Lots of factors could cause something on two wheels to become unstable, but when the term "Dyna Death Wobble" is used it usually refers to something more specific than that, and once the chassis design is really understood it's clear why this particular condition wouldn't happen to a non-Dyna. It's still a confusing set of circumstances to correct, because there are many potential factors that could cause it. But the result is that the rear wheel in some conditions will move in an unwanted manner either vertically or in the yaw axis. The resulting "rear steer" will make the bike wobble, vibrate, weave, or shimmy. This is a Dyna-only condition because it stems from the swingarm being attached directly to the engine/tranny, which is rubber mounted and moves around. It won't happen on an FXR (for example), because the swingarm is located in the frame.

Sorry to recap stuff that most people know, but for those who don't, here is the basic Dyna architecture:

There are two distinct halves to a Dyna: The front wheel, fork, and frame are one assembly. The rear wheel, swingarm, engine and transmission are a completely separate assembly. The two assemblies are connected to each other purely by the two rubber engine mounts, one in the front of the engine, the other on the back of the transmission. The top link is really just a stabilizer/locater for alignment purposes, and isn't really a structural link between the two halves. Any and all movement incurred by the engine is directly carried through the transmission to the swingarm and the rear wheel. If the engine vibrates in the longitudinal chassis plane, this isn't much of an issue. If it vibrates left to right, the swingarm and rear wheel move left to right. If the engine swings like a pendulum from the top link, the rear tire actually rolls onto it's sidewalls a little bit, back and forth. The purpose of all the different aftermarket stabilizers is to limit lateral engine movement, while allowing enough longitudinal movement to keep unwanted vibration in check. This architecture explains why a Dyna is much more sensitive to all chassis adjustments/issues than some bikes are... Air pressure, wheel bearings, steering bearings, swingarm bearings, and particularly drivetrain alignment... That's why the same outcome can be difficult to diagnose from bike to bike.

The good news is that when properly setup, a Dyna chassis is actually a very good handling platform.

 

The cause of this is the way hd designed the swing arm. It’s directly installed on the primary and not the frame. Engine moves sideways and the primary is a part of the engine. The best and most logical is not to only stiffen the sideways movement on the front engine mount, but the rear!!! That’s were the problem is! Look at sputhe or true track.

 

Welcome to the forum.

 

Im glad you said this..cause I was getting really tired of saying these exact same things, (not so much on this forum but on FB , every second post is about the death wobble)...I have said since day one, power train stability and alignment are crucial on any rubber mounted platform, but especially Dyna’s....

 

I was wondering if I had the only dyna that didnt wobble. 2015 fxdb, runs smooth as a dream still , no wobble and no vibration issues.

 

Let your front tire get to 15 PSI and you will know what people are referring to.

I pinched my front tube when I installed my 120 21" tire. It took 11 months before it started leaking bad enough to notice.

Yes I do check my pressures but with this situation it caught me totally off guard. Not a good feeling.

 

You won’t feel this if you only cruising. It’s just stupid to ride with 15 psi in front. Don’t do that.

 

Yes I agree it's stupid...and thank you for pointing that out. If I were after ridicule I would have never admitted it.

 

😂😂😂

stiffen the frame if you push the bike to the limit. If not, no point to use that money on something you won’t feel. That said, hd should have done it from the assembly belt... just saying, stupid people eeeeey😂😂

 

Even the FXR was prone to wobbles and weaves when pushed hard enough.