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swen

Joined:

Aug 08

Posts: 21

swen says:

Sticking brakes...

Hi all. I need your help: when I move my bike in a morning - front brakes(Nissin 4 pots) pops(Suzuki TL1000S).There are pad marks on a disks(abe-aftermarket).First I serviced brakes(new seals,cleaned,pads are Goldfren-plenty of meat left)-same.Next master cylinder repair kit-same.Bled the brakes,fluid level- fine. Now run out of ideas. Could the aftermarket disk are cheap metal or maybe pads are crap somehow?... Cheers

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  • Posted 2 years ago (21 March 2013 19:44)

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swen

Joined:

Aug 08

Posts: 21

swen says:

-

Hi all, thanks for your advice.Lots of replys :) I've been told that spring in a master cylinder pushes oil back not a vacuum. And i also feel its not the vacuum what causes sticking. It's not a big deal-just my other bikes never used to do.The rest of the times brakes are not sticking or binding. Also its sticks even it wasn't raining. Maybe salt.I probably need to read a bit about iron vs stainless... And yeah i heard Goldfren are shit but they came in with the bike. Will see, better weather soon, when its time -will replace with other brand pads. Thanks again

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Arthurshandy

Joined:

Mar 13

Posts: 26

Arthurshandy says:

To push or pull?

Hi again.


Yes there is a return spring in the mater cylinder, but to say that it pushes oil back is not entirely accurate, as far as I can see. 

There is a very good diagram on page 158 of Kevin Cameron's Sportbike Performance Handbook 2nd ed as well as his description of what actually happens. I can recommend this book as a tenner well spent, if you want to brush up on all aspects of a motorcycle.

There will be a combination of factors, some of them tiny, which ultimately contribute to the system returning to "original state", but the main factor seems to be the springiness of the caliper piston seal. This is what seems to push the oil back. The spring in the master cylinder , in my eyes, assists by returning the master cylinder piston, thereby opening up the tiny hole into the reservoir above.

If a brake pad decides to stick itself to the disc, there is nothing in the hydraulic part of the system to get it off. 

Cheers.

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oscarthegrouch

Joined:

Oct 05

Posts: 3133

If the diaphram's

Only Job was to pull the pads back you would find when bleeding your brakes that your brakes would be binding ...... make sure someone hasn't modified the pawl that pushes on the mastercylinder hasn't been packed out or modified to improve lever feel..... i have seen this before .....very dangerous  also on the opposite side some cheap pattern levers can be the wrong profile causing poor lever feel

my bet if the bike moves ok once initially shifted try some different pads abe will probs reccomend a certain compound pad ....

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KrismusSikpunz

Joined:

Mar 12

Posts: 1286

Hi Swen, you said you serviced......

The brakes, replacing seals.


This might be obvious but you sure you fitted them correct way round?

They are usually tapered on the outside edge.

Worth a check in your manual.


Edit: Oh yes, and I agree with eatcs01, those Goldfren pads are for the bin.

[This Reply has been modified by the Author]

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Arthurshandy

Joined:

Mar 13

Posts: 26

Arthurshandy says:

Tapered seals

Hi


The master cylinder seals have a pronounced taper on them, but if they were fitted the wrong way around nothing would happen. No oil (or certainly very little) would be pumped. The "cup" would fold in on itself. The lever would return very very slowly as the piston would be trying to pump on the return stroke and push the oil through the tiny hole. 

Besides, if both master cylinder cup seals were fitted wrong way around, oil would leak out the end  and quite copiously when the lever is pulled. 

Regarding the caliper piston seals, I'm not sure if they are all tapered? If there is a taper, then yes, you would have return problems, but I suspect you'd have severe oil leak problems too.

I'm pretty sure you'd know in both cases. 

Going back to the second post and the vacuum scenario. If there are still any doubters then consider that the diaphragm is more like a bellows. It is made to extend itself freely. It is unable to provide any mechanical support. 

Cheers.

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oscarthegrouch

Joined:

Oct 05

Posts: 3133

tapered caliper seals

Nah

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Arthurshandy

Joined:

Mar 13

Posts: 26

Arthurshandy says:

Caliper piston seals

Hi


Are some caliper piston seals wedged (tapered) on the outer diameter? Fitting the wrong way around in that case would lead to problems with sticking perhaps?

It might tend to squeeze the seal a bit tighter? Dunno.

The seals are meant to deform without necessarily sliding so is this wedge shape done for that reason or some other reason? Seems that this deforming characteristic is the main factor which will return the piston after lever pressure is released. As the seals straighten back again.


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oscarthegrouch

Joined:

Oct 05

Posts: 3133

dont

listen to bad advice by crusty poo pants he ain't got a clue

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Arthurshandy

Joined:

Mar 13

Posts: 26

Arthurshandy says:

Crusty poo coo coo cah choo

Maybe, maybe not. But are the seals wedged shape or not? That is the question.


Cheers.  :)

[This Reply has been modified by the Author]

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kcmc

Joined:

Jan 08

Posts: 7389

kcmc says:

LAR LAR Land

come on now lads get a grip caliper seals are not wedge shaped:wacko: and master cylinder rubber diaphragms don't pull caliper pistons back:wacko:and the moon isn't a balloon:lol:.

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