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Old 07-21-2014, 04:51 AM   #1
jowie OP
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Help please - shudder on takeoff

Hi all,
Recently purchased an 83 r100s as a bit of a project. Have been going over it step by step to make sure everything is in working order and have run into an issue I am hoping the collective intelligence assembled here can assist with before I start stripping parts aimlessly!

There is a distinct shudder on takeoff intermittently (but quite regularly - ie maybe 25 % of the time).

The shudder occurs as I let the clutch out, and is generally so bad that I need to re-clutch and try again. Generally when I do re-clutch, takeoff second time around will be fine.

I have tried rotating the rear wheel back and forth with the bike on the stand (and oil hot) to listen for noises. The gearbox generally seems quite quiet, being only slightly noisier when rotating the rear wheel in reverse as opposed to in the forward direction, when it is almost silent.

However, when rotating the rear wheel back and forward there is a definite clunk from the rear drive on the change of direction of rotation. On a previous bike (r1200) I recall a similar noise, but perhaps not as loud as this bike.

After trawling the web and reading a few articles (thanks snowbum), I have also tried accelerating hard in higher gears to check for a shudder that may indicate a gearbox issue, but thus far have not been able to discern any shuddering during these roll on tests.

Any help/guidance would be gratefully received! I haven't yet cleaned and re-lubed the rear wheel and gearbox splines, which I believe is a standard maintenance procedure. Could this be the fix? Or should I be readying myself for transmission rebuilds?

Anyone had a similar issue?
Thanks in advance!
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Old 07-21-2014, 05:42 AM   #2
Bill Harris
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So you're looking for gearbox problems when there may not be any.

A worn clutch can chatter of judder in engagement. The pressure plate and pressure ring may be grooved, as can the clutch disk. And the diaphragm spring can relax unevenly. And many times clutch chatter will happen at a particular throttle/rpm and clutch engagement pressure. And if the clutch splines have not been lubed with a moly-based lubricant the clutch plate won't slide as well along the input shaft, exascerbating the problem.

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Old 07-21-2014, 05:59 AM   #3
100RT
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As suggested there may be some warped clutch components. Had that problem with a Mustang decades ago.
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Old 07-21-2014, 01:09 PM   #4
jowie OP
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Great, thanks for the comment.
Will start with a review of the state of the clutch and see how we go from there.
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Old 07-21-2014, 02:38 PM   #5
Overdog
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Have you synched the carbs? I went from an old airhead to an old goldwing and this is a common problem with them....you get a rattle (primary chain) when first pulling out from a stop when the carbs aren't in synch. At higher speeds the CV carbs sort of smooth themselves out.
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Old 07-21-2014, 02:59 PM   #6
Brun
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G'day Jowie
Assume the gearbox is just fine for now. They are pretty robust.

If the bike has suffered from lack of maintenance it's likely that you will find the splines on the gearbox input shaft will be dry and crusty, causing the clutch plate splines to bind intermittently. A bad clutch cable can also cause this.

It is definitely worthwhile to pull the gearbox with any newly acquired airhead. You get to clean and grease the swingarm bearings in the process. And while you are in there pull the clutch apart and check everything. Here is what I found when I went in there a few years ago (mine's a '74 R90):

Input shaft wear - the input shaft seal was leaking, as was the engine rear main seal, so at least the shaft wasn't dry.



Strange wear patterns on the clutch plate. The friction surface was a bit conical - ie, more worn towards the outer edge.



The diaphragm plate 'fingers' were well chewed up and the spring height was well below spec.



And those fingers had ground their way into the surface of the pressure plate. For my bike, I think this was the main source of shuddering.



I replaced the lot with parts from Motobins for a couple of hundred hard-earned bucks. Results were very good.

The other issue you mention is slack in the drive train. This will most likely be wear in the rear wheel splines. These can get very worn and the bike will not let you down. However, you will be very pleased when the splines are repaired or replaced. I particularly notice this in our 'roundabouts'.

Do you have a Clymer manual? It has good step by step instructions with pictures for all this stuff.

Edit: Your bike is later, with the lighter 'clutch carrier' instead of the heavy flywheel, but things are similar. Good luck.
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Old 07-24-2014, 04:50 AM   #7
jowie OP
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Big thanks for this Brun!
I'm pulling the gearbox this weekend to do the inspection you suggest. Will revert with results.
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