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Old 01-27-2015, 03:45 AM   #1
ME 109 OP
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81 final drive clunking

Just put the bike in the shed afetr a 1000k 3 day ride. While rolling it, I could here a clunk clunk clunk from the ass end.
I spun the rear wheel and what is going on in there!!

I drained the oil expecting to find the magnetic plug looking like a punk hedgehog, but it was ok.
If I rotate the wheel, I get 12-13 clunks per revolution.
Something has come loose and I think it's the pinion nut, if that's what it's called. That big bastard in the bell coupling.

I can't get to it again tonight but thought I'd post to get some ideas from the experienced folk.
It isn't the wheel bearings, and the lack of metal on the drain plug is promising, I think.

It's about time there was a problem with the bike anyway. I was becoming most concerned there was something wrong with it.

Edited to add, the only symptom was more backlash than usual, but no noise.
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ME 109 screwed with this post 01-27-2015 at 03:51 AM
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Old 01-27-2015, 04:15 AM   #2
damurph
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Pinion bearing but it would be my thought some of it would end up on the drain plug. Never heard of a pinion nut loosening but have seen the backlash affected by a broken pinion bearing.
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Old 01-27-2015, 04:50 AM   #3
100RT
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Did you put it on the center stand and rotate the wheel while you feel the rear end? Can you move the wheel when holding it at the 9 and 3 o'clock positions? What about the U-joint?
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Old 01-27-2015, 05:04 AM   #4
Stan_R80/7
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Sounds like a rear u-joint to me. I don't think there is anything in the ring and pinion gear that can clunk. Good luck!

Edit: there is no rear u-joint, so that isn't the noise. That noise is a bit of a mystery - and one with a foreboding ending. On the bright side, at least it isn't winter there and taking the bike apart won't be quite so miserable.

Stan_R80/7 screwed with this post 01-27-2015 at 05:40 AM
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Old 01-27-2015, 05:21 AM   #5
boxerboy81
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Jeff, when my pinion bearing had 2-3 mm of movement, there were no symptoms whatsoever. I only found the problem at routine fd oil change.
This was the damage as the pinion moved about.




Are your 4 bolts at the gearbox output all tight? Wheel bearing?
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Old 01-27-2015, 05:57 AM   #6
Bill Harris
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Might just be that the wheel spline cup rivets have sheared:



Happened to me last Fall, happened to Voltaire recently. Leading up to the rivet failure there is a rhythmic clunk-clunk-clunk noise and leading up to the noise there was drivetrain slop.

Or, better, if the driveshaft bolts have loosened, you'll also get that rotating noise and slop.

Pull the rear wheel, take a look. If it is OK, pop the driveshaft boot loose and take a look. If them's OK, drain the rear drive oil and see what is on the magnetic drain plug.

Fingers crossed.

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Old 01-27-2015, 11:02 AM   #7
ME 109 OP
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Thanks for the replies gents
I had the bike on the c/stand when rotating the wheel back and forward. It sounds awful, and the noise is very much coming from the fd itself. There is more than one noise.
I'm satisfied without having removed the wheel yet, that the wheel bearings are fine because there is no wheel wobble, and the noise is too loud and heavy.

Drain plug only has normal sludge without any trace of coarse material. I'm hoping that's a good sign.

Off to work now, so I'll rip into it when I get home.
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Old 01-27-2015, 11:07 AM   #8
chasbmw
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Could it be a Fractured spring on the drive shaft.
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Old 01-27-2015, 11:25 AM   #9
Kanticoy
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Not that I doubt you, but I had a U-joint failure as well and I would have sworn that it was a final drive issue. I found out that one of the "crimps" that holds the cap onto the U-joint had come loose. Luckily the needle bearings were in tact so I hammered it back into place and then tack welded it on. Many thousands of miles since and no noise. Found the issue when I pulled the FD and had no noise, but when I moved the flange on the drive shaft, sure enough there was the clunk.
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Old 01-27-2015, 11:30 AM   #10
spo123
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interesting...

I second, Bill Harris's, suggestion......Damaged rivets (if multiple) should cause the frequency suggested.
The LACK of SWARF on the rear end drain plug would point this way, as well...
Pull that rear wheel.
FYI, the u-joint would not produce that many "clicks" in a single revolution of the wheel.
Please keep us "in the loop".
Best wishes as to a "painless" outcome.
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Old 01-27-2015, 11:44 PM   #11
Brun
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Quote:
Originally Posted by ME 109 View Post
It's about time there was a problem with the bike anyway. I was becoming most concerned there was something wrong with it.
Ah now Jeff, I know how worried you were about nothing going wrong with the ol' RS for months on end. Praise the gods - you have a proper problem to deal with. Waiting with bated breath to read the prognosis.
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Old 01-28-2015, 12:57 AM   #12
Voltaire
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Quote:
Originally Posted by ME 109 View Post
Thanks for the replies gents
I had the bike on the c/stand when rotating the wheel back and forward. It sounds awful, and the noise is very much coming from the fd itself. There is more than one noise.
I'm satisfied without having removed the wheel yet, that the wheel bearings are fine because there is no wheel wobble, and the noise is too loud and heavy.

Drain plug only has normal sludge without any trace of coarse material. I'm hoping that's a good sign.

Off to work now, so I'll rip into it when I get home.
Pfft...just use earplugs and keep riding it, lack of forward motion will make it easier to find.
Initially I suspected the clutch, then the U joint, then the FD....but it was waskelly wivvits.
I'd put up a pic but did not use NASA rated bolts or genuine BMW factory rivets with the holes reamed out to a light press fit.
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Old 01-28-2015, 01:39 AM   #13
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You're too modest. The solution you chose was brilliant:

Quote:
Originally Posted by Voltaire View Post
Wheel is back


My mate made up tapered adapters to go under the nuts.
Whilst arguably ( useful word for around here) not the same as the original BMW rivets, most likely better than the 40 year old disintegrating that came apart in the last race at probably over 100 mph.
Looking forward to next two race meets to see how the new rear Ohlins and modified Racetech front end go
For ref, the whole thread:

http://www.advrider.com/forums/showthread.php?t=1032754

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Old 01-28-2015, 04:09 AM   #14
ME 109 OP
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It wasn't the final drive

It's the gearbox.
But I just made the flange puller tools the other day, so the sucker is on the bench with the flange removed.

When I got home from work the first thing I did was to rotate the rear wheel to re-assess. I thought the same thing, that all the noise was from the final drive.

I can turn the output flange by hand in neutral, but it was bloody stiff. I couldn't turn it when in gear.
In neutral, the input shaft appears unaffected when rotated.

I did put a taller 5th in, a year or so ago. I've checked the numbers for the correct non x gear and it matched the receipt. My RS build was Sept, 81

The speedo cable broke on the way home this last ride too. But the speedo cable drive gears are fine.

Hey maybe I should change the thread title to '81 tranny clunking' It's not too late.
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Old 01-28-2015, 05:18 AM   #15
boxerboy81
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Well, the good news is you know how to fix it!
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