Shaft drive question

[fartooheavy]

Hello, Please could anyone help?
I have owned my 900 for a couple of years and have been using it most days to commute.
I have grown to admire it the more I use it, my other bike is a mk3 commando.
I don’t usually go mad on the power but every now and then if I drop a gear and “give it some“ there is a sort of noise and shudder I associate with a slipping chain, it isn’t usually an issue as most of the time I have plenty of time or room to accelerate smoothly enough not to bother.
Has anyone else had this issue and can it be remedied or should I just go easy on the throttle?
I don’t think I’m a speed freak and I don’t want a sports bike, the divvy is brilliant for most things just a little cumbersome to push around manually.
Hopefully unconnected to this I have replaced the head bearings, rear shock, down pipes and front fork seals, all made vast improvements but were far more difficult jobs than needed to be due to seized nuts and bushes and restricted access.
I hope this is the correct place to post this (first post), if not please can the mods move it?
Thanks in advance.

[Greendivvy Beeb]

Welcome, it sounds to me like it's just the shock absorber built in to the output shaft of the gearbox. It's like a dog clutch but releases when the load gets too much so it safe guards the gearbox and the shaft drive. Just keep the throttle smooth.

I feel it normally when loaded up with luggage and pulling away from standing start. May be carrying too much luggage

[fartooheavy]

Thanks for the reassurance, does that spring ever need replacing, could it perhaps lose any length / compress over time?
Whatever, it’s great to know I don’t have to do some serious bearing renewal even if I should lose some luggage

[Greendivvy Beeb]

There is a chance the spring could be broken, which would cause it to come in to play more often but never heard of one playing up before. Depends how often you do feel and hear it and the sort of load your putting on it when accelerating.
May be worth just checking the UJ for play on the drive shaft under the inspection grommet on the swing arm. (Just make sure the grommet is refitted correctly as it can cause water to get in and knacker the swing arm pivot bearings). If this was worn i'd except to feel this at lower speeds and loads and possibly hear it knocking when coasting on and off the throttle.

How many miles has the bike done?

[johnthebowman]

I dont think its caused by too much luggage D9s love luggage
Unless your weight of luggage is more than the wieght of a pillion plus luggage and even then, a D9 is built to carry it. Ive seen a D9 block in bits with a gearbox selector problem at 23k. Mine has done 179k so perhaps milleage wont tell us much but I always find it interesting?

Ive only once ridden a bike with a slipping chain, my first moped. So noise and vibration is something it does in all gears under heavy load?

In 1990 I had a BMW 100 rs gearbox collapse. Backed her out from the garage started it engaged first, clutch bit but no forward movement. Then I could not push it forwards or backwards even by pulling the clutch in. It rather frightened me that any motorcycle could do that, so if it happened whilst riding, theoretically, back wheel locks solid, no warning, pulling in the clutch makes no diference, back wheel stays locked till you screech to a halt The thought of how other road users might respond to this was enough to put me off riding motorbikes for a while.

None of my D9s have displayed the simptoms you discribe. Its certainly not normal Im sorry not to be able to be more helpfull. More people like Greendivvy Beeb will post here and as a club we can sort it

[fartooheavy]

Thanks for replying GD & JTB, Mine's done just over 60k.
It only happens under hard acceleration but I don't consider it to be THAT hard. Dropping a cog or 2 (I'm usually burbling along in fifth) and gunning it a bit to get past someone who is dithering but sitting close to the white line sort of scenario. Usually no problem but when it happens I hate to think of the damage I might be doing.

[johnthebowman]

I was more worried about the potential damage to you; fartooheavy if your back wheel suddenly locked and stayed locked!

However, to my embarassment Ive since learnt that some shaftys have a saftey feature. Two joined cones in the case of a BMW I believe, I dont know about a D9 Unless I A, find the manual or B, someone posts the answer here

[bev]

Is the clutch in good condition ? I've not had Driveshaft problems but I have had a clutch issue which started much as you describe.

[fartooheavy]

I have not looked at the clutch but it doesn't slip,(unless you mean the dog clutch that Greendivvy referred to in first reply). What was the issue with your clutch?

[CD]

Long time no nothing from me.

My 900 did this shudder. it's the suspension linkage under the rear shock and quite possibly the swing arm bearings as well. It's caused by the drive trying to jack the back end (remember the old boxer BMWs?).

A worn shock won't help as it's the rebound damping that controls the jacking effect. You might be able to get it rebuilt or fit a Wilbers. The rocker has needle roller bearings not cheap to replace but it's the only way to stop that clunk. You could consider using Igus polymer bearings which might be lower cost and easier to repair when the wear. That would need sleeves etc to fit them into the roller housings.

[fartooheavy]

Thanks for responding CD. Maybe I didn’t explain properly, the noise and shudder occur at the same time as intermittent power delivery, very like a worn chain slipping over a worn sprocket. For the time being I’m trying not to accelerate over enthusiastically. It’d be good to get a seasoned divvy expert to give it a test ride. I did replace my rear shock and had to replace the linkage bearings at the same time. Maybe worth another look underneath but last time I checked everything seemed fine, nothing loose.

[chris900divvy]

Sounds like you have a worn gear somewhere. If its like a clatter before it bites and accelerates its usually a symptom of the gear not quite holding in place under peak power, its trying to jump out due to worn dogs and/or a bent shift fork. It can feel as if there is no power all of a sudden briefly a bit like a slipping clutch. You could avoid that gear but really it'll only get worse to the point of eventually not being able to select it. Does it happen in one particular gear? I'd be happy to have a little go but am down in Berkshire no idea of your whereabouts.

[fartooheavy]

Thanks Chris, there is no clatter before the clutch bites and I have no problem selecting any of the gears, it only happens with the clutch engaged and it can happen in 1st, 2nd & 3rd. I’m pretty convinced that Greendivvy has got the answer with the dog clutch but replacing that looks like a well equipped mechanics job. These are the part numbers from CMSNL 4KM1752700 & 31A1752601, apologies if I’ve broken any rules copying them here. I live even further down in Brighton so not that far from you. Maybe for now I should just be a bit easier on the throttle, it’ll make the rear tyre and everything last longer if I am.