KDSS Fluid Drain and Fill with Lift Install?

[Bicepus Maximus]

The lift install how-to doesn't mention draining and filling the KDSS system.

The repair manual says to drain the system prior to removing the stabilizer bar, then to pressurize it with fluid and bleed the air towards the end of the install. Makes sense. Don't think you want to force a hydraulic system without relieving the pressure first.

Do you have to set the vehicle on the ground prior to pressurizing the system to compensate for the vehicle's new stance? The operating limits of the stabilizer bars' hydraulic pistons (front and back) will have changed. The vehicle will now have more droop. It seems the system will not be in equilibrium unless it's adjusted post-install.

KDSS explained video.

I'm sure installing new suspension without going through all this trouble is possible, but I think it will hinder the KDSS's effectiveness.

Has anyone installed a lift kit by draining and adjusting the system post-install? Any feedback would be greatly appreciated.

 

[1engineer]

Whoa! You just need to stop. right. here.
Why do you think it will hinder the KDSS effectiveness?
You are simply compressing a cylinder against an accumulator with a nitrogen precharge. It does this on it's own thousands of times every time you drive it. Please read the multitude of posts here on lifting a TE and how to do it with KDSS or you will be in for an expensive lesson.

 

[SOcalTRAIL]

Process for installing new suspension on KDSS equipped vehicle:

1. Detach KDSS sway bar.

2. Detach "old" suspension.

3. Attach "new" suspension.

4. Re-attach KDSS sway bar (search forum for the various clever ways of doing this).

5. Get your front end re-aligned.

6. Enjoy the fruits of your labor.

 

[eddiebx]

All I've got to say is if you do drain it out, good luck getting it back in, lol. I've read here that it's a very expensive mistake and requires a trip to the dealer

 

[Bicepus Maximus]

When the lift is installed, both stabilizer bars are being pulled down from their original (pre-lift) position. Thus pulling the front and rear stabilizer control cylinder pistons down, which hydraulically oppose each other.

The pressure in the "lower" portion of the system will certainly be higher than the norm. The pressure in the "upper" portion will be lower. I don't know how this won't make the compression stroke softer than the rebound. To what extent? I don't know.

Perhaps I'll be the buffoon that took his rig to a dealer to equalize the system.

 

[eddiebx]

When the lift is installed, both stabilizer bars are being pulled down from their original (pre-lift) position. Thus pulling the front and rear stabilizer control cylinder pistons down, which hydraulically oppose each other.

The pressure in the "lower" portion of the system will certainly be higher than the norm. The pressure in the "upper" portion will be lower. I don't know how this won't make the compression stroke softer than the rebound. To what extent? I don't know.

Perhaps I'll be the buffoon that took his rig to a dealer to equalize the system.

One part of the equation you're leaving out is, the sway bar can rotate around the bushings in the piston and the LCA mounts. So if you lift it up, I'm sure some of that amount is compensated by just the bar rotating downwards more (kind of like a standard sway bar). I don't think the forces pulling down on the pistons are as great as you think...

Does lifting it change the pressures like you said? Not sure, maybe it does pull the piston down a bit more, I have no logical answer for you because I didn't measure it, nor would I even know how to, lol. All I can say is, all seems well @~2" of lift

If you really want to know if you need to equalize the system, according to the FSM this is only necessary if the side to side lean is more than ~3/4". Maybe after you finish your lift you can give a quick measure and decide then? OR if you are daring enough, perhaps you could try and follow the KDSS re-calibration steps in the FSM.

Personally, I wouldn't worry about toooooo much.

 

[05Rrunner]

Man good luck with that , I bet not many dealers can perform that correctly

 

[STX4Runner]

Don't mess with your KDSS unless you want to lighten your wallet a lot. I and many others have installed a lift with no problems and have not drained any fluid. Follow the instructions in the thread you mentioned and you will be fine.

 

[Jeremy556]

Has anyone installed a lift kit by draining and adjusting the system post-install? Any feedback would be greatly appreciated.

I think one person did, and it was a very expensive mistake. Seriously, as everyone else has probably stated, don't touch the hydraulic part of the KDSS system.

 

[Intruder]

I think it's something like $1000 to have the system recharged. Most dealerships don't have the equipment to do it either, so you may be better off going to a Lexus dealership. No need to bleed and recharge the system though. Lots of people with lifted TEs that have never had a problem with KDSS even though they didn't bleed and recharge the system. The most you might have to do is a zero point calibration for the VSC afterwards.

 

[UtahSooner]

Has anyone installed a lift kit by draining and adjusting the system post-install? Any feedback would be greatly appreciated.

Only reason I touched my KDSS system afer installing my lift was in a fruitless attempt to fix the passenger side lean that plagues most KDSS equipped vehicles (lifted or not) from Toyota. The lean was present before I installed the lift and it was there afterwards...

As several folks have commented already, DO NOT have your KDSS system touched at the dealer or other installer (fyi, Lexus dealer would be your best bet vs a Toyota dealer if your KDSS system is broken - other threads on why) unless you do like me and others have accidentially done and dumped the KDSS fluid on your garage floor. Absolutely no reason to do anything to it when installing a 3:2 lift like most of us TE owners have.

Oh, and my truck still leans a bit (after having it refilled and fixed at the Lexus dealer) so I might as well have taken a couple benjamins an lit them on fire instead of touching my KDSS system...

 

[1engineer]

When the lift is installed, both stabilizer bars are being pulled down from their original (pre-lift) position. Thus pulling the front and rear stabilizer control cylinder pistons down, which hydraulically oppose each other.

The pressure in the "lower" portion of the system will certainly be higher than the norm. The pressure in the "upper" portion will be lower. I don't know how this won't make the compression stroke softer than the rebound. To what extent? I don't know.

Perhaps I'll be the buffoon that took his rig to a dealer to equalize the system.

Look, if you want a technical explanation on why it won't make a difference I will be glad to give you one but what you are describing above just can't happen the way you think. Why? Because of the accumulator precharge pressure. You would be correct if this were a static closed loop system - that is, no accumulators, just pressurized fluid but it's not a static system. If anything, you would need to change the precharge pressures to do what you are talking about but again, it's not needed.

If you really want to see how little everything changes regarding the KDSS system after a lift then I suggest using Boyle's Law. P1V1=P2V2. This will tell you exactly how much the pressure will change after a lift - and how much the accumulator will compensate for that volume change. In order to do this correctly you will need to accurately measure everything as it sits now, install the lift and measure it then and then determine the volume difference. In order to be quite accurate you would also need to take the KDSS cylinder apart so you could accurately measure the piston diameter too. You could also use ratios to get close though. If you think there is a dealer out there that would even know what I am talking about then by all means, take it there. One thing to note though: The rule of thumb for maximum accumulator discharge is about 1/2 nitrogen pressure to system pressure. Any deviation from that will result in less discharge which will result in less movement of the cylinders, as I'm sure this circuit has been optimized by Toyota engineers. If you change the system pressure then you would need to change the nitrogen precharge pressure too.

Again, I will be happy to explain it to you but several posters above have stated it is no big deal and I wholeheartedly agree with them.

 

[Bicepus Maximus]

I appreciate the feedback, gents.

1engineer, I'm a mechanical engineer myself. And I'd like to make heads and tails of the system before I pull out the pocket calculator...... app on my iPhone.

I actually went through roughly 100 pages of the repair manual today, here's what I got:

The ECU controls the accumulators' solenoid valves based on an number of inputs (yaw, accel, wheel speed, etc.) So it, in fact, can be a closed, static system, but only in certain scenarios like when it tries to controls body roll on a smooth surface.

The repair manual doesn't go into the control sequence. Nor should it. It's a repair manual. But I think you're making a good assumption that default position of the solenoid valves is open, like when the vehicle is turned off and someone is installing a lift kit. The suspension would be nearly rigid if the valves to the accumulators were closed.

There's no way to (dis/re)charge the accumulators. Sounds like they come pre-charged from the factory and if they're low, you replace them.

There's no need to mess with the fluid. And you can't mess with the gas charge. Longer stabilizer piston rods is probably the solution, but not a practical/realistic one either.

Onto the math in the next post to realize the effects of lifting a KDSS vehicle?

 

[eddiebx]

You know what I was thinking...it would be interesting if someone could get in touch with the TRD guys to see what they did with the KDSS stuff (if anything) to lift the front end of the TRD Pro 4runner? This might give us some better guidance regarding this topic...I noticed that the prototype model seems to have KDSS and is lifted up front

Onto the math in the next post to realize the effects of lifting a KDSS vehicle?

 

[1engineer]

I appreciate the feedback, gents.

1engineer, I'm a mechanical engineer myself. And I'd like to make heads and tails of the system before I pull out the pocket calculator...... app on my iPhone.

I actually went through roughly 100 pages of the repair manual today, here's what I got:

The ECU controls the accumulators' solenoid valves based on an number of inputs (yaw, accel, wheel speed, etc.) So it, in fact, can be a closed, static system, but only in certain scenarios like when it tries to controls body roll on a smooth surface.

The repair manual doesn't go into the control sequence. Nor should it. It's a repair manual. But I think you're making a good assumption that default position of the solenoid valves is open, like when the vehicle is turned off and someone is installing a lift kit. The suspension would be nearly rigid if the valves to the accumulators were closed.

There's no way to (dis/re)charge the accumulators. Sounds like they come pre-charged from the factory and if they're low, you replace them.

There's no need to mess with the fluid. And you can't mess with the gas charge. Longer stabilizer piston rods is probably the solution, but not a practical/realistic one either.

Onto the math in the next post to realize the effects of lifting a KDSS vehicle?

Yes, the KDSS cylinder can be "rigid" for brief periods but that is not the default position which is where it's at for a vast majority of the time. My point was a lot of things would need to happen that can't happen realistically. Do me a favor though: When you lift it take measurements of the KDSS cylinder before and after just for grins.

So now what method are you going to use when adding a lift?

 

[eddiebx]

Yes, the KDSS cylinder can be "rigid" for brief periods but that is not the default position which is where it's at for a vast majority of the time. My point was a lot of things would need to happen that can't happen realistically. Do me a favor though: When you lift it take measurements of the KDSS cylinder before and after just for grins.

So now what method are you going to use when adding a lift?

This was one thing I regret not doing just for shits and giggles...but now that you mention it Greg, one thing does come to mind.

When you have the wheels on the ground and you disconnect the sway bar's front LCA mounts, the KDSS piston expands until fully extended; which would support your theory that it's not static, since it appears that the system has a natural tendency to expand due to the gas pre-charge (at least while the vehicle is off).

The rear piston does the same, but to a much lesser effect, in that it takes barely any muscle to get it back into position.



Anyway, since we're getting into the nitty gritty here, let me just put this out here for further discussion.

One thing I did consider is loosening the KDSS piston mount bolts (at the frame) and re-torquing them at the new lifted ride height. I thought about doing this because I noticed that the FSM specifies that you should do the final torquing while the vehicle is on the ground (in order to properly fasten the bushing without pre-load).

It's kind of hard to describe, but if you guys check out either the FSM or just peek under the truck, you might notice that the more you pivot the sway bar downwards the more the KDSS piston needs to pivot backwards in order to "reach", for lack of a better description, lol.

I've thought about doing this simply to eliminate any pre-loading of the bushing on the KDSS piston's mount (at the frame), and possibly reducing an extra "uneven pressure", so to speak.

I did notice that after lifting the front, I needed to actively pivot the front KDSS piston towards the rear of the vehicle in order for it to line up properly and bolt on to the LCAs. Kind of wish I took note of this when removing it before lifting, to see if the angle changed

[MENTION=80202]Bicepus Maximus[/MENTION] maybe you can keep this in mind when doing you're lift and fill us in afterwards!

 

[Bicepus Maximus]

You know what I was thinking...it would be interesting if someone could get in touch with the TRD guys to see what they did with the KDSS stuff (if anything) to lift the front end of the TRD Pro 4runner? This might give us some better guidance regarding this topic...I noticed that the prototype model seems to have KDSS and is lifted up front

That's a good idea. I tried calling TRD on a different issue before. The guys in the know are hard to reach. I'll try though.

Yes, the KDSS cylinder can be "rigid" for brief periods but that is not the default position which is where it's at for a vast majority of the time. My point was a lot of things would need to happen that can't happen realistically. Do me a favor though: When you lift it take measurements of the KDSS cylinder before and after just for grins.

So now what method are you going to use when adding a lift?

I have the full Daystar spacer lift on my FJ right now. There's so much negativity towards a spacer lift, especially on the FJ forum. But I have to say, it's as advertised: comfortable.

Only problem is there's a lot of body roll. You really begin to notice it over time as you become more familiar with your vehicle.

I decided to try the Bilstein 5100's all around with the Daystar 1.5" spacer in the rear. I think this will be a natural progression for me. Step up from the spacer lift and take care of the body roll while maintaining as much of stock ride feel as possible.

My 2014 4R TE Premium is likely on a boat somewhere in the Pacific. Should be here in the first week of March. So I have time to do some homework.

By the way, here's my post after installing the Daystar kit on my FJ, if anyone is curious.