KDSS - low or no pressure? (1 Viewer)

[acruisinf]

Been chasing around a KDSS lean to the driver's side for a few months now.

• '15 Cruiser
• Stock except for OEM 10mm coil spacers in the front
• 1.5" lean to the front left
• 1.25" lean to the rear left

Have read every thread on this site about rebalancing. @duggy and his awesome team have tried everything to address the issue and in their investigations have found that the system seems to have low or no pressure. Which makes sense as the jams appear to be visibly depressed and this explains the lean to the driver's side.

My question is: has anyone attempted to have a shop or dealer service center re-pressurize the system?
I understand this is a sensitive system and most people would avoid this and just live with the lean, but wondering about any prior experiences with rectifying low/no pressure.
Thanks!

 

[Sandroad]

Whether or not you have a lean, you are going to want pressure/fluid in the KDSS. Here is a thread from another member's experience with losing pressure.

KDSS Stupid

Let me start by saying that I'm an idiot. I went to adjust the KDSS system by driving the high side up on a block to see if I could improve "the lean." My first shot (using a 1 1/2" block under the tire) made a 1/4" improvement on a 1" initial side to side difference. So, I decided to try a...

forum.ih8mud.com

 

[Markuson]

Been chasing around a KDSS lean to the driver's side for a few months now.

• '15 Cruiser
• Stock except for OEM 10mm coil spacers in the front
• 1.5" lean to the front left
• 1.25" lean to the rear left

Have read every thread on this site about rebalancing. @duggy and his awesome team have tried everything to address the issue and in their investigations have found that the system seems to have low or no pressure. Which makes sense as the jams appear to be visibly depressed and this explains the lean to the driver's side.

My question is: has anyone attempted to have a shop or dealer service center re-pressurize the system?
I understand this is a sensitive system and most people would avoid this and just live with the lean, but wondering about any prior experiences with rectifying low/no pressure.
Thanks!

It required a special tool that most Toyota dealers have to BORROW from Toyota to do. Super high pressures are involved (like 5 or 6 hundred psi IIRC). So I wouldn’t expect other shops to be equipped for this.

 

[bloc]

Do you see leaks anywhere? The only place compressed gas should be in the system (that might not make visible evidence of a leak) is behind the diaphragms in the accumulators, and without physical damage to the back of the accumulator I can’t see that gas escaping. Otherwise I don’t know how you’d have low pressure without seeing a leak.

Also what are the signs of low/no pressure? Due to the pressure in the system when you remove the DS sway bar link, with the balance screws open, the KDSS arm should push down forcefully. Like, need a jack to push it back up into place to get the link in. Same story for the rear. If those arms aren’t pushing down aggressively then yes your system is low.

Does your truck sit level when the sway bars are disconnected? If not, it’s not a KDSS lean. I firmly believe most people with this “problem” are actually misdiagnosing a lean caused by other things like sagged springs, incorrectly installed aftermarket springs, suspension pivots not torqued at neutral ride height, etc.

Edit: the “no evidence of a leak” argument goes out the window if your system wasn’t pressurized or serviced correctly in the first place or at some point in it’s history.

 

[TeCKis300]

Beware of the fallacy of KDSS lean.

A depressurized KDSS system would be the equivalent of a disabled sway bar. Which symptoms would not result in a static lean. But dynamic (cornering) lean resistance.

KDSS enables or disables the sway bar. Unless there was a procedural installation issue... A sway bars function is to flatten posture and does nothing to apply lean. Nor should the sway bar system be tweaked in an attempt to use it to correct a lean.

The root cause for leans is within the primary springs. Either sagging or taking a set over time. Spring/shim packers (small 5mm or 10mm shims placed at the rear lower end), or replacing springs, is the solution.

 

[bloc]

Oh, and my truck leaned almost 2 inches for as long as I had it. The lean persisted if my bars were disconnected. I recently removed the stock suspension and put on kings. No change to KDSS, other than opening and closing the valves during and after install. My lean is now about 3/8 of an inch.

 

[acruisinf]

Do you see leaks anywhere? The only place compressed gas should be in the system (that might not make visible evidence of a leak) is behind the diaphragms in the accumulators, and without physical damage to the back of the accumulator I can’t see that gas escaping. Otherwise I don’t know how you’d have low pressure without seeing a leak.

Also what are the signs of low/no pressure? Due to the pressure in the system when you remove the DS sway bar link, with the balance screws open, the KDSS arm should push down forcefully. Like, need a jack to push it back up into place to get the link in. Same story for the rear. If those arms aren’t pushing down aggressively then yes your system is low.

Does your truck sit level when the sway bars are disconnected? If not, it’s not a KDSS lean. I firmly believe most people with this “problem” are actually misdiagnosing a lean caused by other things like sagged springs, incorrectly installed aftermarket springs, suspension pivots not torqued at neutral ride height, etc.

Edit: the “no evidence of a leak” argument goes out the window if your system wasn’t pressurized or serviced correctly in the first place or at some point in it’s history.

Thanks for the thoughtful response, @bloc. Good note about the sway bars and it makes sense. I haven't been doing any of the actual wrenching, as I'm not properly equipped. My trusty local Toyota 4WD shop has been helping, so I'll check with them about this method to see if this was a check in the process.

Beware of the fallacy of KDSS lean.

A depressurized KDSS system would be the equivalent of a disabled sway bar. Which symptoms would not result in a static lean. But dynamic (cornering) lean resistance.

KDSS enables or disables the sway bar. Unless there was a procedural installation issue... A sway bars function is to flatten posture and does nothing to apply lean. Nor should the sway bar system be tweaked in an attempt to use it to correct a lean.

The root cause for leans is within the primary springs. Either sagging or taking a set over time. Spring/shim packers (small 5mm or 10mm shims placed at the rear lower end), or replacing springs, is the solution.

Thanks, @TeCKis300. After the diagnosis from the shop today of low/no pressure, they installed the 10mm ARB trim packer on the rear driver's side. Lean improved 1/4", so now a delta of 3/4" between passenger and driver side in the rear.

 

[cboyd]

I Had similar issue with lean after lift and while suspecting a KDSS issue, it went to the dealer for diagnosis. The dealer mentioned there was evidence of a small weap on the front KDSS ram, and recommended a re-pressue. They have no other recourse in the FSM, so that’s all they say.

I did it and $650 later, still had the lean. The dealer had to have their senior tech read up on the procedure and they had to get the special service tool (SST) from the regional pool - they had never done one or heard of one being done.

It might be counter-intuative, but I too read everything I could find on the KDSS and then started doing scientific process on it. For me, it was a small 1/4 trim spacer on the front driver shock, which leveled the rear Passenger. I found this by systematically jacking up each front lower control arm until i found what leveled the rear. Then we started playing with the driver front as that seembed to get the most effect. It only took the small shim on the driver front shock to get there, and it’s been level since.

If you think about the physics of a dynamic roll bar and think through the forces, this starts to make sense... but you have to stare at it awhile.

HTH

edit: BTW, there was no evidence of a real leak - the weap noticed on initial inspection could not be accounted for, and the system held pressure based on the FSM and SST pressure tool over 24 hrs, so they cleared it.

 

[kcjaz]

Whether or not you have a lean, you are going to want pressure/fluid in the KDSS. Here is a thread from another member's experience with losing pressure.

KDSS Stupid

Let me start by saying that I'm an idiot. I went to adjust the KDSS system by driving the high side up on a block to see if I could improve "the lean." My first shot (using a 1 1/2" block under the tire) made a 1/4" improvement on a 1" initial side to side difference. So, I decided to try a...

forum.ih8mud.com

Dang it! My therapist almost had me over that event. Know I’m all PTSD...

Seriously, if your KDSS is depressurized that is like driving without stabilizers. No bueno on the high way and very unsafe.

 

[acruisinf]

I Had similar issue with lean after lift and while suspecting a KDSS issue, it went to the dealer for diagnosis. The dealer mentioned there was evidence of a small weap on the front KDSS ram, and recommended a re-pressue. They have no other recourse in the FSM, so that’s all they say.

I did it and $650 later, still had the lean. The dealer had to have their senior tech read up on the procedure and they had to get the special service tool (SST) from the regional pool - they had never done one or heard of one being done.

It might be counter-intuative, but I too read everything I could find on the KDSS and then started doing scientific process on it. For me, it was a small 1/4 trim spacer on the front driver shock, which leveled the rear Passenger. I found this by systematically jacking up each front lower control arm until i found what leveled the rear. Then we started playing with the driver front as that seembed to get the most effect. It only took the small shim on the driver front shock to get there, and it’s been level since.

If you think about the physics of a dynamic roll bar and think through the forces, this starts to make sense... but you have to stare at it awhile.

HTH

edit: BTW, there was no evidence of a real leak - the weap noticed on initial inspection could not be accounted for, and the system held pressure based on the FSM and SST pressure tool over 24 hrs, so they cleared it.

Thanks, @cboyd. Good input. I’m at the point now where I’m simply interested in learning the physics of the system, like you mentioned.

 

[TeCKis300]

I Had similar issue with lean after lift and while suspecting a KDSS issue, it went to the dealer for diagnosis. The dealer mentioned there was evidence of a small weap on the front KDSS ram, and recommended a re-pressue. They have no other recourse in the FSM, so that’s all they say.

I did it and $650 later, still had the lean. The dealer had to have their senior tech read up on the procedure and they had to get the special service tool (SST) from the regional pool - they had never done one or heard of one being done.

It might be counter-intuative, but I too read everything I could find on the KDSS and then started doing scientific process on it. For me, it was a small 1/4 trim spacer on the front driver shock, which leveled the rear Passenger. I found this by systematically jacking up each front lower control arm until i found what leveled the rear. Then we started playing with the driver front as that seembed to get the most effect. It only took the small shim on the driver front shock to get there, and it’s been level since.

If you think about the physics of a dynamic roll bar and think through the forces, this starts to make sense... but you have to stare at it awhile.

HTH

edit: BTW, there was no evidence of a real leak - the weap noticed on initial inspection could not be accounted for, and the system held pressure based on the FSM and SST pressure tool over 24 hrs, so they cleared it.

Interesting that you found a front suspension trim spacer. Can you share as others I'm sure will find it useful? It's usually compensated for in the rear as the install is much much easier. The front takes either a solid spacer at the top which requires some disassembly. Or more difficult still, an isolator/spring type spacer which requires taking the coilover assembly apart. Aftermarket coilovers with adjustable perches makes adjusting for level easy.

Back in the 100-series days with torsion bars, it was easier still as one could just apply a few screw turns to the front suspension.

 

[bloc]

Thanks, @cboyd. Good input. I’m at the point now where I’m simply interested in learning the physics of the system, like you mentioned.

I have generous user’s rusty old KDSS valve on their way to me with plans to cut it up and understand how it works. Part of a long term project to post and figure this system out. I actually believe it isn’t all that complex, but because it is closed and mostly maintenance/problem free we don’t have as much experience opening and messing with it.

Part of the plan is working with someone to illustrate the operation and I’ll be looking for help with that eventually, as my mechanical aptitude is probably up to the task but not my drawing abilities. But first I need the parts in my hand to confirm some hypotheses.

 

[Sandroad]

Dang it! My therapist almost had me over that event. Know I’m all PTSD...

Seriously, if your KDSS is depressurized that is like driving without stabilizers. No bueno on the high way and very unsafe.

Yah, those of us who do our own wrenching make a lot of therapists richer. There's a lot of "one last turns" I wish I had back.

 

[acruisinf]

I have generous user’s rusty old KDSS valve on their way to me with plans to cut it up and understand how it works. Part of a long term project to post and figure this system out. I actually believe it isn’t all that complex, but because it is closed and mostly maintenance/problem free we don’t have as much experience opening and messing with it.

Part of the plan is working with someone to illustrate the operation and I’ll be looking for help with that eventually, as my mechanical aptitude is probably up to the task but not my drawing abilities. But first I need the parts in my hand to confirm some hypotheses.

I cannot wait for this thread and eventual finished product! Keep us updated!

 

[kcjaz]

I have generous user’s rusty old KDSS valve on their way to me with plans to cut it up and understand how it works. Part of a long term project to post and figure this system out. I actually believe it isn’t all that complex, but because it is closed and mostly maintenance/problem free we don’t have as much experience opening and messing with it.

Part of the plan is working with someone to illustrate the operation and I’ll be looking for help with that eventually, as my mechanical aptitude is probably up to the task but not my drawing abilities. But first I need the parts in my hand to confirm some hypotheses.

I can't wait to see this. How those valves actually work is a mystery to me and I'm sure others. Cutting a set open to see how the internals work would help understanding how the system works a lot. What I think happens when you open the two valves is that a passage opens connecting the upper and lower oil accumulators/circuits together equalizing the pressure on both sides of the hydraulic ram cylinders and allowing the stabilizers to more freely move without any hydraulic force applied by the ram cylinders.

Here is a pretty good video illustrating how the system works. The concept is brilliantly simple and all mechanical. No electronics to screw up. KDSS Video

 

[bloc]

I can't wait to see this. How those valves actually work is a mystery to me and I'm sure others. Cutting a set open to see how the internals work would help understanding how the system works a lot. What I think happens when you open the two valves is that a passage opens connecting the upper and lower oil accumulators/circuits together equalizing the pressure on both sides of the hydraulic ram cylinders and allowing the stabilizers to more freely move without any hydraulic force applied by the ram cylinders.



View attachment 2466608

Here is a pretty good video illustrating how the system works. The concept is brilliantly simple and all mechanical. No electronics to screw up. KDSS Video

Documents like this will go a long way toward understanding things. When I get the valve in hand and start messing with it I’ll likely be posting to the board requesting supporting documents like yours. Any info I can accumulate should help piece this concept together.