BROOKLINEBIKER

Hi folks,
I went to my LBS to have new brakes installed (Shimano Altus C91 Rear Cantilever) just before the COVID 19 lockdowns. I didn't look closely when I took the bike home and the bike seemed to stop fine. I looked again recently and saw that the gap between the pads and the wheel rims on my rear tire are irregular. Does this need to be fixed? If yes, what needs to be adjusted? Is this doable for an amateur mechanic?

view of brakes from top

side view

Left side: large gap between pad & wheel rim

Right side: almost no gap between pad & wheel rim

Hikebikerun

You should be able to put an Allen/hex key in the Spot I circled (to hold it steady), then I believe it’s a 10mm wrench that will go on the bolt head on the opposite side (where the arrow is pointing). Loosen with the wrench as you hold the Allen key steady. This should loosen the pad and allow you to back one side out (or the other side in) to even out the gap.




Do this for major adjustments. For small adjustments, you can just turn the tiny screw sticking out of the side of the left side pad:




Totally doable with no experience. I’d start with the small screw to see if you can get it straightened out.

Disclaimer: I’ve never even seen these brakes, just did a quick google search.

frogman

Excellent instructions

powermatt99

Did you check the installation of the wheel? My wife had a similar issue. Turns out she did not seat the QR skewers properly in the fork.

ClydeClydeson

@powermatt99 says, the problem is almost definitely that the wheel is not straight in the dropouts. This is a very common mistake when adjusting brakes, and will make an experienced mechanic pull their hair out until they realize the simple mistake.

You can tell it is wheel alignment because the way the pads have become misaligned - one pad too close and riding up on the tire, and the other pad a mile away from the rim. THis is exactly what happens when the wheel is not straight.

ClydeClydeson

except that advice skips the troubleshooting steps that will identify the root of the problem (almost definitely the wheel is not straight in the dropouts), and adjusting the brakes to work with the wheel crooked in its dropouts will just become even worse adjusted brakes as soon as the wheel is removed and replaced again.

BROOKLINEBIKER

Hi again,
Thanks for the comments about wheel alignment and skewers. Now the origins of the brake problem make sense. I have a Burley trailer and just added the trailer "hitch" to the quick release skewer. So that may have knocked things out of line? If yes, how do I adjust the brakes or wheel?

ClydeClydeson

To fix wheel alignment in the dropouts, you just have to loosen the quick release, then ensure the axle is fully seated in the dropouts before you retighten the quick release. I bet if you do this right your brakes will no longer be out of adjustment.

ClydeClydeson

ALSO

There are usually two little conical springs on the QR skewer. These should be positioned one on each side so that the smaller end of both springs are pointing in towards the hub. Having a backwards QR spring will make it impossible to get the wheel straight.

cyccommute 

Before you follow any of Hikebikerun’s excellent advice, move the cable from where the red arrow to where the green arrow is pointing in the picture below. You may need to do the other adjustments but start here and see what happens.

fietsbob

Above should look symmetrical .. the main cable passes through the grey tube , it needs to be a little bit tighter/ looser..

use the fixing bolt to adjust its length..
then pad to rim spacing is done with the length of the shaft on the brake pad post.





..

Razorrock

Don't mean to derail this thread but
Every time I remove my rear tire I have to adjust the rear derailleur to get shifting back to perfect. Is that a common problem with QR's? or am I not fully seating it.

BROOKLINEBIKER

Hi, the cable I'm seeking to move is the one that is the end of the brake cable, as opposed to the straddle cable?

fietsbob

You don't have a straddle cable , That cable continues thru the grey tube and is held by the clamping bolt on the right side arm.

It's a fail safe system, so a broken main cable wont drop the straddle cable onto front tire,
with knobby tires the bike stops throwing the rider to the ground..


maybe you need to consider buying a separate transverse cable and the hanger you put on that main cable like this,
which you think you now have, but don't.

like this : ^the top pieces^ you can find them for a few bucks @ bike shops..

ClydeClydeson

Probably user error, possibly not properly seated axle, possible something else. Removing and replacing your wheel should not put your derailleur out of adjustment.

One possibility is that the removable derailleur hanger (if your bike has one) is not properly fastened to the frame. Make sure the bolt(s) that connect(s) the hanger to the frame are tight. If they are loose, the hanger will move when the wheel is installed.

Retro Grouch 

The return springs in those particular brakes are confined within a plastic retainer. Examine those little plastic cups for cracks. If you find a crack, that's your problem. Shimano used to provide replacements at no charge. I've also successfully fixed them by wrapping the cracked cup with wire..

cyccommute 

Look at how the cable on the left comes in at a weird angle. That’s what is pulling your brake over to one side. There are two notches on the straddle cable that the right hand cable can go through. The proper notch is the one on the right as you look at the straddle cable. Yours in the picture goes through the left one. I don’t use this kind of straddle cable but I happen to have one right now. Here’s what yours looks like from the front


And from above.



Here’s what it should look like from the front and



Above



The difference is subtle but if the through cable is in the wrong place, it can pull the brakes off to one side.

By the way, an old style straddle cable and hanger like this one

_IMG4950 by Stuart Black, on Flickr

doesn’t pull the cable one way or the other because of the tension on the one side of the hanger like the link cables can. If they do, you just slide the hanger over.

caloso

Yep. With straddle hangers, a lot of times you can get it to self align with a good hard squeeze of the brake lever.

Gresp15C

I'm voting for wheel alignment, because the tire is also quite close to the fender on the side that it's close to the pad. If the frame has vertical dropouts, then you can usually fix this by just holding the bike straight upright, flick the QR open, then flick it closed again. You'll hear it clunk into place. This will also be a good time to review the correct technique for using QR.

cyccommute 

That’s a good point. I’d still suggest getting the link wire in the right place but absolute check the wheel in the dropout.

Gresp15C

If you toss an old pair of centerpull brakes, keep the straddle hangers.

cyccommute 

The hundreds of them that we have in the parts bin at my co-op have lost them long ago