A/c Related To "clunk"?

[GX 470 law]

Hmmm...just brought an '08. Hot as heck today, so decided to use the A/C. Seems like when the A/C kicks in while stopped, I feel a "clunk." Is this the infamous clunk..or...is it normal A/C noise?

[The G Man]

Do you feel a push from the back when you hear the clunk?

[nc211]

If not feeling it from the rear, then you're most likely just feeling the a/c unit kick on. Although my car is not the GX470, it is the same mechanically (05' 4runner w/ 4.7 V8), and I too can feel a clunk when the a/c kicks on. The a/c units on these engines are huge. It's normal....

I seriously doubt you're feeling "the clunk" from the a/c though, unless if your car moves forward when the a/c kicks on. The cluck is the slider sleeve on the driveshafts unsticking and hitting the U joints at the differential. When you come to a stop, the slider yolk sticks about an inch from it's seat. When you start to move, it frees itself and smacks into it's seat. We have two of them; One on the front, one on the back. The back is usually the one that everyone notices, as it's much bigger and heavier than the front. I have this too in my 4runner. I have to grease the driveshaft about every 6,000 miles with my grease gun. There are 6 zerk "nipples" on the shafts, that you hook up your grease gun to and pump a few rounds of gease into. I also rub some grease around the slider sleeve's pathway.

[GX 470 law]

Do you feel a push from the back when you hear the clunk?

I'll check it later on today when I turn the A/C on.

[denslexusgx470]

Try turning the a/c off when you are about to stop at a stoplight/sign. Then tell us if you feel any "bump" from the back. ;) Possibly it could just be the A/C kicking in if it's really hot in your area

[GX 470 law]

Try turning the a/c off when you are about to stop at a stoplight/sign. Then tell us if you feel any "bump" from the back. ;) Possibly it could just be the A/C kicking in if it's really hot in your area

When the A/C is off, no clunk, nothin' at all. When the A/C is on, and only sometimes, when it kicks in (along with the increase in RPM), I can feel or hear a slight "clunk." Without A/C, no sound whatsoever...smooth sailing.

[The G Man]

Thats not the clunk that this TSB is refering to. Thats just the rpm going up which is normal.

[denslexusgx470]

Yes, that isn't the clunk. ;)

[GX 470 law]

Yes, that isn't the clunk. ;)

Hey guys, sorry to beat a dead horse.

But, I've been testing the car with the A/C on and here's what I get intermittently:

1) At a stop.

2) A/C compressor kicks in and simultaneously see rpm rise. Car moves forward a bit with the rpm rise if foot not firmly on pedal (which seems normal given the increase in rpm).

3) Sometimes, feel like a lovetap from behind when the A/C kicks on.

I know the "clicking" sound when the A/C compressor kicks in, but do any of you feel this "lovetap" from behind when the A/C kicks on? I've only got 900 miles on my car and haven't owned it long enough yet to know what's normal and what's not. Any of you experienced folks have any thoughts on this?

[Omegaman]

No, I have not had that happen to me that I noticed. I will let you know if I do. I only experienced the "clunk" twice, so it did not happen very often, in my case. I do have a little more information that explains, and helps at least me to understand, what is happening with the “clunk” –

The clunk is related to the dynamic height control system. The GX470 dynamically adjusts the height of the back end of the vehicle based on road conditions and how it is being driven, in order to give a smoother ride. When you come to a stop, the height adjustment system will lower or raise itself to place the height at its normal position. When this happens, the driveshaft is going to move forward or aft and the arms are going to experience more or less force/strain. Because of the design of the driveshaft, and its lack of grease, it has heated up and thus now has a tighter fit. When the driveshaft is being forced to move by the height changing it has less friction in the rotational sphere then in the forward/backward directions and then it turns until it seats itself, i.e. relieves the forces or stabilizes. This is what causes the sense of being pushed forward, because in affect you are.

Given the above explanation of what is happening, anything under the vehicle, especially in the back or that is part of the drive train, can have an effect on how much or little you feel the “clunk”. The new driveshaft has been changed to give it extra play forward and back so that it will move more freely in those directions rather than rotating, without causing enough play to cause other noise or functional problems. This is also why keeping it greased helps a great deal. Grease provides less friction as well as keeping the shaft cooler, which also reduces friction. The new arms have been changed to be able to better handle the forces placed on them by the height control system, as well as all the forces present in any vehicle.

About the A/C, it is normal for the RPM to go up for a second or two when the A/C engages. This is to compensate for the extra load placed on the engine when the pump is started. The question is; can the A/C cause the “clunk”. I do not know for sure. One way that it could would be if the increase in RPM causes the hydraulic system that raises and lowers the back of the vehicle to do so faster i.e. increase the pressure. This increase in pressure could put more force/strain on the driveshaft, causing it to turn to seat itself. My suggestion would be to pay particular attention when stopping and see if you ever experience the “clunk” when the A/C does not come on, or is off altogether. If it does, it doesn’t prove the A/C cannot cause the “clunk”, but does prove that the A/C is not the only cause of the clunk. In my case, I saw no correlation between the “clunk” and the A/C. My opinion is that the A/C is not the root cause of the problem, but may have some affect on how often, and/or how much, the “clunk” happens and you feel it.

Finally; the most important thing to remember is that the hotter the components (driveshaft) gets, and the more the height control system has to adjust to find normal, the more often/likely the “clunk” is to occur. This implies that a hotter day, longer driving period before a stop, hard driving, fast starts and stops, etc. should cause the problem to occur much more often. I should add that if not firmly holding the brake when the RPM goes up, the vehicle could/would move forward. This could be in combination with, or entirely separate from, the clunk.

Omegaman

[The G Man]

GX470 Law, you mean to tell me your A/C compressor kicks in everytime you come to a complete stop? The AC will make the clunk problem worst, so will stopping the truck fast. What I did in the past to show the dealer the clunk problem was to turn on the AC, adjuct my rear suspension down and up and back to auto and stop the truck sharp. I can get the truck to clunk almost everytime by doing that.

[GX 470 law]

GX470 Law, you mean to tell me your A/C compressor kicks in everytime you come to a complete stop? The AC will make the clunk problem worst, so will stopping the truck fast. What I did in the past to show the dealer the clunk problem was to turn on the AC, adjuct my rear suspension down and up and back to auto and stop the truck sharp. I can get the truck to clunk almost everytime by doing that.

The A/C Compressor doesn't kick on every time, but it does an awful lot. I am so annoyed that this clunk crap has not been resolved in '08.

[The G Man]

GX470 law, what I am trying to tell you is that your AC compressor does not kick on everytime you you come to a stop. The fact that the AC is on make the clunk happens more often due to the higher rpm.

[GX 470 law]

GX470 law, what I am trying to tell you is that your AC compressor does not kick on everytime you you come to a stop. The fact that the AC is on make the clunk happens more often due to the higher rpm.

Ahh..I see. Got it.