily enough, my old TC GSA used to do the more usual "knocking through the pegs over light ripples" routine... It completely disappeared when I upgraded the rear shock to a higher quality, and slightly longer, unit. I always thought the original shock must have been the source of the noise, but maybe it was the slight change in drive shaft angle that silenced it?


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Update... If anyone is interested!

Cleaned everything up to perfection. No wear that I can identify. Reassembled with correct grease to splines. Axial movement at final drive end is almost frictionless; however, there is about 1mm of axial play at the gearbox end: the C-ring allows this.
As an experiment, I fixed a tie-wrap around the gearbox output shaft to indicate if I was getting movement there, and possibly to reduce the movement (it pushes the shaft back against the C-ring. Not much force here as the other end slides so freely). (See pic).

All finished of with a layer of ACF50 to the shaft, silicone lube on the gaitors and a final drive oil change.

Road test verdict-
After 100+ miles I had a peek behind the front gaiter: the tie-wrap remains in place indicating that I'm not getting axial movement at that end.
The horrible knock appears to be cured, although I've become hypersensitive to all the other rattles and noises!

At least I know it's all in pretty good nick
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Update..... it was nothing to do with the shaft!

The knocking noise came back worse than ever (I'm not sure it ever went away really). This was suddenly accompanied by a rapid deterioration in the bike's handling.... the rear shock had failed!
No oil loss from the shock. No play at the bushings, but a rapid loss of any damping. New shock under the "approved used" scheme and all is well again. No more knocking and a sweet handling, comfortable bike.

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Always good when the source of a problem is identified and sorted
 
Update..... it was nothing to do with the shaft!

The knocking noise came back worse than ever (I'm not sure it ever went away really). This was suddenly accompanied by a rapid deterioration in the bike's handling.... the rear shock had failed!
No oil loss from the shock. No play at the bushings, but a rapid loss of any damping. New shock under the "approved used" scheme and all is well again. No more knocking and a sweet handling, comfortable bike.

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Really helpful information this is nice to know for future. :okay
 
You couldnt make this up........:blast
YOUR SHAFT SPLINES ARE FINE. FFS:rolleyes:
Hopefully this post will stop the scaremongering. :thumb2
 
How do I know ?
Because the lack of post on here that show exploding splines:blast
 


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