Bad lean and pull after changing flat tire...... KDSS??

[ggmanning]

I had a flat on the driver front at about 60mph yesterday.....completely flat in about 10 seconds. Limped off the road and changed the flat. Afterwards I had a terrible pull right and after parking on flat ground to evaluate I notice the entire truck leans right. I am assuming my KDSS is out of whack after the blow out. Put it on my lift all the suspension components look good. Could having a total flat with the rim almost on the ground at speed make the KDSS screw up? Figure I'll try calibrating it first before packing it off to the only dealer close to me that knows KDSS an hour away. The lean right appears the same front and rear...maybe 1.5-2" Thoughts...advice? Thanks

 

[ceb]

You mean like this?

 

[2mountainfish]

Silly question, is the spare the same size as the rest of the tires?

 

[ggmanning]

Yes exactly like that.
Spare tire is the same size. Not a silly question. Even on here I see some very mechanically un-inclined people.

I was surprised just jacking up the truck to change the tire would mess up the KDSS and that it didn't equilibrate on it's own. Looks like my next step is to just calibrate the system.

 

[chilibit]

I suspect it will resume it previous posture after a while. Why not immediately, I have no idea.

 

[bloc]

The following is all me trying to think through this problem.. not prior experience.

Since you jacked it up by the frame (presumably) the suspension didn't cycle as though you were going diagonal across an obstacle, which is what KDSS is designed to allow, while still preventing body roll.

You compressed the right rear suspension, while dropping out the front left suspension.

Yeah, I'm sure the front right and left rear corners came up and dropped out some too.. but I think all of that wasn't enough to offset the aggressive drop of the front left and stuff of the rear right.

I think if you had a rear flat there would be no problem, since you are moving the axle itself and effectively emulating a normal off-road movement.

I agree, now that you are sitting level the suspension will be trying to push it level again and sort itself out. Thing is, since that basically requires fluid to leak past the cylinders to get everything in balance, the closer you get to level, the less force is trying to level it, and the slower the correction will be.

You should be able to go find a flat parking lot, crack the valves, push the vehicle around some, then close again, and be level. Though this doesn't seem to work for my truck with only the 10mm OE spacers in front. Mine sits 1.5" leaned and doesn't seem to want to sort itself out, no matter what I do with the KDSS open (drive around block, rock truck, sit on blocks, etc).

 

[Markuson]

The immediate lean the OP mentions from a mere tire change seems very strange to me.

My passenger front was jacked up over 24 hours (all night) when I was putting on my snorkel. I started it late evening...left it jacked up over night...and finished next day.

Even being jacked that long...There was no noticeable lean after it was finally back on all four corners.

KDSS can certainly change when parked off angle over Time...but I wouldn’t expect a simple tire swap would do that, unless the valves were loosened...and tightened before placed level again.

Weird.

 

[mcgaskins]

If the KDSS would get thrown off from changing a tire, all of us who take our trucks off road would have similar issues since similar actions happen through articulation. OP can you provide pics?

 

[bloc]

If the KDSS would get thrown off from changing a tire, all of us who take our trucks off road would have similar issues since similar actions happen through articulation. OP can you provide pics?

That's the thing.. when jacking one corner from the frame this is the opposite of articulation. Normally when your left front corner is lifted, left rear and right front dropped out, and right rear stuffed.. the front left is stuffed. That wasn't the case here, it was dropped all the way out.

I can't speak to why it happened so quickly, or didn't happen for other vehicles, just that from the point of view of the suspension this "looks like" the opposite type of movement KDSS is designed to allow.

Edit: and perhaps it being driver vs passenger matters, since the driver front being dropped out doesn't have the sway bar brackets putting (significant) tension on the bar to remain at ride height? Again, just thinking through this... but I have wondered whether the sway bar brackets are part of the post-lift lean equation for others.

 

[mcgaskins]

That's the thing.. when jacking one corner from the frame this is the opposite of articulation. Normally when your left front corner is lifted, left rear and right front dropped out, and right rear stuffed.. the front left is stuffed. That wasn't the case here, it was dropped all the way out.

Not necessarily. Also you can see in this pic my front passenger axle is all the way drooped and was sitting this way for probably 60-70 hours. None of the other wheels were articulated, and I didn’t have any strange effects from it. I’m not saying there isn’t a problem, but just changing a tire makes zero sense. I get the feeling we’re not getting the full story.

 

[bloc]

Not necessarily.

Yes, necessarily. What OP did is not the same suspension movement as typical articulation.

Again, I'm not saying the end result is correct. Just that this is not normal cycling of the suspension, even for an offroad-capable vehicle. So it stands to reason that if there were a problem (spitballing: internal KDSS cylinder leak, valve block leak between the circuits?), his changing a tire could have highlighted it when normal driving, even offroad, may not have.

 

[mcgaskins]

Yes, necessarily. What OP did is not the same suspension movement as typical articulation.

Again, I'm not saying the end result is correct. Just that this is not normal cycling of the suspension, even for an offroad-capable vehicle. So it stands to reason that if there were a problem (spitballing: internal KDSS cylinder leak, valve block leak between the circuits?), his changing a tire could have highlighted it when normal driving, even offroad, may not have.

I'm sorry, but you're wrong. There are absolutely situations where only one wheel is articulating, just like in my last post where I posted pictures. In fact, there are many situations in the real off road world where only wheel is articulating...I can find pictures of that too if you think it's not possible.

 

[Markuson]

I'm sorry, but you're wrong. There are absolutely situations where only one wheel is articulating, just like in my last post where I posted pictures. In fact, there are many situations in the real off road world where only wheel is articulating...I can find pictures of that too if you think it's not possible.

Unless I am misunderstanding the question...
I think what mcgadkins is saying is makes sense.

KDSS’s whole trick and purpose is that it releases one corner at a time when just one corner is dealing with a bump (needs to articulate) at a time...and then doing opposite...(staying stiff when both wheels on one side are pressured to normally together—like when avoiding lean in turns in a hard turn on pavement). So by design, it is intended to allow single-corner articulation.

For example...making a hard turn up an obstacle where the front tire on the outside of the turn has to ride up and over a big boulder that no other tire hits...

Or...an obstacle where all but the rear, inside tire ends up having to drive over a large rock as it makes the turn you have to sharply make as you drive out and around.

Or an opposite cause of one-wheel articulation...hitting a deep hole (instead of a bump) on a trail with you front passenger tire in a turn...that your rear on the same side misses. The KDSS releases to allow the front dip into the hole and allow the rear to remain.

If I misunderstand the q...someone will tell me.

 

[bloc]

Unless I am misunderstanding the question...
I think what mcgadkins is saying is makes sense.

KDSS’s whole trick and purpose is that it releases one corner at a time when just one corner is dealing with a bump (needs to articulate) at a time...and then doing opposite...(staying stiff when both wheels on one side are pressured to normally together—like when avoiding lean in turns in a hard turn on pavement). So by design, it is intended to allow single-corner articulation.

...which isn't what's happening here. the body is lifted, also lifting the two nearest corners, just like normal articulation.. but in this case the lifted corner's tire is not compressed also.

For example...making a hard turn up an obstacle where the front tire on the outside of the turn has to ride up and over a big boulder that no other tire hits...

when that front corner TIRE rides up, compressing that corner, the two closest corner TIRES drop out

Or...an obstacle where all but the rear, inside tire ends up having to drive over a large rock as it makes the turn you have to sharply make as you drive out and around.

Again, inside rear TIRE lifts, the closest corners can drop. Normal KDSS.

Or an opposite cause of one-wheel articulation...hitting a deep hole (instead of a bump) on a trail with you front passenger tire in a turn...that your rear on the same side misses. The KDSS releases to allow the front dip into the hole and allow the rear to remain.

For the suspension a tire dipping into the hole is the same as the other tire on that axle going up and over an obstacle.



Really, I'm probably doing a poor job of explaining this. I would go outside and put my truck on ramps and jacks to show the difference to our KDSS cylinders between articulation vs jacking a front corner, but we have a hell of a storm going on down here.

Basically, if you jack up the TIRE the OP did, front driver, KDSS sees it as articulation. Without KDSS the front sway bar would try to keep it level by applying an upward force to the front pass tire. KDSS ties both sway bars together such that if the rear bar tries to go the opposite direction.. that is, rear passenger tire up, it allows the bars to disconnect.

If you jack up the BODY at the location the OP did, things are different. Both front tires try to drop down.. so the front bar stays mostly neutral. However the rear axle sees compression on the passenger side, and lift on the driver side. It wants to disconnect.

The "magic" with KDSS is when the vehicle see compression on both axles on the same side at the same time, and extension on both axles on the same side, (like during a turn or side hill), they stay rigid. When they see compression and extension on opposite corners, they allow disconnect, aka articulation.

OP had his front left tire dropped completely out. KDSS would expect the right rear tire to be dropped out too. It was compressed. Not normal KDSS articulation

 

[Markuson]

...which isn't what's happening here. the body is lifted, also lifting the two nearest corners, just like normal articulation.. but in this case the lifted corner's tire is not compressed also.



when that front corner TIRE rides up, compressing that corner, the two closest corner TIRES drop out




Again, inside rear TIRE lifts, the closest corners can drop. Normal KDSS.



For the suspension a tire dipping into the hole is the same as the other tire on that axle going up and over an obstacle.



Really, I'm probably doing a poor job of explaining this. I would go outside and put my truck on ramps and jacks to show the difference to our KDSS cylinders between articulation vs jacking a front corner, but we have a hell of a storm going on down here.

Basically, if you jack up the TIRE the OP did, front driver, KDSS sees it as articulation. Without KDSS the front sway bar would try to keep it level by applying an upward force to the front pass tire. KDSS ties both sway bars together such that if the rear bar tries to go the opposite direction.. that is, rear passenger tire up, it allows the bars to disconnect.

If you jack up the BODY at the location the OP did, things are different. Both front tires try to drop down.. so the front bar stays mostly neutral. However the rear axle sees compression on the passenger side, and lift on the driver side. It wants to disconnect.

The "magic" with KDSS is when the vehicle see compression on both axles on the same side at the same time, and extension on both axles on the same side, (like during a turn or side hill), they stay rigid. When they see compression and extension on opposite corners, they allow disconnect, aka articulation.

OP had his front left tire dropped completely out. KDSS would expect the right rear tire to be dropped out too. It was compressed. Not normal KDSS articulation

Ya, I really should skip this stuff when I can barely see...Super prone to reading/typing errors and end up reading in part because it is hard for me to decipher without much zooming and visual manipulation.
-Finally figured out how to explain what it’s like to have triple vision...
Go to a 3D movie...and remove your 3D classes.
That...is basically what stuff looks like for me when it’s especially bad.

Carry on...

 

[bloc]

Ya, I really should skip this stuff when I can barely see...Super prone to reading/typing errors and end up reading in part because it is hard for me to decipher without much zooming and visual manipulation.
-Finally figured out how to explain what it’s like to have triple vision...
Go to a 3D movie...and remove your 3D classes.
That...is basically what stuff looks like for me when it’s especially bad.

Carry on...

I've actually been meaning to put together some kind of thread clearly explaining all the components and function of KDSS, from the cylinders to the accumulators, in part to help understand lean and why it is so common after lifts, but frankly it's a complex system that I barely understand and definitely don't yet have the creativity to put it all in a format that would make sense to me.. let alone anyone else.

 

[bloc]

I'm sorry, but you're wrong. There are absolutely situations where only one wheel is articulating, just like in my last post where I posted pictures. In fact, there are many situations in the real off road world where only wheel is articulating...I can find pictures of that too if you think it's not possible.

Forgot this part.

If it was JUST one wheel articulating that's fine. But that isn't what happened.

OP had the driver front dropped out, and the passenger rear compressed, at least somewhat, especially in relation to the driver side rear.


I need to rotate my tires and it should be clear out tomorrow. I'll try to put my truck on ramps and while I'm at it copy what OP did to show the difference with regard to the KDSS system

 

[Markuson]

I've actually been meaning to put together some kind of thread clearly explaining all the components and function of KDSS, from the cylinders to the accumulators, in part to help understand lean and why it is so common after lifts, but frankly it's a complex system that I barely understand and definitely don't yet have the creativity to put it all in a format that would make sense to me.. let alone anyone else.

Ya, I think a lot of smart people don’t fully understand it. I’m no expert, that’s for sure! Many don’t Understand even the basics.

For the **basic** purpose of KDSS, I usually point ppl to this...but the inner workings and quirks like gradual lean are still pretty hard to nail down.

 

[Fisher23]

sounds like a problem they will find when re-aligning the vehicle.

 

[ggmanning]

Alignment is/was perfect. I put it on the lift , backed off the proportioning valves on the KDSS and jacked up the left rear tire 4 inches. Re-tightened the valves and set it down and the problem is gone. Perfectly level now. I would suppose the tire going fully flat at speed and having to slow down and limp to a safe place to change the tire fooled the KDSS in some way. Maybe having the front left all the way drooped, basically on the rim, with full weight on it and driving did it???? After calibrating the KDSS my problem is gone. Appreciate all the input.