spongey front brakes 02 yz250

[yamahootin]

G'day fella's,
The front brakes on my 2001 yz250 are very spongey despite putting a heap of fluid through the system to bleed it. I put 3 fingers into the lever and i am lucky to just lock it up if i keep my weight back. Im no arnie but that is riduculous The pads are near new and there doesnt seem to be any leaks in the lines. Are there any other conditions that could be causing this that need attention?

Cheer's

[azzfox]

The master cylinder might a seal overhaul. There should always be some pressure in the line even when not in use. Might have a worn piston seal letting too much fluid escape back into the resivour. Try pumping the lever a few times to build up pressure then open the bleeder valve, some fluid should run out.

Alternatively the rotors may be glazed. My front brake never used to lock either until I roughened up the pads with a file and sandpapered the rotors. Now I can get it to lock using one finger to this day.

[mephistopheles]

My son's 2008 yz85 was like that Brand New. it took a whole lot of fluid to get all the air out and then I use a trick I learned from road racing.

After you finish bleeding the brakes pump them a few times and then wrap a string around the handle and grip a bunch of times. it will get tighter every time you go around. tie it off and leave it like that over nite. the next morning the handle should be firm but bleed the brakes again and you will find that there will be a few more air bubbles. tie it up for one more night and you should have a nice firm handle.

it always helps to use steel braided lines in my opinion and now the lever on Joey's bike is nice and firm.

[MXtras]

There is one sure fire way to get the brakes rock hard - backbleeding. Get either an irrigation syringe or three from a local animal hospital or a handheld pump can. Get a small section of clear tubing. Fill the syringe or pump, attach the hose and pump the hose full of fluid, then place it on the bleeder fitting and open the master cylinder. Open the bleeder fitting and pump the fluid backwards into the cylinder. This eliminates any chance for air. Don't expect the syringe to last for more than one session - the brake fluid swells up the plunger seal and renders the syringe useless, so grab a few from the vet - they come in handy for doing fork oil, too. I get them for about $1 each and buy 20 at a time.

Another way that gets good results - on the 02 YZs the front hose has a high point down low where it exits the caliper - the hose snakes up and around then under the fork leg then back up. Stupid. Take the caliper off and straighten the hose. Let it hang or rest it on a board and slide a piece of 1/8 plate between the pads then bleed as usual. This is the way I do it at the track (I bleed my front brakes at least once during an event) The stupid high spot in the hose collects air and can be a pain to get bled completely. Straightening out the hose eliminates the hump.

Sorry to be so short - I am at work. Hopefully this helps.

Scott

[yamahootin]

Ur all champions.... Thanks for your help . Ill give all your suggestions a go....minutes before i end up over the hangers imsure :-).

Cheer's

[yamahootin]

Back again fellas. So far i have back bled the front brakes, Tied the lever up overnight, removed and hit the pads and brake disk with a flap disk on a drill and adjusted the lever to maximum travel and still the thing wont halt up. The lever is definately holding pressure and doesnt make contact with the grip when i squeeze the hell out of it, so i figure that master cylinder wouldnt be the major proplem.

Q:Is it common for one of the slave cylinder pistons to seize and the pressure from one piston only isnt enough to stop the bike?

Any thoughts would be appreciated :-)

[MXtras]

Yeah - that's a possibility but unless the fluid was in really bad shape, it's not likely. It's worth a shot though - take a look at the action - if one is hanging up, it will be obvious.

When you are bleeding the system, are you getting a strong stream out of the bleeder? Does the stream correspond with the entire stroke of the lever?

Scott

[yamahootin]

Yeah one of the pistons came out first then the other but it didnt take any extra effort and seemed pretty easy ...maybe just a little bit tighter.

The stream is strong and consistant to the stroke of the lever.

Would fork oil that had leaked on the disk/pads burn away after a few laps or could this put a permenant film on the pads and disk? The oil would sit in the pits of the sintered metal pads and constantly lubricate the disk wouldnt it?

[MXtras]

Oily conventional pads tend to grab - not slip but the sintered pads do simply not grip when wet with oil.

Scott

[yamahootin]

Thanks heaps for the info Scott and i think i may get rid of the metal pads then. Any suggestions on what type/brand i should go for would be appreciated?

Cheer's

[Freak]

Originally Posted by MXtras

There is one sure fire way to get the brakes rock hard - backbleeding. Get either an irrigation syringe or three from a local animal hospital or a handheld pump can. Get a small section of clear tubing. Fill the syringe or pump, attach the hose and pump the hose full of fluid, then place it on the bleeder fitting and open the master cylinder. Open the bleeder fitting and pump the fluid backwards into the cylinder. This eliminates any chance for air. Don't expect the syringe to last for more than one session - the brake fluid swells up the plunger seal and renders the syringe useless, so grab a few from the vet - they come in handy for doing fork oil, too. I get them for about $1 each and buy 20 at a time.

Another way that gets good results - on the 02 YZs the front hose has a high point down low where it exits the caliper - the hose snakes up and around then under the fork leg then back up. Stupid. Take the caliper off and straighten the hose. Let it hang or rest it on a board and slide a piece of 1/8 plate between the pads then bleed as usual. This is the way I do it at the track (I bleed my front brakes at least once during an event) The stupid high spot in the hose collects air and can be a pain to get bled completely. Straightening out the hose eliminates the hump.

Sorry to be so short - I am at work. Hopefully this helps.

Scott

Mxtras, wealth of knowledge bro. Always learn a lot from your posts.

[MXtras]

Thanks, Freak. I really appreciate that!

Scott