The Definitive Answer to the KDSS Clunk. Maybe. Probably.

[1engineer]

Preface:
I know there are dozens of threads on this subject but there are no answers. I think I have come up with the "why" some 4Runners with KDSS have a clunk every now and then.

To begin with, I know some 4Runners have a clunk that is not related to KDSS like the TRD PRO. Also many who upgrade their suspension have suspension noise too. Sorry, this thread won't help. If you have KDSS, read on.

I have a KDSS equipped 4Runner and every now and then it will clunk. Never paid much attention to it until today. I was pulling into a store parking lot and I heard it clunk. I had a bit of time and started testing a bit. The problem:

Most complaints are from guys turning into their driveway or street or going over a bump. A distinct "clunk" and nothing more. It does not happen at high speed nor low speed. It does not happen in a straight line unless it is a hard deceleration. So the test:

Empty parking lot. I attained a speed of about 30mph, started braking and turned into a right hand turn. Clunk.

I did it again. Clunk.

This time, I just coasted around the turn at about 20 mph. No clunk.

I conducted the test several times at varying speeds. The clunk happens between 5-15 mph but only after decelerating from a higher speed. If you drive 10 mph or below and turn, no clunk.

I then suspected what the noise was, so i tried it over a speed hump in a straight line. Same results. Would only give me the clunk after decelerating from a higher speed to between 5-15 mph and going over the bump at that time.

So, what is it? Here is what I think but first a quick explanation:
KDSS basically has two positions and is not controlled by the operator. It is speed activated. What happens is, at a speed from 0-12 (or so) mph, KDSS is active, meaning that it relaxes it's pressure and thereby force against the sway bars. This allows for the suspension to provide more travel at slow speeds off road. Once it passes the speed of 12 mph, a valve shifts which essentially "locks" the KDSS cylinders by trapping pressure in the cylinders. This function provides force on the sway bars and restricts the sway bar movement, which means you get less sway, or body roll, at higher speeds. So from 12 mph up, KDSS cylinders are essentially solid and not moving at all.

So back to the noise. After testing, I think the "clunk" some people hear is simply the KDSS cylinder (and KDSS hydraulic system valves) switching from one mode to the other. You are hearing the mechanical noise of the valves and cylinder relaxing against the sway bars. That's it. Nothing to be concerned with and it does not do it all the time. That's my answer. Many have inspected their suspension, including me, and finding nothing loose. Some people don't hear it. Could be they are hard of hearing or they have other noises masking it but it happens every time you slow down to below 12 mph and somehow load the suspension. If you slow down and keep the sames forces on the suspension, nothing happens. So, you have to have the suspension in a specific situation before it will make the clunk. The clunk is normal. Nothing to be concerned with.

Anyone have a different opinion?

 

[johnbt]

After checking to see if my jack is loose five or six times or if I left something sliding around in the back, I think you're right. Unless something else is loose - and there's lots of stuff sliding around in the back most days. It's not a loud noise, more like a cooler handle slapping something a little bit. It's not like I have all three ball mounts banging around in the back seat with a couple of tire irons and a bottle jack or anything

I turned up the volume and drove on. layball:

 

[1engineer]

I should have named this thread "Color Choice Help" or something... it would have been seven pages long already.

 

[renau001]

Not sure if I've ever noticed this, probably won't stop hearing it now

 

[jrandom]

Sounds good to me. I was steering toward the idea that the end bushings where firming up as they aged. Pressure differential in a switched system makes as good of sense as any.

oh yeah...


RED

 

[Vinsil]

I should have named this thread "Color Choice Help" or something... it would have been seven pages long already.

Or what tint, spacer, are KO2's the best, need HID advice...etc.


Good thoughts and it makes sense. I don't know why people get so freaked out by the kdss..such a simple system.

 

[Antman]

I should have named this thread "Color Choice Help" or something... it would have been seven pages long already.

Easy fix Greg. After the word "Probably." add the word "Boobies."

I got your back Bud.:hiding:

 

[Vinsil]

Easy fix Greg. After the word "Probably." add the word "Boobies."

I got your back Bud.:hiding:

 

[TK-422]

To me it sounds more like one of these than a clunk.

 

[Brandonium]

I never listened for it until last week when there was a thread on it. I heard it the first time when slowing down to make a left turn onto a very shitty road. There's a large low section entering this road and as I turned in and hit it there was a clunk so this makes sense.

Sent from my XT1575 using Tapatalk

 

[sooperslow]

Nice work, I think you nailed it.


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[alphabeast]

I agree. I have had my truck for 3 years and I had this "thunk" the entire time. I figured it was just normal and I really don't notice is much anymore. I was convinced that:

A. The sound was suspension-related (not brakes, loose wiring harness, elves, etc.)
B. That it wasn't something loose or a failed component.

The assessment that this is "normal operating procedures" of the KDSS system makes total sense to me.

So this means we can delete the 600+ "KDSS Thunk" posts, correct? :eyebrows:

 

[nglayton]

Is this different?

I'm not sure I've ever heard this clunk.

Is this different than the clunk for which Toyota issued a TSB? (T-SB-0040-12)

I think for that one, they replaced the drive shaft, something to do with the splines and the rear end having too much play.

That clunk you could actually feel something more than just valves switching. It felt like the guy behind rear ended you at 2-3 MPH.

After having mine "fixed" it was clunk free for 5 years and now recently, every 3-4 months, I get that feeling someone tapped my rear bumper.

 

[wfo9]

I thought you had an sr5... And why no sig? You were the one pushing people to always have one...

Does seem logical the KDSS system would switch modes and possibly make noise.

 

[Friggin Idiot]

I've very rarely heard it in mine, mostly associated with the few speed bumps I slow down for. Guess that means it's not working, I have the radio too loud, or I'm just cornering too fast to have the switch-over. Thanks for a plausible explanation, now if I do hear it I don't have to worry about it. :hail:

SILVER

:girl:
(Can't believe I don't see this stock emoji/gif included in more posts)

 

[philsey]

So ..... so ...... you mean I can buy a TE/KDSS now ..... without fear?

:hug:

 

[Toffees]

If you're looking for empirical data, my LE with XREAS does not make a clunk when turning left.

 

[drtyjerz47]

I just wish I happen to be shopping to see u going 30 mph in a parking lot and then preforming evasive maneuvers....did u happen to have some empire music going?? That would have made it

 

[fishman]

2012 with 109k miles... While pumping gas I hear what can best be described as a pop like a tire seating on a rim with a metallic twang followed by the vehicle gentley rocking/swaying for a second or two.!?

I don't here or feel a clunk but at lower speeds on uneven ground, especially while turning the front end is definitely chirping. There is no lean as a result.

?????

 

[bjohnston115]

Not a bad theory but does this explain why we only hear a clunk in the front from the front piston and not in the rear from the rear one? "Clunk" is also very vague. In my trail with KDSS I heard clunking and felt it under my feet when driving. I had my wife drive and I sat in the passenger seat, the rear seats and the cargo area and felt/heard pretty much nothing.

I ended up replacing my sway bar bushings, front outers and inners and rear inners and all noises and clunks are 100% gone. Upon inspection, the front outer on the driver side was visibly more worn than any other bushing.

IF you are experiencing something similar to what I explained, I would personally recommend spending the $30 bucks (assuming you can do this yourself) and change out the bushings. It took 1.5 hours in my driveway, and the wheels never had to leave the ground.