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.
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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.
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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.
 
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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.
 
One trick I use is to lease the caliper off the fork leg but engaged with the disc, orient the brake parts so they flow uphill as much as possible by tipping the bike and turning the bars and the tap on the various parts to free up the microbubbles clinging to the sides of the lines and other components. A 50year experience motorcycle mechanic showed me this and it definitely worked on my commando to help bleed the microbubbles which may b responsible for the sponginess.

My only disc brake norton ('72 combat) has a rgm modified master cylinder with a 13mm piston, stock caliper and stock lines and it is actually fairly hard compared to some others I have ridden. Oh, and while I am not sure I would do it again it has silicone brake fluid and has held up well for quite a number of years (some of this was when the bike was off the road because the engine threw a valve).
 
If after all the above has been tried, and you are still not happy, borrow one of your significant other's ahem, 'recreational appliances' overnight. (obviously she will not require said appliance at this hour as she has your undivided then) but do obtain consent, as life will not be pleasant if you neglect this important step. Attach appliance to brake hose, observing all fundamental health and hygiene requirements and retract and tape brake lever to fully retracted position (no sniggering please) and as you retire for the evening hit the most adventurous of the settings on the "mothers little (or large) helper. Fully charged batteries are a must.
In the morning awake refreshed and fully bled...
 
johnny Lagdon said:
If after all the above has been tried, and you are still not happy, borrow one of your significant other's ahem, 'recreational appliances' overnight. (obviously she will not require said appliance at this hour as she has your undivided then) but do obtain consent, as life will not be pleasant if you neglect this important step. Attach appliance to brake hose, observing all fundamental health and hygiene requirements and retract and tape brake lever to fully retracted position (no sniggering please) and as you retire for the evening hit the most adventurous of the settings on the "mothers little (or large) helper. Fully charged batteries are a must.
In the morning awake refreshed and fully bled...
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"borrow one of your significant other's ahem, 'recreational appliances' overnight"

How many significant others do you have exactly? 😊
 
Tornado said:
"borrow one of your significant other's ahem, 'recreational appliances' overnight"

How many significant others do you have exactly? 😊
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I dare not disclose, for a number of reasons:
I am a gentleman, and a gentleman never discusses matters of carnal nature, with enthusiastically consenting ladies, in a public forum.
if her indoors gets even a whiff of extra curricular horizontal jogging I am brown bread.
 
With the 13mm system any air that is not bled from the system has a greater affect on the feel of the brake than it does with the standard bore system, getting it out is key. Also, use fresh fluid, compare fluid that has been on shelf for a while and new fluid. Once you have a brake that functions then try a gentle bleed after a few days this will remove any air that has made its way to the underside of the bleed nipple.
You can polish the pistons you have but be careful, in use the seal needs to grip the piston to retract it as well as keep the fluid in the system, the seals will usually settle after some use and be fine and stop retracting the pistons so much as when they were new.
 


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