Bleeding rear brake - bubbles never stop coming?

Tempest · Post by **Tempest** » Sat May 12, 2007 6:15 pm

Bit of a puzzle here.

Bled my rear brake about 6 months ago, and then again last night (after fitting new pads)

Somethings odd though.

I have one of those 1 way rubber/clear plastic bleeding tubes which you pop onto your nipple (ooerrrr missus!) loosen the screw and pump away on the brake lever whilst keep topping up the reservoir.

Yet, for some reason,both times I have done this, I never can get rid of the bubbles coming out into the clear pipe.

I've tried the nipple open quite a bit, and also open just a fraction, and must have topped the reservoir up a good 10 TIMES and pumped it all thru, but all the time, there is a constant stream of tiny bubbles in the brake fluid coming out into my clear bleeding pipe.

there are no leaks anywhere in the system, I can't just can't fathom where these bubbles are coming from?

I did wonder if actually they are NOT in the brake line, just getting into it as the fluid leaves the nipple, perhaps nipple to calipur thread is letting air in at the last second.

I really can't see any other way.

Puzzled?

Post by **kevg** » Sat May 12, 2007 6:52 pm

i've had that problem a couple of times in the past also and came to the same conclusion you did that it was air getting into the system through the threads of the nipple itself. i only crack the nipple open enough to let the fluid out.

Post by **sirch345** » Sat May 12, 2007 9:16 pm

It sounds like the non-return valve isn't doing it's job to me, or the pipe is not making a tight seal around the bleed nipple

You shouldn't need to undo it any more than a quarter to half a turn.

I would try bleeding it in the old fashioned way, shutting off the bleed valve after each compression of the brake pedal and see if you still have as many air bubbles.

Don't forget the piece of clear plastic pipe you will be using needs to be immersed in some brake fluid at the bottom of the jam-jar, stopping any air travelling back up

HTH,

Chris.

alan · Post by **alan** » Sat May 12, 2007 11:40 pm

The reason your getting loads of bubbles is you need to:

Take the nipple completelty out and on the thread put some ptf tape then screw back in, attach the oneway bleeder open nipple slightly just so the fluid comes out, pump away on the leaver you should not get any air in the tube now.

I have one of these oneway bleeders,and did the above on all nipples without any probs.

Post by **kevg** » Sun May 13, 2007 9:44 am

i wouldn't use ptfe tape, it dissolves in hydraulic oil, i just put a blob of copper grease on the threads, the same stuff you put on the pistons when you service them. open the nipple a crack and it should be ok.

alan · Post by **alan** » Sun May 13, 2007 11:49 am

Ptf tape was recomended by the instructions that came with the bleednipple and my local Honda dealer, the reason being the tape stops any air leaks which is probably the reason that Tempest is getting loads of air bubbles.