Front Brake Master Cylinder Reservoir Oring?

Does anyone know of a source for the oring that seals the plastic reservoir to the master cylinder. Yamaha does not even seem to have ever listed it as a part.

I am looking into matching it up by size but thinking it may be a metric dimension and an inch size oring might be just a hair tight or loose.

Just hate to spend lots of time looking if it has already been done.

May just have to take the reservoir and master cylinder to the local hydraulic shop and see what they can do.

Hey Ken,

I went to Monarch Rebuilding a company in London, Ontario who specialize in rebuilding truck master cylinders.
Sold me o-rings#568-131.
Which i think are: ID 1-11/16", OD 1-7/8", Thickness 3/32".
I have had it installed since last Sept. Bike is 'almost' ready to roll again so haven't road tested but have load tested by bungeeing brake lever and no leaks. I think he charged me a buck or two for a couple. If you can't find any, PM me your address and I'll pick up a couple and mail them to you.

Although this has come up in the past I don't think anyone has found a direct "you need this one" solution.
From another thread the dimensions are 45 mm, 1.5 mm thick.
Here is an e-bay link for a used one, but probably could be had cheaper if the hydraulic shop has one.

I bought a metric o'ring at my local True Value Hardware. It worked the charm. I simply matched the one in my hand to one in their stock.

Yup - like nuts and bolts, things like o-rings, bearings, dowel pins, roll pins, c-clips etc. are standardized and by taking an old one into a place that sells mechanical components and telling them..."this one is metric" you can normally get a high quality match for pennies.

Okay I got my oring figured out. Took a spare master cylinder and reservoir to the somewhat local hydraulic shop I have dealt with over the years for heavy equipment seals.

Joe took some measurements and went in the back room and came back with a bin box filled with bags of metric orings.

After trying some in the groove in the master he settled on on size put a little wipe of lube on the oring and the taper of the reservoir and handed them to me. Guess if something went toes up he wanted it to be in my hands!

Well a moderate amount of pressure and a little twisting motion and it snapped together just nice. It's snug but will turn with not too much effort. So I am 99% sure it will be just fine.

Now for the answer some might be looking for the size we settled on is....... 39.7 mm id with a 3.5 mm cross section.

But then there is the price! He had the nerve to stick it to me for $0.46 cents a piece plus tax, so I said I'll take 4 and that gave me a total of $1.99.

Now if someone wants to go in to business stocking these orings McMaster Carr does list them in bags of 25 for $6.87 plus shipping.

kshansen said:

But then there is the price! He had the nerve to stick it to me for $0.46 cents a piece plus tax,

Click to expand...

You woz robbed blind

The nerve!!!!lol

You got 4 for $1.99, I got 2 for $2.00. Man I hate Canadian pricing!

me too....

with exchange rate 2 for $2 bucks is about right...

you really need to pay attention to the o-ring material, brake fluid o-rings should be EPDM material... a lot of times the o-rings at the part counters displays are nitrile, and that's assuming that the part guy even realizes that there are different o-ring materials out there... Nitrile will fit initially, but leave you stranded within days/weeks/months...

Oddjob said:

with exchange rate 2 for $2 bucks is about right...

you really need to pay attention to the o-ring material, brake fluid o-rings should be EPDM material... a lot of times the o-rings at the part counters displays are nitrile, and that's assuming that the part guy even realizes that there are different o-ring materials out there... Nitrile will fit initially, but leave you stranded within days/weeks/months...

Click to expand...

Did not realize brake fluid would be a problem for an oring. I have been checking to find EPDM orings in the correct size but so far no luck.

As this is a static seal application and any leak will be visible I will keep close watch on the master for any signs of seeping fluid. Also will keep an eye out for EPDM orings in this size.