"clunk" in driveshaft on overrun

[oldbiker]

 [smiley=beer.gif]  

Hello
 40 years ago I purchased my first bike in Scunthorpe. At the time I fancied a beemer but was persuaded to buy a bsa 250. I have got back to bikes after an absence of 30 years. Have rebuilt a Bsa  250  440 500 and a Commando. Recently I have purchase a BMW r65 ls 1983 fulfilling my dream of 40 yrears ago. It runs fine and everything works as it should. I have one query that I need help. I get a clunk  :)on the overrun if the engine speed doesnt match trhe road speed. The sound seems to come from the gear box end. I would like advice on the problem. Is it safe to ride. I would like to knock a few more miles out  before the weather gets really bad. I am well equipped to do surgery but my funds are limited.

[nhmaf]

By gearbox - do you mean the gearbox/transmission, or the final drive which houses the ring&pinion gear at the rear wheel end?

How many miles are on the bike?   These airhead transmissions do have a bit of "clunkiness" normally, too.

First thing I'd check is to put bike on centerstand, tip it forward so that rear wheel is in the air/front wheel on ground.  One can put a jackstand under the rear frame crossmember to hold it this way.
Leaving the bike in gear, slowly turn the rear wheel forward and backward to find out how much "free play" exists in the driveline before it tries to turn the engine.   Try this simple test and let us know how much free play - estimate by inches or cm of wheel travel - your bike has.

Possible sources of excess travel/play can be:
1.   worn out drive splines in final drive (final drive has center drive tube with splines that mesh with mating spline assembly riveted inside rear wheel hub.  If the teeth on these are getting worn down to pointy peaks (originally they are square edged teeth) this will cause excess rear wheel slop/play.
2.  There is a cush drive (spring tensioned coupling) in the driveshaft.  If this has become worn or the spring has broken you will have strange sounds and excess play in the driveshaft.
3.  There is also a shaft inside the gearbox with coupled lobes to absorb driveline shock feeding back into the transmission.   It is somewhat rare, but not unheard of, for one of the the lobes to break - though this is not common occurrence, and I'd expect that you'd see metal shards in your gearbox oil if you drained it if this happened.

AFter you do the rear wheel test, it may not hurt to pull the rear wheel off anyhow and have a look at the rear wheel hub splines.   These should be cleaned/relubed with a high moly content grease every few years at least.   I do mine 1x per year, and with any tire changes, brake service, etc.

Let us know how the first test comes out and we can proceed from ther

[oldbiker]

Thanks nhmaf,
I ave raised the rear wheel and turned it while in gear. I am getting 8.5 cm free play wheel travel as measured on the rim. The clunk and free play seem to be in gearbox. There is no appreciable slop in the hub. I can feel the universal joint thro` the rubber gaiter. The response of the joint to wheel rotation is good or tight. The mileage on bike is 40k miles. I am not sure if this is genuine. I have not taken off the back wheel yet. As I get used to the bike I am able to control it and avoid the slop but I would prefer not to have it.
CHEERS
Old Biker

[Bengt_Phorqs]

Howdy Oldbiker!  Glad to have you here.  Does the "clunk" occur when you shift gears?  Beemers are noted for their "box-o-rocks" transmissions.  Hard to tear up and dependable but lordy do they sound like they're going to self destruct.  That's even the case on a lot of the newer ones.

If the bike is new to you it would be a good idea to go ahead and pull the tranny to perform the annual spline lube service.  Chances are it hasn't been done in a while and will tell you a lot about the bike.  That won't cost you anything more than some time and some moly lube provided you have the 27mm socket for the swingarm nuts.

[Bob_Roller]

I think I would drain the oil out of the trans, shaft, and final drives, and take a look, and see if there is an abnormal amount of metal in it .

Another very remote possibility, could be the four bolts that hold the drive-shaft to the trans output shaft coming loose .

But it should give you more problems, than just the scenario you mentioned .

[oldbiker]

Thanks Guys for all the help. Hopefully at the weekend I will remove the back wheel and renew all the oils. That should throw some light on the problem. Strangely I am still convinced tthat the slap is coming from the gearbox/clutch end. Still the bike runs well and there are no problems in any gear.This sound is only heard when changing up and throttling with the road speed not matching the engine speed
Cheers
Oldbiker

[Semper Gumby]

Hi Oldbiker,

If it is a hollow 'thonk' then I think the endplay in one of the shafts inside the gearbox is a bit on the loose side.  Probably need to go in and re-shim...it was during shifting right?

my 2 cents.

[oldbiker]

Hello all
I have drained and replaced oils in gearbox,rear swinging arm and rear wheel drive oil.  Oil was good in all places with a small amount of metal dust in gearbox oil. I then decided to remove the rear wheel-The quick release axle and clamp screw were easily removed. Pulling the wheel from the final drive was impossible. It moved about 3mm and rocked but no further. Am I forgetting something. I tried tapping the rim with a piece of wood but no move. All I could do was replace the axle. Went for a spin and all went well. I am afraid to go too far now fearig a puncture and unable to remove the wheel. Any ideas?

Oldbiker

[Bob_Roller]

What size rear tire do you have ?

If you have a 120 width tire, you need to remove all the air pressure from the tire, and in some instances, put a board under the center stand, to get a little extra room to work with .

The rear brake shoes, may be dragging as well, re-adjust the nut on the brake rod at the arm on the rear drive, to pull the brake shoes in .

[bruce_launceston]

I agree with Bob, if it's only moving 3mm the brake shoes are probably catching an a lip worn into the brake drum. Turning the brake actuating lever by hand might pull the shoes in enough to clear the lip.

Cheers Bruce

[oldbiker]

Thanks Bruce and Bob. We are getting into the winter here with plenty of wet weather. In had my last long tour on my 83, r65ls yesterday. I have the bike on the stand now and managed to remove the rear wheel quite easily after loosening  the brake lever. There is no"slop" in the rear wheel drive.
My next step is to remove the swinging arm and get to the clutch splines . The clunk was still in the tranny yesterday but had got familiar with it and was able to adjust my road and engine speed to match. It is very noticeable when driving in traffic in 1st gear accelerating and slowing down abruptly.  Hopefully I will get to the root of the problem. I have to check my  27mm socket first.

[Bob_Roller]

Glad to hear you got the rear wheel off without anymore difficulties .

Sorry to hear about winter arriving in your area , it's 97 F. (36C.) out on the covered back patio right now, 100 F. (38C.) in the garage, at 1500 .

[nhmaf]

It was snowing at my house yesterday (and you may have noticed the snow at the New England Patriot's football game on the TV).   Fortunately it is back up to a more normal 55F (12C) today and no snow remains..
Winter may well be coming early this year..

[steve hawkins]

old biker - mine does that especially when the engine is hot and I am in a hurry - i.e. getting frustrated in traffic.  I have just learned to ride around it.  I am not sure if it is my relatively new clutch getting grabby when hot combined with a little slack in the drivetrain and perhaps a weak spring on the shaft.  It could be combination of all.

One of these days i will replace the spring in the drive shaft.  And if thats not it, I will probably leave it till the gearbox or whole bike needs replacing!

On the open road theres no issues....114,000 miles as far as I am aware.

Steve H

[oldbiker]

Hi all. It is still raining here and I am making slow progress on my 83` R65LS. I have the driveshaft removed. A standard 1/2 inch Kennedy 27mm socket worked fine  on the swing arm nuts. The shaft and universal joint are fine  with no give on the spring. I notice that the clunk seems to be in the gearbox and there is 45 degree rotation on the output shaft before I get resistance and of course the "clunk". I am feeling sorry for my bike now seeing so much of it apart but I will persist and remove the gearbox. I am wondering if I open the retaining bolts on the gearbox, with the airbox etc removed, will I have enough room to pull the gearbox back with the wheel and swinging arm removed. I am told I will have to move the engine forward. This is my first BMW and I am fascinated with the engineering, the simplicity and complexity so finely tuned. I am enjoying working on the bike but it has been running and starting so easily that I want to avoid goin near anything with the carbs yet until I have it back together again