Shimano brakes piston leak

[teK--]

I have recurring issue with M785 XT brakes and one pad on rear brake causing black streaks on the rotor and squealing/shit braking. Clean, and it's Ok for a ride then returns to same issue. Replaced pads and it is OK for a couple of rides but then returns. have trashed 2 sets of pads.

I presume one piston is leaking at the seal but only just barely as it's not visible. (1.5 years old so out of warranty)

Has anyone tried bumping the piston out entirely, cleaning the piston and seal then popping it back in. Is this successful or am I wasting my time and the seal is already trashed from dirt etc?

Preferably I don't buy myself only a couple of rides and it fails totally mid ride.

Alternatively whole new caliper is $53. But they don't come with new o-rings to fit onto the banjo hose bolt. Can I re-use existing or does anyone know their size so I can buy generic replacements?

Cheers.

 

[ChopSticks]

I have recurring issue with M785 XT brakes and one pad on rear brake causing black streaks on the rotor and squealing/shit braking. Clean, and it's Ok for a ride then returns to same issue. Replaced pads and it is OK for a couple of rides but then returns. have trashed 2 sets of pads.

I presume one piston is leaking at the seal but only just barely as it's not visible. (1.5 years old so out of warranty)

Has anyone tried bumping the piston out entirely, cleaning the piston and seal then popping it back in. Is this successful or am I wasting my time and the seal is already trashed from dirt etc?

Preferably I don't buy myself only a couple of rides and it fails totally mid ride.

Alternatively whole new caliper is $53. But they don't come with new o-rings to fit onto the banjo hose bolt. Can I re-use existing or does anyone know their size so I can buy generic replacements?

Cheers.

Push them out and see if you can save them..... You have nothing to lose
The cost of new pads can just be put towards a calliper (which comes with nonfinned ones?)

The o rings you can reuse
unless they are snapped.... Then I'm sure you can get a generic packet of o rings from bunnings..... But I'm sure there's plenty of trashed callipers floating around here that rb'ers can donate you an o ring or two

 

[pharmaboy]

I have recurring issue with M785 XT brakes and one pad on rear brake causing black streaks on the rotor and squealing/shit braking. Clean, and it's Ok for a ride then returns to same issue. Replaced pads and it is OK for a couple of rides but then returns. have trashed 2 sets of pads.

I presume one piston is leaking at the seal but only just barely as it's not visible. (1.5 years old so out of warranty)

Has anyone tried bumping the piston out entirely, cleaning the piston and seal then popping it back in. Is this successful or am I wasting my time and the seal is already trashed from dirt etc?

Preferably I don't buy myself only a couple of rides and it fails totally mid ride.

Alternatively whole new caliper is $53. But they don't come with new o-rings to fit onto the banjo hose bolt. Can I re-use existing or does anyone know their size so I can buy generic replacements?

Cheers.

Just went through this problem, and as far as I could figure out, it was not a fixable situation - they probably aren't in square and that's the cause.

I ordered an SLX caliper from ebay for $39 delivered - Aussie seller. Came with set of fo1 pads as well ( which are worth $25 as it is). Fitted easily, just remove banjo from old one and fit to new - had the little o ring.

The slx and xt caliper seem identical apart from the pad split pin on the xt, so you can transfer the little Allen bolt across and voila, you have xt brakes!

 

[teK--]

Push them out and see if you can save them..... You have nothing to lose
The cost of new pads can just be put towards a calliper (which comes with nonfinned ones?)

The o rings you can reuse
unless they are snapped.... Then I'm sure you can get a generic packet of o rings from bunnings..... But I'm sure there's plenty of trashed callipers floating around here that rb'ers can donate you an o ring or two

Thanks Chops did you re-use your O-rings when you fit your Saint calipers to XTR levers? Or did you disconnect the hose at the lever end?

Have a packet of various sized rubber o-rings kicking around at home I'm just not sure if they are meant to be a special material (silicon?) given the heat expected at the caliper.

 

[teK--]

I ordered an SLX caliper from ebay for $39 delivered - Aussie seller. Came with set of fo1 pads as well ( which are worth $25 as it is). Fitted easily, just remove banjo from old one and fit to new - had the little o ring.

The slx and xt caliper seem identical apart from the pad split pin on the xt, so you can transfer the little Allen bolt across and voila, you have xt brakes!

Thanks are you saying the new caliper came with new o-rings?

 

[ChopSticks]

Thanks Chops did you re-use your O-rings when you fit your Saint calipers to XTR levers? Or did you disconnect the hose at the lever end?

Have a packet of various sized rubber o-rings kicking around at home I'm just not sure if they are meant to be a special material (silicon?) given the heat expected at the caliper.

I only had to disconnect the lever end, as I bought a complete saint brakeset, and changed over the levers only. So never had to play with the banjo side of things

id be less worried about heat and more worried about the mineral oil eating xxxxx o ring.... Hence safer to source an old or spare o ring from a stuffed calliper

 

[pharmaboy]

Thanks are you saying the new caliper came with new o-rings?

Now you've got me second guessing myself - I seem to remember there was one on the temporary bolt - but I could be wrong - certainly no problem getting a seal at the banjo. As it turned out, didn't leak any mineral oil either - held caliper above the lever when I'd did the swap

Edit - contemplating getting another as a spare - much easier to replace than buggarizing around trying to fix a sticky piston

 

[teK--]

Thanks just gonna buy the caliper and cross my fingers.

I would think (as Chops suggested) if the o-ring is not deformed it should be re-useable.

 

[ChopSticks]

Thanks just gonna buy the caliper and cross my fingers.

I would think (as Chops suggested) if the o-ring is not deformed it should be re-useable.

Consider a zee or saint calliper? You seem to ride pretty hard?

 

[teK--]

Consider a zee or saint calliper? You seem to ride pretty hard?

I have but the cost of the pads are exorbitant? Plus the XTs have heaps of pulling power I'm not that heavy

 

[ChopSticks]

I have but the cost of the pads are exorbitant? Plus the XTs have heaps of pulling power I'm not that heavy

Pad prices aren't all that bad... $30 vs $20 for saint vs xt
how often do you go through pads?

I'd consider then for a front!

 

[takai]

You will be able to replace all the internals quite easily. The seals are simple square o-rings, which are readily available from any hydraulics place. Same with the copper crush washers.

Will be easier to rebuild with an air compressor, but should be doable with hand tools too.

 

[ChopSticks]

You will be able to replace all the internals quite easily. The seals are simple square o-rings, which are readily available from any hydraulics place. Same with the copper crush washers.

Will be easier to rebuild with an air compressor, but should be doable with hand tools too.

I tried salvaging an xt calliper once, but found out shimano do NOT sell parts for the calliper.... Because it's not serviceable.

i tried opening the calliper body up..but even that was a massive struggle (never managed, but I recall Moorey being able to?)

imo its it's just not worth the trouble esp given his pads are rooted already... And that's coming from a tight arise

 

[takai]

Well next time someone kills one sling it over my way and ill see if i cant find part listings for all the internals.

 

[PerthMTB]

I had a similar problem to the OP, and dismantled cleaned and rebuilt the caliper which solved it. I assume it was just a bit of grit or badly seated piston seal as I used the same parts and the problem went away. Its not difficult (not sure why chopsticks found it a struggle), and I wrote up my experiences in a thread on MTBR which you might find interesting if you're going to try it - http://forums.mtbr.com/brake-time/ever-wondered-how-hydraulic-brake-calliper-works-848452.html Here's one of the pictures from the thread as a taster...

 

[ChopSticks]

I had a similar problem to the OP, and dismantled cleaned and rebuilt the caliper which solved it. I assume it was just a bit of grit or badly seated piston seal as I used the same parts and the problem went away. Its not difficult, and I wrote up my experiences in a thread on MTBR which you might find interesting if you're going to try it - http://forums.mtbr.com/brake-time/ever-wondered-how-hydraulic-brake-calliper-works-848452.html Here's one of the pictures from the thread as a taster...

View attachment 295410

awesome to hear !!!!

did you have much trouble undoing the torx bolt holding the 2 sides of the calliper body together? that was the bolt I wouldn't undo, hence couldn't open it up

 

[PerthMTB]

awesome to hear !!!!

did you have much trouble undoing the torx bolt holding the 2 sides of the calliper body together? that was the bolt I wouldn't undo, hence couldn't open it up

Nah, that bolt is a T30, so as long as you've got a proper set of torx bits that fit something with a bit of leverage, rather than just a T25 that typically comes on bike multitools (because that's the size of rotor bolts) you'll be ok.

 

[takai]

Yep. Fairly standard split caliper hydraulic system. CBC or a brake company will be able to match the square seals if needed.

 

[PerthMTB]

Now you've got me second guessing myself - I seem to remember there was one on the temporary bolt - but I could be wrong - certainly no problem getting a seal at the banjo.

Unfortunately the O ring that comes on the temporary bolt on a new caliper (see top of photo) is larger than the ones used to seal the banjo bolt (see bottom of photo). But as you say, should be able to re-use the old ones if you're careful. Failing that, you can buy a spare BH90 hose quite cheaply online which comes with banjo bolt and three O rings for the caliper end, and shroud nut, cover, insert and olive for the lever end. Always good to have a spare hose and fittings around anyway.

 

[takai]

Again. Those o ring sizes all look quite standard. Any decent hydraulic shop will have them in stock.