My favorite brake firming technique doesn't work on my Norton

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The Lockheed master cylinder contains a check valve (item 11, link, below) that other master cylinders often don't have although I haven't found it to be a problem and bleed them the usual way.
A check valve???? It is my understanding a check valve allows fluid to travel in one direction and prevents it traveling in reverse direction. It the case of a braking system would not the result be after the brakes are applied the fluid would be prevented from returning hence the brakes remaining on?
 

L.A.B.

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A check valve???? It is my understanding a check valve allows fluid to travel in one direction and prevents it traveling in reverse direction. It the case of a braking system would not the result be after the brakes are applied the fluid would be prevented from returning hence the brakes remaining on?

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"The check valve at the bottom of the cylinder bore assists in purging air from the system during bleeding by ensuring a fresh charge of fluid each time the piston is stroked"

The complete valve assembly, however, will lift allowing the system to vent if there is sufficient pressure.
 

marshg246

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The caliper has 2 ports!
Both pressure and vacuum applied to both, in an intellgent sequence, using a purpose built design fixture is my mission to perform bubble control.
The Norton caliper inner side has a single hole that the fluid must go in and the air must come out. There is only one port to the inner.
 

maylar

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Swing a dead possum over your head on a full moon while chanting yeha-noha.

The Lockheed brake is notoriously difficult to bleed. I've tried the clamp-overnight trick with no joy. One brake specialist recommended putting the handlebars in full left lock while pumping and that actually worked on my buddy's bike. Vigorous pumping as suggested by Tornado has worked for mine.
 
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After dealing with a few commandos that have had spongy feeling front brakes and the attendant bleeding issues i put the vast majority of problems to the wrong surface finish on the caliper pistons. The original caliper pistons are chrome on steel with a mirror like finish.
After 40 plus years you will be lucky to find that they haven't got some rust on them, rending them useless.
The aftermarket stainless ones available, although looking ok, very often have a surface finish that the caliper seal will hold on to, pulling the piston back from the pad. This gives a perfect impression of air in the system!
Five minutes on the buffing wheel to put a mirror like shine on them, reassembled and bled first time resulted in a firm lever and a happy owner.

Piston hang up can happen with bikes other than Nortons, had to deal with a yamaha FZ1000 with 6 pot calipers and a lever that near touched the bar. Been stood for months, I had to exercise each piston for ages to get them to work properly
 
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Page 3.
.
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"The check valve at the bottom of the cylinder bore assists in purging air from the system during bleeding by ensuring a fresh charge of fluid each time the piston is stroked"

The complete valve assembly, however, will lift allowing the system to vent if there is sufficient pressure.
Thanks for the explanation. I figured there was something I was missing.
 
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I tend to look at problems like this with one question: "Did this 'problem' exist when the [car/bike/boat] was new?" IOW, from new did the Commando front brake need to "sit" overnight to properly bleed the system. Per the service manual, the answer is, "No." Did Norton dealers require "overnight" back in the day to bleed brakes? I don't have any idea but someone here probably does. If the service manual is correct AND the dealers didn't need overnight to do it, that would indicate that the cause is related either to changes/age or faults in the system.

Oftentimes, "upgrades" to things have the opposite effect because the upgrade marketers don't really understand the mechanics involved/why things were designed as they were at the time. Replacing chrome with stainless pistons is a good example...
 
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Tornado

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Page 3.
.
.
"The check valve at the bottom of the cylinder bore assists in purging air from the system during bleeding by ensuring a fresh charge of fluid each time the piston is stroked"

The complete valve assembly, however, will lift allowing the system to vent if there is sufficient pressure.
Is this the reason there are two fluid ports/holes in bottom of reservoir? One larger (outboard), one smaller (inboard)?
 

L.A.B.

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Is this the reason there are two fluid ports/holes in bottom of reservoir? One larger (outboard), one smaller (inboard)?

Both are required regardless of there being a check valve.
 
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This method can work well for those last few little bubbles that refuse to exit the bleed nipple.
However, the entire system needs to be uphill for the bubbles and this includes the master cylinder bore.
Usually I put the bike on its side stand and turn the bars fully left.
With a cable tie around the lever overnight any bubbles left in the system accumulate on the end of the piston and are ejected from the return port when you release the brake lever.
The Holts Easibleed kit, with a small minor modification to fit the bleed nipple, (Loockheed should be OK) works every time with empty master cylinder.
 
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tapping the brake line repeatedly at various points may help when lever is strapped tight. It certainly helped get bubbles to rise when initial bleeding wasn’t clearing air. ( I did wonder whether the new braided line was not ‘wetting’ completely, so holding air on it’s inner surface??)
 
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From Old Brits, the only way I got my system bled after converting to 13mm:

BLEEDING THE NEW BRAKE ASSEMBLY
NOTE: PUMPING� WILL NOT BLEED YOUR NEW BRAKE SYSTEM.


Before attaching the master cylinder to the handlebar, bleed the brake system. Start by draping a few rags across the valley between the handlebars and the headlight. Attach the reservoir cap and gasket to the reservoir. Slip a �� box wrench over the bleed valve of the caliper. Attach the short length of vinyl tube (found inside the syringe housing) to the end of the syringe (provided). Draw fresh brake fluid into the syringe unit the syringe is full. Using the syringe, deposit a little brake fluid at the opening of the bleed valve. Depositing the little brake fluid at the bleed valve opening causes a meniscus to form over the bleed valve opening. This meniscus or bubble of brake fluid displaces any air at the opening of the bleed valve. Displacing air at the opening prevents any air bubbles from being injected when the bleed valve is opened. This is especially important if additional bleeding is required. Force the open end of the vinyl tube over the bleed valve. Make sure there are no air bubbles present at the open end of the vinyl tube. If air bubbles are present, remove the syringe with the vinyl tube attached, squirt a little fluid out of the syringe and then reattach the syringe and tube. Open the bleed valve slightly. While holding the master cylinder vertically in one hand, slowly begin to inject brake fluid into the caliper with the other hand. As you inject the fluid, rotate the upper end of the master cylinder in a circle. Holding the master cylinder vertically and rotating the upper end in a circle which injecting the brake fluid into the caliper insures that all air bubble will be forced out of the line and into the reservoir. Do not fully depress the plunger of the syringe. Stopping the plunger early will prevent injecting the always-present air at the end of the plunger. Leaving a little fluid in the syringe insures against injecting air bubbles into the caliper housing. When almost all the fluid is gone from the syringe, close the bleed valve, set the master cylinder on the rages placed across the handlebars and remove the syringe with the vinyl tube still attached. Reload the syringe and repeat the above operation to insure all bubbles have been displaced. The syringe holds 12 cubic centimeters of fluid. The reservoir will comfortably hold 24 cubic centimeters. If it becomes necessary to bleed beyond two full syringes, some of the fluid may need to be removed from the reservoir.
 

Dellis

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I had issues bleeding my Grimeca after fitting a 13mm master cylinder, it would appear to evacuate all the air but the brake pressure was poor then you’d go back to it after 5 minutes and more air would appear. I resorted to my vacuum bleeder and five minutes later all was good.

Dave
 

Dukepaul

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I'm sure most folks if not all are familiar with the technique of firming a mushy disc brake by securing the brake lever in the "on" position (e.g., bungee the brake lever back towards the handlebar) and leaving overnight or longer.

I've had great success with this technique over the years, on other bikes. But it seems to have little or no effect on my Commando (73 850, FWIW). Is the Norton brake system different from most in some way that reduces or eliminates the effectiveness of this technique?
I hadn't heard of this method until reading it on here as I had just fitted a new brembo master cylinder and was struggling to get a good lever, anyway I am now a convert because this worked a treat and now I have a good pressure on the lever.......
 
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