Avid bb7 lipping

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DarkNewt
Posts: 388
Joined: 12 Aug 2014, 9:55pm
Location: West Midlands

Avid bb7 lipping

Postby DarkNewt » 9 May 2018, 7:28pm

Hi All,

While I am waiting for a replacement crank for my everyday bike I pulled out my touring bike which hasn't been used since last August, I had a knee injury just before a 500 mile tour through spain/france. It turns out the knee injury was a torn meniscus and it's taken this long to be fully functional... Only explaining so you don't think I have been lazy :-)

So this evening I have been giving it a good service so I can use it in the meantime, did all the normal cleaning greasing and noticed the front brake was extremely poor (Avid BB7's - i gave the rotors a good clean and took the pads out to examine them, there was some use left in them but despite readjustment the braking was still fairly poor.

I examined the pads more closely and towards the bottom there was about 2mm of lip so I changed the pads for new ones readjusted the brakes and they are rock solid again.

My question then: Is this lipping normal not seen it before, there's no adverse wear on the rotors they are the ice ones from Shimano. The brakes were set up correctly on the old ones (you will have to take my word on that) , I might have expected lipping if the brakes weren't fitted right and somehow the pads stood proud of the rotors at the outer edge, but the lipping was on the lower edge facing towards the inner of the rotor.

The last cycle was from Santander through to france and there were some pretty steep hills and lots of gradient, I cycle camp so the bike is always heavy loaded kitchen sink etc.. and I am 6ft 1inch and weigh 18.5 stone so they have a lot of weight to stop... could this be the cause although ive not noticed that lipping previously?

Strange so wondered if anyone had any thoughts?
Currently planning my next adventure and trying to get over two operations in 6 months but still going strong!
email: newt@systems-engineer.info web: thedarknewt.blogspot.co.uk

nigelnightmare
Posts: 568
Joined: 19 Sep 2016, 10:33pm

Re: Avid bb7 lipping

Postby nigelnightmare » 9 May 2018, 8:43pm

"Lipping" on the bottom edge should NOT be possible.
The rotor fixing "arms"? (Whatever they're called) where it mounts to the hub would prevent them from forming.
On the top/outside edge it can happen as you said from poorly aligned calipers or incorrectly fitted pads OR even the wrong pads fitted.

JMTPW

Edit
P.S.
Glad to hear you're on the mend.

Brucey
Posts: 36112
Joined: 4 Jan 2012, 6:25pm

Re: Avid bb7 lipping

Postby Brucey » 9 May 2018, 9:06pm

as well as alignment errors there can be a more basic incompatibility between the pads and rotors. There are two or three different swept widths of brake pad (shimano make two, as listed in their compatibility charts) and if you get the wrong one the most common error is that the inner lip of the pads doesn't wear evenly; (errors the other way cause the disc not to fit in the caliper in one direction and/or leave a lip on the disc; in the other direction you get a lip on the OD of the pad ).

With a narrow track disc and wide track pads you can get a lip on the pad ID; what happens is that the disc spokes wear faster than the rest of the disc, leaving a proud area on the pads. This can cause the disc to wear to minimum thickness at the spokes and the disc to be scrap well before it should be.

Solutions are

1) to get the correct disc for the pads/calipers
2) to adjust the caliper position so that the outer edge of the disc is fully used (which it might not be at present)
3) to fettle every set of new pads so that the track on the pads better matches the track on the disc

The last of these is often easiest; just grind/hacksaw/file the pad down (to the minimum allowable thickness) at the edges where you would normally get a lip. Note that any hacksaw or file will wear quickly if you use it on many brake pads; grinding is probably best.

BTW the most common causes of weak braking with BB7s are

- pad contamination and
- cables going draggy

BTW if the old pads went back in and you swapped them left for right, that could cause weak braking too.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

DarkNewt
Posts: 388
Joined: 12 Aug 2014, 9:55pm
Location: West Midlands

Re: Avid bb7 lipping

Postby DarkNewt » 9 May 2018, 9:46pm

Hi,

ive set them up loads of times, and they were in right when I moved them. Cables are fine they had just been changed when I left on my last tour. I could see with the rotors installed that they were in the correct position pad is totally covered by rotor. Definitely didn't swap them left for right on refitting they are marked and swapping them left to right would make the tabs that push back be in the wrong position, agree with the poor braking re contamination hence gave the discs a thorough clean but tbh there was very little contamination.

Also definitely the right pads, I agree it's really strange and the comment "shouldn't be possible" was what went through my mind as well but as the saying goes when you have eliminated the possible.

The only thing I can think of is that I am running 180's on the front and the pad may have been slightly below the thicker part of the rotor which would explain it, in fact I am going to check that right now on the bike.... i haven't adjusted the mounts etc.. and not seen it before but gonna check how low they sit on the rotor again..

Yup thats the issue the pads are sitting slightly lower than the braking surface so the bottom of the pad isn't getting worn until until they reach the point where the 2mm lip is formed and then that reduces the rest of the pads contact with the braking surface I wil have to add an extra washer in to raise the brake up a few mm so it is aligned totally over the braking surface. Until I looked at it more closely it wasn't obvious at all. I can only think that I hadn't noticed this when I put the 180 on the front and when I swapped them out previously I wasn't really looking for a fairly imperceptable lip.

im putting it down to user error :-) now to fettle around with washers on the disc mount.
Currently planning my next adventure and trying to get over two operations in 6 months but still going strong!
email: newt@systems-engineer.info web: thedarknewt.blogspot.co.uk

Brucey
Posts: 36112
Joined: 4 Jan 2012, 6:25pm

Re: Avid bb7 lipping

Postby Brucey » 9 May 2018, 10:01pm

it is easy enough to do a simple test with a new disc and new pads. Just mark up the disc (and one of the spokes) using some marker pen and apply the brakes a few times.

Look at where the marker pen has been worn off the disc and compare the position of the edge of the marks (or their width) with the width of the brake pad.

Note that if the brake pads are made by different manufacturers, the exact position of the friction material on the backing may vary slightly.

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

DarkNewt
Posts: 388
Joined: 12 Aug 2014, 9:55pm
Location: West Midlands

Re: Avid bb7 lipping

Postby DarkNewt » 9 May 2018, 10:07pm

Brucey wrote:it is easy enough to do a simple test with a new disc and new pads. Just mark up the disc (and one of the spokes) using some marker pen and apply the brakes a few times.

Look at where the marker pen has been worn off the disc and compare the position of the edge of the marks (or their width) with the width of the brake pad.

Note that if the brake pads are made by different manufacturers, the exact position of the friction material on the backing may vary slightly.

cheers


Hi Brucye, yet again you have taken me to school, never thought of the variation of pad material between manufacturer, it is something I will be checking when fitting new pads in the future.

Thanks to all those replying really apreciate the prods it made me look further and best of all I have something else to check when fitting new pads lol, it's obvious when someone wiser points it out!! :D :D :D :D :D
Currently planning my next adventure and trying to get over two operations in 6 months but still going strong!
email: newt@systems-engineer.info web: thedarknewt.blogspot.co.uk