Spongy brakes (hydraulic)
- Thread starter Fmitch
- Start date
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mrandmrspoves
Middle aged bald git.
- Location
- Narfuk
Sounds like you have air in the system. It can be bled out quite simply - but you will need a bleed kit to do so.
mrandmrspoves
Middle aged bald git.
- Location
- Narfuk
Often does because the piston seals can leak especially when you push pistons back into the caliper. Auriga's have (in my experience at least) a tendency to seize - so when changing pads I always give the pistons a good coating of a Teflon based spray such as GT85 before putting the new pads in.
Globalti
Legendary Member
No. The reason is that brake pistons don't actually slip through the seals when you apply hydraulic pressure - what do you think would make them slip back again? Those pistons are an extremely tight fit in the seals.
What happens is that you squeeze the brake lever and the pistons slip through the seals to the point where they can't move any further. When you release the lever and de-pressurise the fluid the elasticity of the seals pulls the pads back from the disc. Next time you brake it's only the elasticity of those rubber seals that allows the pistons to move, although they will creep slowly inwards as the pads wear.
So just go and ride the bike and everything will settle down. Air can't have got in if you didn't open the system.
What happens is that you squeeze the brake lever and the pistons slip through the seals to the point where they can't move any further. When you release the lever and de-pressurise the fluid the elasticity of the seals pulls the pads back from the disc. Next time you brake it's only the elasticity of those rubber seals that allows the pistons to move, although they will creep slowly inwards as the pads wear.
So just go and ride the bike and everything will settle down. Air can't have got in if you didn't open the system.
Linford
Guest
The piston to seal clearance is a very tight tolerance...as is the seal to seal groove diameters in thecaliper.
As you use the bike, crud and road salt gets on the diameter of piston on the pad side, also brine (road salt and rain) gets down the side of the seal groove in the caliper. Brakes go through a heat cycle, and this dries out the brine in the seal groove and forms a crystal which will grow between the groove and the seal...this pinches the seal against the piston and increases the friction over the sliding surfaces of the seal and piston (eventually causing seizure of the piston)
Also when changing pads, if the piston is not spotless when being pushed home in the caliper, the crud on it gets wedged in between the seal and the piston...increasing friction again. If the piston can't slide freely past the seal, it never gets the chance to move forward to the disk and find a resting position (the seal holds it off the disk). This is where the spongyness feel comes from.
Best thing to do is strip it, clean it properly (scraping the crud out of the seal grooves) using a smear of the correct grease (red rubber grease) before reassembly.
As you use the bike, crud and road salt gets on the diameter of piston on the pad side, also brine (road salt and rain) gets down the side of the seal groove in the caliper. Brakes go through a heat cycle, and this dries out the brine in the seal groove and forms a crystal which will grow between the groove and the seal...this pinches the seal against the piston and increases the friction over the sliding surfaces of the seal and piston (eventually causing seizure of the piston)
Also when changing pads, if the piston is not spotless when being pushed home in the caliper, the crud on it gets wedged in between the seal and the piston...increasing friction again. If the piston can't slide freely past the seal, it never gets the chance to move forward to the disk and find a resting position (the seal holds it off the disk). This is where the spongyness feel comes from.
Best thing to do is strip it, clean it properly (scraping the crud out of the seal grooves) using a smear of the correct grease (red rubber grease) before reassembly.
OP
OP
Fmitch
Regular
Yes I don't see how air got in if I never opened the hydraulics. The pistons were quickly cleaned with alcohol but only quickly. Should they be pressed fully back into the caliper before the New pads are installed. I know they were not fully in the caliper when I put the pads in as I saw 2mm of piston.
Just ride it and it should settle down. Feel will also vary according to pad make/type ie sintered, organic, kevlar.
If still no improvement after bedding in then maybe consider bleeding it. If you had the bike upside down when you changed them that can upset the things a little depending on make of brake but it normally settles after a bit of use.
If still no improvement after bedding in then maybe consider bleeding it. If you had the bike upside down when you changed them that can upset the things a little depending on make of brake but it normally settles after a bit of use.
OP
OP
Fmitch
Regular
Ok will do,i also hear a pumping noise when pulling the lever which i never heard before. Lever almost pulls to the handlebars and then after 2-3 pumps settles to its normal position. I have read that pumping then tying the lever overnight may remedy this, any truth in that?
mrandmrspoves
Middle aged bald git.
- Location
- Narfuk
There's no need to push the pistons fully back.....unless you are going to bleed them. Despite others telling you they are likely to settle down - what you describe (and my own experience with the same model brakes) sounds as if you do have air in the system and will need to bleed them. I also seem to recall advice about leaving a lever tied on over night - but I cannot think how this would help.
