Back brake grating after cycle in wet

KStaford

I have a new Specialised road bike, I think its this one - http://www.dalescycles.com/2009_Specialized_Globe_Vienna_3_p/09globevienna3.htm

I have been cycling evenings on it for the past three weeks. Last weekend I went out for a spin in the wet. Lots of flooded roads etc.

Ever since, the back brake sounds as though its grating slightly when I use it. Upon visual inspection it look sok, (pad snot missing etc). I notice a dark track formed around the rear rim. The brake works pretty much normalls afaict.

Is this normal? Do I need to be concerned ?

72hundred

Sounds normal enough.

I'd say what you need to do is adjust the brake pad so that it is in a "toe-in" position; that is to say the front of the brake pad closer to the rim. Then rotate the wheel to see if it touch the rim.

You just need to loosen the screw that keeps the brake pad in place and then move it a little "toe-in". This should sort the problem... if not post back up again.

KStaford

you see the grating sound hapens when I actually apply the brakes, the pads seem to grate on the rim "during braking"

Hermy

I reckon you just need to clean the braking surface on the rims and the brake blocks.
An old tooth brush might be useful for the blocks.

KStaford

Hermy wrote: »

I reckon you just need to clean the braking surface on the rims and the brake blocks.
An old tooth brush might be useful for the blocks.

thanks for the reply. is it grit from the puddles then ? and is that common ?

Hermy

What you describe sounds like grit on the rims/ brake blocks and that is perfectly normal when you cycle in wet, mucky weather.

72hundred

KStaford wrote: »

you see the grating sound hapens when I actually apply the brakes, the pads seem to grate on the rim "during braking"

Yea this could be solved with making the brake pad toe-in.

KStaford

72hundred wrote: »

Yea this could be solved with making the brake pad toe-in.

just to be very clear 72, is there an image / diagram / video on the web showing this technique ?

victorcarrera

I would do as Hermy advised above clean the brake blocks and rims. Remove the wheel and inspect the brake blocks thoroughly in good light. This has happened me quite often.I have always found it to be small sharp pieces of grit embeded in the blocks. Never heard of toe in. I would have thought this would trap more grit and cause uneven wear.

Hermy

I'd agree with 72hundred regarding toe-in when setting up the brake blocks.
I just think the problem here is a build up of grit on the brake surfaces.

KStaford

victorcarrera wrote: »

Never heard of toe in. I would have thought this would trap more grit and cause uneven wear.

me too

Gavin

I was under the impression that you used toe-in when the brake pads were squealing. Otherwise, get them aligned parallel to the rim.

72hundred

KStaford wrote: »

just to be very clear 72, is there an image / diagram / video on the web showing this technique ?

There's probably loads and loads of webpages but this is the first that google turned up - see the last paragraph.

http://www.jimlangley.net/wrench/brake1.htm

victorcarrera

Read that article OK.
1.The toe in wears away after a couple of spins?
2.Having seen the photo it is more likely to trap more grit.
3.Never had a problem with squealing brakes. Anybody know what causes it?

KStaford

many thanks everyone for this discussiuon,

DirkVoodoo

Toe in is used for cantilever brakes when they make a squeaking noise because the brakes engage the rim, then bounce off, then engage again, etc.

Side pull calipers don't need to be toed in, I don't even know if the washers are convex/concave to allow this, but it's generally not something you do on these brakes as they don't squeal.

I had a similar problem with my rear brake (ultegra caliper and pad). It sound's like a really gritty pad right? As if someone has replaced the pad with granite? I think it may be that you are accumulating more crap on the pads, road grime and aluminium from your rims can become trapped on them. As mentioned, a quick sanding with some low grit paper will scrub off a layer of rubber taking most of the crud with it.

The dirt is normal, it's just the rubber/dirt wearing down on the braking surface of the rim. Keep the wheels clean to ensure that your braking performance isn't compromised.

zzzzzzzz

DirkVoodoo wrote: »

Toe in is used for cantilever brakes when they make a squeaking noise because the brakes engage the rim, then bounce off, then engage again, etc.

Side pull calipers don't need to be toed in, I don't even know if the washers are convex/concave to allow this, but it's generally not something you do on these brakes as they don't squeal.

Where'd you hear that?

I've had callipers squeal before, and fixed it by toeing them in. There's always been facility to toe them in on any callipers I've had.

Greyspoke

You sometimes get small bits of metal from the rim embedded in the pads - you need to dig them out with point of a sharp knife or something similar. Clean the pads and inspect them carefully. The bits of metal show up quite clearly. If you don't remove this or embedded grit, you'll wear grooves in your rims (and it sounds terrible too)
Wiping the rims clean after a wet ride also helps.

DirkVoodoo

aidan.offbeat wrote: »

Where'd you hear that?

I've had callipers squeal before, and fixed it by toeing them in. There's always been facility to toe them in on any callipers I've had.

Cobbled together from park tool:

Pad Toeing:
This is the setting of pad angle as it touches the rim. Toeing refers to setting the pad so the pad's front edge strikes first, which tends to reduce squeal during braking. Caliper arms tend to have play in the pivots and the arms flex when the brake is applied. This may cause squealing in the brake pads. It is simplest to first ride the bike and see if the brakes squeal.

Loosen and lubricate threads of pad bolt/nut. Adjust height of right pad to strike lower edge of braking surface. Adjust height of left pad to strike the upper edge of braking surface. Most dual pivot pads adjust only for height and tangent. Vertical face and toe alignments are not typically adjustable on dual pivot calipers. Tighten pad-fixing bolts.

If squeal is a problem in the brake, consider filing the pad so there is a slight gap at the back of the pad.

Personally I have never had a problem with brake squeal on dual pivot calipers, only on cantilever brakes as it is a fundamental problem with their construction that they bounce on and off the rim so as to create squeal. Which is why I said I don't know if the washers are convex/concave, I have never had to take the brake block off to check.

Civilian_Target

Cool, I always wondered what that noise was, and I generally end up with a decent load of black crap on the wheel rims before I clean it off, but I thought it was just bits of brake pad....