Brake Problems

[Flog]

I need to replace my pads on Shimano BR-MT520 fronts and the two pots on the left were stuck out a long way - the left pad completely worn out. Went to ease them back in and top one popped out??
Told I need a service kit but cant see anywhere for that model??
What is the fix and where to buy.

 

[Flog]

Sorry, was dashing for the door when I wrote and posted. So yes, the ceramic pad at the top popped out, oil everywhere. Do I just need something like this:
And a case of separating the cover, re-setting the new callipers and seals and then re-oiling / bleeding etc...

I just can not find anywhere if the callipers are brake specific, none mention MT520's. Of course all advice gratefully taken. Thank you.

 

[RickBullotta]

Factoring in time and effort, as well as risk that they still won't work well after the rebuild, you might be better off just getting a new caliper. About $90 USD.

 

[MrPeaski]

If the pistons aren't cracked you should be able to carefully ease them back in, but first you'll need to clean the dirt off them first.

Dip a cotton bud in Shimano mineral oil and carefully wipe the dirt off the pistons. This will also lubricate them.
Both look like they are not parallel to the bore, so when pushing in you'll need to keep them straight.

Try using a good plastic tyre lever or a piece of wood to ease them back in. Open the bleed screw on the brake lever as well.

Once you have them back in, you'll need to do a re-bleed but you'll also have to cure the two stuck pistons in the other caliper half

 

[Stihldog]

There’s a brake block from r3pro that helps free up stuck calipers. I just ordered one for my Shimano brakes. It allows you to extend and clean each piston individually. Calvin from Park Tools uses a cotton string as a floss to clean each piston. I’ve had this problem a number of times with dirt and grime. Looks like it should work. I don’t know about pushing the piston back in though.

 

[Mikerb]

this may help if you fancy some DIY. The calipers are a pretty simple design .

(85) Easy Way To Remove Pistons From Hydraulic Brake Caliper On Bicycle. - YouTube

 

[Flog]

Thanks guys - cant believe these 'could' be described as a throwaway item? I think I'll have a go at taking everything apart and keep the "buy a new one" in the back pocket incase I need it!! Of course, finding a MT520 in stock is quite another thing!

 

[Zimmerframe]

I going to do it .... don't blame me ...

@Gary ?

 

[Gary]

There is no service kit.
if your piston is not damaged it can be reseated in the bore.
if you are struggling to do it on the bike. Remove the whole caliper. (You're going to have to re-fill and bleed the system anyway.

If you can't re-fit the piston. Your only option is to buy a new caliper. It doesn't have to be an MT520 caliper.

I only skim read the thread. Apologies if I've missed something important

 

[Flog]

@Gary - thanks. I'll have a go at some DIY and then if that goes wrong will try a new one. What would you suggest if not the 520 - I'm not a downhiller, just a weekender - don't want to complete change everything - would like to keep the mount and lever if poss without spending the months house keeping on this.
Thank you.

 

[Gary]

what I meant was if you genuinely can't get hold of an MT520 caliper there are plenty other Shimano mtb calipers which could be used.

 

[MrPeaski]

Use this to help with unsticking and balancing the pistons.
It was written for old school saint brakes but will work (with the correct fluid) for any 4 pot brake

 

[RickBullotta]

Use this to help with unsticking and balancing the pistons.
It was written for old school saint brakes but will work (with the correct fluid) for any 4 pot brake

It does assume that the seal(s) are still good, which may or may not be the case.

 

[Crazee horse]

I've got the same callipers, I cleaned mine with miner oil and then importantly cleaned that off! Don't want any lube anywhere near those pads.

 

[Flog]

@Crazee horse which cleaner did you use?

 

[Mikerb]

you can use IPA or brake cleaner.

 

[Stihldog]

I got ISO alcohol and Brake cleaner.
Which is better?

 

[Mikerb]

Take a look at the can...the brake cleaner is probably IPA!! ( Isopropyl Alcohol).

Either will do. Put a rag under the calliper through the mount...you dont want either on your paintwork.

 

[RickBullotta]

I find that automotive brake cleaner leaves a residue on bike parts.

 

[E-Bandit]

I had the same problem with the 4 piston SLX. M7120, piston was cracked on the inside and wouldn’t go all the way back in, had to order a whole new caliber, although I have now seen u can buy after market pistons for Shimano brakes,

I will be doing a warranty with Shimano as they have two year warranty.

 

[Flog]

**UPDATE**
Took everything apart and cleaned all items. Popped the pistons back in and the seemed ok. Did a full brake bleed with. Spun the wheel and perfect stop. spun the wheel again and the screech of death... pads still 'on'. Looks like the pistons are not retracting? Pushed them back in and tried again, the same - first stop excellent but then no return?
Have I missed something? Or will there be an air hole/crack somewhere? Do I need to buy new?

 

[RickBullotta]

**UPDATE**
Took everything apart and cleaned all items. Popped the pistons back in and the seemed ok. Did a full brake bleed with. Spun the wheel and perfect stop. spun the wheel again and the screech of death... pads still 'on'. Looks like the pistons are not retracting? Pushed them back in and tried again, the same - first stop excellent but then no return?
Have I missed something? Or will there be an air hole/crack somewhere? Do I need to buy new?

Either you can attempt more trial and error repairs, with likely the same outcome, or new caliper time.