Bleeding brakes. still air bubbles

[tok78]

Went to change my brake pads this evening, this was completed, but with the following comments:

1. Front Left caliper had to be removed as 'top' piston would not budge. Front right pad change was a straight swap.

2. I vacuum bled the lines on the FL caliper, removed the caliper, cleaned the caliper and pistons (using halford's brake cleaner and a toothbrush), reassembled everything, changed the pads and mounted back on the bike.

3. The FL caliper/brake now appears to be drawing in air bubbles from somewhere. I have flushed nearly 1/2 litre of brake fluid through the front line (upper bleed nipple) and I am still getting lots of little air bubbles and little to no resistance on the lever.

It is definitely new fluid that is being pulled through as the colour is different to the old 'London Pride' shade of the previous fluid.

If I squeeze the lever harder it 'farts' more air bubbles into the bleeder tube.

4. Same issue with the rear brake reservoir and the 'lower line' on the FL caliper.

Am I right in thinking that this is an issue with the front caliper, possibly the brake lines?

Does anyone have any suggestions as what I am doing wrong?

If anyone fancies coming round to lend a hand, I will stand you several beers! (I am in Blackheath, SE London).

 

[snakeskin]

Re the front, leave the reservoir cap on but loose, then tie the brake lever to the bar flat against the bar using elastic bands or similar. Leave overnight then tighten up the cap, release the lever and pump the handle until it goes hard and should then have cleared all air bubbles. You may need to top up the reservoir. Have used this method a few times and works a treat.

 

[tok78]

Snakeskin.

Your suggestion worked like a charm. Thanks!

 

[snakeskin]

Same can be done with the rear brake tok78 with a similar plan re brake pedal and reservoir. I was told about this method a few years ago and has worked every time. @tu*

 

[stevie069]

one thing i learnt the hard way with a vacuum bleeder is that you have to have a good seal around the nipple or it just sucks in air.
but now i know just changed mine and had no problems.

 

[L-J]

Useful tip

Snakeskin, read your tip, seems it worked a treat for tok78. I've heard of this method many a time going back years - do you know how / why it works then out of interest?:dunno:

Thanks.

 

[snakeskin]

When you tie the brake lever back you are opening up the valve in the reservoir, letting the bubbles make a rising exit ! That's all I can think of L-J, but it definitely works.

 

[CBRDEAN0]

When you tie the brake lever back you are opening up the valve in the reservoir, letting the bubbles make a rising exit ! That's all I can think of L-J, but it definitely works.

Opposite way around. When you pull the brake lever it shuts off the reservoir and forms a sealed hydraulic system so it can push on the pistons.

IIRC it is the presurised fluid that pushes any bubbles of air to the top faster so that as soon as you release the lever you allow any bubbles out of the system and in to the reservoir.