SRAM hydraulic brake o-ring

OEM european power steering fluid (15-851OEM)

Appearance: green colored light liquid

May be similar to CHF 11S. Reported here 11S should be compatible with HNBR/NBR:

https://forums.mercedesclub.org.uk/index.php?threads/abc-valve-block-rebuild-pics-is-this-right.138407/page-2

SRAM oring tested in fluid:

• OD swell 20% after 24hrs (10->12mm)
• Thickness seems unchanged
• Caliper seal thickness did increase ~10%, enough to make it unusable

SRAM oring should be EPDM. So maybe 851OEM oil has very similar compatibility to standard mineral oil?

NBR oring:

• No swell

VQM (silicone):

• No swell

https://forums.mtbr.com/brake-time/o-ring-material-question-680609.html

Various available fluids found online that may be appropriate for hydraulics:
 

Pentosin CHF 11S:

• Viscosity (40C): 18.7mm2/s
• Viscosity index: 313
• SDS indicates 68649-11-6 1-decene dimer hydrotreated (also used as a skin product, grinding oil, etc.)
• Recommended on MTBR forums many times

OEM power steering fluid (European):

• Contains highly-refined mineral oils
• Made by Recochem Inc code: 15-851OEM
• SDS has no useful information, other than not hazardous. So maybe does not have major additives?

OEM power steering fluid (Asian):

• code: 15-891OEM, probably the same as above product

Prestone European power steering fluid:

• Stated as alternative to CHF 11s, or CHF202 (which is partial synthetic)
• Contains "seal conditioners and anti-corrosion additives"
• Ingredients: different base oil, and a few additives (zinc and anti-wear)

FEBI hydraulic fluid M6162:

• Viscosity (40C): 16mm2/s
• Seems to be mineral based, not synthetic?

Synthetic DOT3 (eg lucas oil synthetic):

• Different base oil (9004-74-4), could be more hazardous

Advantage of synthetic:

• Wider temperature range
• Maybe more compatible with materials? (seems to not be the case)

Viscosity index: lower = change more with temperature, higher = change less.

Viscosity: higher = thicker. 

Kinematic viscosity: how fast fluid is moving when force applied.

Links:

https://www.pinkbike.com/forum/listcomments/?threadid=140344&pagenum=3

https://forums.mtbr.com/brake-time/mystik-mineral-hydraulic-oil-brakes-1070783.html

https://www.ncbi.nlm.nih.gov/books/NBK304428/ (mineral oils study)

SRAM force 11sp brake caliper:

• 2pc 22.4 x 18 x 2.2mm square cross section (piston seal)
• 2pc 8mm x 1.2mm (inner seals)
• 1pc 10mm x 1.0mm (hose arm seal)
• 1pc 5 x 1mm? (bleed port seal)

Brake lever:

• ? piston o-ring seal bottom, top
• ? cable entry seal bottom, top

Piston: 17.85mm (aka 18mm)

Piston seal sources:

• Official seal/piston kit (sram # ..)
• MYA-018 is close
• Stack two 1mm or 1.2mm round (not thick enough)
• Use single ~18 ID x 2.5mm dia round o-ring (not ideal)
• Ebay: https://www.ebay.ca/ulk/usr/pavlina_kyrychova possibly

Different size piston available here (26mm OD) labeled as PE: https://www.aliexpress.com/item/4000509364502.html

O-rings compatible with:

Mineral oil:

• NBR (nitrile/buna-n)
• PTFE, AU, FKM (fluorine green color)
• VQM silicone (maybe, 10-20% swell)
  

DOT5.1 brake fluid (DOT3, DOT4):

• EPDM
• SBR
• PTFE, FKM
  

Synthetic based hydraulic oils:

• EPDM
• SBR
  

Source:

• https://www.marcorubber.com/o-ring-chemical-compatibility-chart.htm

• https://www.parker.com/Literature/O-Ring%20Division%20Literature/ORD%205700.pdf

Brakes that use:

• Mineral oil: Shimano, Tektro (Giant),

• DOT5.1: SRAM