[SteveF]

I've had two brand new rotors on the back of my new bike, both rotors appear straight. But when installed they wobble enough to rub first on the outside pad, then the inside, so there's quite a wobble in the system somewhere. I shimmed under the rotor on the (six bolt) hub mount in a couple of spots and that helped a little but I wonder if the hub mount is slightly out of spec or if the caliper mount on the frame could need facing. I can't see how a caliper issue could cause the rotor to rub on both sides though? Is there a way to check the hub mount and face it if needed? Suggestions welcome.

 

[J.B. Weld]

If the pads are parallel with the rotor you don't need to worry about facing the caliper mounting posts.

As far as I know there's no way to face the disc mounts on the hub. It's pretty normal to have to true rotors after they're mounted, probably half of new bike builds require at least one of them to be trued. If it were me I'd remove the shims you installed and true the rotor or have a shop do it.

 

[Cleaner]

The order in which you tighten the rotor mounting bolts could cause this. Use a torque wrench to insure all are torqued to the same value and tighten them in a star pattern. This video provides details including the pattern.

Disc Brake Rotor Removal & Installation

 

[Danzzz88]

Worst case your hubs are not faced properly...though I have never come across that myself...considering they are made on a lathe I think the chances of that are slim...but if the rotor is truly flush then that is the only other possibility I can think of.

 

[Pisgah]

Out of curiosity, what brand rotor did you buy?

 

[mlx john]

This is what I use.

Watch your fingers!

 

[BrianRidesBikes]

I've had two brand new rotors on the back of my new bike, both rotors appear straight. But when installed they wobble enough to rub first on the outside pad, then the inside, so there's quite a wobble in the system somewhere. I shimmed under the rotor on the (six bolt) hub mount in a couple of spots and that helped a little but I wonder if the hub mount is slightly out of spec or if the caliper mount on the frame could need facing. I can't see how a caliper issue could cause the rotor to rub on both sides though? Is there a way to check the hub mount and face it if needed? Suggestions welcome.

I've seen rotors wobble due to worn hub internals but not because of differences in rotor mount faces. You could mount the wheel without the rotor and use a dial indicator to check the runout of the hub if you really wanted to.
The practical approach would be to true the rotor to the bike by removing any wobble at the braking surface.

 

[Mountainfrog]

I'm going to assume the new brakes have been bled properly. I'm going to assume the calipers have been adjusted properly to rotors. I'm going to assume the brakes have been bedded in. If the bike is new I'm going to assume the pistons aren't sticking as well, but may be over pressurized (too pumped may be a contributing factor). I've had plenty of new rotors that were off. I don't use a Park Tool or large Crescent wrench to bend rotors anymore, I find my hands work better because usually it's so slight. Wear Nytril gloves and clean rotors with Isopropyl alcohol afterwards.

 

[LVLBTY]

Definitely remove those shims, then simply true the rotor. You can use a goose neck plier, just cover the teeth so you don't mark up the rotor. Gently tugs will get it nice and true.

 

[noapathy]

This is what I use.

Watch your fingers!
View attachment 1964274

No need for pricey one-use tools. Any half decent crescent wrench works just fine (clean it first, of course).

Definitely remove those shims, then simply true the rotor. You can use a goose neck plier, just cover the teeth so you don't mark up the rotor. Gently tugs will get it nice and true.

No teeth on a crescent wrench.

 

[SteveF]

Thanks for the suggestions folks, I'll remove my shims and try to true it. If I can't get it right I'll let a shop have a go. It's a good time of year for it-shops aren't busy and I'm riding mainly on my fat bike.

For a couple of questions: It's a Magura Storm SL rotor on my new FS bike. They have about 350 miles on so they're well bedded and don't act as though they need a bleed or anything. I did use the star pattern bolt tightening procedure to proper torque and the caliper does seem square to the rotor.

 

[Danzzz88]

Why don't you tape/bolt a piece of plastic to the caliper mount and remove the caliper...have set close to the rotor and turn the wheel and see if the distance varies. As if you were truing a wheel. Then at least you can rule out the caliper entirely. Then place the disc on a flat surface and ensure it's perfectly flat. Providing all the above is fine that can only leave the way you are tightening the disc, which personally I find unlikely as the bolts are so close to the centre are unlikely to cause and significant warping... or your hub is off and is not perfectly faced.

Process of elimination is the only way to go about this from the sounds of it.

 

[Loll]

I have bought many shimano disc the past few years. Flat upon delivery, used torque wrench and star pattern tightening. There is usually some minor rubbing. Usually I spend 15 minutes bending the rotor slightly to get it to not rub at the problematic areas.

Eventually I realized that it is me carelessly putting the wheel on or taking it off, that pushes the rotor sideway against the caliper area that captures it. With the tolerance being so tight for some disc brakes to work properly, that haphazard pulling and inserting was the culprit causing the minor rotor rub.

 

[bingemtbr]

Here what I used to do to resolve this with my early Hayes hydros back in 1998:

1. Removed wheel from frame, remove pads from calipers, and use a plastic tire lever to push the pistons in.
2. Reinstall pads, reinstall wheel, loosen caliper mounts (where it fastens to the frame/fork), and press brake levers to lock brakes up. If you're alone, use a rubber band to depress and hold the brake lever to the handlebar.
3. Insert 2 business cards (or credit cards) into caliper: one card on each side of the rotor. Each card should have a pad on one side and rotor on the other. Wiggle caliper to ensure centering.
4. Tighten caliper fasteners. Remove rubber band and check brakes in the stand before riding.

I still use something similar to this when anyone has issues like your describing. Fortunately, my personal, long-term solution is to run 4-piston XT hydros with IceTech rotors. I've been using this set up since 2014 and zero issues. If there's still a chirp, then the rotor's not true. If thats the case, take the bike your lbs or get the Park tool and DIY.

 

[J.B. Weld]

Why don't you tape/bolt a piece of plastic to the caliper mount and remove the caliper...have set close to the rotor and turn the wheel and see if the distance varies. As if you were truing a wheel. Then at least you can rule out the caliper entirely. Then place the disc on a flat surface and ensure it's perfectly flat. Providing all the above is fine that can only leave the way you are tightening the disc, which personally I find unlikely as the bolts are so close to the centre are unlikely to cause and significant warping... or your hub is off and is not perfectly faced.

Process of elimination is the only way to go about this from the sounds of it.

If the rotor is hitting the pad on both sides then the process of elimination is mostly done, the rotor is definitely untrue.

I find it easiest to true it on the bike and use the pads for indicators.

 

[Zeroselect]

I have had 2 sets of Magura Storm Rotors not a single one of them have been perfectly straight. All have had to be trued to make them stop rubbing especially on my Magura MT-7 Caliper (clearance is really tight).

 

[SteveF]

If the rotor is hitting the pad on both sides then the process of elimination is mostly done, the rotor is definitely untrue.

I find it easiest to true it on the bike and use the pads for indicators.

Pretty much what I did. I adjusted the caliper until rub was minimal, then "trued" the rotor with a crescent wrench, using the pads/rub as a guide. It's now rub free at least in the repair stand! I tried truing it with a crescent wrench a while back but I think I was too tentative with it, got it done this morning.

I have had 2 sets of Magura Storm Rotors not a single one of them have been perfectly straight. All have had to be trued to make them stop rubbing especially on my Magura MT-7 Caliper (clearance is really tight).

That's the same brake I have, you're right-tolerances are tight. I sure like the way these brakes work, tho. I was a Shimano guy for years until I bought an Otso Voytek that came with Magura MT-4s. Now that I think about it, they rubbed for quite a while when new too. I guess maybe Maguras are just more prone to it. Great brakes, though and the quality of the MT-4s encouraged me to go with Magura for my latest build. Also, Shimano was back-ordered pretty far out.

I'm curious, several folks recommended taking out my little aluminum shims. They seemed to work ok, is there a reason that rotor shimming isn't a good idea?

anyway, I appreciate the help, folks!

 

[Mountainfrog]

Pretty much what I did. I adjusted the caliper until rub was minimal, then "trued" the rotor with a crescent wrench, using the pads/rub as a guide. It's now rub free at least in the repair stand! I tried truing it with a crescent wrench a while back but I think I was too tentative with it, got it done this morning.



That's the same brake I have, you're right-tolerances are tight. I sure like the way these brakes work, tho. I was a Shimano guy for years until I bought an Otso Voytek that came with Magura MT-4s. Now that I think about it, they rubbed for quite a while when new too. I guess maybe Maguras are just more prone to it. Great brakes, though and the quality of the MT-4s encouraged me to go with Magura for my latest build. Also, Shimano was back-ordered pretty far out.

I'm curious, several folks recommended taking out my little aluminum shims. They seemed to work ok, is there a reason that rotor shimming isn't a good idea?

anyway, I appreciate the help, folks!

Shimming isn't necessary when the calipers are adjusted to the rotor, and rotor rubbing occurs at the calipers. Shimming doesn't hurt anything, just adds extra unnecessary hardware. I adjust the rotors by the webs, avoiding the open spaces.

 

[gocat]

I've had two brand new rotors on the back of my new bike, both rotors appear straight. But when installed they wobble enough to rub first on the outside pad, then the inside, so there's quite a wobble in the system somewhere. I shimmed under the rotor on the (six bolt) hub mount in a couple of spots and that helped a little but I wonder if the hub mount is slightly out of spec or if the caliper mount on the frame could need facing. I can't see how a caliper issue could cause the rotor to rub on both sides though? Is there a way to check the hub mount and face it if needed? Suggestions welcome.

Try installing those rotors up front. If they are true, then its in the rear hub, or you got gunk on the inner face.

 

[slomtbr]

Pretty much what I did. I adjusted the caliper until rub was minimal, then "trued" the rotor with a crescent wrench, using the pads/rub as a guide. It's now rub free at least in the repair stand! I tried truing it with a crescent wrench a while back but I think I was too tentative with it, got it done this morning.



That's the same brake I have, you're right-tolerances are tight. I sure like the way these brakes work, tho. I was a Shimano guy for years until I bought an Otso Voytek that came with Magura MT-4s. Now that I think about it, they rubbed for quite a while when new too. I guess maybe Maguras are just more prone to it. Great brakes, though and the quality of the MT-4s encouraged me to go with Magura for my latest build. Also, Shimano was back-ordered pretty far out.

I'm curious, several folks recommended taking out my little aluminum shims. They seemed to work ok, is there a reason that rotor shimming isn't a good idea?

anyway, I appreciate the help, folks!

Aligning a derailleur hanger can make up for a frame that's not perfectly aligned. It's the same with a brake rotor: think of it as aligning it rather than straightening it.