Had a bit of a braking scare

[marcmax]

Out riding this weekend and had a cage driver pull out in front of me from a side street. I hit the brakes hard expecting to have to fight a skid. Instead I slowed a bit and then nothing. Almost like I had no brakes at all. Luckily the amount of slowing I did was enough to avoid the idiot but when I got stopped I looked and found brake fluid all over the right side caliper and disk.

I was only a few miles from home so I was able to limp home on back streets using the rear brake. I started checking and found most of the brake fluid gone and when I squeezed the lever brake fluid was coming out between the two halves of the caliper housing near where the brake line attaches.

The weather was too nice so I took a caliper off my parts bike, cleaned everything up, installed a new set of pads, bled them and got back out on the road.

My question is what went wrong? I have already ordered a Brembo rebuild kit but should I be worrying about the other side?

[Luca]

It sounds like the o-ring that seals the fluid passageway between the caliper halves let go.

The ATE rebuild kit I got from motobins did not come with this o-ring.

There is a thread in the FAQ section on the o-ring.  This is for the ATE caliper, but according to Julio's thread on the difference between the calipers, the o-ring is the same.

Ian,

You'll need to source locally an EPDM (Ethylene-Propylene-Diene-Monomer) material o-ring for it’s resistance to high heat along with its properties to resist glycol based fluid exposures.  

Size: 0.41"OD x 0.21"ID x 0.10"W.

-Mike V.

[Julio A.]

The o-ring is squeezed between two metal pieces, and is held in place snugly in a groove. i really can't see a way for it to rupture. Even if the rubber had hardened through time, it should have still sealed fluid in as it is a non moving part.

You may want to open up that caliper to see what went wrong. The two halves may be coming apart.

[Barry]

It sounds like the o-ring that seals the fluid passageway between the caliper halves let go.

Can't see how it could be anything else. First time I've heard of it though. It'll be interesting to see if the correct O ring is in there.

[steve hawkins]

Well done for dodging the bullet.

You can always go down to one disc!

Rev Light.

[Luca]

Julio, non moving parts (most seals are stationary) can give way just as well as those that move... and although this o-ring doesn't move, it is subjected to hydraulic pressure.

I agree that he should pay close attention to the caliper bolts when disassembling, but if they are snug and the leak is indeed from between the caliper halves I can see no other culprit than the o-ring.

FWIW, mine were so worn down I thought them washers... reinstalled and still holding.