Another brake question

[ChrisH Kerry]

After problems I had getting the pistons to retract into calipers when I replaced the front brake pads a while ago. In the end, when I finally got the new pads in I noticed only left hand side caliper was working, I seem to remember Smudger had similar problem - a blocked pipe. I decided it was probably a good time to replace brake lines.
Anyway put new brake lines on today - bled it using patented bleeding tool (100cc syringe + plastic pipe ) ABS unit bled no problem but the calipers were reluctant to allow fluid to suck through. Resorted to old fashioned method of pulling in brake lever - open nipple - close nipple - bla bla bla ... and that worked OK, but there still seems to be a bit of air in it. Tied the lever back and will see what happens. The other thing was, when using method #2 as the brake lever was pulled back there was a small 'ejaculation' of brake fluid up from the reservoir which seems a bit odd? At least both calipers are doing something but a little less spongy-ness would be nice
There was never a problem with ABS initializing and wasn't particularly noisy so hopefully the unit is OK. Brakes were good before, just the pads were in need of replacement. Can't understand why fluid wouldn't suck through from the bleed nipples on calipers though? Any ideas?

 

[Steptoe]

The other thing was, when using method #2 as the brake lever was pulled back there was a small 'ejaculation' of brake fluid up from the reservoir which seems a bit odd?

Perfectly normal. It would be odd if it didn't "spurt".

 

[ChrisH Kerry]

Thanks... Just a bit messy when you're trying to bleed them What about the other question regarding vacuum bleeding calipers?

 

[JoeC]

Did you bleed the brakes with the pistons fully pushed in?
Otherwise you can get air bubbles behind them.

 

[monkeyboy]

I know people don't like doing this cos it crimps the hose but whenever I've changed the lines I've never managed to get a fully bled system without doing it. You can't put that much pressure in the lines just by pumping the lever on it's own I find. I pull the brake in, then before letting it off, I use some fuel line pliers and clamp the brake hose not far from the reservoir. Then let the lever out, and as I pull it in again, release the clamp, then repeat until the lever is fully hard. That puts more pressure in for bleeding in the traditional nipple way I find. I've got a vacuum bleeder and all that but it never gets 100% - perhaps I'm not using it correctly! If I'm going to bind the brake lever up overnight I always pressurise the line like this first.

Just have to be careful if you let the pressure off with the reservoir top off cos the spirt can be quite dramatic

 

[DrFarkoff]

Did you make sure all the pistons are free moving now??

They will feel a little spongy if you rebuilt them

Before when the pistons were "sticking" the pads were in close contact with the disc, as they didn't really retract so as soon as you pull the lever you had immediate brake effect

So now they retract a little and you have the slack to take up to bring them in contact with the disc and then more to apply to get them to brake for you Hence a little spongy

You also get the same effect when you change pads on worn discs it takes a hundred miles or so until the flat pad wears to follow the disc contours

As long as you have controlled braking without having to pump them give it a few days to see if they bed in and bleed them again after

 

[ChrisH Kerry]

All the pistons were free, it was just the right hand caliper pipe had a blockage in it so pistons wouldn't push back in. Once I loosened off the banjo bolt the pistons pushed in fine, but the blockage had lodged firmly in place and that side caliper stopped working altogether.
New brake lines and replacement of that stupid yoke on the right caliper with a normal bleed nipple and fluid flowing out of both sides when lever is pulled, but if I try to "Draw off brake fluid until it emerges clear and free from air bubbles" as the manual says it don't work, just seems like air drawing up the threads of the bleed nipple. Not that bothered if I can bleed them OK the other way, just wondering why the vacuum method won't work?

 

[monkeyboy]

All the pistons were free, it was just the right hand caliper pipe had a blockage in it so pistons wouldn't push back in. Once I loosened off the banjo bolt the pistons pushed in fine, but the blockage had lodged firmly in place and that side caliper stopped working altogether.
New brake lines and replacement of that stupid yoke on the right caliper with a normal bleed nipple and fluid flowing out of both sides when lever is pulled, but if I try to "Draw off brake fluid until it emerges clear and free from air bubbles" as the manual says it don't work, just seems like air drawing up the threads of the bleed nipple. Not that bothered if I can bleed them OK the other way, just wondering why the vacuum method won't work?

If your vacuum is anything like mine then the seal isn't perfect and at least some if not all the bubbles will be coming from the outside past the nipple as the air is easier to draw than the brake fluid. Vacuum bleeding will not draw out the little air pockets trapped in the callipers. You can twist and tap the callipers to release bubbles I reckon. I usually bind up the lever overnight. I hate bleeding brakes and it always takes me forever!