Anatomy of a failed hydro caliper

[NATURAL ANKLING]

Hi,
Correct me if I am wrong-

You have suggested silicone grease in Dot 5.1,they are compatible I assume.

Mineral fluid what luibe is used hear.

I believe that Castrol red rubber grease was developed I have read IIRC, that it is fully compatible to be used to lube the seals with DOT 5 etc.IIRC " can be used IN" the system.

Manly I use it to lube the bellows and fluid seals.

Sorry lots to reread, if you already stated above.

[Brucey]

Hi,
Correct me if I am wrong-

You have suggested silicone grease in Dot 5.1,they are compatible I assume.

no; I have suggested that the external parts of the pistons are lubricated with silicone grease (because it won't attack rubber seals), not that it is mixed with mineral oil per se.

Mineral fluid what luibe is used hear.

yes but it clearly doesn't inhibit corrosion to any great extent (else corrosion induced caliper leaks would never get any worse...) and you cannot put much of it on the air side of a piston without risking contamination of the pads. Silicone grease doesn't melt when heated or migrate terribly fast, making it useful in things like brakes.

I believe that Castrol red rubber grease was developed I have read IIRC, that it is fully compatible to be used to lube the seals with DOT 5 etc.IIRC " can be used IN" the system.

Manly I use it to lube the bellows and fluid seals.

Sorry lots to reread, if you already stated above.

yes castrol red rubber grease is one of the few lubes that works with DOT fluid (in which category I do not include DOT 5.0 BTW) and does not attack (EPDM and other DOT compatible) rubber seals. IIRC it uses a vegetable oil base, and it is OK to use it as a seal lubricant during assembly. However any significant contamination of the fluid with grease may alter its boiling point and may interfere with ABS operation etc. Also note that it does (IIRC) soften and migrate more easily than silicone grease does.

cheers

[NATURAL ANKLING]

Hi,
My mistake I said Dot 5 should have been dot 5.1 dot 5 silicone
Just reread my post before your reply, realised my mistake.

[thelawnet]

had this one in the 'pending' heap for a little while; a shimano BR-M447 hydraulic caliper that started to leak really badly after a winter or two's use.

The pics tell their own story really

Does anyone know the source of these piston seal rings?

These read 21.1 25.3 1.9. Presumably internal, external, diameter and thickness. This would obviously suggest a 21mm piston.

I found a seal code for M775 (2007) here http://www.mazoviamtb.pl/forum/index.ph ... oto=20379&, the code may be an aftermarket one, it reads R15 M 20.8x25.1x2 NBR

The M985/M785/M675 generation (2010 onwards) got 'oversized 22mm ceramic pistons'. These are since found on all subsequent XTR/XT/SLX calipers and presumably identical. They are also on most road calipers. What '22mm' exactly means is another question. You can buy replacement pistons online. https://www.aliexpress.com/item/Bicycle ... 20436.html Whether they fit perfectly into Deore calipers I am not sure.

You can also buy pistons for the 4-piston calipers, which are also ceramic. https://www.aliexpress.com/item/Metal-P ... 11748.html