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Old 04-23-2012, 09:05 PM   #1
zoo mob OP
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R100T front end shake

My 1980 R100T has some peculiar front end behavior at speed. Once I get up to about 70 on the highway, the front forks begin to shake. If I look down at them, it appears that they are shaking from front to back, and not side to side. The handlebars don't really shake form side to side either. It is not violent, but definitely not something I can live with long-term.

I should also note that the forks tend to bind a little bit; i.e. after I stop,and I get off the bike, the front forks will spring back up after a delay. I know that I need to make sure they are aligned etc. and have not taken steps to do this yet. My question is does this shaking behavior point to any particular problem?

Thanks.
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Old 04-23-2012, 10:13 PM   #2
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Forks flex back and forth a lot during normal riding. At 100mph it looks like inches to me. They all do that. You had better get use to it.

It sounds like you have some stiction issues. Something could be bent and/or just needs setting up right.
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Old 04-24-2012, 01:17 AM   #3
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What he said. When was the last time they were taken apart and cleaned? If the oil is silver-ish, pull them apart and clean the stuff inside. That silver stuff is normal and can cause things to stick, so can really old oil.
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Old 04-24-2012, 08:41 AM   #4
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If you've got the super stiff (read: normal) Progressive springs, the forks would rather flex than slide up and down.
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Old 04-24-2012, 09:58 AM   #5
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Go here for step by step procedure to spec those forks. I got Wilbers springs from Ted Porter on my RS. Very nice.

http://w6rec.com/duane/bmw/fork/title.html
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Old 04-24-2012, 10:29 AM   #6
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That article has some good points and some bad points and leaves others out completely. Overall, unless you are straightening crash damage, it is a lot easier than that. Personally, I don't straighten the stuff. I just get new parts but that might change the way prices and availability are going.
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Old 04-24-2012, 11:09 AM   #7
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Soften he rear spring a bit ... a couple threads down.
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Old 04-24-2012, 04:48 PM   #8
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Loosen the fork brace but not enough that the nylock nuts are not still threaded through the bolts and ride it. If the problem goes away you have 2 choices. Rotate one of the fork tubes and see if the problem goes away or shim the fork brace between the the brace and the fork sliders with old washers. The only other way to do it is a complete rebuild.
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Old 04-24-2012, 08:07 PM   #9
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Rebuilding the fork internals itself won't do anything for alignment. I guess it could help them slide up and down if they are in real bad shape. You never know? There's really nothing to rebuild anyway except for replacing deteriorating rubber bumpers. The wiper rings are rarely ever worn much in my experience and mind that they take a LONG time to bed in from new. Aligning the forks? The problem is that there are a million ways to get it done IMO. Turning straight tubes in straight trees. Tightening down a pinch bolt a little more or less. Tightening down a fastener exactly the same way ten times over will get you results sometimes. Praying to the Gods might help IMO.
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Old 04-24-2012, 10:58 PM   #10
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Quote:
Originally Posted by supershaft View Post
Rebuilding the fork internals itself won't do anything for alignment. I guess it could help them slide up and down if they are in real bad shape. You never know? There's really nothing to rebuild anyway except for replacing deteriorating rubber bumpers. The wiper rings are rarely ever worn much in my experience and mind that they take a LONG time to bed in from new. Aligning the forks? The problem is that there are a million ways to get it done IMO. Turning straight tubes in straight trees. Tightening down a pinch bolt a little more or less. Tightening down a fastener exactly the same way ten times over will get you results sometimes. Praying to the Gods might help IMO.
If you know how to rebuild forks it does a lot. Part of the rebuild is cleaning, looking and measuring both apart and as your reassembling.
" Tightening down a pinch bolt a little more or less. Tightening down a fastener exactly the same way ten times over will get you results sometimes. Praying to the Gods might help IMO" This is bad advice. Either that parts are straight, working correct and assembled correct or they're not. If they're not then you have problems.
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Old 04-25-2012, 10:36 AM   #11
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Assembled correct or not. Forks? That boils right down to semantics. For instance, put a magnetic V block and dial indicator on the bottom of a tube and torque down the bottom tree pinch bolt. It will pull the fork in or out by quite a lot as it gets tightened. Within reasonable parameters, that is one option of getting your tube tow in correct. There are tons of options along those lines. Most all the fasteners will do that to some degree. Sure, I have had them go together working real well with no trouble before here and there but then there are the other times. It just takes some fiddling. I have never had to use block and tackle per Duane's article but I have had to do some fiddling.

Speaking of semantics, I consider a rebuild as working on the damper rods. You don't have to pull the damper rods to check the tubes for straightness or measure their parallelism. I am just trying to help the OP. Doing things right to the degree I am talking about goes beyond correct or not. Too many variables.
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