Mountain Bike Reviews Forum banner

1 - 13 of 13 Posts

·
Registered
Joined
·
105 Posts
Discussion Starter #1
Last night I was riding my rigid 29er on a long and rough ride. Once I was through the rough stuff, I pulled clamped down the front 203mm rotors and I felt a mean plusation. I don't see any problems with the rotor or how the wheel is mounted or the brakes them selves, but it seems that I can wiggle the arm and adjuster a little too much. I can do the same with the rear but isn't as loose and the rear isn't having the same problem. I just can't see any thing wrong but the brake feel is horrible.
 

Attachments

·
B A N N E D
Joined
·
5,273 Posts
I don't see any problems with the rotor or how the wheel is mounted or the brakes them selves, but it seems that I can wiggle the arm and adjuster a little too much
Don't know about new BB7's but the old ones have a 'Outer Calliper Body Seal' which goes between the calliper body and the torque arm.
The 'Outer Calliper Body Seal would basically fill up the gap and cover the silver part that's exposed between the torque arm and calliper body on your brake where you seem to be having the movement.

The 'Outer Calliper Body Seal' can be seen in some photos in the BB7 Overhaul Guide:

https://www.sram.com/_media/techdocs/Avid%20BB7%20Overhaul%20Guide.pdf


Found a photo where the seal can be seen on a older model BB7:



Another thing is there a 'Spring Tension Adjuster' on your torque arms, I can't see any of those in your photos either, it's the little hex screw that can be seen on the inside of the torque arm in the above photo.

Edit. Forget about the missing 'Spring Tension Adjuster' it's on the underside of the torque arm with new model BB7's, it can be seen on the first photo below. I didn't realise the brake design had changed

It does looks like the Outer Calliper Body Seal is missing on your brakes, the photos below of newer BB7's that don't show any silver between the torque arm and the calliper body. This probably won't stop the wiggle though, it seems to be just a seal to stop dirt and crap getting into the brake. I just looked at my old BB7's which have the seal on, the torque arm on them can be wiggled a bit too, they don't pulse either so that's probably not the cause. Try some pad adjustment for the pulsing and forget about the wiggle.








.
 

·
Registered
Joined
·
2,117 Posts
So that spring adjustment screw is the trick to tuning out the pulse?

My rear brake is doing the same. I have a new rotor back there. I figured the pulse in my case was a weird pattern worn by the old, worn out rotor. I've been too cheap to try new pads and find out.

Can the wear on an old rotor, even if its true, throw off your braking?
 

·
B A N N E D
Joined
·
5,273 Posts
GrantB said:
So that spring adjustment screw is the trick to tuning out the pulse?
No, I just mentioned that because OP said he couldn't see any problem with the brake, he said he could wiggle the torque arm and there seemed like there was too much movement in it. At first I thought that the spring tension adjuster wasn't on the torque arm and it might be one thing that was contributing to the wiggle/movement. The old BB7's have the spring tension adjuster on the upper side of the torque arm, I didn't realise at first that the newer model BB7's have spring tension adjuster on the underside of the torque arm.
The spring tension adjuster regulates how much tension is on spring that returns the torque arm to the open position. If the torque arm doesn't want to return to the fully open position when the brake lever is released it might need some more tension on the spring.
 

·
Registered
Joined
·
2,117 Posts
Hmm.

You mean position the rotor close enough to the non moving pad so that the rotor isn't getting pushed much by the moving pad?
 

·
Registered
Joined
·
12,083 Posts
GrantB said:
Hmm.

You mean position the rotor close enough to the non moving pad so that the rotor isn't getting pushed much by the moving pad?

Yup, if the rotor deflects too much it will start to pulsate....Well you don't move the rotor of course but the fixed pad, and caliper should be adjusted so that the rotor does not deflect but just a little bit.


Definatly the first thing to try, especially if the brake was working good and after a muddy ride or a lot of braking it starts pulsing.
 

·
Registered
Joined
·
473 Posts
Missing pad material will also cause pulsing. This happens when the pad material gets thin and starts popping/flaking off.
 

·
~Disc~Golf~
Joined
·
16,491 Posts
Lule said:
Missing pad material will also cause pulsing. This happens when the pad material gets thin and starts popping/flaking off.
Missing rotor material will make it pulsate too. This happens when the braking area cracks and starts popping off.
 

·
Registered
Joined
·
105 Posts
Discussion Starter #12
I really got no good ideas. I have taken it apart and put it back together. Same problem. Although I still have to get it all set back up proper. The thing is that this wasn't gradual issue. It was fine, then after speeding over miles of large gravel along the rail lines, it started plusating. At first I thought it must be the headset but after checking that and everything else, its all tight. The rotor is as striaght as it can be. The pads are not chunking at all. It turns out the seals are there. The flash of the camera made them look silver. I have nearly gotten rid of the problem by backing the outside pad off all the way. Now I can brake as hard as I want and I only get a little plusation as I come to a stop. But that is hardly the way to solve it. But now it it more then rideable. I'll get it setup proper when I get the time and see if it gets any worse or better. For now I'm on another bike.
 

·
Registered
Joined
·
105 Posts
Discussion Starter #13
Its all good

Well, I finally took the time to get it all put back together correctly and now it is working fine. jeffscott hit it on the head. It must have been the rotor deflecting. I got that inside pad as close to the rotor as I could and now its good. I still find it odd that it could go out of adjustment mid ride like it did and that the plusation could be so bad. It all came out of nowhere for me. Thanx for everyones suggestions and help.
 
1 - 13 of 13 Posts
Top