Hi guys!
I think Ive finished with my 06 dyna build and I have a problem with some heavy frame vibration on low rpm. Here is some of my setup that I think might somehow cause vibration:

- 14' shocks with standard fork length (cartridge)
- Chain drive (25/60t) with bunk king chain slider
- Sputh stabilizer front and rear with new stock motor mounts (rear stabilizer is for taller shocks)
- tbr 2-1 exhaust
- lyndall rotors front and rear
- 00-05 mags conversion

I dont feel the problem when driving solo and its a quite enjoyable ride. Tight on the corners and stable generally. But, when I hit a speed bump and the shocks goes deep, I can feel a "clunk" like its bottoming(but it dont) and hitting something. When I ride duo the whole bike vibrate AF on low rpm. It feels like it comes from the chain rattling and the whole frame is shaking. I also adjusted the chain without shocks so I know the swing arm can move freely without restriction from the chain. The chain dont even touch anything behind the primary.

I also checked if the rear sputh stabilizer touches anything under the swing arm and I also tried without the heim joints on the sputh connected. Still feeling the "clunk".

So, I know that it has something to do with the swing arm area. This vibration didnt occurred when I had my 13.5' shocks. The angle of the chain is now a bit different with taller shocks. It has to be something from this area!

I havent changed the swing arm bearings, but can this be the problem? Hmm. It felt normal when I was inspecting it tho.

When replacing both motor mounts, the exhaust did got closer to the peg mount(mids) but has now "settled" and has a bigger gap. (pip and peg mount).

Rear brake gives a small vibration when Im braking hard. I think the vibration comes from the engine. The vibration is gone when Im braking with engine turned off.

I need help narrowing the cause of the vibration... Everything should be torqued to specs.

And yeah, I also aligned the engine to the swing arm this winter and hoped this could be the case...

 

Vibration change if you pull in the clutch, decel, or change gear?

Wheel bearings good?

Chain still have visible slack when hot and 2-up?

 

Make sure your not chasing something inherent to Dyna’s. I had a few but went without for a couple years after getting a 2018+ Softail. After going back to a Dyna last month I started wondering about vibrations. However realizing Dyna’s normally vibrate at idle and at low rpms, only to smooth out at about 2500 or so.

 

Vibration changes (less)when pulling the clutch, so in low rpm I tend to feather the clutch to avoid the vibration. Decel and gear change doesn’t do anything, it’s the low rpm but not choking low. Chain does have visible slack when hot and cold. When I adjusted the chain, i adjusted it to either be too tight or too loose when the rear axle was furthest away from the front sprocket. Got this tip from Ari Henning.

Both wheel bearings are good, checked them when I installed the new rotors this winter. 2 years ago since new.

 

I know all about the vibration on Dynas and this is not the same. Only happens when 2up.

I will try to put a camera on the chain/swing arm area and see what’s going on down there 🤔

 

Sounds like typical engine vibrations. Adding a passenger will change the loads on the engine mounts. Not certain exactly how the front mount loads up with more weight on the rear but I ~think~ it will compress, causing less room for vibration control. Maybe get a couple friends to sit on the bike and see how the engine sits with them on/off.

 

Are you sure? Doesn’t engine mounts only take the load of the engine, no? It’s the shocks that take the load on the bike. But again, the swing arm is connected to the engine. Hmmm... maybe i got a defect rear mount...? Maybe you’re right, i didn’t felt this HEAVY vibration on the old mounts. Changed both just because I installed sputh. The old ones looked like they have seen better days tho.

 

The weight of the bike is supported by a fairly complex (geometrically) relationship between the front and rear springs and the front and rear engine mounts. Obviously a portion of the front is entirely supported by the fork springs. The rear is far more complicated. Much of the weight is supported by the shocks but some is transferred thru the swinger pivot to the engine mounts. I'm not sure of the vectors, tho. Adding a passenger may be significant to the mounts or it may not.

Adding weight at a specific engine speed range to cause vibration seems to me to point to engine mounts. I could be way off, tho. We all know how flakey the Dyna can be when it comes to this kind of thing.

 

You're right, don’t now what the engineers was thinking on the rear. Maybe I should test with the old rear mount to see any difference

 

Putting more weight to the rear of the frame makes the entire bike lineup lower in the rear shifting more of the engines weight to the rear mount. The rear mount is very close on the frame to where the rear pegs and seats are. You may want to check how much clearance you have on it.