[disasterarea]

cycling along I found that going at a certain speed the front brake disc vibrates loud enough to make a very annoying rattling sound. Below and above this particular speed there's no buzzing - is this a natural frequency thing? Unfortunately, it appears that it's also my current cruising speed I also found that the situation gets worse momentarily when I lean for a sharp turn. I have tried centering the brakes to no avail.
The rattling problem only appeared after I fitted a new and heavier tyre - Maxxis Swampthing 2.1. The previous was a Panaracer Tserv.
I do notice that when I turn the handlebars that there appears to be a slight delay of the rim/tyre to turn. Almost feels as if the hub to rim connection is slightly loose i.e. the spokes aren't tight enough. I have checked the wheel and tightened the spokes as much as possible but it still no good. So do I need to cut some more thread on the spokes of the disc side (left) so I can tighten even more? If so, who makes a thread cutter?
Incidentally the wheel is my first attempt at wheel building and so that may explain why everything isn't as it should. The rim is a Mavic 219 disc and hub is a XT disc. Incase it's a flexy fork, which I doubt, the wheel's attached to a Marz. MX Pro ETA. Thanks for any help.

 

[oldfart]

Thread cutters I know of, Phil Wood, will cost way more than new spokes and threading with a PW would require taking all the spokes out anyway. It would be unusual to run out of thread on a wheel though unless the builder choose the wrong length.

Is the rotor simply rubbing on the pads? If so the spokes have nothing to do with that. Its not uncommon for the rotors to rub whne cornering or standing up etc. Sometimes its just not possible to eliminate it completely. If you suspect loose spokes are causing the slow steering, I'd suggest taking the wheel in to a shop for a wheel guy to look at.

Maybe try tightening the front QR a bit? You should feel resistance when the lever is around 90 degrees from closed.

 

[D_D]

It's worth undoing the wheel qr and rotating the axel in the dropout. Go riding and see if it has solved the problem.

You might need to try a few different positions.

Becase the axel / nuts arn't 100% square and straight putting the axel in at different degrees of rotation can slightly change the relationship between the pads and the rotor.

If you find a good spot mark the axel so you can allways put it back in with the correct orintation. I use correction flud.

That is just one thing that has caused similar problems for me in the past.

 

[RD]

what lacing pattern did you use? what kind of brake do you have? could it be just your pads rattling, etc?

 

[disasterarea]

oldfart

the buzzing was not a problem until I switched to a heavier tyre and I have also checked that the rotor does not rub against the pads before cycling, and the QR started to have resistance just before 90 degrees. As I mentioned before, the vibration only appeared at a certain speed range.
I took the wheel off last night and had a look to see if it was still true. It wasn’t out too badly, about a millimeter in parts, though I did find out I could tighten about a turn and a bit more for each spoke. There were some loud and nasty sounding pinging going on though.

D_D

I will look into the axel position after I’ve had a chance at trying out the trued wheel…under progress. Good call though, something I wouldn’t even know to look for.

RD

8” hfx9 rotor fitted to a 32 hole 3 cross wheel. I have already checked the pads and they do not appear to be loose.

Thank you all for you comments and suggestions. Sure am looking forward to silent riding once again.

 

[sub6]

well, i wouldn't run an 8" rotor on a MX Pro, but that's kind of a side issue. Check to make sure everything's SUPER FRICKIN TIGHT, your QR, headset, and hub bearing cones. Anything there that's loose could set up a vibration. Especially the QR since you're running an 8" rotor.

 

[RD]

RD

8” hfx9 rotor fitted to a 32 hole 3 cross wheel. I have already checked the pads and they do not appear to be loose.

I'd look again at the spring retainers on teh back of the pads, sometimes they can become un-tensioned and cause teh pads to rattle on the piston post at certain speeds. I know mine do it every once in a while. Also, how are your spokes? all seated properly, etc? do you find the tension changing, habe you used/did you use a tensiometer when you first built the wheel? (newbie builders often don't know what proper tension feels liek when they grab spokes during/after a build) Who did your spoke length calculations? Did you possibly over tighten your spokes and are somehow ripping/loosening the eyelet/rim connection?I'm just tryign to figure it out without having the bike in front of me. Please keep us updated.

 

[disasterarea]

Sub 6
I have checked the spokes, hub, cones, QR, rotor screws etc… They are all tight as can be. As for fitting an 8” rotor up front, I use to have center pulls on my touring bike and became rather paranoid after too many close shaves and actual hits because the brakes were not up to the job.

RD
I don’t have tensiometer, so that might be something to get in the future shopping list. I did manage to take the retensioned wheel out for a spin and had the lhs mechanic to have a look as well. He said all the spokes were tight and OK but, he also said that 8” rotors will always give that rattling sound. I sincerely hope he’s wrong and only trying to get rid of me quickly rather than being the case.

One thing I did find out eventually was that if I tapped the rotor on it’s side, and if done hard enough or at certain frequency it gave me the exact sound that I get when riding. So this looks like it’s a vibration problem with the rotor itself and has nowt to do with the rest of the wheel. Is there anything I can do to dampen this vibration?
Possible things to do that I can think of include trying to (i) true the rotor – which isn’t out of true much, (ii) apply grease to where the hub and rotor meet to give some form of damping – probably a very dodgy idea as grease + rotor = hello accident, (iii) change brake pad springs and (iv) change to a different design of 8” rotor with stronger rotor “spokes”. Has anybody else encountered this resonance problem before? If you have, how did you get ride of it? Thanks.

 

[Grimey]

Hmm... how about a 6" rotor?

I think you are stressing out the fork with a heavier tire and rotor than what it was designed for?

Also, what type of quick release are you using?

 

[Kornphlake]

did you tighten the rotor bolts to the right torque and in a star pattern? I'd also look to see that your tire isn't rubbing on something other than the ground. Maybe it only does it when you are turning and the wheel deflects or at a certain speed where the little fuzzy's are affected by centrifugal force or something.

Could be one of those things you're just going to have to live with. My brakes always drag a little, either when they are hot or when they're cold. It seems like no matter what you do you'll always have some little problem.