Help, replaced brake pads and they "chirp"!

[dmd]

Just replaced all my brake pads with original ACDelco replacements and had all four rotors machined on my '96 LT4. My right front is making a constant chirping noise, at a rate that increases with speed. It stops as long as my foot is on the brake pedal, and quiets down if I get the pads good and hot from repeated hard stops. I shimmed it and lubed the shims, as well as the pad clips. I've taken these things apart multiple times and I can't find the source of the noise. The caliper pin is on the bottom of the frame, and the pads were labeled for L & R so I'm confident I got the installation right. The rotors are well above minimum spec and I brushed off the excess rust. If anyone's got any ideas or been through this before, do let me know, it's driving me nuts.

 

[jmccloud]

Brake chirp

I always use spray on the back surface of the pads for anti squeal. It's really gooey stuff that keeps the pads from slipping around on the caliper piston or the outside 'nose'. Look at the old pads to see where the contact surfaces are. The stuff I have is Permatex 'Disc brake quiet' but surely there are many brands. Again, it goes on the back of the metal pad support, not on the braking surface.
Good luck

 

[dmd]

Don't your pads have those large round retainer clips on them? I can't imagine how they could possibly move around with those.

 

[LT4man]

I know you do not want to hear this, but I will tell you EXACTLY what is wrong.

Take the two front rotors off of the car and throw them away. ad

Buy two (2) new rotors.

Clean rust preventive goop off with Brake Clean.

Install new rotors.

Noise will disappear.

It does not matter you had them machined. You should buy both because on a brake system, parts should always be replaced on the entire axle.

Purchase the rotors from Chris May at Superior Chevy in Kansas City (he also has AC/Delco drilled rotors for not much more!) or a parts store in town.

38 years experience repairing cars & trucks will point you in the right direction!

SAVE THE

 

[dmd]

Okay - thank you for your advice, greatly appreciated and I respect the years of your experience. But can you tell me why it's doing this? And why I can't just burnish or blanchard the rotors instead of $hitcanning them? I'd really like to understand what's going on here.

 

[LT4man]

All of the C4s have brake rotors which are too small in diameter and too small in mass.

In 1995, Chevy started putting the J55 "Heavy Duty Brakes" on every Vette built. They had the rotors & calipers left over from the ZR-1 supply.

Even tho the General improved the C4 brakes through this upgrade, the brakes are only adequate if one does not flog their Vette. They are marginal, at best.

The C5 has a much improved braking system. Much larger than the C4. Many C4 owners install the C5 system because it is a bolt-on system which gives enough stopping power to the C4.

SAVE THE

 

[dmd]

I know about all that. What I don't know is why the rotors are causing this chirping noise.

 

[LT4man]

Out of round and not true.

SAVE THE

 

[dmd]

That can't be. They were warped before I did this and they didn't make any noise at all. I turned them to make them true, and now they're making noise. Doesn't make any sense at all.

 

[LT4man]

We are talking about the auto repair industry!

In my 38 years, how many times do you think I saw something that did not make sense? I will answer for you: Many, many times! otfl

How many miles on the Vette?

SAVE THE

 

[dmd]

It's up to 147k now. I've got a replacement rotor on its way, we'll see if it cures it in a couple days!

 

[LT4man]

I drive mine almost every day. I am very close to 100,000 miles.

Yours has quite a bit more mileage. Congrats!

The reason the brakes would chirp would be the following:

Something attached to the spindle would have to be out of round. The hub & bearing assembly very well could be. You would need a magnetic dial indicator attached to the hub of the rotor to ascertain how far out of round (if at all) the hub or rotor is.

If the hub & bearing assembly check out OK, then the only other part which rotates around the spindle would be the rotor. Hence, the rotor should be replaced.

If there was ablsolutely NO noise before you replaced the brakes and now there IS noise, something that you replaced or did would have to be the culprit!

Let us know how this turns out! No pun intended!

SAVE THE

 

[JimBobC4]

Thought about the brake lathe you had them turned on being out of round ? I have seen where the adapter was warped and caused issues.

Also, and this is rare, I have seen where metallic brake pads had a bigger metallic particle emdedded in the brake pad. Look for a part thats much more shiny on the pad. If this is the case, return and replace the pads.

just for giggles, you may try and sand the pad face with a hand sander or on a flat surface. Just enough to remove the glaze. If you overheated the pads in your test run, you may have glazed them over. A metallic rotor shaving embedded in the pad will make a chirp as well.

If it is the rotor thats out of round, you can tell by spinning the rotor by hand with the tire off. if it grabs a little in one spot and freewheels in another, you prolly have a warped rotor.

One last item, make sure you didnt bend the " squeak" tab into the rotor when you assembled it if it has one.

Good luck !

 

[dmd]

I replaced the rotor with a new ACDelco and the holding pin last night, and the noise is gone. The squealer tab mysteriously broke off the inner pad during the removal process, but I don't think it was scraping the rotor to cause the noise.

Another question - aren't the rotor vanes supposed to be scooping air in? The rotor was clearly labeled RH, but the vanes were pointing opposite the direction of rotation. I reversed them from how they were installed before, thinking that someone had put them on backwards - but now I'm not so sure. It's looking like I have RH rotors on both sides of the car.

Also, this hasn't cured the pulling to the right that I'm experiencing. It's very strange. Hard braking when cold or at regular temperature gives me a hard pull to the right. After a lot of hard stops and getting them really heated up, it goes away and it brakes straight. Cools back down and it pulls right again.

 

[JimBobC4]

I replaced the rotor with a new ACDelco and the holding pin last night, and the noise is gone. The squealer tab mysteriously broke off the inner pad during the removal process, but I don't think it was scraping the rotor to cause the noise.

Another question - aren't the rotor vanes supposed to be scooping air in? The rotor was clearly labeled RH, but the vanes were pointing opposite the direction of rotation. I reversed them from how they were installed before, thinking that someone had put them on backwards - but now I'm not so sure. It's looking like I have RH rotors on both sides of the car.

Also, this hasn't cured the pulling to the right that I'm experiencing. It's very strange. Hard braking when cold or at regular temperature gives me a hard pull to the right. After a lot of hard stops and getting them really heated up, it goes away and it brakes straight. Cools back down and it pulls right again.

As far as the viens are concerned.
Lemme check mine tonight. I have the whole brake system disassembled and labeled in the floor.

As far as the pulling to the right, thats a tough one. If the rotors are different thickness it can cause this.

Yeah, yeah I know the theory on brakes and the pads move to the width of the rotors, I'm just saying what Ive seen.

I've seen situations where a flex brake line expands at a different rate than the other causing one side to clamp faster than the other. Might want to check that as well. This happens on older lines. You may be able to feel the line expand with your hand on it.

A semi-siezed caliper piston can create this situation also. More force is needed to move the piston so one side grabs faster than the other.

Worn A arm bushings can also create this. The worn bushing puts the arm at an odd angle causing the tire to turn outward, which causes the car to move to the right.

I will post a pic of the rotor veins tomorrow.

Good luck !

 

[JimBobC4]

ok. couldn't wait I had to check.

The viens on the rotors pointed or angled toward the rear of the car. So I suppose its scooping are from inside to outside of the rotor. So it cools from bottom to top.

Also, I thought about it while I was looking and remembered a few past episodes of a car pulling one way or the other. Excluding the issues I had mentioned previously,as those items were most prevalent, I recall a few other issues of a car moving left or right under braking and what was done to repair it.

1. A really worn tie rod, .
2. A larger tire on one side
3. A blown or seized shock absorber
4. bad lower a arm bushing
5. wierd wear pattern in the center of the tire ( no $hizzle)
6. bad steering component ( rack, pitman arm, trailing arm whatever)
7. Clogged brake line
8. Beer

Hope this helps.

 

[dmd]

Wow, thanks for all that. I'm trying to figure out which of those would most likely be affected by the heat of the braking system, and my guess is the bushings. And I know they're hard to replace too.

 

[JimBobC4]

maybe piston seizure in the caliper. As the caliper heats up it expands, loosening the grip on the piston.

Again its thought. If it were bushings it would do it all the time I think.

 

[RoyalViking]

I'd go with the caliper.

Oh, going back a couple post's. The chirping may have been that the rotor flange was not true when they turned the rotor. Each revolution was bumping the pad causing a chirp.

 

[dmd]

I took the chirping rotor that I removed from the right side and put it on the left last night. No chirp, no pull. Figure THAT one out.