CB400 - Front Brake Bleeding.

[Integra99]

Hi all,

Has anyone had issues bleeding up the front brake.. I have rebuilt the caliper, new pads, new M/C so all good. I have brake pressure but not much.. unfortunately I dont have use of a compressor to assist as feel it might need a little help. All the lines are tight but I keep getting bubbles in the line so I have no idea how its getting air in.. I assume the brake switch is an area for air to get trapped. The switch works as its operating the rear light I'm just struggling to get a firm lever.

Any tips.. its off for an MOT soon so my friend can do it on his system but would be nice to turn up a little more prepared.

[taysidedragon]

All I can suggest is fill the reservoir slowly so you don't introduce bubbles there. Keep pushing the fluid through and make sure you close the bleed valve while still squeezing the brake lever each time.
It should work once enough has gone through. Patience required.

[Integra99]

Thanks yes I probably haven't been patient enough.. one thing I am getting is bubbles out of the reservoir when releasing the brake lever.. not a lot but seem odd"!

[taysidedragon]

Is that after closing the bleed nipple then releasing the lever?

[Tomb]

Persistence pays off, I ended up cracking open all the banjo bolts on the lines on my 500, lots of air came out there, bloody messy though.

[Integra99]

Yes I bled the bolts.. really messy and panicking with all my nice paint ha!

the bubbles come when I pump the lever a few times to build up some pressure after a bleed and tightening of the nipple.. in the mechanical sense ha!

[taysidedragon]

It sounds like there is either air bubbles still in the fluid and need to keep bleeding through - or you may have a leak somewhere in a joint or in the m/c.

[Integra99]

Thanks I will keep persisting.. I have a brake but must just be lots of air.. the M/C is new and worked perfectly before the strip down. Will bleed the banjos again top to bottom, then leave a strap around the leave and the cap off over night maybe to force air up.

[taysidedragon]

Yep, keep at it. Those pesky air bubbles are a pain! You'll get there. 

[kevski]

Put a couple of wraps of ptfe tape around the thread of the bleed nipple this will stop air getting in there, I always draw fluid through using a 50ml syringe and it only ever takes about half an hour.

[Integra99]

Thanks all,  do you draw fluid out of the bleed nipple with the syringe once slackend off..?

[kevski]

Thanks all,  do you draw fluid out of the bleed nipple with the syringe once slackend off..?

Yes, its awkward but it works for me, squeeze the lever while drawing syringe then keep drawing while shutting nipple you almost need three hands.

[Integra99]

I'll have a go this evening! 

[MrDavo]

It is possible that you are pulling the lever too far, past its normal travel when you are trying to bleed it. if this is the case, particularly if you are pulling the lever all the way to the grip,  you'll never do it, ask me how I know.

I'm pretty sure there is a service bulletin that advises you to tape a suitable object to the grip, to stop the lever from travelling further than it should.

The rear disc on my Sportster can only be bled using 'baby steps' - if you push the pedal to far, even just once, the piston sticks in a part of the bore it never normally sees, and you are fecked until you take it to bits again. I learned this the hard way, too

[Integra99]

Interesting.. yes I guess I am pulling all the way in.. its how I've always bled brakes same on a car.. foot to the floor and up.  I didnt get a chance last night so will try again.