Disc brake rubbing frame

mbuckhurst

I've noticed my rear rotor is rubbing against the frame when under strain, and even when not there can be only 1-2mm clearance at the best of times.

What's the best way to deal with this problem? I've considered putting a washer between frame and hub, or perhaps swapping to a smaller rotor - but don't know the ins and outs of doing any of this.

Presumably the washer could compromise the security of the wheel clamps, but does changing the rotor mean I have to get some kind of adaptor? I think (off the top of my head) I've got Shimano XT rotors, probably 180mm.

thanks

mike

Chunkers1980

Don't washer it.

I'd go down to a 160 as that is plenty for most and yes you will the the correct adaptor.

Are the discs center lock?

There does appear to be something else up from what you say. Might be a very tight frame, something not quite tight enough so it flexes and or the frame flexing...

Pics would be good.

Paul 8v

Are you sure you haven't taken some paint off getting the wheel in and out, I've done that before..

mbuckhurst

Ok here goes, some images:



This is a close up of the rotor where it almost touches the frame, as you can see even mud particles are too large to fit in the gap, even the smallest amount of flex I think would be enough to cause rubbing.



The brake mechanism itself.

Unfortunately, the disk is 160mm so not even sure if it's possible to find a smaller rotor, but then I am a complete novice, the bike was an impulse buy.

So any advice gratefully appreciated, even if it's buy a lovely new bike

cheers

mike

nicklouse

the hub may be missing bits or have been incorrectly assembled/serviced.


or needs a service.

Andy!

crikey that is close!

A long shot but check a couple of things:

1. is there anything between the hub and the rotor spacing it towards the frame?

2. unbolt the caliper bracket and check the writing on it that is says R160 and not F180.

Front and rear adapters are not the same thickness. A rear 160 will allow you to fit a 180mm rotor on the front but the caliper will not be in the right place.

You can get 140mm discs and to fit one to the rear you need to use a front 160mm adapter with about a 1mm shim to move the caliper inwards a bit.

I learnt the width difference the hard way when Merlin used a rear 160 to fit my front 180mm brake and it was always catching no matter what I did.

nicklouse

Andy! wrote:

crikey that is close!

A long shot but check a couple of things:

1. is there anything between the hub and the rotor spacing it towards the frame?

2. unbolt the caliper bracket and check the writing on it that is says R160 and not F180.

Front and rear adapters are not the same thickness. A rear 160 will allow you to fit a 180mm rotor on the front but the caliper will not be in the right place.

You can get 140mm discs and to fit one to the rear you need to use a front 160mm adapter with about a 1mm shim to move the caliper inwards a bit.

I learnt the width difference the hard way when Merlin used a rear 160 to fit my front 180mm brake and it was always catching no matter what I did.

Sorry 2 is wrong.

a rear 160 is the same as a front 180. ( but not the same as a 183 or a 185 front.

the difference in the standard is 10mm (on the radius).

have a read of the info in the FAQs.

Andy!

nicklouse wrote:

Andy! wrote:

crikey that is close!

A long shot but check a couple of things:

1. is there anything between the hub and the rotor spacing it towards the frame?

2. unbolt the caliper bracket and check the writing on it that is says R160 and not F180.

Front and rear adapters are not the same thickness. A rear 160 will allow you to fit a 180mm rotor on the front but the caliper will not be in the right place.

You can get 140mm discs and to fit one to the rear you need to use a front 160mm adapter with about a 1mm shim to move the caliper inwards a bit.

I learnt the width difference the hard way when Merlin used a rear 160 to fit my front 180mm brake and it was always catching no matter what I did.

Sorry 2 is wrong.

a rear 160 is the same as a front 180. ( but not the same as a 183 or a 185 front.

the difference in the standard is 10mm (on the radius).

have a read of the info in the FAQs.

got both sitting here and one is marginally thicker. FAQ must be wrong when it comes to genuine shimano ones.

nicklouse

what do you mean by thicker?

yes the ones of 20mm forks (Marz. and some others) are thicker but the are the same height.

like i said the standard gives the info. yes some makers rotate the caliper a bit but the distance is the same.

eg.


and

Andy!

I just went and got my calipers.

Genuine shimano R160: 11mm thick.

Genuine shimano F180: 10mm thick.

I can get you a picture tomorrow if you don't believe me. This is how I know to fit a 140mm disc on the rear you need to use a 160mm front mount with some 1mm shims to shift the caliper in a bit.

I did notice a bracket just like those one you posted earlier today and thought it was odd because of the difference between the front and rear shimano ones.

By thickness I mean in the dimension measuring the face with that writing on.

Andy!

those measurements are not exact btw as the digital calipers are in the office and I had to use some old rusty ones.

One other observation was the metal between the IS mouting bolts on the F180 is thinner in profile (not the thickness dimension) than the R160 adapter across the same section.

They are VERY different adapters.

My LX calipers have oval holes but even with this there was not enough adjustment to clear the rotor properly with the R160 mounted on the front.

PS it is this profile thickness in the picture which leads me to believe that there is an F180 adapter on the rear of the OPs bike.

EDIT: also look at this superstar picture, there is a different mount for the F180mm and R160mm:

nicklouse

OK lets put it this way.

why does a Hope No3 caliper fit on either the front or a rear IS mount and the difference is the rear rotor is 20mm less in diameter? beacause of what i have already said.

have a read.

and have a look at the PDF files at the bottom.

http://www.bikeradar.com/forum/viewtopic.php?t=1590919

thanks.

Andy!

I know all about the IS designs - I have designed brake mounts in the past for retrofitting to discless frames so I have studied the geometry well.

I am telling you that shimano front 180 and rear 160 adapters are not the same thick. I have them here in front of me on my bike :roll:

The more I look at the pictures above the more it looks like a front 180mm mount on the rear. The section between the IS bolts is the thinner one and the bracket itself looks thinner - thus moving the caliper away from the wheel.

Andy!

Just noticed you did the FAQ, guess you need to add a bit about shimano as there is probably a lot of people who don't know about the difference. Merlin didn't or they picked up the wrong one which is easy to do.

A picture says a thousand words so...

here is the proper rear 160mm: http://www.chainreactioncycles.com/Mode ... elID=13749

Note it is quite chunky where the writing is.

Here is the front 180mm: http://www.chainreactioncycles.com/Mode ... elID=17390

the writing is in a different place because the design is different but the dimension I am referring to as causing the problem is the one across the face where you bolt the caliper to. The rear is ever so slightly thicker and I don't think the bolt holes are not central unlike the thinner front ones. The holes are slightly towards the wheel so the instead of just being about 0.5mm out (half of the overall thickness increase) the total misalignment is actually about 1mm. I bet the OP is having problems with the rotor binding unless it has been spaced out at the hub.

Anonymous

ignoring your mounting argument for a minute (see what I did there?), how the hell does tht have any effect on the disc rubbing the frame?
It's the DISC that is touching, moving the calliper won't solve that.

F@RRR

yeehaamcgee wrote:

how the hell does tht have any effect on the disc rubbing the frame?
It's the DISC that is touching, moving the calliper won't solve that.

thats what i was thinking :?

Andy!

yeehaamcgee wrote:

ignoring your mounting argument for a minute (see what I did there?), how the hell does tht have any effect on the disc rubbing the frame?
It's the DISC that is touching, moving the calliper won't solve that.

because if the person who fitted it then spaced the disc out because it was rubbing it could touch the frame (as point 1 above).

Or

if the caliper is too far out and the disc is binding then it could be distorting the disc so is actually pointing towards the seat stay and not parallel with the wheel.

Something has to be off alignment. The frame designer should have put the lugs in the right place so for the disc to be so far over it touches the frame the caliper must also be in the wrong place.

It was a suggestion for the OP to check out, it didn't need a whole essay on IS mounting but unfortunately it ended up being so because Nick refused point blank it was possible for R160 to not be the same as F180.

OP - where are you? Have you taken that caliper off yet?

Oh and putting a washer between the hub and frame wont help as the caliper will still be in the same place. If you have 180 discs on the front then also check that is the right adapter and the builder didn't mix them up.

Andy!

Only other reasons I can think if the wheel is properly located in the drop outs and the hub is fine is that the frame is bent - which I hope for the OPs sake is not the case.

mbuckhurst

Thanks for all the replies so far, I didn't imagine how complicated this would all get, so my understanding of the fix is either

1) Check the wheel and make sure the rotor is mounted correctly - this is as it was from the manufacturer but I guess could be wrong. Presumably if the rotor is incorrectly mounted, mounting correctly would then necessitate a new adaptor, hence the questions about whether the existing is front or rear?

2) Fit a new adaptor and a 140mm rotor, presumably the rotor would need to be from a different manufacturer to Shimano?

I'll check what's fitted tonight hopefully and report back.

thanks

mike

F@RRR

ah yes i see now Andy .

Mike 1st thing Andy is suggesting is to remove the brake caliper from the frame as its possibly distorting the disc and forcing it toward the frame

Andy!

Hi Mike,

sorry for taking it a bit off topic there.

Best case situation really is that it is the wrong adapter on there. Everything else is a lot more serious.

A shimano F180 adapter should have writing visible on that picture you posted but that could be missing if it is an OEM part.

things i would do:

1. double check the wheel has no play in the hub.

2. check the tyre is evenly spaced between the seat stays (would give an indication of a frame bend provided the wheel is fine).

3. Get the caliper off and see if the disc moves away from the frame and check for markings on the adapter.

4. get the disc off and lay it flat and check for distortion and spacers between it and the hub. There should be some springy metal plates on the outside of the disc between the bolt heads and the disc but they should not be thick enough to cause this problem if put in the wrong place.

Andy!

F@RRR wrote:

ah yes i see now Andy .

Mike 1st thing Andy is suggesting is to remove the brake caliper from the frame as its possibly distorting the disc and forcing it toward the frame

I thought I was going mad there for a minute. thank God someone sees it too.

I could be wrong of course, it was a suggestion to check.

It is amazing how much discs can distort if the caliper is not int he right place or working right. My old Hayes Sole with single piston used to bend the discs quite a lot when applied.

Ps back to Mike, if it is the wrong adapter about 1mm of spacing could correct it but i would replace the adapter as it would be more stable. Check your front is not wrong too but if the front is fine and you need a rear 160 I have one here that Merlin fitted to the front of my bike and I was just about to buy another 180 front for the other bike.

Andy!

Just looked at my set of Deore brakes (was looking at my LX ones last night) and can confirm that the OEM caliper adapters don't have any writing on them. The ones you buy separate will be labeled up.

Mike, I have put the camera on charge so I can get a picture up to show you what I mean as the only way you have to check is going to be the shape of the bridge in between the 2 sets of mounting holes, the thickness and id the caliper holes are slightly off centre as they should be on the rear one.

With digital calipers:

Front: 9.8mm, hole central

Rear: 10.8mm, hole about 5.8mm from side against the frame lug.

mbuckhurst

Thanks again for all the help.

Looks like the wife will have to wait for me to fit the new shower I'll have to do this work at the weekend.

Presumably if I'm carefull there's nothing wrong with riding in this condition? So far the paint has rubbed of the frame a bit, but I don't think it's digging into to the metal.

cheers

mike

Andy!

tbh I wouldnt like it rubbing or being that close. the disc is steel and the frame aluminium and if it rubs it will wear the frame and generate heat - a nick in the frame and localised heat = bad for aluminium especially. It looks like you have a nice light XC frame there with carbon seat stays.

The Deore calipers will have oval holes to allow you to move the caliper so try backing off the bolts between the caliper and the adapter and see if you can move it over a bit. you should get someone to hold the brake on while you bolt it up to it is aligned right but you can just use a cable tie on the lever.

also double check that the disc does not touch the frame when you apply the brake as it may miss when the brake is off but touch when on.

shm_uk

+1 to most of the above


A 160mm disc is average size and should not be contactng the frame under any normal riding conditions.


Get it checked out by your LBS, and don't accept "it's meant to be like that" or " your rotor's too big" for an answer.


I would not ride the bike any more until you've solved the problem as it's not worth causing (potentially significant) damage to your frame for the sake of a few hours of trail time.

mbuckhurst

Update:

Looking at the wheel, rotor and adaptors. All seem consistent and correct with a 160mm rotor, so I'm guessing the frame isn't suitable for whatever reason, for this size rotor.

Am I correct in assuming if I buy and Avid Clean sweep G3 and 140mm rear adaptor, this would work with my Shimano setup?

thanks

mike

Anonymous

I didn't even know they made discs smaller than 160mm :shock:

Kiblams

yeehaamcgee wrote:

I didn't even know they made discs smaller than 160mm :shock:

Aye, the rear on the wifes bike is a 140 rotor, looks quite strange TBH. I have thought about swapping so I have it as I find it far too easy to lock the back wheel with my 160 rotor.

Anonymous

Of course it's easy to lock the back wheel when braking. When decellerating, all your weight is transferred to the front of the bike, unweighting the rear, causing it to break traction.

nicklouse

mbuckhurst
so have you checked the disc mounting face to dropout distace?to check that the hub is correctly set?

it should be 15mm.

Drawings and further info in the FAQs.