Replacement piston seals for Shimano hydros

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gregoryoftours
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Replacement piston seals for Shimano hydros

Postby gregoryoftours » 10 Nov 2018, 2:45am

Has anybody ever had any success sourcing suitable replacement square seals for Shimano hydraulic caliper pistons? (And/or master cylinder seals) I know Shimano don't make them available.

Airsporter1st
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Re: Replacement piston seals for Shimano hydros

Postby Airsporter1st » 10 Nov 2018, 11:34am

gregoryoftours wrote:Has anybody ever had any success sourcing suitable replacement square seals for Shimano hydraulic caliper pistons? (And/or master cylinder seals) I know Shimano don't make them available.


If you have the seal dimensions, or the housing/piston dimensions, you can almost certainly buy seals from Erik's. See handbook below:

https://o-ring.info/en/technical-info/technical-o-ring-handbook/

Unlike a lot of manufacturers/suppliers, they have a low minimum order value and also sell over the counter (or at least they did the last time I used them a few years back). They have stockists in many of the bigger cities.

gregoryoftours
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Re: Replacement piston seals for Shimano hydros

Postby gregoryoftours » 15 Nov 2018, 9:19pm

Thanks for that info, I guess the best way is to find an Eriks outlet and take the part in. I haven't managed to find anything that looks right in that manual or on their website yet. It looks like the original Shimano seals are made by a Japanese company called Nok. I always assumed that the caliper piston seals are square section but in actual fact they are grooved on the back face.

Brucey
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Re: Replacement piston seals for Shimano hydros

Postby Brucey » 15 Nov 2018, 9:32pm

yep, a groove on the back; amongst other things this allows the seal ID to be in raised letters on the air side of the seal and this doesn't really interfere with the seal performance. [However it might help the corrosion to take hold in the aluminium parts...]

Stupid questions;

a) what makes you think the seals need replacement? and
b) what makes you think that (say) a leaking caliper will be cured by new seals?

I've stripped down quite a few calipers with leaks in them and in no instance were the piston seals damaged; the leaks were all due to corrosion in the caliper body and no seal will turn a bad caliper good. [I think some caliper bodies can be recovered by polishing, but that doesn't require new seals per se.]

FWIW when the seals first come out of a leaking caliper they looked terrible, because they have been pressed up against a very lumpy corroded groove. However after a couple of days the seals normally recover their original (smooth) shape.

BTW if you take a seal to a potential suppliers, best to take the piston to which it fits also; this will allow the seal to be accurately measured.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

gregoryoftours
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Re: Replacement piston seals for Shimano hydros

Postby gregoryoftours » 15 Nov 2018, 9:49pm

The seals did seem to have some denting after I'd scraped the corrosion off them with my thumbnail where they'd been pressing against the uneven surfaces, so I thought that if I could find replacements cheaply enough it would be worth a go with new ones.

But yes the main problem seems to be corrosion in the groove where the seals sit, and getting to them effectively enough to clean thoroughly. I scratched them out as best I could with what I had to hand and ran a bit of clean rag around the channel to get as much of the debris as possible. Hopefully it improved things rather than making them worse. I've put them back together now but it remains to be seen if there's any improvement.

gregoryoftours
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Re: Replacement piston seals for Shimano hydros

Postby gregoryoftours » 15 Nov 2018, 9:54pm

There are replacement pistons and seals sold on eBay now from China but the price is only a few quid less than a cheap Shimano caliper in an online UK shop with pads included.

Brucey
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Re: Replacement piston seals for Shimano hydros

Postby Brucey » 15 Nov 2018, 10:15pm

as per another post there is a way of treating the grooves so that they will allow a seal to have a good chance of working; I have trialled this method with some success. The method is to use a small brush (like a miniature chimney-sweep's brush) mounted in a dremel tool and to use a metal polish (like solvol autosol) and to polish the grooves. The objective is to leave a clean, blemish-free surface on the groove OD, at least at the back of the groove; if it seals there, and there only, that is usually good enough.

Just scraping the groove will not be effective; the smallest blemish can constitute a leak path for the fluid, and any porous material (corrosion product is always porous) is absolutely fatal.

To see if the groove is in a good shape, I recommend examination of the seal groove using a x10 or x15 binocular microscope.

cheers
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LinusR
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Re: Replacement piston seals for Shimano hydros

Postby LinusR » 15 Nov 2018, 10:21pm

Interesting discussion on this thread. The fit of the seals are quite important as they also perform the function of automatically adjusting the pistons in relation to the disc rotor as the pads wear. A simple and elegant design but requiring a precise fit around the piston. I'm wondering how we can prevent the corrosion of the caliper around the seals that leads to fluid leaking. Would cleaning and then lubing the pistons with a cotton bud more often tan pad changes or bleeding combat the corrosion?

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LinusR
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Re: Replacement piston seals for Shimano hydros

Postby LinusR » 15 Nov 2018, 10:23pm

Brucey wrote:
To see if the groove is in a good shape, I recommend examination of the seal groove using a x10 or x15 binocular microscope.



Or possibly a digital camera set to macro mode and then viewing on a computer screen (and posting to this thread).

Brucey
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Re: Replacement piston seals for Shimano hydros

Postby Brucey » 15 Nov 2018, 10:25pm

if you want to see pictures
https://forum.cyclinguk.org/viewtopic.php?f=5&t=122398&start=45

FWIW some kind of silicone grease may be the best thing to coat the pistons in when the caliper is reassembled; this will help to deter water ingress and yet won't melt when the caliper gets too hot.

cheers
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Gattonero
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Re: Replacement piston seals for Shimano hydros

Postby Gattonero » 17 Nov 2018, 11:22am

I think is worth spending time on this ONLY if the pistons are in very good conditions: the Shimano calipers that use ceramic pistons are prone to develop cracks in the piston. This can happen even from the inside of the piston, i.e. when the pistons are not pushed in perfectly square.
Ceramic is a good material as far as heat resistance and has a low weight, but is very brittle...
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