Brake bleeding

Can someone please tell me the process for brake bleeding? I've rebuilt the calipers with new seals and pistons but no matter what I do I can't get rid of the sponge in the lever feeling. Pump it and it's fine for a few mins but then goes back to spongy. Fluid IS going through (I've gone through about 2 litres!) . I've tried manual, I've tried a hand held air pump and I just can't get rid of the feeling. I've even tried the Teflon tape on the threads of the bleed nipple

 

Are the caliper pistons and seals clean? Can you move the pistons with a finger? If not, you'll never have good lever feel?

With each piston slightly out, clean with toothbrush and Simple Green until spotless 360 degrees around. Then rinse with H2O. One at a time.

IMHO, bleeding is nearly never the problem.

 

Yes, as above, they're all brand new.

 

Sorry. Just because they're new doesn't mean that they move freely.

Maybe crack each joint with a rag around them during a tiny squeeze?

 

I'll check again in the morning but fairly certain they're all free.

 

Hi Daniel, difficult to diagnose like this. Are you following the correct procedure ? I'm assuming you have a pipe connected to the nipple going into a container before you start.

1. Pressurise the brake by pumping the lever and hold.
2. Slacken off the bleed nipple slowly until you feel the lever give all the way back to the bar. Nip up the nipple. Let the brake lever out slowly.
3. Repeat.

Do this a few times, then do the other caliper.

Keep going doing both calipers in turn until the lever is firm.

One other thing, check the pad retaining springs are on correctly. You can get them misplaced, and it does affect the movement of the pads giving an odd feeling to the lever. Leave purged out fresh brake fluid overnight before re-using to allow bubbles to disperse. Always keep enough fluid in the reservoir otherwise its start from scratch time again ..

The left hand caliper has the small pads driven from the rear brake, has that bled ok ?

 

Hi, yes process followed as normal. I'll double check the pistons and pins but I'm not getting any binding anymore. I've even tried to use a hand held air pump. The rear circuit (so top two front pistons and rear) seems somewhat better albeit not perfect. It's driving me absolutely insane! I even tried to force the ABS on a ride this afternoon to see of that was the issue. I've now left it until morning with the reservoir lid off and lever pumped and tied back to the bar.

It just reeks of an air bubble somewhere. Pump it and it'll be fine until its used a few times and it turns to shit again.

 

OK, I've unbolted the calipers again. Seems on the rhs one (not checked left yet) the pistons weren't moving properly. When pressure applied 3 closest to the wheel would barely move and then sink back in again. I've now got them all moving pretty much in sync. Assuming this is a likely cause of the feeling?

Sorry, about rudely ignoring this to begin with. I've had a twat of a week doing this and an old CZ!

 

Some have found that removing a caliper at a time, raising it up as high as you can, then bleeding it can help in odd situations ? ( with a bit of wood where the disk should be)

 

You need to work out how far the pads retract when you release the lever. If the pistons are moving too far back into the caliper you are never going to have a fim lever apart from after pumping it a few times. Did you put the seals in the right way round?

 

Have you tried securing the brake lever fully on and leaving overnight? Sticky tape should do or anything that will hold the brake lever tightly on.

 

Cable ties work. Never had much success with this. I think it compresses the air into smaller bubbles that can mover more easily up the hose to the master cylinder.

 

As far as I know, Nissin main piston seals are square, so new ones can go in either way around. The groove has a small taper on it to get the slight angle needed to grip the piston I believe.

 

Get a brake hose clamp and choose one of the front hoses, clamp it off, does that improve the lever? Work round all the hoses in turn. To check the master cylinder clamp the hose leading from it. See what happens.