PS 15 Brembo round m/cyl O-ring

FastFred · Post by **FastFred** » Wed Apr 27, 2011 5:19 am

Does anyone know what exact size the O-ring is that fits between the plastic round fluid reservoir and the master cylinder. Mine came out and just looks/is way too big to get back in. Don't know if it changed size when I cleaned in petrol but it ain't going back in. It is approx 37mm Inside diameter x 2.5mm cross section.
Thanks.

FastFred · Post by **FastFred** » Thu Apr 28, 2011 8:41 am

Found one to fit thanks

Post by **BevHevSteve** » Thu Apr 28, 2011 9:10 am

Why not post up the spec / part number etc so the next guy needing one will be helped out?

FastFred · Post by **FastFred** » Thu Apr 28, 2011 12:31 pm

I will Steve next week. I got 4 big O-rings from work, two from a yellow box, two from a red box. I assume that one box was metric, one imperial. I now need to put the spares back to know which I used!

It was very tight but I put a little Brembo seal grease from my master cyl recon kit and it went in with a very satisfying pop!

Cheers

rwhc80 · Post by **rwhc80** » Thu Apr 28, 2011 7:06 pm

G'Day FastFred,

Ironic that I am also looking for exactly the same part, so as Steve suggested can you post the part number please if you have it.

I am also interested to know what type of o-ring you used, as I understand it Nitrile is the most common compound for o-rings but is not resistant to the Glycol based Brake fluids that we tend to use. EPDM seems to be the one to use, but is not resistant to Petroleum based fuels, which may explain why yours distorted in petrol ?

Any light you or anyone else can shed would be a big help to me cause I have been unable to find out what the originals were, and I want to make sure I get the correct type ??

Kind Regards
Rick

FastFred · Post by **FastFred** » Fri Apr 29, 2011 1:04 am

Yes interesting. I also have a Norton Commando and have just relined the front brake master cylinder with a kit a company supplies that has a nitrile washer (!) to seal it and then advises DOT 4 fluid probably out of ignorance. I am not overly concerned if I have used a nitrile 0 - ring here as it's on the low pressure side but I will check and advise.

FastFred · Post by **FastFred** » Fri Apr 29, 2011 1:49 am

This seems to state Nitrile is ok with glycols....
http://www.rlhudson.com/material_profiles/nitrile.htm

FastFred · Post by **FastFred** » Fri Apr 29, 2011 1:58 am

and then you get this....

http://www.epm.com/sealsfast_materials.htm

rwhc80 · Post by **rwhc80** » Fri Apr 29, 2011 3:13 pm

Thanks FastFred,

The first website seems to contradict itself a little as it does indicate Nitrile being ok with Glycol products, but then clearly states not suitable in Automotive Brake Fluid. I am certainly no Chemist, but from the little bit of searching I did, it seemed to me that the most common Brake Fluids were in fact Glycol based. Dot 3. Dot 4 & Dot 5.1( Go Figure ?)

As I suggested prior, I have no idea what they originally were, but the fact that your o-ring distorted in petrol would seem to indicate not being Nitrile, as it is supposed to have excellent resistance to Petroleum based fluids ??

I'm still unsure, so any info would be appreciated ????

Regards Rick.

FastFred · Post by **FastFred** » Tue May 03, 2011 12:46 am

It was a 33mm I/D x 3mm cross section nitrile O-ring. Find one the same size in a different material preferably but this is only on the low pressure side of the system so I will keep an eye on it. Cheers.