850 MkII - Front Brake spongy - new pistons and brake hose

If anyone is having bleeding problems with there disc brake. What I have found is to make sure the line is below the master not looped above. My next trick is to pack the pistons all the way in with timber blocks expelling all the fluid and air you can. Then bleed as normal pull the blocks out fit the caliper to rotor and pump the lever until you get brakes this normally works for me.
Good luck
 
I have an old 650 Bandit. It has twin front discs, with a line that loops over the front mudguard. So it trapped air in that section when I replaced the brake lines. My solution was to empty the system then put the brake fluid in from the lowest point, using a syringe attached to a clear tube onto the bleed nipple. I pumped the fluid in from the syringe until I had half filled the reservoir on the handlebars. Job done, with a firm lever.
 
Mart UK said:
I have an old 650 Bandit. It has twin front discs, with a line that loops over the front mudguard. So it trapped air in that section when I replaced the brake lines. My solution was to empty the system then put the brake fluid in from the lowest point, using a syringe attached to a clear tube onto the bleed nipple. I pumped the fluid in from the syringe until I had half filled the reservoir on the handlebars. Job done, with a firm lever.
Click to expand...
Aye,
that's common practice in the motor trade, it's known as 'reverse bleed', often used on hydraulic clutches etc.

Good call...
 
marshg246 said:
The seals have two jobs. The obvious job is to contain the fluid. The other is to retract the piston when the pressure is off. With OEM or AN stainless pistons, that retraction is small. IMHO, in all calipers, the seals must "hold onto" the pistons so they can do the 2nd part of their job.
Click to expand...
Normally that is what they do. It's when they 'hold onto' the piston too much is where the problem starts, like i said, the wrong surface finish causes this. Usually with the std 5/8" bore M/C this problem is not so noticeable as you are moving more fluid. Its when a 13mm bore M/C is fitted, you need everything to be working as it should to get the best results. Wasting lever movement just to get the pads in contact with the disc has to be kept to a minimum.
 
Last edited:
I had the same issue. Fixed completely by the stainless hose. The 13mm produces more pressure so can balloon an old rubber hose.
 
While we're on the subject, what is the function of the MASTER CYLINDER DIAPHRAGM part-no: 06.6032 ?
 
The stock Norton caliper is a real pig to bleed. The inboard piston is the culprit and requires special attention to fill it after the rebuild. I remove the caliper (or before installation) and use an eyedropper bottle filled with brake fluid. Angle the caliper so that all fluid goes to the inboard puck. drip in the brake fluid. Then insert a thin wire or sewing needle and with a back and forth motion coax out the bubbles. Do this several times.
 

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