Binding brakes - Front caliper pots not going back in easily

[Buzz]

Morning,


In the past couple of weeks I've noticed that my brake lever is getting further out as I ride and the disks are really heating up, so much so that the last time I got home I could feel a real rolling resistance.  I just went out to clean the pots but found it a real struggle to push all 4 back into the caliper...I've cleaned them many times before and could always do it with 2 hands on the 4 pots, but today it took 30 mins of struggling with clamps and screwdrivers before I could get enough space for the pads and disk.  The movement of each pot is very smooth.  I didn't even bother with the other caliper.


To make matters worse I've pretty much rounded off one of the master cylinder screws...not a good start to the weekend!


Any advice as to what the brake issue could be, it's like the fluid returning to the MC is being blocked by something? New master cylinder/rebuild?  I've got standard lines and the brakes haven't been bled for about 2 years, I've never had a problem until now!


Cheers...Dan

[limax2]

I agree it sounds like the fluid is being prevented from returning to the master cylinder. If the fluid is not returning the brakes will bind more and more as it all heats up. Unlikely all four pistons would be sticking but to be sure you could see if it is easier when you push one piston without restricting the others from moving out, that way you'll know it is definitively the fluid not returning.  Or you could release the bleed nipple a bit while at the same time pushing a piston for the same effect. Having confirmed it is the fluid holding them back you could try bleeding the whole system and the fresh fluid might clear any obstruction. Also make sure there is nothing stopping the brake lever from returning to the fully off position. i.e. something jammed behind the pivot. Failing that it is master cylinder dismantling time.
The screws for the master cylinder cap are countersunk and it is not difficult to drill the head off without damaging the cap. Then with the cap removed there is a bit left to grip and the rest of the screw usually comes out easily as there is no longer any tension on it. You then need a 4mm countersunk headed screw 10 or 12 mm long.

[Buzz]

Deffo not the pots, if I push 3 to push one out then I can slide that one back in easily..repeated for all 4.  Good point about the lever, I'll check but I've not noticed any change in position.


I've got a new set of braided lines to put on so will see if there's any difference when it's all installed and bled (when I get that MC screw out  [size=78%])[/size]

[Megawatt]

If you're going to replace the brake lines, pump all the pistons out first, check the seals and rebuild using red rubber grease. Then you can discount the caliper end when you rebuild. A master cylinder rebuild kit is about £30.

[Bretty]

I rounded one of my master cylinder screws. Easily done when they are rusted in, brake fluid is incredibly corrosive.

I bought some reverse thread drill bits from b&q for a fiver and got it out pretty easy.

Can you get a service/seal kit for the master cylinder? That might be worth considering.

I would suggest changing the seals in the caliper but you say they are all moving freely.
Else it might just be worth bleeding especially If they have been binding and overheating.

[darrsi]

I rounded one of my master cylinder screws. Easily done when they are rusted in, brake fluid is incredibly corrosive.

I bought some reverse thread drill bits from b&q for a fiver and got it out pretty easy.

Can you get a service/seal kit for the master cylinder? That might be worth considering.

I would suggest changing the seals in the caliper but you say they are all moving freely.
Else it might just be worth bleeding especially If they have been binding and overheating.

You can buy a master cylinder kit.
The screws are made of Fazer cheese, don't feel singled out, just replace them all.

[His Dudeness]

Did you top up the brake fluid recently or put new pads in? It might be something as simple as there's too much brake fluid in the system. Which is preventing the pistons from retracting.

[Buzz]

Did you top up the brake fluid recently or put new pads in?

Not topped up the level for a couple of years and I might have switched the orientation of the pads in each caliper but they're deffo not new - as I said I used to be able to push all 4 back to the caliper with ease a few months ago.  I've drilled the old screw out and ordered a couple of SS replacements.  I'll investigate the return port of the MC when I get another spare second, probably after work on Mon/Tues.

Cheers for the help!

[darrsi]

You mustn't forget that some of the rain we get is nothing short of toxic, which is why sometimes i'll go out to my bike at work after a downpour and it'll be covered in a dusty residue.
This will also find its way to the calipers so unless you plaster the red rubber grease on the outer pistons like i do there is that chance it can gradually create a bit of friction.
Changing the standard brake lines is a huge plus anyway so i'd start by sorting them out first.

[Bretty]

I might have been dreaming this (last week was a long one)...  but I seem to remember, if you took the reservoir cap off you could see the lever actuating the piston and the hole where the fluid went into the line/cylinder and where it would flood back into the reservoir when you pushed the pots in.

Don't forget, as someone has probably already said. If the reservoir is filled with fluid and the cap is on, fluid won't easily flow back into. Try taking the cap off... and watch it overflow when you push the fluid back.

I still don't understand why the put the reservoir and bleed nipples directly about the pads and discs, so if your a clumsy Muppet (like me) you can p* brake fluid all over your pads and discs at every opportunity. :-)

[Bimbam]

Any recomendation on new brake lines?
Many types on EBay

[darrsi]

Any recomendation on new brake lines?
Many types on EBay

Had Venhill on mine for years now without any issues, but i think any brand of new braided lines will be an improvement over OEM anyway.

[Buzz]

Any recomendation on new brake lines?

I'm assuming that the HEL 25% discount is still active, seemed to be in Oct '15?  http://foc-u.co.uk/index.php?topic=8879.0

[Bimbam]

I can buy Hel at the local mc pusher. 

[limax2]

In the past couple of weeks I've noticed that my brake lever is getting further out as I ride and the disks are really heating up, so much so that the last time I got home I could feel a real rolling resistance.  I just went out to clean the pots but found it a real struggle to push all 4 back into the caliper...

Having just had another read of the above and another think it still sound very much to me that the piston in the master cylinder is not returning fully.
Here is my reasoning. When you release the brake lever the master cylinder piston is helped to return by the spring behind it, and faster than the caliper pistons are pushing the fluid back. To prevent a vacuum forming, which could draw in a very small amount of air at the caliper seals, fluid can flow past the master cylinder piston seal as it is retracting. When the seal clears the little hole in the reservoir the fluid can return and everything is at zero pressure.  All that is how it is designed to work. However if the piston does not come back far enough to uncover the little hole in the reservoir, the fluid that flowed past the seal each time you release the lever is trapped. This would gradually increase the pressure in the system and give the symptoms you describe.
I hope you could make sense of my theory but why the piston would suddenly stop coming all the way back I don't know.

[bootz76]

Drill the master cylinder cover screws out use a 5mm drill bit. They are m4 x10mm just drill the head off the rest undoes by hand a common prob on All bikes.

[Paul]

I had a problem with my front disc brakes binding, it was around 10 or 12 years ago.
But from memory it was the seals in the calipers that needed changing.


The seals act as springs to return the piston slightly and stop it rubbing on the disc.
In any event I changed the seals and the brake fluid and I've not had a problem since.


From memory I reckon what caused it was either:
1) Caning it backwards and forwards over the Hard Knot and Wrynose pass... and over-heating the brakes.
or
2) Bleeding the brakes with the wrong brake fluid.


Never found out which though.

[Buzz]

Well that's 10 points to limax2, the lever wasn't returning fully..probably about 1/2 cm to go but enough to stop the fluid returning.


After I got back from the Alps I refitted my hand guards but omitted a couple of spacers, this narrowed the gap in the guard just enough to rub against the lever adjuster and prevent it from returning.  I've put the spacers back in and can now feel the lever click at the end of its travel, all four pots can now be pushed back in each caliper.


However the pads are still binding slightly, left disk is a lot hotter than the right so I probably still need to strip them.


Am I OK to re-use the same seals if they look fine?  A full set seems a bit steep to me, yes I know it's my life at stake and it's not really that much cash etc. etc. but is this really bad practice?