brake question on new bike

[geoff]

Hi,

This weekend I purchased a new Trek 7.6FX so I didn't have to commute on my mtb anymore.

Well, occasionally, when I brake hard, the whole front end vibrates quite a bit. It feels like the front tire starts bouching around and I noticibly lose traction. It's happened twice on different sections of road.

I can't imagine that this is normal operation. Do you guys have any ideas what I can adjust to fix this?

Thank you.

[nuovorecord]

A few things to check:

Is the quick release lever snug? If it's not, it could be causing the vibration.

How about the headset? Adjusted properly?

Brake arms secured to the fork properly? Brake pads snug in their holders and tight in the brake arms?

The rim could have a poorly welded joint which can cause vibration during braking.

Since it's a new bike, take it back to the store from whence it came and have them make it right. It's under warranty. It's pretty common for bikes to need a bit of adjustment once they've been ridden a bit. I bought a new Trek recently and it had a couple of little problems that the bike shop (Bike Gallery) corrected immediately and with no hassle whatsoever.

[umsl9178]

This might be one of those Duhhh answers. Make sure the quick release lever is on the left side of the fork.

[Oldguyonabike]

And that the hub quick release is tightened.
I nearly totalled out once after changing a flat when I forgot to tighten the hub....

[geoff]

I checked all of that stuff, and it happened again this morning.

I guess I'll have to bring it back in to Bike Gallery.

Thank you for all of the suggestions.

[brock]

Front fork chatter is common with canti brakes. It can be quite disconcerting for sure, especially if the chatter causes loss of traction.

- If the bike is new, this might just settle down once the pads start to wear.
- Try toeing in the pads slightly.
- Some pad/brake/rim/form combos just chatter, so trying alternatives is an option (start with pads, the cheapest)
- There's always disks...

[Haven_kd7yct]

If the bike you bought is the same one my boyfriend bought, you will want them to take a close look at the rear wheel, hub, and derailleur.

He had his less than 24 hours when it started to make a weird "clunk" in the rear. BG at first thought it was the shim between the hub and the dropout, but that didn't fix it. Turns out they finally had to replace the entire rear wheel, re-adjust the derailleur, replace the chain... and I think there was a couple of other things they adjusted/fixed but I'll admit to not listening that closely when he was going over the list.

But, it's a cool bike, he loves it, and now I don't know how I'm going to keep up with him. Hmph. Maybe I'll have to look into getting another bike and keep the Schwinnster for commuting.

[geoff]

Ok, I've been too busy riding to bring it to BG. However, I decided that I would completely remove the front wheel and re-seat it. The vibration has substantially decreased. I think this weekend I am going to pick up a new set of pads and play with the their positioning anyway though.

BTW, Brock, disks would be awesome, but that means a new fork and new hubs. This bike has an awesome wheelset though, so I’m not going to mess with it (for now)…

And Haven, my girlfriend and I have the same problem, so when I ride with her, I use my mtb and ride in the middle chainring. If nothing else, it makes her feel like she’s really fast!

[mtmann]

Originally Posted by brock

Front fork chatter is common with canti brakes. It can be quite disconcerting for sure, especially if the chatter causes loss of traction.

- There's always disks...

Disc brakes will do it too. I have a new Lemond Poprad (disc) and have experienced the same phenomenon. Here's the deal to my understanding. Forks flex (thank God) but flexing causes vibration when wheel is turning AND brakes applied. The higher the brakes on the fork (farther away from hub) the less vibration, so cantis get more than sidepulls, and disc can get even more than that. solution is partly in making sure everything is tight and adjusted properly, but also in just being aware, easing off front brake when chatter sets in, and remembering brakes just slow you down anyway

[lazlo]

I've had this same problem on my Cross Check, and was told it's a normal characteristic of steel frame cross bikes. It only happens at high speeds when braking hard, but it is quite disconcerting. I, too, can see the fork flexing quite a bite. If the only fix is a stiffer fork, I'll just get used to it.