Truck unsettled, rocks side to side over bumps - King 2.5 level kit

[Wilder]

I have a Thuren 2.5 suspension on my truck and I am experiencing unsettled "rocking" side to side when i hit bumps. I don't know if this is what people refer to as "death wobble" - I always assumed that was wobble in the steering system, this feels more like it is concentrated in the rear end, although that feeling is probably somewhat subjective. This is a low speed, underdamped feeling, not the classic "rough ride" that people sometimes complain about. The issue has seemed to appear in the last few weeks, seems far worse than when it was newly installed. It happens unloaded, I hauled a relatively heavy motorcycle in the bed of the truck last week and that made the rocking way worse - having weight up high center of gravity. I have done a cursory check - none of the shocks are leaking and all of the sway bar links are still attached. Anyone else experience a similar issue, or have any ideas of where to start looking for a problem? Here are the details of the kit:

2500 truck, CTD, coil springs no air.
Truck has 50k Miles on it, kit was installed at 10k miles
King 2.5 Shocks, Leveling length
Front shock axle mounts replaced with Carli Weld-on brackets (one of the factory mounts failed snapped off last winter)
Thuren Springs F/R
Thuren Active rate sway bar - front
Thuren sway bar links F/R
Thuren Trackbar
Stock steering damper
Tires - 37x12.5R17 Kenda Klever Pressure 40F/40R
Haven't had a recent alignment but no abnormal wear. this doesn't feel like an alignment issue but I could be wrong

 

[firemansdiesel]

Two things come into mind. 2500’s are known for the rear sway and Thuren rear trac bar takes care of that. The other is check the nitrogen pressure. Over time they will lose some and makes a difference if low.

 

[phatboy64]

So it ran fine for 40k miles and now you are having issues? Something is missing in this timeline.

1. You changed the suspension at 10k.
2. Did everything work fine after that.
3. When did you start to experience the issue you describe above
4. What has changed between when everything was ok to when you experienced the issue above
5. What caused the front shock mount to “snap off”…seems strange under normal use

 

[BikePilot]

It may just be that the shocks are due for a service. I'd start there if they haven't been done before as they are overdue. It'll also rock more if the radius arm bushings are shot.

 

[Wilder]

So it ran fine for 40k miles and now you are having issues? Something is missing in this timeline.

1. You changed the suspension at 10k.

Yes this is true

2. Did everything work fine after that.

Yes it worked fine from when I installed it until about 2 weeks ago

3. When did you start to experience the issue you describe above

2 weeks ago, I hauled a heavy motorcycle in the bed, the side to side rocking started, it was quite unsettling with the bike in the back. I took the bike out and it got much better but it certainly feels worse than it "used to." I noticed the rocking before hauling the bike but I wrote it off as nothing at the time.

4. What has changed between when everything was ok to when you experienced the issue above

As far as I can tell, nothing.

5. What caused the front shock mount to “snap off”…seems strange under normal use

A really big "pot hole" - more like a bathtub hole on a road in rural maine. It was the middle of winter, about -10F out when it happened. The hole was covered with light snow, between the snow and the darkness, I didn't see the hole so I couldn't swerve or slow down, and I hit it head on at about 55mph. When it's that cold the oil in the shocks are pretty stiff and the axle mount couldn't take the force of moving them. Apparently these mounts are only 1/2 welded on from the factory, when thuren builds trucks they basically complete the weld to strengthen the mount. I bought the Carli shock mount so I didn't have to re-use the existing (likely bent) mount.

This happened in february, After replacing the mount the ride went back to normal, and I didn't notice any wobble.

 

[Wilder]

Two things come into mind. 2500’s are known for the rear sway and Thuren rear trac bar takes care of that. The other is check the nitrogen pressure. Over time they will lose some and makes a difference if low.

Looks like 200psi is the correct level - I will check this.

 

[Wilder]

Update -

I checked the pressure in the shocks,

Rear Pass. = <25psi
Rear Drv. = 50psi
Front Pass. = 60psi
Front Drv. = 230psi (this is the one that experienced the shock mount failure)

I pumped them up to 200 with a shock pump that i use on my dirt bike. I know they are supposed to be nitrogen, not air, but I wanted to see if increasing pressure would fix the ride. A quick ride around town and it feels alot better, basically back to normal. I will probably have them purged and filled with nitrogen but then again if plain air is good enough for WP air forks on a dirtbike it probably won't do anything to these shocks either

 

[jsalbre]

Update -

I checked the pressure in the shocks,

Rear Pass. = <25psi
Rear Drv. = 50psi
Front Pass. = 60psi
Front Drv. = 230psi (this is the one that experienced the shock mount failure)

I pumped them up to 200 with a shock pump that i use on my dirt bike. I know they are supposed to be nitrogen, not air, but I wanted to see if increasing pressure would fix the ride. A quick ride around town and it feels alot better, basically back to normal. I will probably have them purged and filled with nitrogen but then again if plain air is good enough for WP air forks on a dirtbike it probably won't do anything to these shocks either

The reason they use nitrogen instead of “air” is largely because of the moisture content in regular compressed air. It causes large pressure changes with temperature change, as well as corrodes parts.

 

[phatboy64]

Update -

I checked the pressure in the shocks,

Rear Pass. = <25psi
Rear Drv. = 50psi
Front Pass. = 60psi
Front Drv. = 230psi (this is the one that experienced the shock mount failure)

I pumped them up to 200 with a shock pump that i use on my dirt bike. I know they are supposed to be nitrogen, not air, but I wanted to see if increasing pressure would fix the ride. A quick ride around town and it feels alot better, basically back to normal. I will probably have them purged and filled with nitrogen but then again if plain air is good enough for WP air forks on a dirtbike it probably won't do anything to these shocks either

Yes this is true

Yes it worked fine from when I installed it until about 2 weeks ago

2 weeks ago, I hauled a heavy motorcycle in the bed, the side to side rocking started, it was quite unsettling with the bike in the back. I took the bike out and it got much better but it certainly feels worse than it "used to." I noticed the rocking before hauling the bike but I wrote it off as nothing at the time.

As far as I can tell, nothing.

A really big "pot hole" - more like a bathtub hole on a road in rural maine. It was the middle of winter, about -10F out when it happened. The hole was covered with light snow, between the snow and the darkness, I didn't see the hole so I couldn't swerve or slow down, and I hit it head on at about 55mph. When it's that cold the oil in the shocks are pretty stiff and the axle mount couldn't take the force of moving them. Apparently these mounts are only 1/2 welded on from the factory, when thuren builds trucks they basically complete the weld to strengthen the mount. I bought the Carli shock mount so I didn't have to re-use the existing (likely bent) mount.

This happened in february, After replacing the mount the ride went back to normal, and I didn't notice any wobble.

View attachment 63071

I was going to say it sounds like a bad shock but based on your truck no below it sounds like you found that out. Drain them and fill with the right level of nitrogen

 

[BikePilot]

I'd really recommend having them serviced, not just putting more air in them. They work similarly to the rear shock on your KTM and should be serviced regularly.

 

[Rockcrawlindude]

Removing the swaybars from my truck fixed all of the strange handling characteristics.

*ymmv
*don’t try this at home

 

[H3LZSN1P3R]

Removing the swaybars from my truck fixed all of the strange handling characteristics.

*ymmv
*don’t try this at home

Agreed the front sway bar is a one use item use it from the dealer lot to your driveway then remove it

 

[Zuber]

Wilder, what you were (are?) experiencing is called 'Head Toss' in the motor industry.

 

[H3LZSN1P3R]

Wilder, what you were (are?) experiencing is called 'Head Toss' in the motor industry.

No its not unless thats a new term for the automotive industry

 

[Wilder]

I'd really recommend having them serviced, not just putting more air in them. They work similarly to the rear shock on your KTM and should be serviced regularly.

Anyone know anyone in Maine or southern NH who can service shocks like these? I've been searching and haven't come up with much

 

[Wilder]

Another thought I had - I have the Thuren Mid-rate, stock height coils. They are now really soft, like i can make the truck bounce up and down alot just moving in the bed. I tried towing a dump trailer loaded to 5000lb total weight this weekend and the truck was squatting worse than a 1500. I really don't ever remember it being that bad as far as squatting, so I am wondering, do these springs wear out? Honestly can't imagine any less spring rate in this truck than these, yet they sell a lighter one.

The trailer wasn't loaded that poorly or anything, relatively distributed load of construction debris.

 

[Rockcrawlindude]

Another thought I had - I have the Thuren Mid-rate, stock height coils. They are now really soft, like i can make the truck bounce up and down alot just moving in the bed. I tried towing a dump trailer loaded to 5000lb total weight this weekend and the truck was squatting worse than a 1500. I really don't ever remember it being that bad as far as squatting, so I am wondering, do these springs wear out? Honestly can't imagine any less spring rate in this truck than these, yet they sell a lighter one.

The trailer wasn't loaded that poorly or anything, relatively distributed load of construction debris.

Springs generally don’t wear out. Generally springs take a slight set when first installed and then they remain the same essentially forever. The exception is if you bend or break them due to extreme use or if they rust and snap.

I can’t comment on your specific spring rate other than me thinking it’s silly to put softer springs on a heavy duty truck.

shocks can go bad you can check those.

You can have suspension components improperly torqued or loose. You could have preload in your bushings if the control arm bolts weren’t loosened and relaxed when the lift kit was installed.

 

[Bajaboy7]

You have to get those shocks rebuilt. Those are race shocks designed for frequent service and maintenance. 40k miles and no nitrogen pressure is a sign that they need love.

 

[MtnRider]

You have to get those shocks rebuilt. Those are race shocks designed for frequent service and maintenance. 40k miles and no nitrogen pressure is a sign that they need love.

^^ This. Those high end shocks require a lot of TLC and maintenance compared to regular shocks.

.

 

[Wilder]

The sad fact is that I can't find anyone willing to touch these in Maine, NH, or northern mass. Rather than shipping them out (at high cost) and renting a vehicle while they are in service, The only real option i see is to get new ones and scrap these.

I see you can order seal kits, has anyone tried to rebuild these themselves?