KDSS Long term reliability?

[jhguth]

I'm not 100% sure on this and it is a bit hard to explain. But from observation it does seem to work to some extent (how much is very difficult to measure)

It has to do with the positioning of the pistons on opposite sides front to rear (cross width). It seems to somewhat encourage opposing articulation front to rear, but discourages same side as the fluid flows and attempts to balance pressure. Again, can't say for sure as there is some mystery in the flow and the movements. But the side closer to the piston clearly has a higher motion ratio. There is quite a bit over overall binding with KDSS as implemented on the 5th gen, so some of it could be that too. Whatever the case, it does pretty well on side hills compared to no sway.

the pistons are on the drivers side

 

[mo_mo]

My very little understanding of shocks is that they fail under heat, and so a smaller piston like described here will be at greater risk of failure trying to keep up in a "baja like" situation

Also, although a fascinating experiment, seems like it's a little over-engineered and so at greater risk of failure. I'm not trained in cars, but in other activities the benefit of systems is both redudancy and specificity. So KDSS with a smaller, better defined role will give it less chance of failure and greater chance of happiness. Can't have everything, at least not with the money I have available.

KDSS does not have a 'shock' (aka damper) like a normal suspension system. Don't get me wrong, the vehicle does have dampers but they are independent of the anti-sway bar (KDSS) system.

The KDSS piston(s) are either hydraulically locked or hydraulically free to move. A valve opens or closes and allows the flow of fluid into/out of the piston. That fluid has to come from or go somewhere, which is the accumulator (reservoir).

The KDSS piston(s) won't heat-up like a traditional suspension shock. When the piston is 'locked', it won't move and won't generate heat. When the piston is 'free', it won't generate heat unless the piston velocities are extremely high such as creating cavitation due to pumping the fluid too fast. It's more likely that piston velocities may exceed allowable seal velocities and create leakage through friction/wear vs. heating. The piston is limited in velocity due to the valve being open or closed, and due to the shocks of the vehicle limiting suspension velocities. I'm guessing that Toyota thought about these things before putting them on, and the 4Runner is not the first Toyota vehicle with KDSS so it is 'tried and true' for Toyota.

Note that Toyota put the 2010 4Runner with KDSS through the paces. They ran parts of moab, rubicon, and the baja 1000 (where it rolled, breaking the ADD [automatic axle disconnect], running in 2WD for the remainder and still finishing). Here is the rolled vehicle with KDSS intact being driven two years after baja:
https://www.youtube.com/watch?v=fJwLeYHTwDw&feature=youtu.be
(skip to 1:08 to see the rear piston still connected)

 

[Jetboy]

Just as a point of reference here. This is the accumulator from and LC200. You'll note how similar it is visually minus the solenoid valve.

This is the 4Runner version:

You can see where the valves are in the 4Runner version as compared to the LC200. I am surprised they don't use the same part for both. The 4Runner has electronic valves. The LC200 uses some sort of pre-loaded check ball system much like a digressive shock would be my guess. At a certain pressure the ball moves and fluid will pass to prevent damage. So the LC200 is normally closed at all speeds to the accumulators, but after a pressure threshold is met the system has a relief mechanism.

A few things I certainly don't totally understand: why they use a metal accordian style diaphragm instead of a rubber one. I can only assume it lasts longer. But I really have no idea otherwise. An internal floating piston would also work, but my guess is that they don't last long enough. But they use metal bellows instead.

I believe the valves are by default - low signal - open. And they close when signal is received from the ECU - high signal. So they are open when turned off. And close when reaching 12mph (although that varies slightly due to steering angle).

 

[Toffees]

KDSS does not have a 'shock' (aka damper) like a normal suspension system. Don't get me wrong, the vehicle does have dampers but they are independent of the anti-sway bar (KDSS) system.

The KDSS piston(s) are either hydraulically locked or hydraulically free to move. A valve opens or closes and allows the flow of fluid into/out of the piston. That fluid has to come from or go somewhere, which is the accumulator (reservoir).

The KDSS piston(s) won't heat-up like a traditional suspension shock. When the piston is 'locked', it won't move and won't generate heat. When the piston is 'free', it won't generate heat unless the piston velocities are extremely high such as creating cavitation due to pumping the fluid too fast. It's more likely that piston velocities may exceed allowable seal velocities and create leakage through friction/wear vs. heating. The piston is limited in velocity due to the valve being open or closed, and due to the shocks of the vehicle limiting suspension velocities. I'm guessing that Toyota thought about these things before putting them on, and the 4Runner is not the first Toyota vehicle with KDSS so it is 'tried and true' for Toyota.

Note that Toyota put the 2010 4Runner with KDSS through the paces. They ran parts of moab, rubicon, and the baja 1000 (where it rolled, breaking the ADD [automatic axle disconnect], running in 2WD for the remainder and still finishing). Here is the rolled vehicle with KDSS intact being driven two years after baja:
https://www.youtube.com/watch?v=fJwLeYHTwDw&feature=youtu.be
(skip to 1:08 to see the rear piston still connected)

That's not really my question, I don't think. What would happen to KDSS if it were "open" at higher speeds?

 

[Jetboy]

That's not really my question, I don't think. What would happen to KDSS if it were "open" at higher speeds?

I believe the difference would be that it would be softer. It would open the fluid flow to the accumulators and the result is that the system would have an air spring buffer. It would still provide the same functionality, but the effect would be moderated by the air springs. Air springs are very progressive in force, so you can't say exactly how much softer - but what you can determine is that it would be softer initially and progressively firmer as the forces increase. Closed system would still allow fluid flow between cylinders, but has no buffer from the air spring.

 

[Toffees]

I believe the difference would be that it would be softer. It would open the fluid flow to the accumulators and the result is that the system would have an air spring buffer. It would still provide the same functionality, but the effect would be moderated by the air springs. Air springs are very progressive in force, so you can't say exactly how much softer - but what you can determine is that it would be softer initially and progressively firmer as the forces increase. Closed system would still allow fluid flow between cylinders, but has no buffer from the air spring.

I think I understand that; would they fail under heat/stress if "always open"

Seems like surely they would, or at least would require re-engineering to prevent such failure, and so it's simpler to "turn the system off" at a specified speed than make it more flexible at all speeds.

It was a question on *increasing* KDSS function and performance that prompted my question (was it yours above)? My suggestion is that "restricting" KDSS makes it more reliable, and useful (at least at costs people like us can afford).

Or maybe I'm wrong, won't be the first time.

 

[mo_mo]

That's not really my question, I don't think. What would happen to KDSS if it were "open" at higher speeds?

'higher speed' is relative, and the answer is 'no one knows' except for maybe one or two engineers at Toyota that have done the math and qualification testing of the components/vehicle. Hitting a curb at 10 mph (square wave) vs. driving over a dirt/gravel road at 60 mph will have very different 'speed' inputs to the piston, and my money is on the curb at 10 mph being much 'faster' than cruising a dirt road at 60 on the piston velocities. Of course hitting a curb at 60 would probably move the piston faster unless the vehicle suspension (shocks) limit the velocity... think of a door with a 'damper' on it. Sometimes you can push 100 times harder on the door but it still won't move any faster.

Give it a test and let us all know!

 

[Toffees]

'higher speed' is relative, and the answer is 'no one knows' except for maybe one or two engineers at Toyota that have done the math and qualification testing of the components/vehicle. Hitting a curb at 10 mph (square wave) vs. driving over a dirt/gravel road at 60 mph will have very different 'speed' inputs to the piston, and my money is on the curb at 10 mph being much 'faster' than cruising a dirt road at 60 on the piston velocities. Of course hitting a curb at 60 would probably move the piston faster unless the vehicle suspension (shocks) limit the velocity... think of a door with a 'damper' on it. Sometimes you can push 100 times harder on the door but it still won't move any faster.

Give it a test and let us all know!

Hah, I don't have KDSS. What I implied earlier is that the "limits" of KDSS are built in so that it's more reliable, but that's more of a logical inference than driven by my experience.

Then again, maybe it's the wrong question to begin with. If the purpose of KDSS is to allow a stiffer sway bar at speed (but "disconnect" it at low speed, to allow desired flexibility/articulation) then "turning it off" doesn't really provide much benefit. Maybe what KDSS needs is an intermediate mode for washboard roads and such?

 

[mo_mo]

Hah, I don't have KDSS. What I implied earlier is that the "limits" of KDSS are built in so that it's more reliable, but that's more of a logical inference than driven by my experience.

Then again, maybe it's the wrong question to begin with. If the purpose of KDSS is to allow a stiffer sway bar at speed (but "disconnect" it at low speed, to allow desired flexibility/articulation) then "turning it off" doesn't really provide much benefit. Maybe what KDSS needs is an intermediate mode for washboard roads and such?

The fundamentals of an anti-sway bar is they increase spring stiffness when one side deflects differently than the other (inside vs. outside tires). I would personally probably run full open, but there is an unquantified risk. Personally I don't see the risk being heating at full open, but possibly relative seal velocities = seal wear = seal failure. Running the system 'half way' between locked and free would create heat at the valve that creates the 'half way' fluid state. These systems do not use a valve that can be positioned 'half way'. It's an on/off, open/closed (I don't know if this is a normally open or normally closed valve so no one infer anything from that statement), so selecting a partial modulation / restriction of the piston would require a lot of aftermarket work for very little value.

Decrease tire pressure and stop running Load Range E tires (Load Range C at the max) would help most people out when running washboard roads.

 

[Toffees]

Decrease tire pressure and stop running Load Range E tires (Load Range C at the max) would help most people out when running washboard roads.

Yeah, but the 'gram though

 

[DesertFish]

http://www.toyota-4runner.org/5th-gen-t4rs/220221-only-kdss-w-lift-need-apply-4.html#post2374362

The OP in this thread disconnected the module which seemed to leave it in a permanently 'open' position.

http://www.toyota-4runner.org/5th-gen-t4rs/220221-only-kdss-w-lift-need-apply-6.html#post2934158

He then replied nearly 2 years later, after leaving it completely disconnected and had no issues to report(other than the KDSS light on the dash). From his previous testing simply reconnecting the module would cause the light to go out right away and behavior to return to normal.

 

[GChristo]

I guess I'm the next guinea pig here. When I bought my new-to-me 4Runner, I thought it didn't have KDSS (wasn't on the window sticker). After a few weeks at home I realized that KDSS was there and decided to live with it. My copilot loves dispersed camping and exploring yet hates a rough drive and that's made me consider KDSS along with other aspects in regard to creating a smoother more compliant off-road ride. Tires, psi, suspension all aside, I wanted to see if modding the KDSS system could improve the ride.

So far, after limited testing as a recent modification, I can say that yes, forcing KDSS into the 'open' mode improved the off-road ride. An example of improvement is when hitting a mild, unexpected rut, it's no longer a PTSD inducing experience. Forcing KDSS into the open mode on-road absolutely makes the ride worse when cornering with more body-roll. While I mention it's improved off-road driveability for me personally, it's not a cure-all. Tires, PSI and suspension come way way before. The subjective improvement may not be worth all the potential costs.

I'd discourage anyone from permanently setting KDSS to open unless you know what you're getting into as that body roll sucks on-road. If you modify the system and your modification fails while driving aggressively, well you can guess there. Then there's unexpected early wear or failure as the system is not operating as intended. If you botch a modification and cause an electrical issue, who knows how much that would cost to recover from. Finally if you have to ask for directions how make this kind of modification then you probably shouldn't be a pioneer here. Disclaimers aside I'll be testing over the next camping season. If something fails prematurely then I'll definitely report back.

 

[epjfsa]

I guess I'm the next guinea pig here. When I bought my new-to-me 4Runner, I thought it didn't have KDSS (wasn't on the window sticker). After a few weeks at home I realized that KDSS was there and decided to live with it. My copilot loves dispersed camping and exploring yet hates a rough drive and that's made me consider KDSS along with other aspects in regard to creating a smoother more compliant off-road ride. Tires, psi, suspension all aside, I wanted to see if modding the KDSS system could improve the ride.

So far, after limited testing as a recent modification, I can say that yes, forcing KDSS into the 'open' mode improved the off-road ride. An example of improvement is when hitting a mild, unexpected rut, it's no longer a PTSD inducing experience. Forcing KDSS into the open mode on-road absolutely makes the ride worse when cornering with more body-roll. While I mention it's improved off-road driveability for me personally, it's not a cure-all. Tires, PSI and suspension come way way before. The subjective improvement may not be worth all the potential costs.

I'd discourage anyone from permanently setting KDSS to open unless you know what you're getting into as that body roll sucks on-road. If you modify the system and your modification fails while driving aggressively, well you can guess there. Then there's unexpected early wear or failure as the system is not operating as intended. If you botch a modification and cause an electrical issue, who knows how much that would cost to recover from. Finally if you have to ask for directions how make this kind of modification then you probably shouldn't be a pioneer here. Disclaimers aside I'll be testing over the next camping season. If something fails prematurely then I'll definitely report back.

And wouldn't leaving KDSS open on the road be like having, essentially, no sway bar?

 

[mo_mo]

I guess I'm the next guinea pig here. When I bought my new-to-me 4Runner, I thought it didn't have KDSS (wasn't on the window sticker). After a few weeks at home I realized that KDSS was there and decided to live with it. My copilot loves dispersed camping and exploring yet hates a rough drive and that's made me consider KDSS along with other aspects in regard to creating a smoother more compliant off-road ride. Tires, psi, suspension all aside, I wanted to see if modding the KDSS system could improve the ride.

So far, after limited testing as a recent modification, I can say that yes, forcing KDSS into the 'open' mode improved the off-road ride. An example of improvement is when hitting a mild, unexpected rut, it's no longer a PTSD inducing experience. Forcing KDSS into the open mode on-road absolutely makes the ride worse when cornering with more body-roll. While I mention it's improved off-road driveability for me personally, it's not a cure-all. Tires, PSI and suspension come way way before. The subjective improvement may not be worth all the potential costs.

I'd discourage anyone from permanently setting KDSS to open unless you know what you're getting into as that body roll sucks on-road. If you modify the system and your modification fails while driving aggressively, well you can guess there. Then there's unexpected early wear or failure as the system is not operating as intended. If you botch a modification and cause an electrical issue, who knows how much that would cost to recover from. Finally if you have to ask for directions how make this kind of modification then you probably shouldn't be a pioneer here. Disclaimers aside I'll be testing over the next camping season. If something fails prematurely then I'll definitely report back.

Awesome!

Do you mind sharing if you spliced into the factory wiring or did you make a custom plug-in harness? If the latter, do you mind sharing PNs of the connectors to purchase?

 

[Hydguy]

Is this a good place to ask about some basics--so are the accumulators* electrically activated at the speed indicator (12mph)?

I tried to ask a question like this relevant to the conversation on the guy who was going to "turn off his kdss" but never got anywhere and was gently eviscerated (all fair, of course).

*or valves or whatever turns the system "on"

No. The accumulators are never 'activated'. They don't work that way. The switches regulate the flow of hydraulic fluid based on the inputs from the ECU.
The purpose of the accumulators is essentially 2 fold. It maintains pressure on the system, through the nitrogen pre-charge, which pushes the hydraulic fluid when the ECU opens the valves (and maintains the pressure) and serves as minor reservoir when one side of the system pushes the fluid, because hydraulic fluid doesn't compress.
The schematic isn't correctly drawn for a hydraulic system, based on my experience dealing with hydraulics. Is that a Toyota schematic?

 

[Jetboy]

Yes. That's a Toyota schematic. I think it is drawn correctly. It just doesn't work how you think it works. That was the case for me. And it's a bellows type mechanical diaphragm. That is very strange for this function.

 

[Richmond Dan]

Yes. That's a Toyota schematic. I think it is drawn correctly. It just doesn't work how you think it works. That was the case for me. And it's a bellows type mechanical diaphragm. That is very strange for this function.

Sorry if I'm asking a basic question, but I'm new to this forum and to 4Runners. I thought I read somewhere that the KDSS on the 4Runner is entirely mechanical/hydraulic, whereas the implementation on the Lexus models has an electronic component. Is that accurate, or do 5th gen Runners also have an electronic component as well?

 

[Jetboy]

Sorry if I'm asking a basic question, but I'm new to this forum and to 4Runners. I thought I read somewhere that the KDSS on the 4Runner is entirely mechanical/hydraulic, whereas the implementation on the Lexus models has an electronic component. Is that accurate, or do 5th gen Runners also have an electronic component as well?

The 4runner is partly electric. The system is always open to fluid flow and the system is based all on mechanical pressure. There is an electronic valve that opens and closes to block off the gas chambers that soften the system. It's open, meaning the system includes a gas chamber making it softer under 12mph. But it has no pumps. The land cruiser 200 is similar but no electronics at all other than a pressure sensor. The lx570 is a very complex system with hydraulic pumps, air springs, coil springs, and shocks all integrated with a bunch of electronics. The limited 4runner is hydraulic, but in the shock absorbers and totally different called XREAS. Hope that helps. Lots of different systems out there. The KDSS in the 4runner is among the most basic of them.

 

[Richmond Dan]

The 4runner is partly electric. The system is always open to fluid flow and the system is based all on mechanical pressure. There is an electronic valve that opens and closes to block off the gas chamber that softens the system. It's open, meaning the system includes a gas chamber making it softer under 12mph. But it has no pumps. The land cruiser 200 is similar but no electronics at all other than a pressure sensor. The lx570 is a very complex system with hydraulic pumps, air springs, coil springs, and shocks all integrated with a bunch of electronics. The limited 4runner is hydraulic, but in the shock absorbers and totally different called XREAS. Hope that helps. Lots of different systems out there. The KDSS in the 4runner is among the most basic of them.

Thanks for taking the time to summarize. I'm very happy with "among the most basic" (less to fail).

Followup question: if the system is "softer" under 12mph, what does this mean for wheel articulation and passenger ride? More, or less, swaying and jarring at low speeds?

 

[honda250xtitan]

I guess I'm the next guinea pig here. When I bought my new-to-me 4Runner, I thought it didn't have KDSS (wasn't on the window sticker). After a few weeks at home I realized that KDSS was there and decided to live with it. My copilot loves dispersed camping and exploring yet hates a rough drive and that's made me consider KDSS along with other aspects in regard to creating a smoother more compliant off-road ride. Tires, psi, suspension all aside, I wanted to see if modding the KDSS system could improve the ride.

So far, after limited testing as a recent modification, I can say that yes, forcing KDSS into the 'open' mode improved the off-road ride. An example of improvement is when hitting a mild, unexpected rut, it's no longer a PTSD inducing experience. Forcing KDSS into the open mode on-road absolutely makes the ride worse when cornering with more body-roll. While I mention it's improved off-road driveability for me personally, it's not a cure-all. Tires, PSI and suspension come way way before. The subjective improvement may not be worth all the potential costs.

I'd discourage anyone from permanently setting KDSS to open unless you know what you're getting into as that body roll sucks on-road. If you modify the system and your modification fails while driving aggressively, well you can guess there. Then there's unexpected early wear or failure as the system is not operating as intended. If you botch a modification and cause an electrical issue, who knows how much that would cost to recover from. Finally if you have to ask for directions how make this kind of modification then you probably shouldn't be a pioneer here. Disclaimers aside I'll be testing over the next camping season. If something fails prematurely then I'll definitely report back.

TEASE.:rockthrow: