Anatomy of a KDSS valve (1 Viewer)

[bloc]

I think you guys and gals are gonna like this..

HUGE thanks to @jimoldguy who shipped me his rust-damaged KDSS valve after it was replaced for him with a new one. That can't have been cheap. Fortunately for me he kept the old one, and when I PM'd asking if he'd send it for a project I'm working on he boxed it up.

So my plan was first to clean it up to the extent I could, to avoid tetanus, then cut the thing up and understand it. Then, post all of it. The eventual goal is a comprehensive thread on our KDSS system with details on the functions of it, and this thread is one small part of that effort. For the thread on the operation of the cylinders I'll need some help illustrating everything.. if you have some skills and want to be a part of this let me know.

Anyway.. first, a teaser of where this is going.

So I'll start with some general information.

There has been discussion on this board about the KDSS system being automatic and needing no electronic input. Also disagreement on whether their valve had a harness or not, or a harness attached being for a light under the truck.

As the above valve shows, some of them did come with some electronics. But that appears to be a pressure transducer, I'd assume to keep the brains of the vehicle informed on whether the system pressure went too low or high. This one is off a 2011, but I don't know the build date of it. Could be the first version of the valve.

Speaking of year models.. there were a few iterations of these valves, and other than the elimination of the pressure transducer and the eventual move to an 8mm external hex for the balance screws from the 5mm internal, I'm not sure of the differences. Either way here's the breakdown

Part number Vehicle build date
48006-60020 09/2007-07/2010
48006-60021 08/2010-07/2011
48006-60022 09/2011-06/2014
48006-60023 08/2014-11/2016
48006-60024 01/2017-on

As mentioned it appears only the early valves had the transducer, but when looking up the original part number in toyota's system everything supercedes to the latest 60024 number. I'm assuming this means you can install a non-electronic valve into a vehicle with the wires, and it won't throw any codes or anything.

If someone with an early build truck has techstream, I'd be interested to see if you can find KDSS system pressure in the live data.. if so please post.


One well-known issue with these is the "shutter valves" or balance screws rusting in place. Most here have probably read about the issue, but for those that haven't.. loosening the valves NO MORE THAN THREE TURNS helps make front or rear suspension work easier because it allows the front and rear bars to move independently of each other. Also this basic "balance" is needed any time the height of any corner is changed to let the front and rear bars find their new neutral position, since once the screws are closed they are effectively locked to each other.

I'll show more about the screws later in this thread. Ultimately that's not why @jimoldguy had his valve replaced. His suddenly developed a lean and the dealer diagnosed the issue as the valve. It came with one accumulator removed, so I'm not sure if that one developed a leak, but I couldn't see any other obvious reason for the lean with the valve I had to cut up.


So here's what I was sent. Excuse the filthy work bench.. I have a couple other big projects at the moment.

Top two holes are the main hydraulic circuits to the cylinders, the lower hole is for the missing accumulator.

This angle shows another major rust area for these valves, and it would be very hard to deal with because it is up against the frame rail. Those hex plugs start out bright silver, and the bores they sit in have bare metal, like the lower balance screw face. The good thing is they shouldn't ever need to be removed, but it is just another place for the cancer to take root and go deep.

I'm going to reserve some more posts and edit them to make this appear a little more clean. I'll need all the help I can get to make all of this make sense.

More to come...

 

[bloc]

The pressure transducer is a 3-wire sending unit. When you look up pictures of the newer valve designs online the hole for it is just a big blank of metal, they didn't change the casting but simply left out the machining for this part.

Maybe someone can do something with the numbers on the part

Typical supported o-ring seal design for moderate pressure systems.

This is the cavity it is screwed into. There are 2 other branches for that hydraulic circuit: one over to the bleed screw on the other side of the valve, and where these two bores meet a branch that runs down through the two center valves I'll describe later, eventually on to the accumulators, and the blank sides of the balance screws.

 

[bloc]

On to the accumulators.

As I said this assembly only had one on it. I'm not sure why the other was removed, or frankly how they got it off. The remaining one was very solidly stuck. I didn't have a pipe wrench big enough so I had to get creative, and a bit destructive. Which is fine.. that's the whole point of this right?

So first some background. Accumulators in hydraulic systems are basically pressure reservoirs. They usually have some kind of strong rubber membrane, or floating piston, or as I learn with this one a really cool stainless bellows. Either way the point is to have a compressible gas on one side, and hydraulic fluid on the other. This allows for volume changes in a system filled with stuff that can't be compressed (aka fluid). The reason for the diaphragm/piston is to separate the fluid, which you generally want to keep free of bubbles, separate from the compressible gas.

These are not a rare thing, used commonly in older automatic transmissions, and in every AHC-equipped landcruiser/LX built. On our KDSS though, the accumulators are far more passive than on AHC. They are mostly there (as far as I can tell) to account for pressure changes from temperature and possibly system over-pressures.. there is more complexity than immediately apparent in these valves. For instance it seems there is a system to allow a KDSS cylinder that has gone over pressure -say from hitting something hard and imparting lots of force into the sway bars- to bleed into the accumulators. Also, for anyone that has done front-end work and loosened the balance screws, and had to jack the driver's side arm back up to get it into place for it's linkage.. the pressure you are pushing against is the gas behind the diaphragm in the accumulators pushing down on that cylinder and arm.

One more note about their use in the context of KDSS on a 200. Seeing two of them from the outside, and knowing there are 2 main hydraulic circuits, and 2 KDSS cylinders, I assumed one accumulator was used for each. Wrong. Their plumbing goes straight through the valve so at all times they share pressure/volume and work in unison.

Anyway, the pictures.

First I bled pressure behind the diaphragm so it didn't blow up in my face. See the small hole on the flat back. I went a bit too quick and it depressurized pretty quick, blasting an oil mist all over my drill and shirt. Fortunately I did think ahead and wear eye pro. Trust me I've learned that lesson a few times already.

Poking in there with a brake cleaner straw, it didn't feel like a rubber membrane. Interesting.

Now, time for a larger hole in the side to see what comes out. A fair amount of clear oil. No pressure. But what looks like corrugated metal or a spring inside..

Still, putting a bar in there and turning wasn't getting this thing loose. So I started a new hole closer to the body and worked on that with a punch and hammer.

Past the surface rust it's good to see all the internals being so clean.

 

[bloc]

Accumulators continued..

So with that one off and the pressure out of it I simply cut the back end off.

It appears these use a stainless bellows that allows a change in volume while doing a good job of keeping the gas behind it from mixing with the oil on the other side. Also the front end of the bellows is a relatively thick metal face, and when the bellows is completely extended seems to seal on a rubber gasket in the hydraulic "end" of the accumulator. Plus a small plastic ring to keep the face located in the center.

I'm not exactly sure what the purpose of the gasket is.. possibly once it is completely extended it traps pressure within the accumulator.. thereby allowing the sides of the bellows to be weaker than they would need to be if the hydaulic end was open to atmosphere and subjected to whatever that pressure differential is. But then again I have no idea how much pressure is in this thing when charged.. only that whatever came out when I drilled it did so with a fair amount of drama, and this was with the hydraulic side of it completely open to atmosphere.

 

[bloc]

Things get interesting....

So now I spent some time with a wire wheel in an angle grinder and reduced the tetanus risk. While I was at it I decided to see if I could get one of those side hex covers loose. It quietly laughed at me. No heat, no penetrating oil, nothing. No matter.. I'll have the last laugh.

Note that it cleaned up pretty well, and the internals looked great as far as I could tell. But those balance screws were in trouble. Possible welding could have moved them, but with Jim saying his developed a sudden lean.. just replace it.

So I start cutting. Sadly I couldn't find a stand-up band saw capable of cutting a block of metal this large, so out came the reciprocating saw and metal blades. It's just cast steel, right?

Ehh...

Things were going great until the above photo. I got that far quickly on one blade, not dulling appreciably. Exactly as I'd expect from cast iron. But when I hit that bore is when I dulled 3 blades in quick succession. Hack saw same story. Hm.

I didn't get good pictures but decided to try cutting just the cap and hammering that out. And got this.. Some unidentified part made of very hard steel, with filters on each end, and o-rings clearly meaning to separate the bore into three distinct chambers. Held in with a plug and o-ring, then the screw in plug.

You can see how far I got with those three blades, and some gaps and holes that elude to some interesting complexity.

 

[bloc]

I did a similar job on the other bore and got the cap out. That valve was much harder to remove though, requiring a hole drilled on the other side and I had to drive it out with a small punch.

Note that the lower valve is a different diameter than the upper one. Otherwise similar.. filters on both ends, two holes in each section, plug holding it in.

And, your first clue to how the internal plumbing works. The upper large holes are through the whole valve and go to the "upper" and "lower" hydraulic circuits to the cylinders. I'll cover the plumbing in more detail later. For now, these valves.

I felt like I had a good understanding of this whole assembly but these threw me for a loop. Time to take them apart!

I tried to chuck one up in the vice and unscrew it, as there seemed to be a gap (that was hard to get pictures of) within the central section of each one. It laughed. The steel is so hard it just flattened out the knurls in the vice..

so I cut one open.

Knowing my cutting wheel was likely to destroy most of the internals I stopped halfway to get a picture. Above you can see a large spring, and possibly small pressure seats that are plumbed to the holes in the near end of the valve.

The above picture pretty much tells the story. A large spring, which fully disintegrated with my cutting, pushes outward on the plugs, and those hold back pressure from the upper and lower hydraulic circuits, but if pressure in either gets too high, it is allowed to vent into the center circuit, which connects to the accumulators.

Again, don't worry, I'll lay out the plumbing in more detail later.

 

[bloc]

Another picture with the plugs and seats flipped over

So, on to the lower/larger of the valves. Seemed odd to me there would be two of these, of different sizes, if they had the same function. Why not just 1? or maybe a 2-stage setup with different opening pressures and flow rates? Thing is the holes in each seemed the same size.

Plus, on the ends of the larger one there was a notable difference. In the picture above you can see the ends are solid metal, if anything there is a tiny shallow bore for the lathe work.

Well the bigger one was different..

Also seeing in the cut up one the assembly wasn't screwed together, but pressed, I got to seeing if I could chuck it up and drive it apart.

Success..

The much smaller spring with different ends, and filter were both inside that valve. Also, it was impossible to photograph, but in each end was a very small ball bearing that was apparently inserted into the end, then the plug added after. I believe these act as some sort of check valve.

The filter on the inside of this is curious too, as it implies fluid may flow both directions. Filters on the outsides of the ends, keeping debris from getting inside that way, but a filter on the inside of this one, perhaps to control flow from the central circuit out to the ends.

Plus, the plugs on the ends of the spring were special. Hard metal, with a notch to allow flow, but the shaft protruding out was finely polished and seemed to seal tightly into the small bore in the end of the valve.

So I'll admit I still don't fully understand this valve. If the smaller one is to prevent overpressure by bleeding fluid to the accumulators, the spring in this one isn't nearly strong enough to avoid the same issue, especially with such low surface area on the small shaft above. I'm thinking the ball bearing acts as a check valve to prevent pressure going into this valve from the ends.

But if the goal is to let fluid back out from the accumulator into the cylinder to equalize things again after a high-pressure and bleed event in the other valve, the finely machined shaft should prevent that nicely. I'm thinking maybe there is a controlled gap and it is designed to allow a small amount back from the center circuit into the side circuits if the differential is great enough. If I had a good way to measure the bore I could support this theory, but I don't. I'll have to see if I can find some drill bits to investigate this further.

 

[bloc]

Shutter valves / Balance screws

Now to what a lot of people are probably curious about..

Clearly rust was a problem here. I gave a half-serious attempt to get them moving, but without a welder wasn't interested in putting a ton of effort into them. Plus, I was gonna cut it in half anyway.

So from the above picture you see why TOO MANY TURNS IS BAD. If the o-ring in the groove on the screw is allowed to go past the parallel part of the bore, all the pressure stored in that half of the system can escape.

When closed, the screw basically blocks pressure into each side of the valve. Toyota calls the left side (with the bleeder at the top) the "lower chamber" and the right (frame side) the "upper chamber". Per my reading this is in reference to whether the circuit connects to the top or bottom of the KDSS cylinders at the sway bars. I do plan to get into the flow paths and effects on the bars in my bigger KDSS thread.

In the above picture you can see how fluid moves freely up and down each side but if it needs to get to the center circuit with the accumulators at the bottom, and bleeder/transducer at the top, it has to flow through the 2 valves in the center. Open your screws in the bottom, and the side circuits are connected to the center. If you only open one valve, you aren't truly balancing the system, but letting that side equalize with the accumulators, but not the other side.

Note that the hole in the end of the lower valve cylinder in the picture above is the one I drilled to remove that valve. Normally it is blank and this part is sealed.

 

[bloc]

Today I went and got some more cutoff wheels for my dremel tool so that I could be more precise in cutting up the end of the large valve to see exactly what that ball bearing does.

Now, I understand the purpose. The smaller upper valve is clearly intended to prevent over-pressure situations in either the upper or lower chamber hydraulic circuits, by the small "pop off" valves pictured above allowing excess pressure into the central accumulator circuit. Thing is, eventually that greater pressure in the center needs to get back out to the chamber circuit to equalize everything again.

Enter the lower, larger valve.

@smorris you definitely got me wondering if it was for wear resistance, but as I looked closer the ball seemed to move, and that made me think of a one-way ball valve. When I got it apart it was a lot more clear.

So yes there is a bore with 2 diameters and a chamfered edge where the 2 diameters meet. The smaller diameter goes into the valve, the larger points outward. The ball bearing is dropped in there, then a pin is driven in from the end to keep it in the hole.

The ball totally blocks flow from the end of the valve toward the center, but allows flow from the center out. Which is the opposite of the upper valve.

The internal spring and machined pin seem to be to provide minimal pressure to keep the ball off the seat, but as soon as there is any pressure differential, IE pressure in either chamber circuit goes up compared to the center circuit (as would happen when cornering), that pressure pushes the polished pin in, and the ball in with it, and it hits the tapered seat, and no more flow. If pressure in the circuit gets too high, it can vent to the center via the upper pop-off valve.

I'm fully aware I may not be doing a good job explaining this, so you get my sad attempt at a technical drawing representing what I saw when I took it apart.

But first, pictures. I cut it almost even with the cross-drilled hole. Tried to keep things outside of the pin that is pressed in from the end.

Clearly that ball moves around a bit, because there is a decent mark on the end of the pressed pin from the ball hitting it. Keep in mind the ball was allowed to float back and forth in this bore a millimeter or so. It was not pressed up against the indentation in the pin in the picture below.

Valve seat with ball and spring pin removed

In this one I tried to show the inner spring pin protruding upward as a stand-off, which keeps the ball off the seat. As soon as pressure goes up in either the upper or lower chamber circuit though, it would push in, the ball with it, and no more flow to the center through this valve.

And now, my attempt to draw out this simple one-way valve. Far from perfect and about all I can accomplish on my ipad for now but it gets the point across. I might work on this and add a flange to the spring pin (on the left) hitting the left side of the main body preventing it from going much further out.

 

[bloc]

The following pictures will hopefully explain some of the states of the KDSS valve in normal operation.

First, @Sandroad brought up a good point in what the thing is expected to do during cornering or articulation. For that I want to provide a VERY simple explanation of what the cylinders do in concert to control body roll OR allow articulation, depending on the need.

A very simple way to think of the KDSS cylinders is to break it down to just the left side of the vehicle, and simplify their movement to correspond with the up or down tire movement on that side. So we'll use the left side, because that is where the cylinders are.

Now, imagine turning the vehicle to the right at speed, and the tendency to lean to the left. This would push up on both the front and rear left tires. Imagine the tire being at the end of each of these cylinders.

When you turn right, both left tires want to push up, but the hydraulic lines connecting the tops of both cylinders force them push against each other, and the cylinders resist wheel up travel and therefore body roll.

Keep in mind what I said about the hydraulic lines passing right through the KDSS valve. For this scenario it basically doesn't do anything. It's sole purpose is to handle over-pressure situations and make bleeding the system possible.

Now, imagine driving diagonally over an obstacle.. say through a ditch, or over a long curb. Or simply driving your left front tire up onto an RTI ramp.

As that front left tire compresses upward, the rear tire is dropping out. The hydraulic force at the top of the front cylinder is actually helping push the rear tire downward. If we had static sway bars, the front would be resisting flexing, and the rear too. But with this system, we can run both a stiff sway bar, and automatically "disconnect" it when needing articulation.

Obviously this is a vast oversimplification, as we have four tires instead of 2, and bars, and geometry, and levers, and lots more going on. But it gets the point across. Toyota has come up with an ingenious way to let these things corner quite flat for a tall 6000lb SUV, while doing impressive stuff off-road.

A thorough explanation of both sides of the vehicle and the arms and levers involved is in the plans for the big KDSS thread.. by the way.



Now, for a few more pictures, showing different states of the valve.

First is normal, sitting still, or driving in a straight line. The orange parts represent the chamber circuits from the cylinders, and the teal line represents the central circuit with the accumulators, transducer, etc. In this scenario everything should be at roughly the same pressure, with the lower "outward" flowing valve letting the system equalize. Shutter valves closed, upper and lower chamber circuits isolated from each other..

Now, imagine going into a turn, loading up the suspension on the left side (and causing the upper chambers of the cylinders to work against each other, raising pressure), and hitting a huge bump in the road. The lower valve has already sensed the pressure rise on that side, and let the ball bearing fall into the seat blocking flow back that way. This bump might over-pressure the system on that side. Enter the top pop-off valve to keep pressures reasonable, and vent some to the accumulators as it gets too high.

This also brings up why the inner spring and pins inside the lower valve are needed. If you vent high pressure from one side to the center very aggressively, without anything to control flow OUT of the lower valve into the other chamber circuit, pressure would rise there too. And pressure is much lower on that side, because it is the one "unloaded" because of the cornering attitude of the truck. So that polished pin with a specified annulus to control flow rate means some fluid can flow, but not so much that it will cause problems in the timeframe of this big bump we've hit.

So now we've finished our corner, recovered from the bump, and pressure is higher in the center than before, and lower in the side that needed to vent pressure. The lower valve is responsible for letting this happen automatically. I do believe it isn't a free-flow. The pin on the end of the internal spring and the annulus will restrict flow, but eventually everything will equalize, and be ready for the next corner or bump.

So.. that's my best interpretation of all of this. I still have some questions overall. Like how @jimoldguy and a couple others have suddenly developed a lean from a failed valve. I'm guessing a blocked flow path inside the valve keeps pressure too high or low in one spot, and that puts force on the bars.

Also, I'm even further convinced that the common "drive onto a 4x4 KDSS 'fix'" bandaid is absolutely not the correct way to address things. If the valve is working right, and we assume it is, if the vehicle didn't have a lean before the lift, your lean after the lift is a function of spring length or bushing position, NOT an imbalance.

IMO using the 4x4 to trap high pressure in one side of the system doesn't let things equalize as they are supposed to. It would force that ball in the lower valve against the seat, but not provide enough pressure to let the upper one pop open and bleed.. so.. imbalance.

I DO think with different geometry than intended at stock ride height on the front and rear KDSS arms opens the door for some strange forces but even if that's the case, the wood block method is still a bandaid.

Anyway.. again, any questions, suggestions, or rants about my confusing attempt to explain the way I see things.. hit me with them. I'm on a mission to figure this thing out, and hope to drag some of you along the way while I'm at it.

 

[TLC2013]

This is great, thanks for the investigative work. Very cool stuff.

 

[gaijin]

Excellent work - well done!

 

[Sandroad]

You’re right, I like this! I suspect it’s something only you would do (and I mean that in a good way!). It’s interesting to see how small the passages are, considering how much fluid needs to move for the system to work. Or maybe not? Perhaps the accumulators help minimize fluid movement?

 

[bloc]

You’re right, I like this! I suspect it’s something only you would do (and I mean that in a good way!). It’s interesting to see how small the passages are, considering how much fluid needs to move for the system to work. Or maybe not? Perhaps the accumulators help minimize fluid movement?

So that’s an interesting point. During cornering when the bars are meant to stay engaged, there is very little flow, just a large pressure differential from upper to lower chamber circuits as the bars work against each other. But during axle articulation, yes a fair amount of flow. Thing is, it doesn’t flow through the small passages, it basically flows through the top of the valve into one lower or upper chamber port, and right out the other side of the valve on to the cylinder. Most of the flow through the small internal passages shown above will be when bleeding the system, doing suspension work with the balance screws open, or apparently small movements over temperature changes or bleeding pressure back from the accumulators into the cylinder circuits.

Your post gives me an idea for how to easily illustrate this, so thanks for asking. I’ll work on that today too.

 

[CharlieS]

This is my favorite tech thread ever! So interesting. Thanks, @bloc.

 

[USMCVader]

 

[scooterp7]

Very well done. Thanks for the knowledge

 

[mcgaskins]

Wow this is awesome! Nice work!

 

[vcheng]

That's it for tonight.. I have to do some drawing on the overall valve to explain the circuits, but I'll get that done and finish editing tomorrow.

Feel free to post any questions though.

Thank you for starting this thread to share valuable information. I look forward to more, and specially the part of which fittings and air-over-hydraulic pump will work to service these valves without recourse to a limited number of dealers with the SST.

 

[BlackMammoth]

Fascinating! Excellent work...