whir...clunk

[forestdan7]

2002 4Runner Limited 4WD

OK, this noise is driving me nuts. It sounds like something is pressurizing (whir whir whir), then something like a solenoid cuts it off (clunk). The whir comes from the driver's side of the engine near the firewall, the clunk from the passenger side. It happens all the time, usually with several minutes in between. Happens at a stoplight, while driving, while turning, while braking. Seems to have no pattern.

Any ideas? The only thing I can think of is something in the traction system is depressurizing, repressurizing, and clicking off. What is that nitrogen pressure canister by the brake master cylinder for anyway?

Sorry, new to the 3rd gens. I had an 87 4Runner for 14 years, and have had my 60 for 4 years now. Much simpler vehicles than this 2002 I just picked up.

Thanks for any help. You could help lower my blood pressure.

 

[raydouble]

Sounds like maybe the hydraulic assist electric motor for the brakes is kicking on randomly?

Is it the motor on page 2 of this?...
http://www.ncttora.com/fsm/1996/SIL...toypdf/02rmsour/2002/024runne/br/hbb/comp.pdf

Do you have any ABS lights or otherwise?

 

[forestdan7]

I think that's exactly where it's coming from. No ABS or brake lights ever come on. Traction control seems to be functioning normally.

When would that motor usually kick on? When braking, or just whenever it needs to so it keeps a certain pressure level built up? Seems like maybe it's losing pressure, so the motor has to kick on to keep the pressure up.

Thanks for the reply. I'll see if I can confirm that's the source with the hood up.

 

[raydouble]

Look through the owners manual here....
https://forum.ih8mud.com/95-gen-toyota-trucks/341631-3rd-gen-4runner-faqs.html
or yours, if you have one....

I think it cycles right when you turn the key to "run" before you start it (or is it after it starts? can't remember)

I'm not sure if it's supposed to cycle the one time or periodically while running...

I don't remember it cycling while driving, unless I just have not heard it.

I also have never heard a clunk associated with it....

 

[forestdan7]

Thanks for the link. I just downloaded those, and will be checking them out more closely.

I think the clunk is some kind of solenoid shutting it off, but it seems like it comes from the opposite (passenger) side under the hood.

This used to be my dad's truck, and he heard it too, but of course it wouldn't make the noise when he took it in for service. I might see if I can get a recording of it. If I could figure out what it is, I'd be all right. I just don't like noises I can't trace to the source.

 

[raydouble]

Thanks for the link. I just downloaded those, and will be checking them out more closely.

I think the clunk is some kind of solenoid shutting it off, but it seems like it comes from the opposite (passenger) side under the hood.

This used to be my dad's truck, and he heard it too, but of course it wouldn't make the noise when he took it in for service. I might see if I can get a recording of it. If I could figure out what it is, I'd be all right. I just don't like noises I can't trace to the source.

Is there any kind of average amount of time that goes by before you hear it again? or does it seem completely random?

Found this on pg 197 of my manual.....so the random motor running seems normal....clunk, probably not so much

 

[forestdan7]

That could be it. Although that might refer more to the pulsating I hear when the traction control goes off.

It doesn't seem to be related to the number of times I hit the brakes, either. And there doesn't seem to be much of a pattern to it. I'll hear it before I get to the first stoplight a 1/4 mile away, and throughout the drive. Seems pretty random.

Thanks very much for the help. I'll try to get a Toyota tech to ride around with me next time it goes in the shop.

Funny thing is, my 60 makes so many noises, but I'm used to them. This thing is normally so quiet, every little noise drives me nuts. I guess as long as it's driving fine, it's no big deal.