Hydraulic brake lever not returning. Avid Code lever

[handmadematt]

Hi guys.
This new downhilling bike I'm converting has a front brake lever problem.
It's flapping around and won't return... It does nothing and is loose.



I dismantled it to have a look and can see the cupped location for the rod on the lever to push against. This is solid. Apart from that the aluminium casting is all one piece so I can't dismantle it anymore.
It's as if the piston in the cylinder connected to this cup is stuck and won't return. The lever itself has a spring but I don't think it's that spring that pulls the piston back.
Any ideas where to start?

Thanks.

 

[handmadematt]

SOVLED.

I managed to remove the piston from the cylinder by inserting a thin pin from the oil tube end. It then appeared that a nylon washer behind the piston seal was swollen or too large for some reason. I filed it down gently and evenly before polishing it with 1000 grit paper. I reassembled the whole thing and it now works great. Really great! The best brakes I've ever know actually.

So, the only thing is that it says "DOT 5.2 DOT 4 ONLY." I had a bottle of DOT 3 which I've used to reassemble and it seems to work fine, shall I leave it like this or get the proper oil?

What could possibly go wrong?

 

[Martin@e-bikeshop]

Hi,

The washer and seals can expand from the DOT itself. Its likely these will need replacing at some point in the future. They are pennies though. So no issue.

DOT 3 will work. Although you should replace with the correct fluid when you redo the seals.

The boiling point differs between them, however probably won't be too much of an issue on your push bike. That said the 5.1 is silicone based so will last much longer, and so will your seals

I used to run straight water in my hydraulic rim brakes on my trials, instead of the recommended DOT. Some say it can rust internals. However I never had a problem and it gave a better feel than Magura Blood... Plus it was cheaper..

That said I also used to run Helium in the (Latex) tubes, because it was lighter than air.. Won't go into that

Martin

 

[handmadematt]

Unbelievably it's happened to the other lever now. These are very expensive brakes and clearly have a flaw, not good. I've never had it on the two other hydraulic disc cycles in my life.
This time it's after the bike's been parked in hot sunshine this morning. I'm certain that the nylon washer has also expanded. I've moved the bike back into the cold garage and we'll see if it contracts on it's own otherwise it's a strip down, file and buff then reassemble tonight.

 

[Deleted member 4366]

If you use the wrong brake fluid, that can happen - if you're lucky. What fluid do you have? Did you change it from the original?

 

[handmadematt]

It's not my bike and the chap I'm converting it for bought it second hand so it's hard to say. Searching Google it does seem to be a common problem with these and other Avid levers though.

 

[handmadematt]

Update.
As I suspected putting the bike in the cold garage has released the piston. It'll need attention long term.

 

[Deleted member 4366]

I know that nylon absorbs normal oils, and if you use the wrong type of oil in your brakes, the O- rings swell up and lose their ability to seal. . Maybe it's just a design fault.

 

[handmadematt]

Who knows.