What controls swingarm alignment?
Thread Starter
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Extreme HDF Member
Joined: Jun 2014
Posts: 11,448
Likes: 2,299
From: NW Ohio
What controls swingarm alignment?
I'm not talking tire alignment here.
So, correct me if I'm wrong at any point...I haven't had the drivetrain from my Dyna out of the frame yet...
statements/assumptions:
- The engine/trans/and swingarm are effectively one unit.
- The swingarm pivots on an axle that passes thru the trans case.
- The drivetrain connects to the frame at only three points. (swingarm, therefor, is not directly attached to frame)
- Drivetrain misalignments in any axis translate directly to the rear tire.
Questions/concerns:
- How is drivetrain yaw controlled and adjusted?
- How does a by-the-book rear axle alignment contribute to a perfect overall chassis alignment?
- How is lateral movement of the swingarm controlled at the trans pivot (I'm sure there must be a bearing pre-load, does the race simply rest against the trans casting?)
Bottom line, I'm somewhat concerned that I have never seen a procedure to ensure that the actual drivetrain/swingarm is properly aligned to the frame. How would one go about measuring and adjusting this? Has anybody done it? If so, effects of doing it?
Or am I WAY overthinking this? (I tend to do that).
So, correct me if I'm wrong at any point...I haven't had the drivetrain from my Dyna out of the frame yet...
statements/assumptions:
- The engine/trans/and swingarm are effectively one unit.
- The swingarm pivots on an axle that passes thru the trans case.
- The drivetrain connects to the frame at only three points. (swingarm, therefor, is not directly attached to frame)
- Drivetrain misalignments in any axis translate directly to the rear tire.
Questions/concerns:
- How is drivetrain yaw controlled and adjusted?
- How does a by-the-book rear axle alignment contribute to a perfect overall chassis alignment?
- How is lateral movement of the swingarm controlled at the trans pivot (I'm sure there must be a bearing pre-load, does the race simply rest against the trans casting?)
Bottom line, I'm somewhat concerned that I have never seen a procedure to ensure that the actual drivetrain/swingarm is properly aligned to the frame. How would one go about measuring and adjusting this? Has anybody done it? If so, effects of doing it?
Or am I WAY overthinking this? (I tend to do that).
Last edited by cggorman; Jun 1, 2016 at 03:03 PM.
Road Captain
Joined: Jan 2007
Posts: 645
Likes: 215
From: Minneapolis
I'm not talking tire alignment here.
So, correct me if I'm wrong at any point...I haven't had the drivetrain from my Dyna out of the frame yet...
statements/assumptions:
- The engine/trans/and swingarm are effectively one unit. CORRECT
- The swingarm pivots on an axle that passes thru the trans case. CORRECT
- The drivetrain connects to the frame at only three points. (swingarm, therefor, is not directly attached to frame) FRONT RUBBER MOUNT, REAR RUBBER MOUNT, TOP SPHERICAL ROD, AND (BY MEANS OF THE SWINGARM) THE SHOCKS.
- Drivetrain misalignments in any axis translate directly to the rear tire. CORRECT
Questions/concerns:
- How is drivetrain yaw controlled and adjusted? BY THE RUBBER MOUNTS IN COMBINATION WITH THE SHOCKS
- How does a by-the-book rear axle alignment contribute to a perfect overall chassis alignment? THE DRIVETRAIN NEEDS TO BE ALIGNED BEFORE ANYTHING. THE AXLE ALIGNMENT IS ALSO FOR THE DRIVE BELT
- How is lateral movement of the swingarm controlled at the trans pivot (I'm sure there must be a bearing pre-load, does the race simply rest against the trans casting?) THERE SHOULD BE NO LATERAL MOVEMENT IF THE AXLE IS CORRECTLY TORQUED.
Bottom line, I'm somewhat concerned that I have never seen a procedure to ensure that the actual drivetrain/swingarm is properly aligned to the frame. How would one go about measuring and adjusting this? Has anybody done it? If so, effects of doing it? THE SERVICE MANUAL HAS A DETAILED SECTION ON DRIVETRAIN ALIGNMENT PROCEDURE. IT INVOLVES LOOSENING ALL THE MOUNTS AND RUNNING THE ENGINE TO CENTER THEM.
Or am I WAY overthinking this? (I tend to do that). YOU ARE... LOL
So, correct me if I'm wrong at any point...I haven't had the drivetrain from my Dyna out of the frame yet...
statements/assumptions:
- The engine/trans/and swingarm are effectively one unit. CORRECT
- The swingarm pivots on an axle that passes thru the trans case. CORRECT
- The drivetrain connects to the frame at only three points. (swingarm, therefor, is not directly attached to frame) FRONT RUBBER MOUNT, REAR RUBBER MOUNT, TOP SPHERICAL ROD, AND (BY MEANS OF THE SWINGARM) THE SHOCKS.
- Drivetrain misalignments in any axis translate directly to the rear tire. CORRECT
Questions/concerns:
- How is drivetrain yaw controlled and adjusted? BY THE RUBBER MOUNTS IN COMBINATION WITH THE SHOCKS
- How does a by-the-book rear axle alignment contribute to a perfect overall chassis alignment? THE DRIVETRAIN NEEDS TO BE ALIGNED BEFORE ANYTHING. THE AXLE ALIGNMENT IS ALSO FOR THE DRIVE BELT
- How is lateral movement of the swingarm controlled at the trans pivot (I'm sure there must be a bearing pre-load, does the race simply rest against the trans casting?) THERE SHOULD BE NO LATERAL MOVEMENT IF THE AXLE IS CORRECTLY TORQUED.
Bottom line, I'm somewhat concerned that I have never seen a procedure to ensure that the actual drivetrain/swingarm is properly aligned to the frame. How would one go about measuring and adjusting this? Has anybody done it? If so, effects of doing it? THE SERVICE MANUAL HAS A DETAILED SECTION ON DRIVETRAIN ALIGNMENT PROCEDURE. IT INVOLVES LOOSENING ALL THE MOUNTS AND RUNNING THE ENGINE TO CENTER THEM.
Or am I WAY overthinking this? (I tend to do that). YOU ARE... LOL
Thread Starter
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Extreme HDF Member
Joined: Jun 2014
Posts: 11,448
Likes: 2,299
From: NW Ohio
Near as I can figure, this just relieves lateral stresses on the isolators so they don't bind up and cause excessive vibration. Letting the drivetrain "find it's own center" seems inherently inaccurate and insufficient with regard to vehicle alignment. What if it decides it likes to sit, say, 4° yawed in the frame? That would translate to a rear tire, when "correctly" aligned, that is also 4° yawed.
Tourer
Joined: Feb 2016
Posts: 309
Likes: 39
From: Southlake Texas
I'm not convinced a misalignment would necessarily translate to tire wear. It would make the bike track with the rear wheel offset to one side. A bike isn't like a car, where a left and right wheel can fight each other. The front and rear wheels on the bike will find a straight track...but the tracks will be offset if there is a misalignment. No scrubbing to cause wear.
The "yaw" alignment is set by the front and rear engine mounts. You have to assume they are molded accurately, or you would be correct that they would be unreliable in fixing the swing arm in relation to the frame.
The swing arm is positioned in the tranny case by tapered bearings that are, indeed, preloaded. If they go bad there could be play in the arm.
Sputhe struts are very high on my list of upgrades, for exactly the reasons you are worried about.
The "yaw" alignment is set by the front and rear engine mounts. You have to assume they are molded accurately, or you would be correct that they would be unreliable in fixing the swing arm in relation to the frame.
The swing arm is positioned in the tranny case by tapered bearings that are, indeed, preloaded. If they go bad there could be play in the arm.
Sputhe struts are very high on my list of upgrades, for exactly the reasons you are worried about.
Last edited by CJD197; Jun 1, 2016 at 09:05 PM.
Thread Starter
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Extreme HDF Member
Joined: Jun 2014
Posts: 11,448
Likes: 2,299
From: NW Ohio
Tire wear doesn't concern me in the slightest. I'm only thinking about handling. Stability, Predicability, transitional linearity, etc.
I know I'm talking about a fat *** Harley here, but if there is a relatively simple adjustment that generally gets overlooked or ignored, why not exploit it?
I know I'm talking about a fat *** Harley here, but if there is a relatively simple adjustment that generally gets overlooked or ignored, why not exploit it?
Last edited by cggorman; Jun 1, 2016 at 09:49 PM.
Thread Starter
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Extreme HDF Member
Joined: Jun 2014
Posts: 11,448
Likes: 2,299
From: NW Ohio
Had to look up the Sputhe stuff. I assume you are talking about their "Positrac" system. Looks like that addresses exactly what I'm concerned about. For less than $400, it seems like a great upgrade to accurately adjust and control rear suspension geometry. That will be on my to do list for this fall. Thanks for the tip!
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Road Master
Joined: Aug 2007
Posts: 837
Likes: 35
From: Northern California
How about alignment of the handle bars / front forks while we are discussing this? I spent time making sure the handle bars were parallel to the front forks but when riding in a straight line my left arm is outstretched an amount compared to my right arm (handle bars about 2-3 deg to the right).
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Thread Starter
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Extreme HDF Member
Joined: Jun 2014
Posts: 11,448
Likes: 2,299
From: NW Ohio
Yeah, my stock risers and mini apes are less than great with regard to that. They're going away this fall in favor of some riserless drag bars so I'm just gonna deal with it this season
Tourer
Joined: Feb 2016
Posts: 309
Likes: 39
From: Southlake Texas
How about alignment of the handle bars / front forks while we are discussing this? I spent time making sure the handle bars were parallel to the front forks but when riding in a straight line my left arm is outstretched an amount compared to my right arm (handle bars about 2-3 deg to the right).
The bars are held by the rubber bushings in the upper tree, so aligning the bars to the fork isn't hard. Are you saying your fork seems to not be centered when you are rolling? If so, that is a sign that your rear wheel is not aligned.