Front fork vibration under braking

gsd

Hi all,

I'm from a road biking background so am fairly new to suspension forks and disk brakes - please bare with me!

I have a hard-tail with Fox RL 32 100 forks. I went out on Saturday and had a great ride, nothing too crazy but now my front forks vibrate visibly when I use the front brake. I had a flat so thought it might be low tyre pressure but it's not that. The front brake disc was had a tiny bit of play but it's not that. I've just tried tightening the headset but that hasn't fixed it either! I've checked the fork air pressure which is at 80psi which is the rating for my weight (~165lb). I've put the rebound in the middle (6/12 clicks). So... now I'm out of ideas... The only thing I can think of is that I might have hit a pressure release on the forks and lost some oil? They seem to have a bit more give now when locked out and I did go down a few steps quite hard.

Any suggestions as to what to check next would be great! My knowledge of suspension stuff is very limited!

Thanks!
Scott

nicklouse

forks do move under breaking.

any noise?

gsd

Yeah, it's noticeably worse now though! I'm riding on the road to work and I get a big judder through the handle bars that I didn't get last week! The travel is probably 5-10mm forwards and backwards. When I lock the front brake and try and roll the bike back and forward there isn't a whole lot of travel though - I guess my weight isn't on the bike then though.

There's no noise at all, just the vibrations and juddery feeling.

sloppycowpat

could be contaminated pads and a dirty rotor, loose rotor, or cones/ bearings in wheels, potentially a loose headset or cracked brake mount

should give you a few things to check

nicklouse

gsd wrote:

Yeah, it's noticeably worse now though! I'm riding on the road to work and I get a big judder through the handle bars that I didn't get last week! The travel is probably 5-10mm forwards and backwards. When I lock the front brake and try and roll the bike back and forward there isn't a whole lot of travel though - I guess my weight isn't on the bike then though.

There's no noise at all, just the vibrations and juddery feeling.

could this be coming from the fork moving through its travel?

gsd

I was wondering about the fork travel causing it but the air pressure is normal. I don't know if it's possible to lose some oil from the forks but if that's possible then i guess that might be it.

I was wondering if worn brake pads could do this too? They're definitely fairly worn but I've got the adjuster screw at maximum and they still seem to work well and at an early biting point when I pull the lever.

386ka

What are your brakes, and rotors? Disc brakes exert more force on the fork, so you might not be used to it.
Ps, what travel sag are you at?

eiran1

hi
I'm having the same problems' and I have tried to change everything' wheel, brake, and also the fork!!
I'm puzzled.
did you solve this?

The Rookie

I had this on mine, changed to a disc with less 'saw tooth' effect on it (the ONLY change) and it went away, if you have organic pads (sintered are more tolerant) and a heavily saw toothed disc it can give pulses in brake effort, at certain speeds this was resonanting my lowers on the stanchions (yes the bushes are a little worn, but normally work fine).

TheCloud

I've got an A2m saw tooth disc that looks like a ninja throwing star on my xc bike (Rockshox SIDs) and have the same pulsing effect with sintered pads, even though they're only 160mm rotors, it's especially pronounced on the road. When I put the standard disc back on the problem goes.

jairaj

Sounds like the disc brake pulsing many do this depending on the shape of the disc. or a quick check is with the bike stationary, hold the front brake on tight and rock the bike forwards and backwards and sideways. If something is loose in front end you should feel some pay here. Note the forks will compress slightly so try to ignore this. Common areas for play are in the headset and hub.