brake bleeding xj650 uk - twin disc

i have a sealey vacuum bleeding tool, used on several other bikes successfully, so was feeling confident when about to bleed after new pistons, seals etc. i opened the banjos at the caliper joint and let gravity do its thing, then attached the above tool, with hopes of a cup of tea after 30 mins. nothing but air bubbles out of the nipple after 2 hours and several pints of fluid.
I noticed the new (not oem) master cylinder spat fluid at me if i squeezed the lever too quick (dont recall that happening before on other bikes). i put the lid back on to see if i could bleed it the old school way, and attained a solid feeling in the brake lever after 5 minutes! maybe a lucky breake - (dad joke) but i dont care, it worked.

 

Small bubbles or big bubbles?
Air will get sucked past the bleeder threads when using a vacuum. That will cause small bubbles. None of that ends up in the brake system.

 

Big bubbles! mainly on the left caliper, the right caliper had small bubbles and sucked the fluid out of the master cylinder real quick, the left caliper had big bubbles and didnt seem to suck the fluid as quick as the right.

 

I can tell you how I bleed my brakes. It works perfectly for me every time, but that does not mean it is the perfect solution.

1. I fill the system from the bleed nipple(s) until I have some fluid in the master pump
2. I top up the master pump reservoir to minimum level
3. If I have time, I fit the lid, place the bike on the sidestand, turn the handlebars fully left, zip tie the brake lever pulled all the way into the throttle grip and leave for 24 hours or more
4. Sometimes, this alone have left the system free of air. If so, I top up the reservoir to max level and call it a day
5. If air is still present in the system, I push in the brake piston(s) by pushing the (floating!) caliper against the brake disc(s), then pump the pistons back into contact with the brake disc. 1 to 4 times, depending on the amount of air, is all it has taken to get all the air out of the system. I check the reservoir level and fill to max. Job done.

This works because air wants to go up. So filling fluid from the bottom push most of the air ahead of it. More on a single disc system than on a twin disc in my experience. Leaving the lever pulled in seems to, illogical enough, give the air a path to escape as long as the master cylinder is the highest point of the system, hence the sidestand and handlebar turning. Finally, pushing in the caliper pistons will give a flood of fluid rushing upwards, bringing any air bubbles with it.

YMMV

 

now thats different, and interesting, i will give it a try next time, thanks

 

It works every time.

 

That is what was happening to mine so I put a bit of the sealing tape plumbers use on compression joints. That fixed it.