Spongy front brakes

[gixeriain]

My bandit 12 front brakes have been spongy for some time. Ive bled them a few times. Ok for a few mins then back to being spongy.

Today, I fitted a master cylinder repair kit. Bled the system fully. 

Still spongy as fuck. Whats going on ?

[Rene EFE]

What lines are you using?

[gixeriain]

standard. 

[markfoggy]

Bin

[no class]

You still have air in the system . Even the standard lines have a small amount of firmness . I have found the majority of tiny bubbles hide in the master cylinder ..... give her another go .

[gixeriain]

Ive tied the brake lever in for the night.

[suzook12]

Most likely got air trapped in the splitter. I would go round all the banjo bolts and bleed each one in turn

[Rene EFE]

Do away with the lines, they're probably (way) past their best

[dupersunc]

11 hours ago, gixeriain said:

Ive tied the brake lever in for the night.

Did you read it a bed time story too.

 It does bugger all to get rid of air in the system. 

[Dezza]

Change the lines and buy a new bottle of fluid. If your fluid has inadvertly been shaken in the past or knocked off a shelf, dropped etc. it could have a load of tiny air bubbles in it that will not come out. If so, every time the reservoir is topped-up a tiny amount of air is introduced into the system. I learned this many years ago bleeding a 250lc front brake and was pulling my hair out until I bought some new fluid.

[strima]

Another vote for fresh fluid. Even a tiny amount of water/moisture in the old stuff can make a massive difference.

[Rene EFE]

@gsxr884 will happily sort you a set of lines

[markfoggy]

On 5/18/2017 at 9:55 AM, strima said:

Another vote for fresh fluid. Even a tiny amount of water/moisture in the old stuff can make a massive difference.

Not entirely true, you can usually get a good brake with shit fluid. 

Problem comes when you get it hot, the water absorbed into the fluid boils and you can exit stage left pursued by an ambulance.

Brake fluid come in small containers for a reason. It is highly Hygroscopic and a used bottle should always be treated with deep suspicion. I write dates on bottles when I open one.

[Solcambs]

In order:

• New fluid,
• bleed top and bottom
• Tie the lever overnight
• I assume the physical components are all in good nick e.g. make sure the disks have no edge that the pads are sitting on, that all of the pistons are moving, that sort of thing.

Spongy brakes are normally fluid related ... 

[markfoggy]

58 minutes ago, Solcambs said:

In order:

Bin standard brake lines even if only 2 years old.

• New fluid, Yes a brand new un-opened bottle
• bleed top and bottom - but replace every washer with new, if you want to reuse copper washers get them cherry red on the cooker and quench in cold water.
• When this doesn't work try bleeding the bottom first, usually where the air is to start with. Geting the caliper above the master cylinder will speed things up.
• Tie the lever overnight. It can help but only if the master cylinder is at a weird angle, cracking the banjo at the master cylinder is better, but is a good technique id you are transporting a bike in a van between race meetings.
• I assume the physical components are all in good nick e.g. make sure the disks have no edge that the pads are sitting on, that all of the pistons are moving, that sort of thing.

Spongy brakes are normally fluid related ... 

Oh and the best advice ever.

Always back bleed brakes.

Start by getting new fluid in there, with every thing on the bike. Open the bleed nipples and pump new fluid in from the top. Traditional way., open bleed nipple pump lever. close nipple, repeat. Topping up the master cylinder reservoir as you go.

Remove wheel and pump the brakes gently until the pistons are just about to fall out. Remove the old lines and fit new.

Now, cable tie the brake lever back to the bar and push the pistons in by hand. If they move, you have a leak somewhere and need to get some new seals.

Now cut the cable tie and you should find it easy to push the fluid back up to the master cylinder and all the air should get chased out.  Just be aware that you might need to empty the reservoir a couple of times.

Do this and you will be amazed how much shit will come out of your calipers, some of that fluid will be a nasty milky colour, some of it will be full on black shite.

Enjoy.

 

[Madb]

as the man says. ^^^ plus use red rubber grease on the rubber seals when rebuilding. stops the pistons pulling back.

[markfoggy]

4 minutes ago, Madb said:

plus use HT silicone grease on the rubber seals when rebuilding. Helps the pistons pulling back.

 

[Madb]

oh. ht silicone better then rubber grease then? yes, pulling back,oops. meant to say stops the rubber seals sticking to then pistons.

[Madb]

err, yer up late.

[markfoggy]

:lol: History of 24 HR races, can be a bit antisocial.

[Sam-Jaffa]

What brakes are they, 4 pot or 6 pot?

[canamant]

Tying the lever back does naff all.  The reason for spongy brakes is little bubbles trapped in the system.  If it is in the master cylinder, take the assembly off the handlebar and with the lever pointing up give the lever a waggle, the air trapped in the high point of the cylinder will bubble up the cylinder into the reservoir.  Much more effective than putting a rubber band on the lever.

 

[strima]

Don't tell my wife but I used one of her vibrators to tease the air out of one set of brakes hoses...  

[bluedog59]

Tying the lever back has a use. You put pressure in the system, you can't compress a fluid but you can compress the air in the system and so the air pressure in any bubbles rises and the bubble are more inclined to rise up in the system.

 A few taps on the hoses and they'll all be waiting for you when you "waggle the lever" and back bleed it up through the m/c.

Been doing it like that for years. 

[SiBag]

I had issues with a set of Six Pots not bleeding up, tried all of the usual suggestions.

In the end I took the callipers off, pumped the pistons out and then pushed them back in all the way. This managed to shock the air back up through the system. Now they have a nice firm leaver.