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Discussion Starter #1 (Edited)
The pull to the left on my K16GTL was significant enough that I would not be able to "just live with it." So I started considering the options.

Assuming the pull is caused by the center of mass of the bike not being directly over the line between the tire contact patches, one of the tires needs to move laterally. On my 1999 R11RT, I had a right pull that was cured by moving the swingarm 2 mm to the right.

On my K16GTL, the swingarm cannot move any further to the left. So I started thinking about how to move the front wheel to the right. That means either (i) shifting the wheel relative to the wheel carrier (not possible); (ii) shifting the lower A-arm to the right; (iii) shifting the upper A-arm to the left (moving to the left causes the wheel carrier to move to the right, pivoting about the lower ball joint).

The upper A-arm is mounted on two pivot bolts: the one on the left is a fixed pivot bolt (#7):


The right pivot is a pivot pin (#5) with a lock nut (#6). I took a look up the nose, and saw there were several threads-depth of left-moving room left on the upper A-arm -- so the chance of moving the upper A-arm was there.

The next question was: How is the access to the left and right ends of the pivots? The answer was: Good -- once the fuel tank is removed, it is a straight shot to both ends (the nose extensions of the tank exactly cover the pivots). The lower A-arm pivots are buried under much equipment.

Left upper:



Right upper:



So, the obvious answer was to remove the left pivot bolt, place some shims under the bolt, and drive the right pivot pin further in to drive the A-arm to the left.

Before removing the left pivot, you need to support the bike, so that the fork/A-arm/frame arrangement don't shift when the pivot is removed. I used a small jack under a piece of wood under the front of the headers, in front of the cat converters:





Adjust the jack so that the front tire is just touching -- i.e., so the bike weight load on the front tire is just "neutral" so the upper A-arm does not want to shift front/back when the left pivot bolt is removed.

Note the upper A-arm is not a bike weight load-bearing component in the Hossack design -- weight is carried between the lower arm and the frame via the shock. However, the upper arm locates the top end of the wheel carrier (the non-telescoping fork) and therefore can see small fore-aft forces.

After setting up the jack, insert a 12 mm Allen bit into the left pivot bolt and loosen. Mine "popped" loose suddenly at ~70-80 ft-lbs of torque. No Locktite (actually, some anti-seize on the pivot's bearing-seat section):



The right pivot pin is held by a 30 mm lock nut; once loose, the 12 mm Allen bit can be used to advance the right pivot pin to the left.



So how to move the left pivot pin to the left, given that it is fixed by resting its head against the frame? By placing shims under the bolt head.

The first attempt at this fix I installed one 1.03 mm shim:



Not enough pull reduction with one shim, so I ended up using 4 shims (just a hair over 5 mm thickness,which translates into roughly a 15 mm shift to the right of the tire contact patch):



The "shims" are washers from the local hardware store -- 1" ID by 1 1/4" OD. 1" ID is too small to get over the left pivot bolt threads (the threads are 25.8 mm, so a 1"=25.4 mm washer won't fit), so they have to be opened up (I used a grinding stone). You could use a 1 1/8" ID washer, but I could not find one that had a small enough OD to fit within the machined recess of the left pivot.

Note: As I understand it, the bearings in the A-arm are ball bearings, which do NOT like axial loading. [[EDIT: The MaxBMW fiche sez they are angular-contact ball bearings -- so a little more tolerant of axial loads -- but not much.]] So after reinstalling the left pivot bolt, advance the right pivot, but don't apply much torque (6-7 Nm should be sufficient). I do NOT have the proper torque values for the left pivot bolt and the right lock nut (my dealer's service dept. doesn't have them yet). I re-torqued these to approximately what it felt like I needed to loosen them, keeping in mind the left pivot bolt is Aluminum, going into an Aluminum frame -- in other words, tight, but not gorilla-thread-stripping tight. Once I find the correct torque levels, I'll post them. In the meantime, I have marked the position of the components with paint to be able to tell whether they have loosened.

Hope this helps!
Mark
 

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Did you happen to check the wheel alignment before you started using the string or clamped straightedge methods? Just curious. Does the change you made mean that the front wheel is no longer vertical since you shifted only the upper A-arm?

I'm sure this is obvious, but why doesn't moving the contact patch to the right cause even more weight imbalance to the left, worsening the overall problem? I must be missing something.
 

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Being a relative idiot when it comes to wrenching, all I can say is.. wow.

Thanks for the play-by-play. I hope that my bike doesn't have this issue when I finally get it in the next couple of weeks. But, if it does, I'm sure glad you figured out a fix!
 

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Color me impressed. Did it fix the problem?

My Goldwing pulled left terrible. It didn't go away untill a forks rebuild with new springs, valving, and ADV disablement.
 

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Impressive work Mark - and you explained it really well too. That said, I'm not sure I'm willing to tackle this particular job right at the moment. Perhaps your fix, once it's been shared with BMW Motorrad, might result in a TSB so the dealers will correct this for us? One can only hope!
 

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Mark,

It sounds like much more of a job than I am willing to undertake but I might take your post and show it to my dealer to see if he can do something like it.

A couple of things I don't understand are:-


  1. If the bike has any means of adjustment to ensure that the wheels are in line.
  2. With your fix, the front wheel is presumably not running in a vertical plane any more - how will this affect tyre wear and handling?
 

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Great write up Mark. I am lucky that I do not have this problem, but if I did it would be up to BMW or the dealer to fix it.
 

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Discussion Starter #8 (Edited)
Did you happen to check the wheel alignment before you started using the string or clamped straightedge methods?
No, my experience with the R11RT and a bit of thought about the mechanics/physics gave me sufficient confidence in the likely source of the problem.

Does the change you made mean that the front wheel is no longer vertical since you shifted only the upper A-arm?
That assumes the front wheel was truly vertical before I began. :D As it is, the change is small and not visually evident.

I'm sure this is obvious, but why doesn't moving the contact patch to the right cause even more weight imbalance to the left, worsening the overall problem? I must be missing something.
With a pull to the left, the CG is not over the thrust line, it is sitting off to the left. (The pull is the result of the moment generated by the offset CG -- a constant force trying to lay the bike over to the left, which the bike responds to by trying to turn to move the thrust line back under the CG. This is why a constant countersteering pressure must be maintained to actually ride in a straight line.)

If the CG is not too far out, you can move the thrust line to align with the CG. For a left pull, you can move the rear wheel to the left relative to the front wheel. Alternatively, you can move the front wheel to the right. With the Duolever, to move the front wheel to the right you can either move the lower A-arm to the right, to the upper A-arm to the left.

Did it fix the problem?
Yep -- if I cared to take the bike apart again (not!) I might add another 1/2 mm shim to 5.5 mm, but it's now close enough that how I load the saddlebags will have a greater effect on whether the bike pulls left or right.

Perhaps your fix, once it's been shared with BMW Motorrad, might result in a TSB so the dealers will correct this for us? One can only hope!
I'd like to think so, but it's not clear to me that they would be willing to pay for the 2-4 hours of shop labor that would be allowed for the job, particularly where the variations in upper A-arm position across different bikes is unknown, and thus there is no way to tell how much shimming is needed for each bike. The trial-and-re-shim approach I used is hardly a cost-effective way to deal with the issue. BMW would need to develop a way to ballpark assess the amount of correction needed before starting on each bike. I could theorize a couple ways, but I'm out of time for typing for now. :D
 

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Mark, Thanks for the amazing detailed research and write up. Mine pulls slightly to the left, but it is only noticeable when your hands are off of the handlebars. It's going to be interesting when I bring it up to the local dealer this Wednesday. They have asked me to write down everything that need to be adjusted!

I'm going to have a copy of your report available.
 

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Discussion Starter #10 (Edited)
1. If the bike has any means of adjustment to ensure that the wheels are in line.
None that I am aware of -- from what I can see in the drawings both the front and rear pivots rely on a fixed pivot on one side of the arm, with an adjustable pivot on the other side which is adjustable only to push the arm over against the fixed pivot. If the pivot is the wrong length, the frame is mis-machined, the arm itself is inaccurately dimensioned, whatever, there's no left/right adjustability I see in any of the three primary locations. And given what I had to go to with the shimming, I assure you that I looked for a built-in alternative first! ;)

2. With your fix, the front wheel is presumably not running in a vertical plane any more - how will this affect tyre wear and handling?
That assumes the wheel was aligned in the vertical plane in the first place -- something I have every reason to doubt is the case. These bikes are assembled from parts on the shelf -- whatever their as-delivered dimensions -- with no provision for assembly-line adjustment that I can see (i.e., the line workers install the fixed pivot, install the A-arm, and push it over to the fixed pivot with the right pivot pin). I suspect that the varying levels of left pull are due to stack-up of tolerances in all the parts, and there is no checking of F/R alignment anywhere in the process. If I am correct, I would expect the wheel carrier to be *not* in the vertical plane from the factory more often than straight up and down.

As to tire wear, if anything I expect it to be better, as the front tire is no longer being scrubbed sideways by the constant countersteering required to keep the bike going straight. Handling is still superb; rock solid.

Mine pulls slightly to the left, but it is only noticeable when your hands are off of the handlebars.
Hi, Dan -- I suspect that if your bike "only pulls when the hands are off the bars" it actually pulls 100% of the time, and you are not noticing that you are actually using a constant light amount of countersteering pressure to go straight when you hands are on the bars . In fact, as a matter of machanics and physics, this has to be true -- these conditions cannot, not mutually exist.

Just something to consider on your next ride.
 

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Discussion Starter #12
Yep -- if I cared to take the bike apart again (not!) I might add another 1/2 mm shim to 5.5 mm, but it's now close enough that how I load the saddlebags will have a greater effect on whether the bike pulls left or right.
Just a follow-up: I would not bother with the extra 0.5 mm on my bike at this point -- today I rode into the office with a bit more weight in the right bag than the left, and experienced my first (ever so slight) pull to the right. That tells me I'm just about spot on for neutral tracking. :D
 

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Just a follow-up: I would not bother with the extra 0.5 mm on my bike at this point -- today I rode into the office with a bit more weight in the right bag than the left, and experienced my first (ever so slight) pull to the right. That tells me I'm just about spot on for neutral tracking. :D
Have you had any discussions with your dealer? It would be interesting to hear what they had to say.
 

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Discussion Starter #14
Have you had any discussions with your dealer? It would be interesting to hear what they had to say.
My dealer has been very supportive, so they were happy to hear the initial report of success.

The more important question is: How is this being received at BMW NA, and what are they doing with the information?

My guess is that --assuming that they are thinking of doing anything at all with the information (other than issuing a "don't do that!" warning to the dealers) -- they would have to forward it to BMW AG before issuing any guidance to the dealer body. I further suspect that any direct communication with the customers on the subject is not even on the table.
 

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I took my GTL to the dealer in Daytona yesterday, described the issue and provided them with your write-up. They verified the pull to the left with my bike and also with a brand new GTL on the show-room floor. With that they filed an email report to BMW and we are awaiting a response. I will keep you updated on the result.
 

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Don't know about the US but in the UK such a modification would be classed as a significant modification from manufacturers specification and would require notification to and approval by your insurer, at the risk of invalidating the cover if not approved. Assuming of course they could find the mod after any claim!
 

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Discussion Starter #18
My GTL is dead nuts on money no pull but if it did pull that would be BMW,s problem.
I agree -- but what do you do when you're told by a BMW Rep (as I was in 1999): "The bike pulls to the right when you take your hands off the handlebars -- don't take your hands off the handlebars"??? The old BMWNA washed their hands of it, i.e., it "wasn't a problem" so no effort to fix was forthcoming. Hopefully today's BMWNA will be more responsive/proactive with BMWAG to address the growing number of complaints on this.
 

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Don't know about the US but in the UK such a modification would be classed as a significant modification from manufacturers specification and would require notification to and approval by your insurer, at the risk of invalidating the cover if not approved. Assuming of course they could find the mod after any claim!
Which is why I left Old Blighty and moved to the Colonies. :D
 

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I wonder if the brand of tires has anything to do with the pulling left. I don't know how to set up a poll, but it would be interesting to see the brand of tires used by those with the left pull.
 
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