Disc brake alignment issues

[Sketchyxup]

Re: Re:

Ian,

How is the disc alignment if you seat the axle fully into the dropout? given you have disk brakes, other than the aesthetic annoyance of the rim/tyre being slightly off centre, the incorrect dish shouldn't actually cause too much of a problem in the short term.

As for the damage to the mount. Quite a lot of callipers come with a set of convex & concave washers which allow for some vertical, as well as the usual horizontal adjustment for alignment. I might have some kicking around, but you should be able to get a set off blag for a couple of quid I'd have thought.

This^ and if you're an avid retro biker you can steal them off V'brake pads, they are exactly the right size for caliper bolts. Normally call them pillow washers, not sure why but they are a good tool for getting things lined up suitably.

 

[cherrybomb]

If the caliper/mount isn't designed to use a concave/convex pair. Don't.

You'll either have to keep filing the friction surface to remove the newly formed lip. Or one day you'll suddenly have no brakes as the two lips will meet.

This is true. You may need another calliper mount adapter made to take the washers to get the disc & pad to align correctly, but if you can try some with what you have and get the brake to run without rubbing at least you know you're on the right lines.

 

[mk one]

Hi, just a couple of questions, obviously you are going to have issues while the hub is not sat in the dropouts squarely, but what issues do you have when it is?, bad wheel building aside without seeing it is hard to gauge. Is the disc straight, not warped? is it the correct thickness for the caliper? as that can make a difference if things are slightly out. If its still not right when the hub is centered, doesnt matter about the rest of the wheel, unless you try to compensate by mounting it wonky then either take it to a shop, not your lbs, or try borrowing the facing tool to do the job, im sure park used to make one.

Mark

 

[ishaw]

Disc is a brand new hope floating rotor. Brakes are hope x2 so should work well with each other. With the wheel straight in the drop-outs it looks much better, haven't tried fettling yet as I want to sort out the master cylinder seals first. Pretty sure once I've sorted the seals and the wheel is dished right, it won't need facing when using washers, but may get it done anyway.

 

[02gf74]

Re:

Firstly fit the wheel correctly. The disc rotor attaches to the hub so non central rim is irrelevant to this problem.

Exactly what happens as you tighten up the calliper bolts?

The recommeded way to centre the calliper about the disc is to do up the bolts so calliper can still move, apply the brake and tighten up the bolts.

Now what can happen, due to calliper - post face mismatch, is that the calliper can move so that the rotor drags on the pads. Some callipers, e.g. avid have conical washers (as found on shimamo xt xtr v brakes) to allow adjustment.

Those that do not, eg formula then what i do is to do the above then loosen bolts so calliper can just about move, then push calliper at one bolt so rotor is central - use your eyes buy looking fo a gap between pads and rotor, hold it and do up bolt. Check for drag then repeat for other boky. This may need several attempts. I have undone one bolt at a time to do the tweak, there is enough flex to do this.

Also fit a washer under the bolt head as the slot in the calliper can force the head into postion so the calliper moves.

I would not mess with filing the posts, this is a sure way of ******* things up.

 

[legrandefromage]

I use the Avid method of domed convex/ concave washers from v-brake pads to centre calipers on post mounts.

Works a treat

 

[02gf74]

Yes but thats because the mounting lugs on avids/sram are made so they allow for tbe thickness of the washers. Try that on formula or shimano and youll find thr pads sweep a smaller area due to being further out. It may so happoen that the thickness of the conical washers plus addional washer means next size up rotor fits perfectly, and thats fine if you want to go up one size.

 

[ishaw]

Re: Re:

Firstly fit the wheel correctly. The disc rotor attaches to the hub so non central rim is irrelevant to this problem.

Not exactly true when the wheel is having to be aligned to compensate for the incorrect dish, but I get what you mean and this will be corrected.

I've fitted many a disc brake in my time as well as worked on a number of other brands, but this is the first time it has been a headache, in fact the hope race brakes on my scion were a 5 minute fit job, hence trying to rule in/out possible causes that have added up to where I am now.

Cheers for the input though, all useful and I will prevail!

 

[ishaw]

Yes but thats because the mounting lugs on avids/sram are made so they allow for tbe thickness of the washers. Try that on formula or shimano and youll find thr pads sweep a smaller area due to being further out. It may so happoen that the thickness of the conical washers plus addional washer means next size up rotor fits perfectly, and thats fine if you want to go up one size.

I agree, not sure hopes were designed in this way so I'll avoid that if I can.

It's on a small bike for a small person, so running 160mm rotor on front and 140mm on rear. I could stick on an adaptor and run 180/160, but don't really want to, nor will the rider need the extra braking power. The bike is an exercise in vanity really, it won't see trails or high speed action, just wanted to build a nice bike for my wife that was not fit for a basket at the front from various spares I had.

This is the bike in question, though the stem has been changed to a black one of the same variety, and the forks are now no longer remote lock out:

 

[stevet1]

Re:

The recommeded way to centre the calliper about the disc is to do up the bolts so calliper can still move, apply the brake and tighten up the bolts.

Not on hope brakes it isn't.
Centre the caliper over the disc with the pads out, then put the pads back in and tweak them* so that they meet the disc at the same time.

* There are guides on this, including one on the hope website but basically you push on the back plate of one pad to move the opposing pad back in a gnats todger and repeat until it's running smoothly.

As for your wheel alignment, I'd agree with putting it in the other way round to check if the problem lies with the fork or with the wheel. If its the wheel, 5 minutes with a spoke key loosening and tightening alternate nipples by a quarter or half turn should see it right. If its the fork, check the dropouts, is one worn at all where the wheel axle sits?