Today one of the riders was pushing out the pistons to fit new pads and suddenly felt less resistance. He found that the small plastic plug on the reservoir had vanished and the fluid was leaking out (due to the bike being upside down). He later said he’d often noticed people had wound tape round the reservoirs of these brakes, and this was a possible explanation for it. Am I right in thinking it’s a crap design ?

Happened to me on first ride on a new bike!
Bimbling along with missus and sprog on tag along and suddenly no front brake and fluid dripping from the hole.
Not impressed to say the least.

Used Hayes 9’s for years and years, never any problems with it. The plug isn’t exposed to hydraulic pressure unless the system is way over-filled so it doesn’t matter that it’s just a push-fit.

simon, i suffered this on 2 sets of hayes.
once halfway round the marin trail in wales, left me with just a back brake.
not good when you are a bit on the large side……. 😀

I had this happen but I had put too much oil in when I bled them.

but I had put too much oil in when I bled them.

why have a design that can be overfilled ?

Any system can be flooded.

Exactly, you can over-fill any hydraulic brake – what happens is that you end up in the situation where you can’t push the pistons back to fit new pads. If you force it hard enough with Hayes, you’ll pop the plug out. Other systems, you just won’t be able to push them back at all and hence won’t be able to fit new pads.

Any system can be flooded.

On my Hopes you fill them to the top and put the lid on. There is no way to get any more fluid in. On my Shimanos, you fill them up and put the rubber bellows on, which forces out any surplus…

The problem is when you fill them with the pistons out, I can’t see how any design gets around that (but then all bleeding instructions I’ve read have a bit about forcing back the pistons before you start).

I fitted a set for a mate who mail ordered them. They arrived in the post in a plastic bag in the bottom of which was one plug and a few ml of fluid. No excuse for that one!

FW nailed it.

It can happen sometimes if the one of the seals go on the MC piston. The pressure can bypass the 1st seal, pressuring the MC itself & blows out the plug, replace the piston & seals (easier to change the lot) & job done.

The problem is when you fill them with the pistons out

ah yes, I missed that!