NOSLO6

Hi everyone,

Last week in my C6 I had what seems to be a repeat of a hub failure I had last fall (that thread here);it happened under the exact same somewhat unusual circumstances and I'm looking for some more feedback to make sure I'm not missing some other root cause of the problem. Thanks for taking the time to read the details below.

Both times the following happened and it's the fact that the noise started at the same point in my trip that has me puzzled:

• I ran a track day at NJMP without any issues.
  
• Drove home from NJMP for an hour on the highway and pulled off at my exit into the city. After I came to a stop and started moving again I heard a growling from what sounded like the front passenger side of the car. No noise on track or on the highway prior to that. Exact same spot in my commute as the previous failure.
  
• Growling and vibration happened whether in gear or coasting in N but even very light brake pressure made it go away.
  
• A few times, sharply turning left made it groan more, back to right and it quieted.
  
• I pulled the front wheels and inspected the rotors, pads, calipers, abutments, wheels-- basically anything I could lay hands and eyes on. Nothing obviously broken. Hubs seem okay-- no play and they spin without noise or unusual resistance.
  
• Drove the car for a while the next day and was not able to get the noise to pop up again.

After this happened last fall I replaced both front factory hubs with SKF HD hubs from the great folks at Phoenix and ran several track days afterwards with no problems. With this happening again to the pretty darn indestructible HD hubs, I'm wondering if I missed something else. Any thoughts on what could be behind this, and how to check it or to size up the hubs?

• Could something in the brakes be fouled up and causing heat to build up on the longish highway drive, for example? I ran on a new set of XP12s (instead of the XP10s I usually use) and upon inspection the backing plates look ashed, but I'm not sure if this is typical of that pad. Thumbnails of pads and rotors below, the picasa gallery here has the big versions.
  
• I suppose I could also be mishearing the source of the noise and having it come from a rear hub (which I did not replace last year), but it's hard to tell since I haven't been able to replicate it.

Just don't want to put $s to new hubs without understanding what's going on here. Any and all ideas appreciated.

Thanks!

mgarfias

You lube the slide pins on the caliper lately?

NOSLO6

Yep, I lubed the slides when I swapped pads before the event.

Bill Dearborn

You could have a rear hub going. Depending on how much track time you have on them both rears might need replacing. I had a similar type of scenario happen with my 97 and ended up replacing all 4 hubs over the period of a week as the noise kept changing. None of them were loose they were just growling and you had to hold them in your hand to feel the grinding inside when you turned them.

Bill

NOSLO6

Thanks Bill. It did sound like the front, but I know noises can travel.

What puzzles me is that the mode of failure is the same as the first one-- no noise during the track day or trip home until I pull off the highway. Keep the thoughts coming folks, thanks!

NOSLO6

Bump for the weekday forum readers.

froggy47

mgarfias

The GF's pontiac had a LF wheel bearing go out. At first it growled only in right hand corners, then got progressively worse until it growled everywhere. Sounds like you have a bearing goin out.

NOSLO6

How do the pads / rotors look to folks?

I'm trying to get a sense for whether they might have been dragging and overheated the hub. As I understand it failures in the heavy duty SKF hubs are pretty rare.

froggy47

The two darker rings (like the rings of Saturn) indicate glazing (an uneven deposit of pad material on rotor) but most of us have had that and not had a bearing fail.

The white ashy appearance is unusual in my experience ( on the backing plate) but I do not run that brand of pad, so it my be "normal".

I have also "heard" that the skf race is almost indestructable, so your failures are a puzzle, especially hours afer the event????

Since the sound has gone away, you really don't know yet if the hub is bad. Maybe something else caused the "sound" in an intermittent way. So don't jump to the conclusion it's the bearing.

I have had a rock kick up & get in the rotor/brake/wheel area & sound like hell & then it drops out & sound goes away.

Are there dirt/rocks where you pull off?

Sorry can't help more.

NOSLO6

Thanks for the thoughts Froggy-- that's exactly what I'm trying to troubleshoot since this is my 2nd dose of this issue under similar circumstances. Trying to build a good list of stuff to check. (FWIW, no debris or other unusual features where I pull off the highway, just a nicely paved exit ramp.)

I also don't recall seeing the ashing with my the XP10 carbotech pads I've run for years, but this was my first day with XP12s.

I haven't ever rebuilt or replaced the calipers, but haven't seen any signs that they're going south.

RX-Ben

If you have some taper to those pads or rotated them, you may be getting brake pad moan (relatively low sound that went away when touching the brakes). I have gotten this to an impressive degree in the off season, on race pads. 1-2 laps on the track fixed it.

Olitho

I don't run Carbotech any more, but I always remember burning off the paint on the backing plate after the first session. It leaves that white/greyish ashy look.

taken19

All four sets of Carbotechs I have run so far have ashes or even burned the backing plates after one or 2 sessions - nothing to worry about.

With respect to the wheel bearings, I wouldnt suspect the SKF hubs. If anything, I would go after the rears first (especially if they are the originals). The noise you describe certainly sounds like a wheel hub by the way you describe rocking the steering wheel back and forth and the noise coming and going.

NOSLO6

Thanks for all of the replies, really appreciate it.

So are folks thinking that it's just a coincidence that the hub noise popped up in the same place & not on the track? I still can't figure out what it would be about the highway drive that would trigger the noise it when 4-5 track sessions wouldn't.

It's not knowing the above that makes me squeamish about replacing existing hubs again. I could do the rears since they're still factory, but man did this ever sound like it was a front.

brkntrxn

The ash color on the back of the Carbotech pads is normal. Congrats, you finally put a good amount of heat into your brakes.

From what you are describing, I think you are simply hearing the brake pads after they have cooled off. When a race pad cools off from being hot at a track event and then you use the cool pad against a cool rotor at low speeds, you are going to hear groaning/growling/grinding type of noises. The pad is WAY below its operating temperatures at the moment and will make weird noises. Especially when the pad is slightly dragging against the rotor when starting after a stop. The funny looking areas on your pads are another confirmation to me that this is what has occured. The XP10 and XP12s are designed to work in a specific range of temps. When used at temps less than idea (ie on the street against a cold rotor), you will see unusual wear patterns in the friction material.

I hope my opinions help. I have been running Carbotechs on multiple cars for quite a few years now.

NOSLO6

Thanks for the helpful thought-- 2nd suggestion to this effect so let me ask a few questions.

I run these pads on the street and am used to the squeal and quiet grinding they sometimes make. Haven't ever heard this noise when they're full cold. If there's something particular about going from full hot to full cold that causes it to happen that could be the difference-- but I'm not sure why that difference would matter.

The piece I can't figure out if this was the issue is why sharply cutting the wheel back and forth would make the growling stop/start.

RX-Ben

All that matters is uneven pad buildup on the rotor, which most people call "warped" rotors. You will get noises when using race pads when there is uneven deposition and your rotors look like they have a considerable amount. If this goes away after some relatively brutal highway stops or a lap or two at a track, then I think you found the culprit.

I would imagine that the correlation with turning has something to do with the floating caliper OEM design causing some contact.

brkntrxn

I agree with Ben. The pads flop back and forth against the rotor when you turn sharply with applying the brake.

Soloontario

Doesn't sound like a hub to me but more likely a brake pad sticking etc.

Any sign of caliper spread?

You might try mounting some different pads (and poss rotors) and see what happens.