Low-frequency resonance from front brakes

[timmo]

Has anyone had a low-frequency resonance type sound from their brakes? I had my Hawk HPS pads worn down to ~30%, so swapped the fronts back to stock for a bit, but I've just re-installed the HPS this evening. Went for a quick drive, and the front brakes make what sounds like a low-frequency resonance when at very low speeds. At first I was concerned the calipers were sticking, but when I re-installed the guide pins, I made sure that the caliper could still slide on them when it was installed, and after the drive the front wheels near the hubs were ever so slightly warmer than the rear (so not scalding hot which is indicative of a sticking caliper).

I have a video below, the sound can be heard starting at 0:55 when I start off slowly from a standstill. The sound generally stops around ~10 km/h. Unfortunately audio quality is quite bad since my phone was on its mount, but you can still hear what I'm talking about

One possible cause I'm thinking of is the anti-squeal shim - it has come loose from the pad, and consistently falls off whenever the pads are uninstalled. I just pressed it back on and installed the pads with it. Given the caliper doesn't seem to be sticking, I may just give it some mileage (& more braking events) and see if it disappears. I have a ~1 hr drive each way to autox tomorrow

https://photos.app.goo.gl/wYHWFceMj2QKS51P7

[mrgizmo04]

For anyone looking for the sound, skip forward to 0:55, that is when the sound shows up.

Did you swap back the hawk pads with 30% pad or new ones? Did you rebed them?

I sometimes get a similar noise with fresh pads on the way to bedding them, since new pads are a lot thicker than the old ones and the pistons have not fully adjusted.

Sent from my SM-G950U using Tapatalk

[Estoril]

I don't hear anything. Did you bed them?

[timmo]

For anyone looking for the sound, skip forward to 0:55, that is when the sound shows up.

Did you swap back the hawk pads with 30% pad or new ones? Did you rebed them?

I sometimes get a similar noise with fresh pads on the way to bedding them, since new pads are a lot thicker than the old ones and the pistons have not fully adjusted.

Sent from my SM-G950U using Tapatalk

[QUOTE=Estoril;n45759]I don't hear anything. Did you bed them?[/QUOTE]

Swapped back from stock pads, to my HPS with 30% (down to just above the end of the centre slot in the pads). I did re-bed them - this is the first time I'm putting the HPS pads on a rotor that been used by other pads though. I wonder if the pads are just that sensitive to cross-pad contamination on the rotor, and just needs an extended re-bedding session, or the rotor needs to be cleaned before swapping pads. When the HPS were new, they were installed on these Zimmermann rotors which were also new, they didn't make a sound.

[Estoril]

[QUOTE=Estoril;n45759]I don't hear anything. Did you bed them?

Swapped back from stock pads, to my HPS with 30% (down to just above the end of the centre slot in the pads). I did re-bed them - this is the first time I'm putting the HPS pads on a rotor that been used by other pads though. I wonder if the pads are just that sensitive to cross-pad contamination on the rotor, and just needs an extended re-bedding session, or the rotor needs to be cleaned before swapping pads. When the HPS were new, they were installed on these Zimmermann rotors which were also new, they didn't make a sound.


[/QUOTE]

Proper bedding lays down a layer of the current pad compound on the rotor. How are you bedding?

[Icecream]

[QUOTE=Estoril;n45759]I don't hear anything. Did you bed them?

Swapped back from stock pads, to my HPS with 30% (down to just above the end of the centre slot in the pads). I did re-bed them - this is the first time I'm putting the HPS pads on a rotor that been used by other pads though. I wonder if the pads are just that sensitive to cross-pad contamination on the rotor, and just needs an extended re-bedding session, or the rotor needs to be cleaned before swapping pads. When the HPS were new, they were installed on these Zimmermann rotors which were also new, they didn't make a sound.


[/QUOTE]

Did you check if the piston was seized? That is more likely to seize or cause problems rather than the guides.

[timmo]

Proper bedding lays down a layer of the current pad compound on the rotor. How are you bedding?

I did the Hawk recommended bedding procedure, though admittedly not as many. So I think 4-5 medium stops, and 1 or 2 hard stops, all from ~70 km/h.

Did you check if the piston was seized? That is more likely to seize or cause problems rather than the guides.

Below are 2 things I've done that makes me think the piston isn't seized:

- Used a brake caliper push tool to retract the piston
- Qualitatively checked the temps of the hubs, which weren't scalding hot, which leads me to believe the piston is retracting that small amount due to the elasticity of the seal



I had autox today, prior to the event starting it would happen about 1 of every 4 or 5 take-offs from a standstill. After the event, I believe it only happened once, and it was very, very faint, almost imperceptible, and it happened while I was going up my driveway in 1st gear with the clutch fully out. It might be that either I didn't bed them in properly, or the HPS is just that sensitive to x-contamination between different compounds? Either way, seems like there is a definite improvement after heavy usage of brakes at autox.

[Estoril]

I did the Hawk recommended bedding procedure, though admittedly not as many. So I think 4-5 medium stops, and 1 or 2 hard stops, all from ~70 km/h.

Use this procedure. Don't shorten it and pick a road where following it won't be a problem. https://www.zeckhausen.com/catalog/i...Path=6446_6443