Brake howl - but only when coasting

nakedape

nakedape

Likes Dirt
As the title says, my rear brake howls worse than when Bronnie found out she couldn't use a chopper to go shopping anymore - but only when I'm coasting (not braking).

The problem started a while ago, and each time it would start I'd find that the axle was loose - which made sense, i.e. loose axle allowing the rotor to wobble. I've loctited the axle but the howl persists.

Rotor is tight, pads are new.

I've trued the rotor as best as I can without a lathe and finger indicator (it has about 0.25 wobble left in it). Also re-adjusted the caliper. Both of these see the howl disappear for half a ride but after a few big bumps it comes back.

I'm open to any suggestions...
 
moorey

moorey

call me Mia
nakedape said:
Shimano XT, Icetec rotor 180mm, Icetec sintered pads (with fins)
Click to expand...
Cook your pads, clean rotors with isopropyl (Rotors could have picked up some much that has contaminated new pads) . Its possibly rotor alignment, but more likely contamination in my experience. I run the same set up on 4 bikes, only ever had a howl when I tried cheap pads, or buying s/h brakes with dirty pads.
 
redbruce

redbruce

Eats Squid
moorey said:
Cook your pads, clean rotors with isopropyl (Rotors could have picked up some much that has contaminated new pads) . Its possibly rotor alignment, but more likely contamination in my experience. I run the same set up on 4 bikes, only ever had a howl when I tried cheap pads, or buying s/h brakes with dirty pads.
Click to expand...
If it only occurs when coasting it is a pad alignment issue.
 
9

99_FGT

Likes Bikes and Dirt
Is the rear axle a QR or 10/12 through axle?
Could be that the rear wheel is going out of alignment as you said it comes back after a 'few big bumps'.
 
The Duckmeister

The Duckmeister

Has a juicy midrange
I'd be looking at uneven piston movement, causing one pad to remain in contact with the rotor and glazing the surface.

Take the wheel & pads out, squeeze the brake a few times to push the pistons out a bit (but not right out of the caliper!), you'll see if one isn't moving as much. Hold the more mobile piston in with a spanner while you squeeze the lever to free the sticky one. Lubricate the sides of the piston with the correct brake fluid for your system, push the pistons in, give a few squeezes to make sure they're working evenly, then push the pistons back, pop the pads in after sanding the glazing off, and away you go.
 
Last edited:
moorey

moorey

call me Mia
The Duckmeister said:
I'd be looking at uneven piston movement, causing one pad to remain in contact with the rotor and glazing the surface.

Take the wheel pads out, squeeze the brake a few times to push the pistons out a bit (but not right out of the caliper!), you'll see if one isn't moving as much. Hold the more mobile piston in with a spanner while you squeeze the lever to free the sticky one. Lubricate the sides of the piston with the correct brake fluid for your system, push the pistons in, give a few squeezes to make sure they're working evenly, then push the pistons back, pop the pads in after sanding the glazing off, and away you go.
Click to expand...
Thread closed :nod:
 
nakedape

nakedape

Likes Dirt
99_FGT said:
Is the rear axle a QR or 10/12 through axle?
Could be that the rear wheel is going out of alignment as you said it comes back after a 'few big bumps'.
Click to expand...
It's QR - might have a little look at the dropouts.

Swapping out the pivot bearing s this arvo. Might even try an old wheel/ rotor set up to eliminate those too.
 
nakedape

nakedape

Likes Dirt
The Duckmeister said:
I'd be looking at uneven piston movement, causing one pad to remain in contact with the rotor and glazing the surface.

Take the wheel & pads out, squeeze the brake a few times to push the pistons out a bit (but not right out of the caliper!), you'll see if one isn't moving as much. Hold the more mobile piston in with a spanner while you squeeze the lever to free the sticky one. Lubricate the sides of the piston with the correct brake fluid for your system, push the pistons in, give a few squeezes to make sure they're working evenly, then push the pistons back, pop the pads in after sanding the glazing off, and away you go.
Click to expand...
Will do - thanks!
 
nakedape

nakedape

Likes Dirt
Soooo, did all the above - twice - and still no good.

Interestingly, while I had the bike in the stand I noticed the caliper flexing under hard braking - might need to find some more substantial mounting hardware! :frusty:
 
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