Brake noise when stopped (light pressure on brake pedal)...

[mvbighead]

Car is exhibiting a chirping sound when stopped. Recently replaced rotors and brakes, and the same sound was occurring before and after the replacement. Brake fluid is topped off. Can't think of any other reasons, so figured someone here might know.

Jeep GC 2000 4.7l V8.

 

[mvbighead]

Anyone? Any ideas?

 

[cprince]

wait..you're hearing the noise AFTER you had stopped? Might be an old/loose belt or something.

 

[mvbighead]

Precisely, only when stopped. If I feather the pedal a bit, it usually chirps or a little chirpy groan.

 

[cprince]

Precisely, only when stopped. If I feather the pedal a bit, it usually chirps or a little chirpy groan.

sounds like it could be the booster leaking vacuum. Does your engine rpm change when you feather the pedal? If not, I'm thinking it's just the brake pedal linkage needs oiling.

 

[AMCRambler]

Chirping? Best guess, I'd say a belt. If it makes the noise when the car is stopped and changes when you let off the brake and the car rolls I'd say probably the serpentine belt, the alternator pulley or a belt tensioner squeaking. If it changes pitch when you move your steering wheel back and forth, power steering belt.

 

[mvbighead]

Well, here's the thing... the noise only happens as I feather the pedal, but not so much as to allow the car to move. Basically instead of having the pedal pushed halfway in, I have it pushed about 1/8 to 1/4 of the way in, and there is a sweet spot somewhere in there. Some times it is a simple chirp... if I find the sweet spot and hold it there, it can be a long, drawn out chirp. But again, at no point does the vehicle move. The chirping is directly relational to where I have the break pedal pushed in, which doesn't make me think it's a belt, though I can't really say for sure.

At this point, cprince's suggestions seem likely... especially the brake pedal linkage business.

One last note, if it aids in the cause, is that when I checked the fluid, it was full. I haven't had to add any fluid yet, which, as far as I know, would suggest that it isn't leaking fluid anywhere... though that could be a poor assumption as well.

Thanks for your suggestions thus far, and keep em coming.

 

[thomsbrain]

cprince's ideas seem to be the most likely culprits.

 

[JCH13]

Every car I've driven has made a weird noise like that just as the brakes are starting to slip an imperceptible amount. I wouldn't worry about it, I think it's just the brakes talking to you.

 

[mvbighead]

Alright guys, it's been long enough. Finally decided to upload my first video to youtube as I feel I didn't do a very good job describing it. Here it is:

http://www.youtube.com/watch?v=YdSsJ6FhIyU

Note - Car is in park.

 

[LTC8K6]

That really sounds like a vacuum leak. A bad one.

 

[mvbighead]

Thanks for the reply.

I will say this, sometimes (every day or so), the noise goes completely away. But it generally can always be made at some point. Essentially, it doesn't make the noise every time I press the brakes, but odds are it will (about 50/50).

 

[SpatiallyAware]

+1, vacuum leak of some sort. Hopefully it's a hose, but I suspect the booster itself. See if you can get someone to hold the pedal while you chase down the noise..

 

[Mxylplyx]

I had a cherokee once that had a vacuum leak in the booster so bad that it would stall the engine if I slammed the brakes.

 

[mvbighead]

My engine can idle a bit rough from time to time, honestly. In fact, the past few mornings or so, it has been starting and then basically choking (almost to the point it dies). I hit the gas a little and she fires right up.

 

[mvbighead]

sounds like it could be the booster leaking vacuum. Does your engine rpm change when you feather the pedal? If not, I'm thinking it's just the brake pedal linkage needs oiling.

Should've listened to you a long time ago.

Well guys, after getting down under there and fiddling with the pedal by hand, it does seem like the noise is coming directly from the brake booster.

I have checked the hose in the engine bay, and it seems to be in good shape. I am guessing that means I'll be buying a brake booster and replacing it in the near future. Hopefully that'll be it.

 

[LTC8K6]

Could it be the check valve on the booster?

 

[mvbighead]

Could it be the check valve on the booster?

Hmm, probably a good question. I'll see what I can do about figuring that one out. Won't have much time tonight, but hopefully tomorrow or this weekend.

 

[mvbighead]

I should add that one thing that really makes me think it's the booster (specifically) is seeing how it has that nice big opening and it really seems like the sound is being piped into the cab of the jeep. Granted, I am certainly not as knowledgeable as some of you guys, so anything you point me to will be looked at.

 

[natto fire]

Yeah, I am going to say booster as well, or possibly something in the ABS circuit. Might try disconnecting the ABS fuse(s) and reproducing the results.

Most ABS problems occur during ABS events though, and a dieing motor or leaky accumulator have more of a hum, but it's always better to rule things out than add more variables, IMO.

 

[mvbighead]

One more point, I did have the engine off, key off, and pressed the pedal down by hand and it still made the noise. I would assume ABS is completely unpowered, and therefor should eliminate that as a problem, right?

 

[mvbighead]

Well, got tired enough of it this weekend and went and replaced the brake booster. Problem solved!

Only issue now is the pedal is not in far enough to trip the brake light sensor, which means that the lights would stay on all the time. For the time being, I have rigged an extension on the sensor so that it does get pressed, but am not seeing any way to adjust the arm on the brake booster.

Perhaps it is screwed in, and rotating it a few times will change the position of the pedal, and push the sensor without my extension. Any ideas on what I am missing? I have tried fiddling with the sensor, but I cannot seem to get it closer to the brake pedal arm.

 

[LTC8K6]

The switch is likely adjustable. Could be screw type, ratchet type, or 1/4 turn and pull type. You'll figure it out.

 

[mvbighead]

The switch is likely adjustable. Could be screw type, ratchet type, or 1/4 turn and pull type. You'll figure it out.

Well, it was a complete PITA, but I finally got it done. Ended up pulling the switch out and disconnecting it. Looked it over good and hard, and tried and tried to turn what appeared (to me) to be a screw adjustment. Trying hard not to break it, I finally gave up on that idea. I tried pulling the sensor with my finger tips, but no dice. I was pulling and twisting this thing a number of different ways, and felt like I was going to break it.

Finally decided, the hell with it, if it breaks, I'll run over to the dealership and buy one for 30-40 bucks if I do. I took an old hard drive mounting bracket (had a hole size similar to the size of the sensor switch) and hooked it to the switch and pulled hard. It extended out just and to my surprise, without breaking. Put it all back and everything is great.

Thanks for the help guys, much appreciated!

 

[LTC8K6]

That's the self adjusting ratchet type, I believe. You pull it out too far, and then let the brake pedal push it back in when it comes up.