HELP - No feel/resistance at front brake lever after caliper

[votejc]

After my difficulties of removing my stubborn pistons and finally getting them out, I have stripped, cleaned sprayed and reassembled my calipers with new fluid and dust seals. I have put them back together and refilled the brake lines with fluid and bled till pure fluid comes out with no bubbles on both calipers.

Still I have no resistance at the lever, it just comes straight all the way back to the bar. Taking the calipers off I can see that only a couple of the pistons on each caliper are actually moving and even those move very little. Not enough to push the pad onto the disk. I have done everything as by the book as I could, but the pistons may not be in their original bores :-s

Please somebody tell me they have had this issue and resolved it! Its glorious outside and she is stuck on her bastard paddock stand in the garage!

[Username]

There's still air in the system. Just pump the lever rapidly and the pistons will start to move out of their bores. Once they've taken up any slack just bleed the brakes again until a firm lever is obtained.

[amorti]

First check is as above, also try slipping the top banjo bolt open to allow any air out of the banjo bolt. If no joy:

Did you renew the master cylinder seals?

What often happens, is that they are worn, and then when you bleed the brakes, the piston slides along a normally unused part of the bore, which may have dirt or debris in it. This can make the seals bad. The master cylinder won't necessarily leak as there are two seals, and if only the first one goes, you will get symptoms as described (no pressure) but no leak. This is because fluid can't get out, but also any pressure you apply just forces fluid up through the transfer port, which the seal normally blocks.

The insides look like this(it's off a Revere and on a Diversion but insides are all the same), and it only needs the first seal to very slightly fail for the master to be no good.

You can open and inspect, if I am wrong and all is good, put it back together as-is. If you do need a rebuild, fill the cavity under the top hat seal with silicon grease, don't use mineral grease to lube the pivot but only silicon grease as this is kind to rubber seals.

[votejc]

Thanks for the posts guys. I tried continuing to bleed and after a good few pumps of clear brake fluid a massive air lock came out of both calipers and then I started to get a good firm lever. So basically all sorted.

Hooray!