R100 Dakar rear end clunk

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Raven
Posts: 12
Joined: Wed Jan 18, 2017 10:12 pm

R100 Dakar rear end clunk

Post by Raven » Mon Jan 30, 2017 8:57 pm

New to the forum and adventure bikes.

I picked up this 1990 bmw airhead R100 gs dakar late last year with the intention of cleaning it up and riding it on weekends. Did the same thing to a R65 last year and got the bug for airheads and their old school quirky charm.
The Dakar has 135k on the odometer and I am now the fourth owner. The bike came with a small book detailing the history of work done by the previous owners with the second in particular. Overall the bike was looking tired and was in need for some attention but had some mods done over the years. It has had a front brake upgrade, progressive front springs and rear suspension Ohlins shock. All good so far as over the coming weeks I start to tinker with it by changing oils, balanced carbs electrical issues etc.
Noticed more than the usual vibration than the comments made on the forum for these motors. Had no real comparison to make until a friend purchased a 93 R100 gs. I was curious about a clunk in the rear end particularly after a ride. The 93 gs was really smooth with no noise at all when rotating the rear wheel on the stand.
So basically started pulling the rear drive train apart. I have removed everything and have come to the conclusion the transmission is the issue. It's very stiff to turn and wants to stop every quarter turn.
I dumped the transmission oil when I got the bike to find some normal metal paste on the sump plug. Cleaned it and replaced the oil to find metal filings yesterday on the plug after 400 km. I have ordered some tools (output flange puller and shim measuring plate) to open the transmission (can't wait). Also have a receipt in my little book for a transmission service with new bearings in 1999 but no mention of a c clip. What years did the c clip start to rear its head? I'm thinking by 1999 it would have been all the rage?
The tail shaft has been modified by a bush mechanic!!! Uni's with grease nipples have been installed to I think is the stock shaft and closed of with welded washers. Can the original stock shafts be balanced? The splines show normal wear as does the final drive. The final drive is very smooth with no backlash.
The splines on the transmission/clutch look good. I have yet to remove the clutch but will probably replace the friction plate and also the rear main seal while I'm there. What are the thoughts on the drive shaft ? Looking at the pricey rebuild version to start a new chapter in the little book.
I will have a crack at servicing the transmission. C clip, bearings, 5% low and high gear plus anything else required.
What has been the experience with the 5% mod to the transmission? Noticeable difference? Motobins have clutch friction plates that are oil proof made from Kevlar. Has anyone used these before?
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1coolbanana
Posts: 1949
Joined: Wed Sep 23, 2009 5:14 pm
Location: NW Sydney

Re: R100 Dakar rear end clunk

Post by 1coolbanana » Mon Jan 30, 2017 9:22 pm

Bike looks great mate :thumb:

That tail shaft does not look like a pro job at all.
Like you said, looks like a back yarder has done some work on it.
By the sounds the FD sounds good and maybe the tail shaft is ok :ne_nau:

Maybe its just the gearbox.

Keep us posted :D
Cowabunga dudes .......

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1coolbanana
Posts: 1949
Joined: Wed Sep 23, 2009 5:14 pm
Location: NW Sydney

Re: R100 Dakar rear end clunk

Post by 1coolbanana » Tue Jan 31, 2017 7:41 am

With all that swarf on the magnet, Ill be very interested to see inside the gearbox!
Cowabunga dudes .......

Raven
Posts: 12
Joined: Wed Jan 18, 2017 10:12 pm

Re: R100 Dakar rear end clunk

Post by Raven » Tue Jan 31, 2017 7:40 pm

Yes I am keen to open the box to see what's going on. Riding the bike, as I throttle on there would be a vibration. With the altered tail shaft, I can assume it would increase the load on the output shaft bearing if not balanced. Maybe I just caught it before it got out of hand. Thank you for the reply.
Lots of parts to be cleaned before reassembly!

Raven
Posts: 12
Joined: Wed Jan 18, 2017 10:12 pm

Re: R100 Dakar rear end clunk

Post by Raven » Sun Feb 12, 2017 9:40 pm

Still waiting for the special tools! In the interim decided to do a cosmetic resto. Pulled the motor and touched the frame and engine parts. Still lots to do!
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1coolbanana
Posts: 1949
Joined: Wed Sep 23, 2009 5:14 pm
Location: NW Sydney

Re: R100 Dakar rear end clunk

Post by 1coolbanana » Sun Feb 12, 2017 9:59 pm

Geez, I thought you were just fixing a gearbox :lol:

Awesome work mate, cant wait to see it :D
Cowabunga dudes .......

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