How to unseize a disc caliper piston?

[Falco Frank]

Pretty sure the inner piston, rear caliper on my bike is near seized, quite used to this on motorbikes but those calipers can be split or the piston rotated to free it up. All I can see on my Magura Julie piston are some fashioned type indentations and nothing to latch hold of.

Ive tried gently squeezing the brake lever and the other piston moves and can be pushed back again but no movement from the problem side.

Ideas very welcome!

 

[Profpointy]

with car or motorbike ones I used to wedge the free one eg a g-cramp or mole grip, or couple of nuts and bolts and steel bar, then press the pedal / handle to free the stuck one. Once free, you can clean it up in the usual way. Problem is if the free one pops out, then it's a bit harder

 

[Cubist]

I'd be tempted to try soaking the stuck piston with Isopropyl alcohol and even using a sharp pick to pry out any visible gunk from round the edges. Then as above, if you can find a way to stop the free-moving piston from moving, apply pressure through the lever to try and move the stuck one. The calipers are a one-piece design, so the only way to fit a new seal (if you can get hold of one...) is to pop out the piston altogether and then push it back in once you've cleaned it up. The various tech docs don't list pistons or seals as available spares, but Magura have a support forum, where you might find a bodge or a workable solution.
http://www.support-english.magura.com/index.php?

 

[User33236]

[QUOTE 3747523, member: 9609"]never worked on bicycle disc brakes - but do they really have dual piston callipers ?[/QUOTE]
Hydraulic brakes certainly do as do a small number of mechanical models. E.g TPR Spyre.

When the non-adjustable side of my BB7s got stuck I sprayed with brake cleaner and left for a bit. May be worth a go on your piston.

 

[Milkfloat]

Pads out, then Isopropyl to try and clean it a bit and then very carefully wrap some cloth around a flat head screwdriver and lever the piston back in. Keep cleaning with isopropyl and fingers crossed. I used to have to do this regularly with Avid Elixr's, in the end I got fed up and bought Shimano.

 

[Yellow Saddle]

Pads out, then Isopropyl to try and clean it a bit and then very carefully wrap some cloth around a flat head screwdriver and lever the piston back in. Keep cleaning with isopropyl and fingers crossed. I used to have to do this regularly with Avid Elixr's, in the end I got fed up and bought Shimano.

Shimano is the only known cure for Elixir's. What utter rubbish.

 

[Milkfloat]

Shimano is the only known cure for Elixir's. What utter rubbish.

Wow - where did that come from, did you get out of bed the wrong side? I did not state that Shimano is the only known cure at all. In fact it is pretty obvious that I stated I got fed up maintaining the Elixir's, not that they could not be maintained. I am sure I could have continued soldiering on with the Elixir's, but I have better things to do with my time then repair them repeatedly and have them lock up which on a ride. Even the LBS had a go. Do a quick google search and you will see how common the Elixir problem is.

 

[Yellow Saddle]

Wow - where did that come from, did you get out of bed the wrong side? I did not state that Shimano is the only known cure at all. In fact it is pretty obvious that I stated I got fed up maintaining the Elixir's, not that they could not be maintained. I am sure I could have continued soldiering on with the Elixir's, but I have better things to do with my time then repair them repeatedly and have them lock up which on a ride. Even the LBS had a go. Do a quick google search and you will see how common the Elixir problem is.

Ahem.....I mean Elixir is utter rubbish. Shimano is the only known cure. Syntax is everything in a world where body language is not available to either party.

Edit: FYI, I am the honorary chairman emeritus of the Hate Elixirs Society.

 

[Cubist]

Wow - where did that come from, did you get out of bed the wrong side? I did not state that Shimano is the only known cure at all. In fact it is pretty obvious that I stated I got fed up maintaining the Elixir's, not that they could not be maintained. I am sure I could have continued soldiering on with the Elixir's, but I have better things to do with my time then repair them repeatedly and have them lock up which on a ride. Even the LBS had a go. Do a quick google search and you will see how common the Elixir problem is.

No, he meant that the only way to cure the utter shite that are Elixirs is to replace them with Shimanos.

Edit... crossed in the post.

 

[Yellow Saddle]

[QUOTE 3747523, member: 9609"]never worked on bicycle disc brakes - but do they really have dual piston callipers ?[/QUOTE]
Some even have four pistons but two is the norm.

 

[Milkfloat]

Ahem.....I mean Elixir is utter rubbish. Shimano is the only known cure. Syntax is everything in a world where body language is not available to either party.

Edit: FYI, I am the honorary chairman emeritus of the Hate Elixirs Society.

Ha - you are right about syntax being everything. Can I be vice chairman? - I must have tried to fix those buggers 10-20 times within a couple of years.

 

[Yellow Saddle]

[QUOTE 3747879, member: 9609"]so are they essentially the same as callipers on a car with the pistons on the same side ?

< a very long way off topic> replaced some discs on a Scania tractor a little while ago, the disc were something like 18" in diameter and weighed about 5 stone each takes two people to lift it onto the axle..[/QUOTE]
The better ones have pistons either side of the disc, older, mechanical ones had one piston only and relied on flex in the disc to make the disc touch both pads.
Four pot calipers are for downhill bikes with long pads that cover more of the disc's surface.

 

[Yellow Saddle]

[QUOTE 3747958, member: 9609"]so the calliper itself does not slide ?[/QUOTE]
No

 

[Yellow Saddle]

[QUOTE 3747988, member: 9609"]you're in ambiguous mood today - No to my question or No it doesn't slide[/QUOTE]
No, the caliper does not slide. It is static. The single piston from one side contacts the disc and flexes it over to the waiting static pad on the other side. The static pad does have some adjustment by way of a dummy piston that sits behind it and can be adjusted with a screw mechanism so that it sits closer or further away from the disc.

 

[Falco Frank]

Some light reading for you:

http://www.epicbleedsolutions.com/blog/how-hydraulic-brakes-work/