Another can't pressure brakes question.

[omamari]

Yup, can't do it. FXR. Last race I realized my front brake wasn't releasing nicely. Front wheel would barely turn when it was raised off the ground.
Took off caliper, pulled out pistons, really dirty. Cleaned pistons and cylinders. Didn't replace seals. Put back in. Can't get any pressure in the lever. I've raised the caliper up high. Do the squeeze open bleed techniques, nothing. Fluid comes out the line, I got air initially, but now nothing but fluid. Pistons aren't moving at all. I think master is ok as I had solid braking during the race. What am I doing wrong here guys? 312124

[speedpro]

FXR, says it all!

[Drew]

The trapped air is at the master.

You need to angle the bars so that the fluid port in the master is higher than the banjo bolt. Then pull the lever ever so slightly a bunch of times. You'll see the air come out.

[omamari]

Sorry, i don't quite grasp. I'm not sure what the fluid port is, but I guess I just need to have the banjo bolt being the lowest part of my MC?

[omamari]

. You'll see the air come out.

Should it come out through the master?

[omamari]

Drew, legend. I have a little pressure now so it moves the pistons a little bit. But the pistons just get sucked back in again. Can't get them to stay out and take up the gap between pads and disc

[nodrog]

Drew, legend. I have a little pressure now so it moves the pistons a little bit. But the pistons just get sucked back in again. Can't get them to stay out and take up the gap between pads and disc

Pull the caliper off, remove the pads

Pump the pistons out as far as you dare, clean and apply rubber grease.

the seals are pulling the pistons back in by the sound of it

[omamari]

They are, when I reinstalled I did not apply rubber grease. In fact, never heard of it

[Drew]

Drew, legend. I have a little pressure now so it moves the pistons a little bit. But the pistons just get sucked back in again. Can't get them to stay out and take up the gap between pads and disc

Yeah, banjo bolt the lowest bit when bleeding.

Did you take the seals out when you cleaned the caliper? Sounds like you've got them in the wrong way round. The piston doesn't actually slide through the seal when braking. The move through as the pads wear, but most of the time the seal actually rolls to allow the piston to move the pad to the disk.

They are ever so slightly tapered on the piston face to accommodate this.

[FJRider]

The trapped air is at the master.

You need to angle the bars so that the fluid port in the master is higher than the banjo bolt. Then pull the lever ever so slightly a bunch of times. You'll see the air come out.

Cruiser style bars were renown for needing this .. the angle of the dangle ... so to speak .. :laugh:

Nodrog is on to it ... most likely a bit of grit in the fluid jamming the piston. Often best to pull the pistons out and checking for damage ... and replacing the entire amount of fluid (new seals never hurts [except the wallet] either).

[omamari]

I've got them in correctly. It's feeling better now I've got it on the actual disk. I had a bit of ally spacing them when caliper was raised. It was a bit too thick.

Interesting about the rolling.

Thanks heaps guys. Now, seeing as I've got some fresh fluid, KTM time. ..

[omamari]

Cruiser style bars were renown for needing this .. the angle of the dangle ... so to speak .. [emoji23]

Nodrog is on to it ... most likely a bit of grit in the fluid jamming the piston. Often best to pull the pistons out and checking for damage ... and replacing the entire amount of fluid (new seals never hurts [except the wallet] either).

Pistons were a bit rough, but passable. Yea I was surprised they were so expensive.

[Drew]

Pistons were a bit rough, but passable. Yea I was surprised they were so expensive.

Outfit down here makes them to order. Cost me $35 for two seals last time I got some.

[FJRider]

Pistons were a bit rough, but passable. Yea I was surprised they were so expensive.

Passable ... but still not working properly .... but only a bucket ... right .. ??

DIRTY pistons indicate fluid contamination.


My advice ... change the seals AND fluid.

Blow out the line of all fluid and clean all parts. Then replace with new fluid ...

[omamari]

Nah they are working an absolute charm now. Polished the pistons, cleaned out cylinders and seals. All new fluid

[jellywrestler]

Pistons were a bit rough, but passable. Yea I was surprised they were so expensive.

so if you haven't even got the nouse to bleed a basic brake system, how did you have the knowledge to assess the pistons were not perfect but good to go? brakes are there for two reasons, to slow you down and to stop you running into someother person, somebody needs to think of the children here.

[nodrog]

They are, when I reinstalled I did not apply rubber grease. In fact, never heard of it

Brembo calipers on late model Ducatis are awesome for the seals pulling the pistons back of the disc face when they become dirty and/or dry.

2 pump braking is an art form.

[Drew]

2 pump braking is an art form.
It's interesting all right. Terrible on a chair with masiver lever throw too.

I find it's often caused by the seals having worked their way to the lip closest to the disk.

[omamari]

I've done the brakes on my prev bikes, tf125, rmx250, bandit, exc. Never had the problem of air in mc plunger. Learn something new don't ya. I'm also a mechanical engineer, so I've got a bit of common sense regards a seal piston interface. I won't go into a race/road knowing I have bad brakes, it hurts me as well as the children.

[nodrog]

It's interesting all right. Terrible on a chair with masiver lever throw too.

its took me fucken ages to work out why the brakes were so shit.

Googling the problem only came up with retarded yanks spending a fortune on aftermarket master cylinders and still not solving the issue.

5 mins with a set of feeler gauges and I found that it was the pistons retracting, 30mins with some brake clean and rubber grease had it sorted.

[F5 Dave]

Sorry I've missed something here. You sat it wasn't releasing? Either the piston stuck, or more likely the wrong aftermarket lever pushing the MC piston a bit.

Would get worse when hot.

Take lever off to see if releases then file lever do over or buy right lever.

[omamari]

Pistons were really dirty, grimy. Bike I guess was outside a lot, as there was water in tank too. Took out pistons and cleaned. Now they release a lot better.

Now not as firm as before, so will put some red grease on them. Hopefully then they I can get good pressure up. Have spent the day making knobs for the dirt bike, getting a bit excited about it ..http://images.tapatalk-cdn.com/15/05/24/4555931f39cfebef2ebe044b94acd00e.jpghttp://images.tapatalk-cdn.com/15/05/24/531d1e04be6c9c3a8a4a01bdba53f47d.jpg