Thesoundofpanic9
New member
The other day I drove the 4R with an empty tank for the first time in a while. The lean was obviously much more dramatic. It bothered me so much I went home and ordered front and rear Toytec spacers for the pass side.
KDSS Lean after install
- Thread starter Jasalvas
- Start date
Cytronus
New member
Hey guys, I'm a 3rd gen owner considering upgrading to a 2014-2015 TE with KDSS and an ICON Stage 5 lift. It occurred to me reading here that the lean may have a simple explanation. Has anyone measured the lengths of all 4 OEM coils before doing a lift? And then measuring all 4 new lift coils before they go on to note the differences?
On the 3rd gens, the OEM driver side front coil is longer/taller than the passenger side to compensate for the drivers weight. Stock springs are pretty soft, much softer than after market lift coils so different lengths makes sense. I'd bet the KDSS system is tuned accordingly and I'd also bet most lift coils are the exact same length between left and right, which would make perfect sense why spacers would be needed on the passenger side.
I'd love to hear from anyone that's done an ICON stage 5 lift on a KDSS Trail about the experience and if it's doable by oneself in the home garage with jacks and stands.
On the 3rd gens, the OEM driver side front coil is longer/taller than the passenger side to compensate for the drivers weight. Stock springs are pretty soft, much softer than after market lift coils so different lengths makes sense. I'd bet the KDSS system is tuned accordingly and I'd also bet most lift coils are the exact same length between left and right, which would make perfect sense why spacers would be needed on the passenger side.
I'd love to hear from anyone that's done an ICON stage 5 lift on a KDSS Trail about the experience and if it's doable by oneself in the home garage with jacks and stands.
Jetboy
New member
SO... I've been tracking this a bit more lately. Something is happening with the KDSS. I've noticed that over time I have been adding more air to the passenger side airbag to balance out the system and sit level. At first I was balancing pressure side to side, but it developed an inch plus lean over time. I did adjust my front coilovers during this time up about 1.5 inches for a trip to moab. I need to drop them back down and see what happens. I count the rotations of the collars and I assume that moving each the same amount should give equal lift to both front corners. I'll keep updating this as I learn more. There's obviously an asymmetry in KDSS, but it doesn't make sense to me why it would cause a lean or develop a lean at a different ride height. I actually don't understand how it can develop a lean without some internal issue with the valves or something like that.
adam2562
New member
i have an adjustable trac bar and that didn't fix it
just helping your theories by ruling that out
Jetboy
New member
I haven't read this for a while, but I've had some PM conversations regarding it. As of now my working opinion is that you must either spacer or have different springs side/side to balance KDSS lift. I haven't had time to calculate the difference yet or exact measurements to get a better calculation of spring rates. But this is a copy/paste from a conversation I've had about the front to give an idea of what I think is the issue and how to solve it.
Also note that the rear is more complex because of the suspension is "dependent" side to side, so it's a more complicated calculation to get it right.
The downsides are the complexity and one design flaw. The problem with using two pistons in this way is that the piston rod that extends has volume. And as a result as the piston moves the volume of fluid in the combined chambers changes. The excess volume from the piston rod has to go somewhere. To account for this the system uses a pair of accumulators. They are basically just small tanks that act as reservoirs for the extra fluid. But then how do you have a closed system and still allow for expansion without mixing air in the oil? The small accumulator tanks have a rubber diaphragm inside them that is pressurized on one side. - Like a little balloon inside them. As more oil comes in, the balloon full of air gets compressed. No big deal. That's actually exactly the same thing that happens inside of a shock absorber.
Where this becomes an issue is that both pistons are cross linked to make them act as reverse master/slave - when one compresses the other extends. The piston rod area is deducted from the surface area that the hydraulic force of the fluid pushes on. So the top of the piston without the rod has at he full area of the piston, the bottom has the area of the piston minus the rod diameter. Why does that matter? - the answer is that the accumulators are pressurized to about 500psi. And as a result the entire hydraulic circuit set is also pressurized to 500psi. That pressure in the system along with the slight mismatch in the top and bottom of the pistons due to the piston rod means that both KDSS cylinders has a constant pressure pushing down on it of somewhere around 1-300 lbs of force. It's a complex calculation to do without any exact measurements. I can probably do it whenever I get some actual measurements. But my guess is that it results in somewhere around a net force of 100ish lbs of force on the front and rear sway bars pushing down on the driver's side and up on passenger. By that I mean it wants to tilt the vehicle to the passenger side by around 100lbs on each axle. That doesn't sound like a lot -but it results in a slight lean.
If the normal spring rates are around 600lbs/in on the front coils - but they have a 2:1 leverage ratio, that means effectively they are 300lb/in and the same is roughly correct for the rear. If you have 100lbs of extra lift on the front and rear on one side, you would expect approximately 1/6" of lean. It could easily be as high as 300lbs though. I just don't know. If you had 300lbs of effective difference you'd expect a full 1/2 inch of height difference left to right if all else were equal.
For this reason Toyota balances the KDSS lean with slightly longer springs on the passenger side of KDSS 4runners. (Ideally you want a longer spring not a stiffer one - it's a long explanation, just trust me.)
Most aftermarket lift springs will not have a different spring length or spring rate side to side. The result is that you often end up with a "KDSS lean" when you lift them. It's not necessarily a result of the lift, rather it's a result of the spring changes from two different springs to matching ones.
With a 600lb spring and a goal of counteracting the KDSS lean effect, I think you would be pretty darn close by adding somewhere in the range of 3/16 and 1/4" spring spacer to the passenger side front coilover.
Also note that the rear is more complex because of the suspension is "dependent" side to side, so it's a more complicated calculation to get it right.
The downsides are the complexity and one design flaw. The problem with using two pistons in this way is that the piston rod that extends has volume. And as a result as the piston moves the volume of fluid in the combined chambers changes. The excess volume from the piston rod has to go somewhere. To account for this the system uses a pair of accumulators. They are basically just small tanks that act as reservoirs for the extra fluid. But then how do you have a closed system and still allow for expansion without mixing air in the oil? The small accumulator tanks have a rubber diaphragm inside them that is pressurized on one side. - Like a little balloon inside them. As more oil comes in, the balloon full of air gets compressed. No big deal. That's actually exactly the same thing that happens inside of a shock absorber.
Where this becomes an issue is that both pistons are cross linked to make them act as reverse master/slave - when one compresses the other extends. The piston rod area is deducted from the surface area that the hydraulic force of the fluid pushes on. So the top of the piston without the rod has at he full area of the piston, the bottom has the area of the piston minus the rod diameter. Why does that matter? - the answer is that the accumulators are pressurized to about 500psi. And as a result the entire hydraulic circuit set is also pressurized to 500psi. That pressure in the system along with the slight mismatch in the top and bottom of the pistons due to the piston rod means that both KDSS cylinders has a constant pressure pushing down on it of somewhere around 1-300 lbs of force. It's a complex calculation to do without any exact measurements. I can probably do it whenever I get some actual measurements. But my guess is that it results in somewhere around a net force of 100ish lbs of force on the front and rear sway bars pushing down on the driver's side and up on passenger. By that I mean it wants to tilt the vehicle to the passenger side by around 100lbs on each axle. That doesn't sound like a lot -but it results in a slight lean.
If the normal spring rates are around 600lbs/in on the front coils - but they have a 2:1 leverage ratio, that means effectively they are 300lb/in and the same is roughly correct for the rear. If you have 100lbs of extra lift on the front and rear on one side, you would expect approximately 1/6" of lean. It could easily be as high as 300lbs though. I just don't know. If you had 300lbs of effective difference you'd expect a full 1/2 inch of height difference left to right if all else were equal.
For this reason Toyota balances the KDSS lean with slightly longer springs on the passenger side of KDSS 4runners. (Ideally you want a longer spring not a stiffer one - it's a long explanation, just trust me.)
Most aftermarket lift springs will not have a different spring length or spring rate side to side. The result is that you often end up with a "KDSS lean" when you lift them. It's not necessarily a result of the lift, rather it's a result of the spring changes from two different springs to matching ones.
With a 600lb spring and a goal of counteracting the KDSS lean effect, I think you would be pretty darn close by adding somewhere in the range of 3/16 and 1/4" spring spacer to the passenger side front coilover.
deedubb
New member
I have lean after my dobinsons spring install. Front driver side is about an inch lower
Vinsil
New member
Did you mix up the front springs? It's the passenger side lean that people are seeing with kdss.
I haven't installed mine yet so I can't say what I'm going to deal with.
deedubb
New member
I don't think so. The springs were only marked with stickers that said left and right, which drives me nuts since perspective can change what that means. I went with right being passenger side (right side when sitting in vehicle)
Vinsil
New member
I would agree but these are Aussies and they drive on the wrong side of the road.:boxing:
I'd contact Mike and see what he says to be sure. Odd.
A.Wilson013
New member
Sorry to quote such an old post, but I am at a loss right now with my KDSS.
Back in April I installed BP-51s with toytec superflex HD springs. Everything was great (and level, left to right) until this last weekend at the NW Overland Rally. After a rather rough trail run I noticed (from the drivers seat) that my vehicle was tilting to the right a bit. Thought nothing of it until I was getting ready to head home and noticed just how bad it was. My driver's rear was nearly 4" taller than the passenger, and front driver was about 2" taller than passenger. This was with a full tank of gas, and a yeti 105 full of food, beer, ice, etc. well over 100lbs, on the drivers side.
In addition to looking silly, left hand turns on the highway made my already top-heavy vehicle (rooftop tent, etc) quite discomforting. To the point that my wife asked me to slow down on a 60mph banked curve, where I was going 40.
I did the shuttle valve adjustment procedure as outlined in ARBs install instructions to no avail. Then, I opened them again, jacked the rear driver tire 12" off the ground, let it sit, and closed the valves before letting it down. After this, the front is 1" higher, and the rear is 2" higher. Progress, but that's as far as I could get it.
I dropped it off at Lexus today and they're stumped. They've had the vehicle for a full 12 hour day, and have seemingly made no progress. They hope to have an answer tomorrow, but I am not feeling too hopeful.
Would you recommend just paying the diagnosis fee ($450 so far) and installing a spacer in the rear, and adjusting the passenger front coilover to be taller?
It seems like a terrible bandaid fix, but if it works, it works. My fear would be the front not wanting to align correctly.
Thanks in advance. (This is on a 2006 GX470 Sport)
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b407driver
New member
If your GX did that over a short period of time after sitting level, I definitely would not fix it with spacers, as it may re-correct itself and then you'll be left listing the other way.
I have a theory that there is something about the vehicle being in 4 Low and being tossed around that can effectively (temporarily?) re-set what the system thinks is level. If I were you, before I did anything further I'd take it out on some bumpy dirt and drive around for awhile in 4 Low. In other words, work the system at low speed (<12 mph), then get it on level ground and return to 2H.
Might not do a thing, but it's an easy thing to try.
A.Wilson013
New member
Interesting, thank you.
If Lexus cannot get it figured out today without charging me more money, I'll give that a shot. At this point I am willing to try anything.
b407driver
New member
And, after reading through this thread for the first time, there is indeed a tremendous amount of misinformation about KDSS systems, which is compounded by the fact that it is a bit of a 'black box' in regard to how it actually does what it does.
No two KDSS vehicles are the same, and will likely have their own unique lean characteristics, thus the most effective fix being leveling spacers. Ride height from week-to-week can vary by +/- 1/2", regardless of fuel quantity. Lifting the front end absolutely DOES result in weird changes in the back, contrary to assertions in this thread that it does not. Trust me on this one; I went through the exasperation of trying to level the front by initially switching the front L/R shocks (TRD suspension at different perch settings), and it wildly affected the height of the rear. Again, no changes to rear suspension were made, but ride height changed by 2-5/8" in the rear (i.e. the rear went down 1" on on side, and up 1.5" on the other). KDSS did that, there is no other explanation.
Lastly, KDSS vehicles lean opposite of SR5s (go measure a bunch on the lot, I did), and Trail/Off Road variants no longer come with mis-matched shocks, the way the TRD Pros do. Along those lines, my KDSS-equipped TRD suspension was most level in front when the perch settings were identical, not asymmetrical as in the stock TRD Pro.
No two KDSS vehicles are the same, and will likely have their own unique lean characteristics, thus the most effective fix being leveling spacers. Ride height from week-to-week can vary by +/- 1/2", regardless of fuel quantity. Lifting the front end absolutely DOES result in weird changes in the back, contrary to assertions in this thread that it does not. Trust me on this one; I went through the exasperation of trying to level the front by initially switching the front L/R shocks (TRD suspension at different perch settings), and it wildly affected the height of the rear. Again, no changes to rear suspension were made, but ride height changed by 2-5/8" in the rear (i.e. the rear went down 1" on on side, and up 1.5" on the other). KDSS did that, there is no other explanation.
Lastly, KDSS vehicles lean opposite of SR5s (go measure a bunch on the lot, I did), and Trail/Off Road variants no longer come with mis-matched shocks, the way the TRD Pros do. Along those lines, my KDSS-equipped TRD suspension was most level in front when the perch settings were identical, not asymmetrical as in the stock TRD Pro.
wfo9
New member
How much is your lean now...We fixed my buddies lean with a OME spacer in the passenger rear and some adjustments to the coil over upfront. He had the system bled first by another friend who is a Toyota master tech and had access to the special service tools.
I'm still not sure why KDSS does this and I doubt anyone understands it completely. You will hear many KDSS owners claims there is no possible issue.. until they have exactly what you experienced (which matches exactly what I saw). It has something to do with being lifted and pushed hard offroad and some other air bubble or malfunction in the system. I will say.. Once my buddy had the system bled an we did the spacer.. he has had no lean since. That is how I would approach it.
The 470 system may be a bit different also. Each one is a unique snowflake making things even more of a mess to deal with.
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A.Wilson013
New member
When I dropped it off the driver's side was ~2" higher than the passenger side.
They could find nothing wrong (all pressures were correct, no codes, nothing) so they drained all the fluid in the system, reset all the electrical parameters, and crossed their fingers.
It worked.
Out the door I paid $441. They forgot to ask me before replacing the fluid, so they did not charge me for it.
For future reference, I asked what they would charge if I were to bring it in again and request the system be flushed. They said it would likely be 4 hours of labor @ $150/hr + cost of fluid @$18/qt.
Soooo figure $672. Ouch. Hopefully I never have to do this again.
T4Ranger
New member
I'm currently dealing with this... level surface vehicle tilt calibration was not a success so I took it to 3 separate toyota dealerships, 2 of which had no clue what KDSS was, and a 3rd who didn't want to bleed the system (giving me one excuse after another) and a lexus dealership, who would do the fix, but not under warranty, the tech referred me to this video...
https://www.youtube.com/watch?v=xtURdW66WM4
As soon as I unpack from moving and can get to my tools, I'm trying this.
https://www.youtube.com/watch?v=xtURdW66WM4
As soon as I unpack from moving and can get to my tools, I'm trying this.
Thanks for posting that. Going to try it this weekend.
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