Spongy front brakes

[G-Bek]

So I bought a dirt bike and the front brakes were crap so i bled them. Still no good so i tried clamping the lever to the bar overnight to let air bubbles out, re-bled them again taking the caliper off, keeping it above reservoir and using a syringe to suck new fluid through from reservoir. After that i couldn't get any pressure in the lever so i took it to a bike shop. They bled them, brakes were good for about 1 hr then they touched the grip again. Could there be a seal or something that's shot and causing this? Cheers

[Huggy]

Mine are fucked atm too.

I've tried bleeding them a shitload of times but never get any pressure. I did a gravity feed kind of method similar to what you've done G-Bek, finally got some pressure, but not until the lever was pulled till almost touching the bar. Rode around for a couple of days like that, but felt really unsafe so I thought I'd give it another shot tonight. Cracked the bleed nipple on one of the calipers, a good amount of fluid came through, closed it off, released the lever, went to pump it again and nothing. Have left the lever cable tied to the bar overnight, will see how it is in the morning.

Keen for any advice as well.

[Screamin TE]

There could be a busted seal in the master cylinder. Probably wouldn't cost much to buy either.


In regards to bleeding, take off m cyl cover, attach a hose to the bleed nipple, put the other end in a jar, submerged in brake fluid. Or buy a one man bleed kit. Anyway, squeeze in lever and hold, crack bleed nipple just enough for fluid to start coming out, before the fluid stops, nip it back up. Do that until all bubbles stop, or you get completely new fluid coming through.

[burlyoaf]

have you given the caliper pistons and seals a good clean, it gave may brakes a new lease for a while, after trying different master cylinders,
good clean and new seals may be the way to go... pricey though..

[out_in_front]

Certain types of brakes are known for this - for example my 05 636...

It can just be the seals pulling the pads a bit back off the discs - or even them having some spring in them etc. The only way to fix it on my bike is to buy the 2007 caliper... In reality the brakes still work great - they just feel soft compared to other bikes.

You can fix the feel somewhat buy buying braided lines too.

[G-Bek]

Is this whole replacing master cylinder and piston seals gig hard to do? I'm pretty mechanical but i don't want to end up for a hefty bill if i mince it.

Was thinking of braided lines but didn't really want to go down that path until i have the general feel back in the lever

[G-Bek]

And does anyone know where i can get seals fairly chep should i decide to replace them?

[Renton]

Is it a KTM? If so it's quite a common problem. You'll need to get a caliper seal kit, probably a master cyl kit too. Not hard to change. Personally I don't mind the brakes a bit spongey on the dirty. That way it's not as easy to lock up the front. But if the lever is pulling to the bar that's too far.

[ninjaa]

Seals for mine weren't too expensive, bit fiddly but not too bad. Be careful not to scratch it when removing the old seals

[g0zer]

could also be the rotor

there is a subtle difference between spongy brakes and lever lash

to me, spongy brakes is air in the system while lever lash is caused by well lash in your braking system. for example, if the pads are relaxed off the rotor then you need to pull the lever a certain amount with no resistance (which is the lash) until the pads contact the rotor after which point pressure can build.

its pretty easy to check, pull the caliper off and put a square block of wood inbetween the pads and compare result with the rotor.

calipers square to a square rotor minimises lash, like with anything there are manufacturing tolerances and you get not so perfect brakes. i think most rotors are floating which permits some tolerance so the rotor is pulled square when you apply the brakes, given its not so on the piss that it takes up your entire lever travel to pull it square.

i also dont like the two pot caliper design that uses a large piston with a small, in the interests in giving smooth brakes. one pot presses harder than the other, i think it wears the pads unevenly cocking the pad depth and creates lash as the pads wear.

[ninjaa]

I wondered about that when i was doing the seals

Is there any practical reason? Sure seems like enough room to go a couple mm bigger like the larger piston

[darkfibre]

I wondered about that when i was doing the seals

Is there any practical reason? Sure seems like enough room to go a couple mm bigger like the larger piston

Gives a more progressive feel.

[G-Bek]

Ahh yeah, I'm going to put an oversize disc on it. I'll check for lash then but I'm sure some seals or something must be fucked. Bike is a honda crf450r

[filbert]

I turned up to help a mate bleed his brakes because of the lever hitting the bar, his brake pads were worn out I've seen warped rotors cause similar issue by pushing the pads away each rotation.

[GSX IN SHED]

Just clamp the hose after master cylinder ....if lever is better problem is in caliper/s
Lever stays the same problem in master cyl.... generally worn seal ...rubber gets into compensating port ( small hole in res.) with top off master cyl....while moving lever you WILL see fluid move..upwards from base...caution ...can splash out onto paintwork........if there is no movement/spray upwards....seals might need to be replaced.. ok?
the easy way to flush/ change fluid is to clean out master cyl. First......then add clean fluid THEN bleed as described in above text........pop..

[G-Bek]

Ahh good one GSX, do u just clamp it with a small g clamp or something similar yeah? Won't it damage the line? Its not braided

[19andrew59]

Ahh good one GSX, do u just clamp it with a small g clamp or something similar yeah? Won't it damage the line? Its not braided

You can use a 'G' clamp or vise grips. Use a couple of pieces of plastic between the tool and the line, the tops of ice cream containers work fine.
Alternatively, there is a tool made for the job.

Brake-and-fuel-line-clamp.jpg

[agrid]

A lot of complicated solutions here. ScreaminTE has the old school bleeding wired, do that. If it still gets spongy after use you may be using fluid from a container that has been open for a while, moisture will be absorbed into the fluid, it boils off when you use the brakes and forms bubbles.

[polonY]

Aside from all the wonderful advice, give gravity bleeding a go. Easiest bleeding method on the planet, and no one seems to know about it.

Take off you master cylinder cap, and keep it topped up as it goes down. Crack a bleed nipple until the fluid starts to drip, and then let it drip for as long as you feel like. Gravity pushes fluid from the master cylinder downwards, and as the bleed nipple is at the top of the caliper, the air has a habit of rising out of it. Close the nipple when you are done and you should have good feel (provided everything else is ok).

I use this method in conjunction with a suction bleeder at least once a day (suction bleeders are notorious for leaving air in the caliper) and have not had an issue with it once, ever. Admittedly, only ever on cars, but I can't imagine why a bike would be any different. It works especially well for clutch slave cylinders & drum cylinders, no other method I've used seems to give the same result.

[G-Bek]

Oh yeah good one polony. Do I need to keep the lever taped to the bars or will it still run through?