Mountain Bike Reviews Forum banner
1 - 6 of 6 Posts

·
Registered
Joined
·
120 Posts
Discussion Starter · #1 ·
Hi, I just installed a 203mm alligator disk rotor - the one with the shark fin pattern - on my 29er reba with bb7s. (The 185 seemed to fade too much after a long downhill with my 220 lbs + 30lb bike)

I'm getting a fairly strong vibration when I test them on the street braking hard. I can actually see the front hub moving forward and backwards to the vibration. The frequency is fairly fast. I'd be a bit nervous on a steep trail with that.

Anybody got any thoughts on fixes? The rotor seems nice - fairly light.

I noticed there is a bigger gap from the brake to the rotor. Ie, the brake sits slightly higher on the rotor than on the 185 which would put it more in the fin area of the pattern. Tho I suppose I could get new pads too. Or might it just go away?
 

·
Registered
Joined
·
115 Posts
I'm pretty new to disc's as well, but it sounds to me like you may want to go with new pads if you've put on a new disc.
 

·
Registered
Joined
·
1,058 Posts
Can you remove some spacers from the caliper to put the pads further down on the brake track?

IIRC, the avids are set-up for 185mm rotors whereas the alligators are 180mm, thus the pads would be grabbing further out on the discs (finned area) and the lack of firm contact could be causing the vibration.

I would also get some new pads. Get some sintered pads, EBC gold pads are some that have been recommended. Check out the weight weenie forums for a huge thread on these discs.
 

·
Registered
Joined
·
120 Posts
Discussion Starter · #4 ·
Thanks for responding civil.

I wasn't aware I could make that kind of adjustment on bb7s. I did contemplate trying to mill the post extension but that seems like a last resort. I'll take a look to see if I missed an adjustment for the offset of the caliper.

These are 203 rotors btw but I don't think that would make a difference.
 

·
Registered
Joined
·
1,058 Posts
drdre said:
Thanks for responding civil.

I wasn't aware I could make that kind of adjustment on bb7s. I did contemplate trying to mill the post extension but that seems like a last resort. I'll take a look to see if I missed an adjustment for the offset of the caliper.

These are 203 rotors btw but I don't think that would make a difference.
Oops, sorry, I didn't see that. It was too late at night. I wouldn't remove any material from the post extensions, that would reduce the length of the thread engagement.

When I installed my set of alligators, I kept the existing pads but they performed like garbage as the pads were worn into the old rotor shape. Big improvement as soon as I replaced the pads to some sintered ones.

I'm not familiar with the bb7's, but to adjust the offset for my 180's on my juicy 7's, I removed one of the flat washers and replaced it with thinner ones (by slowly sanding the washer thickness) until the pad made batter contact with the brake track.

Hope that helps.
 

·
Registered
Joined
·
120 Posts
Discussion Starter · #6 ·
Yup, it doesnt seem like I have much adjustment. The little washers are already as thin as I can imagine and even then by sanding, I don't think I'd get more than a mm. Here's a pic.

For the milling, I meant shortening by 3mm or so the extension needed for the 203 size rotors. That would not shorten my thread count.

Actually, looking by the the wear marks on the disk from the test ride, it seems to not be engaging flatly. One mark is by the base, the other is at the top on the fins. So, maybe new pads would be best. However, I do think the calipers are too high. Is this the way it looks on yours? Hmm.
 

Attachments

1 - 6 of 6 Posts
Top