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Brake lever sponginess

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fisjon:
Hi Mate,
I posted about spongy levers a while ago and have pasted it below. Hope it helps. Ps Make sure that the little hole in the reservoir is not blocked. You can carefully poke it with a needle, (I did say carefully) to clear it out. the fluid must have a method of return and this little hole is it.
cheers
john

Hot tip for bleeding brakes after refitting pistons and seals!

Half fill reservoir and GENTLY pump fluid into system topping up as you go until it is obvious no more fluid required.

IMPORTANT Do not force the lever at any time as this will compress the air into the fluid, yes brake fluid will suck in air and it will become elastic.

Leave overnight. The weight of the fluid will want to go down and the air will want to come up. In the morning the air will be at the top of the system, and by GENTLY moving the brake lever in and out WITHOUT APPLYING FORCE you will see lots of bubbles rising into the reservoir. Do this for several minutes until the air bubbles stop rising. Leave for 15 minutes and then gently move the lever again to see if there is any more air. Repeat if necessary until no more bubbles.
 
The important thing about this process is not to apply pressure on the lever until the system has no air in it or you will compress the air into the fluid and this will give you a spongy lever.

Also you should avoid leaving the cap off the reservoir for long periods as air will ingress into the fluid merely under atmospheric pressure.

This method requires a little patience but beats the s--t out of spilling fluid over your nice clean bike!

Oh! One more thing, always use new fluid, if it has been in a can that has been opened for some time  it is useless.

Dan:
Bryan - agreed, but not to the point that you can't get a solid feel at the lever. And there shouldn't be crap built up around them from road contaminants, salt, etc.
After a caliper overhaul my similar problem with brakes was fixed and its an easy and inexpensive task if nothing else is working.
Dan

Dan:
The seals on my bike had so much crap built up around them that they were basically glued to the pistons and not allowing the pistons to move through them to compensate for pad wear.
You could bleed the brakes all day long (pointlessly 😤) but still have a spongy feeling at the lever because more travel was needed to get the pads against the disc.

This will probably turn out to not be your problem Lobo haha
Dan

Lobo:
Hi gents: thanks.

The bike has just undergone a major rebuild, and whilst the m/c wasn't touched, the caliper was cleaned / repainted, as was the intermediate pressure switch junction, and all hoses / pipes renewed OEM.

It has been bled...and bloody bled... carefully, by the book, with nothing but fresh DOT 4. The posting above above is in opposition to previous ones... ie 'no pressure into the fluid.. leave overnight' versus maintain pressure overnight.... but all to no avail. (surely the 'no pressure / leave overnight' method is what we're doing 365 nights over the year? - ie the brake should tighten up with time?)

I can only see that I'm down to a master cylinder overhaul now; and am quite happy to spend that cash as everything else about the bike just about perfect. Will report back...!

tom400f:
Lobo

I did what you did (I assume you used a new seal in the caliper) plus (as stated earlier) the m/c overhaul kit. I used Earls hoses but I don't reckon that makes any difference. Will post pic later of my bleed technique. I'm pleased with the overall result (using EBC pads). Firm and effective (using four fingers as others have said).

Aside: took it for MOT last Sat. Apart from the general furore surrounding her the thing the test guy remarked on was the thickness of the disk!

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