Avoiding air getting into the system on disc brakes

[grams]

The OPs symptoms are extreme and a properly bled system should not behave like that.

However, if you do end up with a tiny amount of air then it will migrate into the reservoir in the lever where it will do no harm unless disturbed by - for example - turning the bike upside down. But this shouldn’t be the case for a freshly bled bike.

The suggestion of not turning the bike upside down (a) solves the problem and (b) is generally good practice.

(I’ve used the meathooks on the new GWR trains a couple of times this year and didn’t notice any brake issues riding immediately afterwards)

[PhilO]

In my experience, hanging a bike up by its front wheel can cause migration of air from the reservoir into the active circuit over time, but generally speaking it needs to be overnight or longer. My current bike was bought SH and the front brake would go spongy over a couple of days. When I investigated the reservoirs were nearly empty.  The chap I bought it from claimed to be an engineer...

When bleeding I always remove the cap and diaphragm completely (even on Shimano brakes as I don't trust the funnel). After eliminating all air from the system, I deliberately over-fill the reservoir to overflowing. The diaphragm then needs carefully laying over the top, avoiding trapping any air. If you're not displacing fluid out of the reservoir at this stage then there isn't enough fluid in it - use a rag to catch the overflow. Replace the cover.  Often, there's now too much fluid in the system and the brakes drag a little. Just open the bleed nipple slightly and gently squeeze the lever to eject a little - on no account release the lever before closing the nipple, or you'll have to start again!  Remember to thoroughly clean the fluid off the brake lever! 

No brake I've dealt with this way has ever required a rebleed. The fluid should last for a number of years without requiring attention.

[Brucey]

I have carried out a similar procedure as Phil describes above, for similar reasons and with similar results.  Thinking about it, next time I have to do the job (on an 'open' system with a diaphragm)  I will probably

a) get the main circuit bled out OK
b) use a rubber band to pull the brake lever back (so the brake is on)
c) tip the bike up so that the bleed port is uppermost in the reservoir
d) use a syringe in 'push-pull' mode so that the diaphragm is flexed through its full range and the air is eliminated from the reservoir
e) push the syringe piston in so the diaphragm is pushed out almost as far as it will go
f) disconnect the syringe from the bleed port, whilst holding a tissue/cloth to catch any fluid that escapes (because the diaphragm returns to its usual shape) as the disconnection is made
g) release the brake lever and again catch any extra fluid
h) replace the bleed screw

This will work even better if there is a T piece in the line and there is a valve on one leg of the T, leading to a funnel.  This will allow surplus fluid to be discharged from the system without spillage.

One of the appeals of this method is that it separates the system bleed from the process of eliminating air from beneath the diaphragm.

cheers

[simonp]

I had this issue last week. Bled the brakes last night. Seemed to be a lot of air in there.

It is worse than I thought. Rear calliper seal has failed. Seems to be a common Shimano thing. I’ve barely done 600 miles. At least it’s still under warranty. I’m hoping there’s enough hose length to shorten the hose and replace the olive or it’s a whole new hose, new bar tape etc. 

Explains why the rear brake has been a bit noisy.

[Torslanda]

IME it's not the hose connection unless it has been left loose.

Anyway, that's the bike shop's concern. They should be changing the caliper/seal etc. under warranty, surely?

[simonp]

IME it's not the hose connection unless it has been left loose.

Anyway, that's the bike shop's concern. They should be changing the caliper/seal etc. under warranty, surely?

Yep. I bought the groupset from Evans so am waiting for a response. It’s defintely not the hose connection - area around it is bone dry. It’s from either a piston seal or the transfer port seal.

[Torslanda]

Hurry up & get it sorted. Once Ashley's got the bit between his teeth customer service is going take a dump.

On the plus side I think it's highly unlikley that you're going to need a new barb & olive, I've changed quite a few calipers and never had a leak from there.

[sojournermike]

As nice as they are to use, this thread isn’t selling hydro discs from a low maintenance long life on all weathers perspective, which is their prime benefit on a road bike.

FWIW, I’ve not had any issues with the TRP HY-RD on the ‘Yellow Peril’, but it’s not been upside down and the fluid is all contained in a small area by the caliper. I’ve got a set of Shimano road hydros to install soon - perhaps I’ll keep them for summer only!

[simonp]

Hurry up & get it sorted. Once Ashley's got the bit between his teeth customer service is going take a dump.

On the plus side I think it's highly unlikley that you're going to need a new barb & olive, I've changed quite a few calipers and never had a leak from there.

Agreed re Mike Ashley. A double edged sword there.

Interesting re the barb and olive. Thanks.

[Ben T]

As nice as they are to use, this thread isn’t selling hydro discs from a low maintenance long life on all weathers perspective, which is their prime benefit on a road bike.

Newsworthy in the same way as a man bites dog story.

[sojournermike]

As nice as they are to use, this thread isn’t selling hydro discs from a low maintenance long life on all weathers perspective, which is their prime benefit on a road bike.

Newsworthy in the same way as a man bites dog story.

I have a set waiting, but confess I hadn’t picked up on the implied level of failing seals and corroding bores. So to me it is interesting.

[simonp]

Initially Evans replied with a formula email which implied they hadn’t properly read my email. I sent back more info and got back an apology and an offer to look at the bike in the Bristol shop. If they are able to swap the part for me that will probably be less hassle.

[salar55]

Don't see why people have problems with air in system, if it's been bled properly everything should be fine. Lots of cyclists fly with bikes and not had any problems, have you seen the loading and unloading ofbikes on the runway . Bikes upside-down etc. Never seen anyone use a strap to pull in brake lever, most remove pads and fit the plastic block between the pistons then start bleeding the system. A quick dodge is to fill reservoir to the top and give the lever a few sharp flicks to move the air up.