Rear wheel howl

[noodles]

My rear wheel howled very loudly at me on the highway this morning @ 70 mph and I could smell that brake pad smell.  I pulled over checked quickly for anything really obvious and carried on to work since I was on a limited access highway.
The noise was sudden, loud, and irregular in that it would come on for a few seconds then go away. It was repeatable when I exceeded 70 mph but eventually stopped altogether along with the brake pad smell disappearing when I continued down the highway. 
 
The brake still worked when applied, the rotor wasn't glowing, the wheel turned freely when I got to work without resistance or obvious warpage. The fluid was changed a month ago and the piston was cleaned. Anyone on have an idea what I should look at first when I get home? I'm thinking rebleeding at the least and inspecting the piston, hoses, master cylinder, and disc for alignment or wear issues... 
 

[Beemer]

I can't say for sure what the problem is but I can't help but get the feeling it's possibly a caliper hanging up for whatever reason. It sounds like you're on the right track to finding it. Be sure and check your brake cable/lever to make sure they are going back to where they belong after using them. I had a friend that had a problem with a sticking caliper on his car and after $1500 for all new brakes to correct the problem, but didn't, I went out and bought a $5 foot pedal spring for his car that corrected the problem. His one caliper was hanging up because the pedal wasn't being pulled back up all the way after he depressed the pedal. Just a weak spring was all it was.

[rick]

Well, unless the caliper is leaking fluid, not sure why bleeding the system or doing anything at the rear master is gonna change anything.
 
I would look at pads 1st to see if maybe they've been contaminated with something that's getting hot and burning, or for any abnormal wear. Brake pads can also make noise between the piston and the steel backing or where the tabs rub/mount in the caliper that applying a thin layer of brake caliper grease will fix.
 
You might have caught a stone or maybe even a bit of plastic that burned up and is now gone.
 
I'm curious as to why you removed the pistons to that caliper? Unless a caliper's piston gets stuck, this is not really a routine maintenance thing, imo.
 
 

[noodles]

Well, unless the caliper is leaking fluid, not sure why bleeding the system or doing anything at the rear master is gonna change anything.  
I would look at pads 1st to see if maybe they've been contaminated with something that's getting hot and burning, or for any abnormal wear. Brake pads can also make noise between the piston and the steel backing or where the tabs rub/mount in the caliper that applying a thin layer of brake caliper grease will fix.
 
You might have caught a stone or maybe even a bit of plastic that burned up and is now gone.
 
I'm curious as to why you removed the pistons to that caliper? Unless a caliper's piston gets stuck, this is not really a routine maintenance thing, imo.
 

I didn't remove the pistons I cleaned them by pumping them out of bore without removal then brushing gunk off then back in the bore they go after brake cleaner.  
I want to rebleed since I may not have put in enough fluid when I bled them last and if I'm going to top it off I may as well crack the bleeder to be sure the results is no air in the lines. 
 
While it was making noise I pushed up on brake pedal with my foot made no difference. At 17000 miles brake pedal never needed adjustment so I doubt it's that. Glancing at pads in parking lot at work I didn't say any obvious wear or discoloration and the disc has no scratches or discoloration. All parts are where they're supposed to be and both pins are in etc.
 
Hope I don't have to rebuild rear caliper 

[rick]

Ah, ok.
 
Well, if the brake lever feels good, you've probably done a good job bleeding air out - just top up the master.
 
hmm, guess it's possible one of the pads hung up for a bit for some reason. I would pull the caliper and inspect the pads friction surface and backing plate and also have a look at the any spring clips (not been into mine yet). Also have a close look at where the pads are glued to the steel plate. BTW, if you remove a set of pads and put them back in, it's always a good idea to put them back where the side they came from so that the forces on them don't get reversed.
 
If you find/see nothing suspicious, where the pads are seated up against the body of the caliper, I'd put a small film of this stuff (or similar) https://www.permatex.com/products/lubricants/specialty-lubricants-brakes/permatex-ultra-disc-brake-caliper-lube-4/ pretty much any parts store will carry it. Don't think the pins need to have lube - unless they've become rusty - then I'd lube them as well. There will be people who say it just attracts dirt, but OE car pads will frequently come with a metallic antiseize-like stuff to go on the back pads (to cut down on squealing) as well as a small tube of this synthetic grease to lube contact spots.
 
Still think you might have caught something between the rotor and pad that made a racket and then escaped. You might see this as a scar on a pad after pulling them.
 
 
 

[noodles]

Ah, ok.  
Well, if the brake lever feels good, you've probably done a good job bleeding air out - just top up the master.
 
hmm, guess it's possible one of the pads hung up for a bit for some reason. I would pull the caliper and inspect the pads friction surface and backing plate and also have a look at the any spring clips (not been into mine yet). Also have a close look at where the pads are glued to the steel plate. BTW, if you remove a set of pads and put them back in, it's always a good idea to put them back where the side they came from so that the forces on them don't get reversed.
 
If you find/see nothing suspicious, where the pads are seated up against the body of the caliper, I'd put a small film of this stuff (or similar) https://www.permatex.com/products/lubricants/specialty-lubricants-brakes/permatex-ultra-disc-brake-caliper-lube-4/ pretty much any parts store will carry it. Don't think the pins need to have lube - unless they've become rusty - then I'd lube them as well. There will be people who say it just attracts dirt, but OE car pads will frequently come with a metallic antiseize-like stuff to go on the back pads (to cut down on squealing) as well as a small tube of this synthetic grease to lube contact spots.
 
Still think you might have caught something between the rotor and pad that made a racket and then escaped. You might see this as a scar on a pad after pulling them.
 
 

I have high temp antiseize I'll put that on the back of the pads. I'd rather keep the pin dry and shiny, I remove corrosion once a year. The pads I got didn't come with shims so I reused OE shims. OE has insulators too, not sure why, but I reused them anyways. Still theyre so thin I think it's unlikely they would cause drag. We will see what the pads look like I suppose.  
Ugh the ONE day I don't bring my saddlebags w/ tools to work!! 

[rick]

I've used and reused all of those clips and springs over the years w/o any issue. As long as they are clean and in good shape, should be fine to reuse all the spring clips or whatever.
 
Having that happen is a really goofy thing, so this will be interesting. That it happened w/o you applying the brakes 1st, still makes me think something got flung up in there, made some ugly noises, caused some pad smells and smoke and then ejected itself clear - maybe just fell off when you stopped to have a look.
 
 

[noodles]

I've used and reused all of those clips and springs over the years w/o any issue. As long as they are clean and in good shape, should be fine to reuse all the spring clips or whatever.  
Having that happen is a really goofy thing, so this will be interesting. That it happened w/o you applying the brakes 1st, still makes me think something got flung up in there, made some ugly noises, caused some pad smells and smoke and then ejected itself clear - maybe just fell off when you stopped to have a look.
 

Yeah it scared the bejesus out of me at 75 mph on a busy interstate w/ somewhat cold tires and cold morning air & cold morning pavement w/ surrounding traffic and a gravelly shoulder!! I thought rear lockup was coming but it never did. Loud howl/hum like when a bicycle caliper is dragging you know? But about 20x louder... Almost painfully loud even thru my helmet, my earplugs, and the wind noise @ 75mph 
I installed new pads (EBC HH series) front and rear maybe 3000 miles ago w/o issue - was when I did the brake fluid change and piston clean up. Cleaned the rotors even! Didn't think I'd have to touch the brakes until next spring after the snow stops and the bikes come out to play.
 
Think what I'll do is, after I exclude pad/rotor/alignment/fluid issues, I'll get some silicone brake lube, put that on backs of pads (didn't do that when I installed them), and also gently lube the boot + slide + pins. Be totally sure this doesn't happen again. Pics when I take a look tonight ...

[r1limited]

More than likely your foot was resting on the brake pedel.

[rick]

Hmm, are you sure it wasn't something that got stuck between the tire and the hugger/fender thing? That would be loud and cause a vibration felt thru the bike. Would also cause some burning smells w/o causing the bike to slow down much. Have a look at you chain as well.
 
The front brake on that old /6 BMW in my Avatar would cause the wheel's spokes to go into resonance when the brakes/rotor were wet. As I would come to a stop, the entire front wheel would sing.

[noodles]

More than likely your foot was resting on the brake pedel.

I do not ride with my foot on pedal unless going through traffic. But going home before I take pads off I won't even touch it just in case 

Hmm, are you sure it wasn't something that got stuck between the tire and the hugger/fender thing? That would be loud and cause a vibration felt thru the bike. Would also cause some burning smells w/o causing the bike to slow down much. Have a look at you chain as well.

This was maybe 10 minutes after starting it up after some light traffic and about 45mph cruising, I got on the highway, hit 75mph, and bam, noise from nowhere. No wobbles just noise

[r1limited]

What color is your brake fluid? Clear, Tan or dark

[dmoney]

You obviously need a louder exhaust ?

[shinyribs]

If everything checks out with the rear brake, is it possible you may need to inspect the wheel bearings?
 
When you said it was howling and you pressed the rear brake and saw no difference...did you see no difference in the howling? Or did it seem like the pressing the rear brake made no difference in slowing the bike? Did the brake pedal move like normal, or did it feel stuck?
 
Sorry for jumping in here, but this is just very interesting. Curious to see what you find. Good luck!

[rick]

Wheel bearings will cause a rumble and some vibration that you would feel more than hear, but once they go bad, they don't get better and then all of a sudden stop making noise.
 
Yeah, this will be interesting. I think there's gonna be some telltale evidence left behind somewhere.
 
Aprilia's of vintage like mine have a bad habit of getting air in the rear caliper that's hard to get out w/o pulling the caliper and raising it well up. The fluid in the master will look perfect, but the fluid in the caliper will look kinda ugly. If it gets really bad, the lever will lose all feel and do nothing when pushed to its stop(don't ask how I know), but this doesn't result in any noises - just no rear brake.

[rick]

You obviously need a louder exhaust ?

and ear plugs, lol.  
 
 

[noodles]

Front wheel,  brakes, and rotors were fine. 
 




Rear brake looked fine.

 
Seeing no issue in the brakes, I tried to remember what the noise was like. Sounded like something unbalanced hit a resonance to make sound. But if it wasn't a pad rubbing, what could it be? The front was fine. Without the brakes the wheel spun and spun. Bearing felt fine. And this machine only has 17,000 miles on it so what likely? A bearing failure or... An axle problem. Seeing no wobbles on front wheel I left that alone. I pulled the rear axle and look what I found. Now both axles have sliders from OES - great value, let me say - and when I remove the rear axle I must pop out the sliders and their retaining bar. I stupidly tried to remove the brake lever side slider. This was put in with red thread locker and should not come out. As I realized I had started on the wrong side, Pop it breaks thread and starts turning out. Sounds like the slider may have seen some heat... Uh oh. Sure enough I try to push it out of the axle and it won't budge. I removed the other slider and took this photo. I think I found the cause.

 
Now, sighting down it and looking at the axle, it looks fine to me.
 

 
A little bit of silicone lube and it came out.
 

 
I'm thinking when I dropped the bike maybe a month ago when I was making a U-turn with the new brakes, as the Sliders took the impact it jammed the rod in there at an angle. Why it would only recently start making noise over a certain speed is beyond me.

[rick]

Hah, well, that wasn't on anyone's radar. Good find.
 
Well, not only do the wheels go round and round, they also go up and down. You got to a speed that caused that tube to start bouncing inside the axle and once it started, it buzzed about until you slowed down - problem gone.
 
I have the same sliders on mine and even though used blue loctite - every now and then the wrong end will unscrew 1st.
 
 
There's no way that aluminum alloy tube will do any harm to that steel axle. But make sure you clean that axle thoroughly and give it a nice coat of new grease before sliding it back into your wheel bearings.
 
HH pads are sure hard on rotors.

[shinyribs]

Wheel bearings will cause a rumble and some vibration that you would feel more than hear, but once they go bad, they don't get better and then all of a sudden stop making noise.

 
 
99.9999% of the time I would agree with you! Once I had a bearing lock up without ever making a sound. Felt like I suddenly had a loose bearing, and upon inspection I found the bearing had just seized and was spinning the outer race inside the wheel. Toasted my hub.
 
That rod is a very interesting find. Glad you found something. Hope it proves to be the cure.

[noodles]

There's no way that aluminum alloy tube will do any harm to that steel axle. But make sure you clean that axle thoroughly and give it a nice coat of new grease before sliding it back into your wheel bearings.  
HH pads are sure hard on rotors.

Believe it or not the axle still had plenty of grease on it from the last time I pulled it ... which was maybe 10,000 miles ago? Not a lot, mind you, as much as I had put on the first time... just tacky and slippery.
 
And yeah, they are, but I figure I'd rather replace rotors than hit something because I couldn't stop in time.

[markstertt]

I'm kind of lost here, the axle is static, the slider rod and sliders are static inside the axle...no relative motion anywhere between the two. The grease on the exterior of the axle reduces any wear in a case where the bearing inner race may creep and may reduce potential corrosion but that's it. So help me understand what you think you found because I'm not seeing your initial problem being solved...Mark

[shinyribs]

That's a solid point. ^^^

[rick]

I'm kind of lost here, the axle is static, the slider rod and sliders are static inside the axle...no relative motion anywhere between the two. The grease on the exterior of the axle reduces any wear in a case where the bearing inner race may creep and may reduce potential corrosion but that's it. So help me understand what you think you found because I'm not seeing your initial problem being solved...Mark

Ever go to pull an axle out of a wheel to find it rusted solid to the inner races of the bearings? - and I do mean solid to the point that pounding with a hammer didn't work and the axle had to be cut thru both spacers. Been there, done that with a friend's dual purpose Honda long time ago.  
Dat's what the grease is for. And yeah, it doesn't go anywhere or really satisfy a need for lubrication, but w/o, it can be (and was) a nightmare. And it may as well be cleaned and regreased every time the axle is pulled - every manual will tell you this. If only every factory was as good as their service manuals during initial build..
 
The axle's not any more static than the back wheel - especially with that OE shock, erm, controlling it. Yeah, seems a bit nuts, but there's lots of room inside the hole thru the axle for that alloy rod to bounce around. A rough road at a fairly high speed, with that alloy rod just floating in there, get the axle moving up/down at just the right frequency - guess it could start vibrating enough to make some noise. That the noise kicked up all of a sudden and quit just as quickly suggests something goofy just like that.
 
Besides, have a look at that nice gold anodized rod - it's all banged up. I'll pull mine over the weekend and take a pict. It won't look anything like that 
 
Crazy enough, but if his problem doesn't come back and that was the only thing found suspicious - yep, stranger than truth. Time will tell. 
 
Of course - the control experiment is to put the rod back in and go find that same stretch of road at 70mph and see if the noise comes back. It's the scientist in me. 
 
 
 
 

[noodles]

I'm kind of lost here, the axle is static, the slider rod and sliders are static inside the axle...no relative motion anywhere between the two. The grease on the exterior of the axle reduces any wear in a case where the bearing inner race may creep and may reduce potential corrosion but that's it. So help me understand what you think you found because I'm not seeing your initial problem being solved...Mark

After it was dropped the slider bar became jammed inside the axle so that it was no longer perfectly parallel with the axle's hollow portion. You're right that shouldn't be a problem normally, but I'm thinking over a certain speed the vibrations from the rod inside being off balance the axle were enough to make noise.
 
If, on my drive to work tomorrow, the noise returns, my only other thought would be the rear wheel's bearings are shot. The wheel turned just fine but I could hear a little quiet noise... Aw crap I don't have to replace the bearings already, do I?
 
I just checked the rear wheel's side to side play and didn't feel any throughout the whole rotation. I did take a video once I'd removed the rear caliper but before I took the sliders out. You'll hear a clunk sound as the wheel turns. After the slider was removed the clunk went away, but I didn't record the wheel again.
 
[video size=medium]

 
What's interesting is that I never heard this noise when backing up to park, etc. And like I said the noise disappeared once I'd replaced the wheel without the slider.

[ralph]

I once had a buzzing noise but not has loud as you describe and it turned out
to be two solid steel bars inserted in the handlebars to damp vibration,
no moving parts as such and they were quite a tight fit needing some force
to remove but it was definitely them.