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

Hi

I am sorting the front disc brake on my '74 850 Commando Roadster.
I have

- a new AN 13mm Master cylinder
- a rebuilt Caliber with stainless pistons

After several bleeding session (also tying the lever to the handle overnight) I have managed to expel all air from the system.
But I feel the lever pull is excessive (not leaving room for the fingers on the throttle grip).
I believe that the cause is that the pistons grip (in stead of slide) in the piston seals - leaving too much of an air gap btw pad and disc (plenty of air to be seen as the pistons retract).
I have tried rebulding the caliper twice with the same result

To get the perfect brake, plan is now to:
- Upgrade to a braided brake hose (Goodridge, Venhill or similar)
- Get some new SS pistons with a highly polished surface

Questions:
1) What are the brake line thread sizes where it attaches to the master cylinder and the copper pipe union?
Anybody know a good source for braided brake hose for a low handlebar roadster?
Are there some good vendors online manufacturing brake hose to order?

2) Where do I get new SS pistons with a perfect polished surface?
The SS pistons that I have now, are not exactly rough but I feel they could have been finished to a higher standard. I have been looking at

Both appear to have a good finish on them.
Anybody with experience of these?

I am keen to preserv the orginal Caliper and MC - I do not want to swap a modern setup.
Thanks for your help.

Br,
Søren, Denmark

You can polish your current ones, polishing alone will not alter the size. But the grooves the seals sit in are designed to orientate the seal to pull the pistons back slightly when the pressure is taken off. Have you cleaned out the grooves fully or cleaned them out so much you have altered the slight angle in the base of the groove.

An example of groove shape in a caliper (not a Norton)

sorped1977 said:

1) What are the brake line thread sizes where it attaches to the master cylinder and the copper pipe union?

Click to expand...

3/8" UNF.

L.A.B. said:

3/8" UNF.

Click to expand...

sorped1977 said:

Hi

I am sorting the front disc brake on my '74 850 Commando Roadster.
I have

- a new AN 13mm Master cylinder
- a rebuilt Caliber with stainless pistons

After several bleeding session (also tying the lever to the handle overnight) I have managed to expel all air from the system.
But I feel the lever pull is excessive (not leaving room for the fingers on the throttle grip).
I believe that the cause is that the pistons grip (in stead of slide) in the piston seals - leaving too much of an air gap btw pad and disc (plenty of air to be seen as the pistons retract).
I have tried rebulding the caliper twice with the same result

To get the perfect brake, plan is now to:
- Upgrade to a braided brake hose (Goodridge, Venhill or similar)
- Get some new SS pistons with a highly polished surface

Questions:
1) What are the brake line thread sizes where it attaches to the master cylinder and the copper pipe union?
Anybody know a good source for braided brake hose for a low handlebar roadster?
Are there some good vendors online manufacturing brake hose to order?

2) Where do I get new SS pistons with a perfect polished surface?
The SS pistons that I have now, are not exactly rough but I feel they could have been finished to a higher standard. I have been looking at

Wheels :: Brakes :: All Disc Brake Parts :: Brake Calipers :: Norton Commando Lockheed type Brake Caliper Piston - Stainless Steel

Norton Commando Lockheed type Brake Caliper Piston. Fits all 750/850cc Commandos. Supplied in highly polished Stainless Steel. Sold Each. Premium quality stainless steel Piston! Made in England. OEM: 06-1896

www.feked.com

Norton 750 850 Commando Stainless Caliper Piston Kit

Magically lovely, and far superior to original equipment. These stainless steel pistons are precision ground and will never rust or pit. They are suitable for any hydraulic brake caliper fitted to the last Norton Commandos of about 1972-on. CNC machined and polished, Norton's part number is...

www.eurojamb.com

Both appear to have a good finish on them.
Anybody with experience of these?

I am keen to preserv the orginal Caliper and MC - I do not want to swap a modern setup.
Thanks for your help.

Br,
Søren, Denmark

Click to expand...

When fitting my AN 13mm master cylinder I noticed it gave a more spongy feel and the brake lever had greater travel than the original master cylinder. But much improved braking.


But was also pulling my hair out trying to bleed the bastard.

In the end this trick worked for me:-
Gravity bled with just the nipple loosened enough to allow the brake fluid to run out freely (without pumping the brake lever) until clear of air bubbles.

Then tightened the nipple and very gently and slowly partially applied the brake lever several times until the stream of tiny bubbles exiting one of the casting holes in the base of the master cylinder reservoir stopped.

And that's it, a result.


I have Goodrich braided stainless hoses and fittings made to measure and purchased from the Goodrich service stand at the IOM TT many moons ago.


Good luck

Skoti


Edit:-
forgot to mention that it helps if you have the handle bars turned fully to the left when bleeding the master cylinder.

sorped1977 said:

Hi

I am sorting the front disc brake on my '74 850 Commando Roadster.
I have

- a new AN 13mm Master cylinder
- a rebuilt Caliber with stainless pistons

After several bleeding session (also tying the lever to the handle overnight) I have managed to expel all air from the system.
But I feel the lever pull is excessive (not leaving room for the fingers on the throttle grip).
I believe that the cause is that the pistons grip (in stead of slide) in the piston seals - leaving too much of an air gap btw pad and disc (plenty of air to be seen as the pistons retract).
I have tried rebulding the caliper twice with the same result

To get the perfect brake, plan is now to:
- Upgrade to a braided brake hose (Goodridge, Venhill or similar)
- Get some new SS pistons with a highly polished surface

Questions:
1) What are the brake line thread sizes where it attaches to the master cylinder and the copper pipe union?
Anybody know a good source for braided brake hose for a low handlebar roadster?
Are there some good vendors online manufacturing brake hose to order?

2) Where do I get new SS pistons with a perfect polished surface?
The SS pistons that I have now, are not exactly rough but I feel they could have been finished to a higher standard. I have been looking at

Wheels :: Brakes :: All Disc Brake Parts :: Brake Calipers :: Norton Commando Lockheed type Brake Caliper Piston - Stainless Steel

Norton Commando Lockheed type Brake Caliper Piston. Fits all 750/850cc Commandos. Supplied in highly polished Stainless Steel. Sold Each. Premium quality stainless steel Piston! Made in England. OEM: 06-1896

www.feked.com

Norton 750 850 Commando Stainless Caliper Piston Kit

Magically lovely, and far superior to original equipment. These stainless steel pistons are precision ground and will never rust or pit. They are suitable for any hydraulic brake caliper fitted to the last Norton Commandos of about 1972-on. CNC machined and polished, Norton's part number is...

www.eurojamb.com

Both appear to have a good finish on them.
Anybody with experience of these?

I am keen to preserv the orginal Caliper and MC - I do not want to swap a modern setup.
Thanks for your help.

Br,
Søren, Denmark

Click to expand...

If the pistons/seals are not leaking, then they are unlikely to be a problem.

The Norton OEM, even with a 13mm master cylinder, will never be a "perfect brake" or even a really good brake. However, they can be acceptable as long as not compared to modern.

It is likely that you don't have all the air out. Norton calipers are very difficult to bleed since the drive-side air must come out where the fluid is going in. There is one easy, but messy, way to do it for sure:

1) Remove the caliper and take out the pistons and bleed screw.
2) Inspect the hole from the bleed screw to the drive-side chamber. Some were poorly drilled and stopped short of a clean hole into the chamber.
3) With the caliper lying on its back, fill the now bottom chamber 1/3 full of fluid.
4) Put in the bottom piston and push it home just enough that you will be able to put the pad in when installing the caliper. Go slow - fluid will squirt out of the bleed hole.
5) Put in the bleed screw and snug it.
6) Put in the other piston, again far enough for the pad to be in place.
7) Fill with fluid
8) Screw in the cover. Go slow as fluid will squirt out of the hose connection.
9) Screw a 3/8" UNF bolt into the hose connection to close it off.
10) Clean everything
11) Install the caliper - it is bled.
12) Bleed to get the air out of the master cylinder and hose - the caliper is already bled.

I have custom braided lines made for every bike, but the shipping from my guy to you would be more than the hose. A braided line will help some.

As above, you probably have some air that needs to be bled.
It sounds like the 13 mm master cylinder is new to the bike and you.
Keep in mind that going from a 5/8" piston to a 13 mm piston will mean that you have more travel in the lever.
It doesn't explain all the symptoms you describe, but even when fully bled the brake will feel a bit "spongier" than the old setup. But it will stop significantly better.

Was in a similar situation with my mkII 850 resleeved MC. Tried all the usualy tricks, reverse bleed, lever tied in overnight, etc etc. In shear frustration, I started flicking the lever dozens and dozens of times with the cap off the MC watching the fluid inside. Then, after maybe 30 or 40 flicks, suddenly saw micro bubbles emerging out the tiny holes in MC floor. Lever went firm...kept flicks another 20 or 30 times. No more bubbles and feel was great. Been fine for several years and fluid changes since.

The rapid flicks must somehow setup a pressure pulse/vibration that frees up a stubborn trapped air pocket.

New stainless pistons can have the wrong surface finish, they look ok but they hang up in the caliper seals giving the exact same symptoms as air in the system. If you can feel grooves along the piston surface with a finger nail they have the wrong finish, Cure can be as easy as polishing the grooves off on a buffing wheel. AN 13mm M/c can also give trouble, Too much lever travel before the relief port is closed off. Cure then is to have a 'top hat' shim installed on the M/C piston to take up the excess travel. Thickness of this shim depends on the M/c and lever relationship.

On some bikes, not sure if this applies to Nortons, frustrated owners have success with pulling the brake lever in hard, zip tying it as tight as they can in that position, and leaving it overnight. Next day, the sponginess is gone. Presumably the air works its way out of the brake caliper and up through the mc. Exactly why beats me. Just repeating what I have heard.

Tornado said:

Was in a similar situation with my mkII 850 resleeved MC. Tried all the usualy tricks, reverse bleed, lever tied in overnight, etc etc. In shear frustration, I started flicking the lever dozens and dozens of times with the cap off the MC watching the fluid inside. Then, after maybe 30 or 40 flicks, suddenly saw micro bubbles emerging out the tiny holes in MC floor. Lever went firm...kept flicks another 20 or 30 times. No more bubbles and feel was great. Been fine for several years and fluid changes since.

The rapid flicks must somehow setup a pressure pulse/vibration that frees up a stubborn trapped air pocket.

Click to expand...

That’s exactly the way I do it. I think that method momentarily opens the smaller hole rather than it being closed by pulling the lever in completely. Whilst doing that I also rapidly tap the hose with the handle of a screwdriver.

The first time I did this I observed what I thought was dirty fluid coming out of the port, but using a torch and a magnifying lens I was able to see thousands of minute bubbles coming out. Exactly as you mentioned.

Another tip, once you think you have it bled, push the pistons back, and start flicking the lever again.

Genlty re-bleed the the system after few days use as this will improve the brake. By this time the caliper seals will have 'set' nicely and the remaining air in the system makes it way to sit under the bleed nipple. if you look at the way the caliper is manufactured, it is designed for the pre-MK3. On the MK3 the bleed drilling to the nipple is not in the best place and this tiny amount of air trapped in the caliper takes some patience to remove.

Madnorton said:

Genlty re-bleed the the system after few days use as this will improve the brake. By this time the caliper seals will have 'set' nicely and the remaining air in the system makes it way to sit under the bleed nipple. if you look at the way the caliper is manufactured, it is designed for the pre-MK3. On the MK3 the bleed drilling to the nipple is not in the best place and this tiny amount of air trapped in the caliper takes some patience to remove.

Click to expand...

Would the solution to that problem be to remove the caliper from the fork leg and position it so that the bleed nipple is upper most and the trapped air could then escape?
Then refit and test the brake.

But I have a MK2 so don't have that problem.

Thanks a lot for all the good answers.
I have already bled, re-bled, tied the lever to the handle and watched tiny bubbles escape in both MC and from the nipple.

My next move will be to buy a new set of polished pistons (don't have the equipment to polish existing pistons myself).
I will also renew the brake hose - will probably buy the fittings (3/8 UNF) and a piece of braided hose and do the brake line myself.

Information on bleeding is much appreciated. I will probalby try and assemble the caliber with fluid as described - messy, but will save a lot of bleeding I guess.

Will keep you all posted on how I get on with it.

sorped1977 said:

My next move will be to buy a new set of polished pistons (don't have the equipment to polish existing pistons myself).

Click to expand...

What do you think polished pistons will do for you? IMHO, if the pistons/seals are not leaking, then they are fine.

Assuming your master cylinder is not incorrectly made, the passages in the caliper are clear, and the seal grooves are spotless, I'm sure you are not completely bled.

Most calipers have a way for the fluid to go in and it flows through the caliper to the bleed screw. The Norton caliper is not that way! You are trying to force air out the hole that fluid is going in.

If you use normal bleeding procedures from dry, the first 40-50 pulls will seem to do nothing, at about 90 pulls it will begin to tighten up, and at 96-100 pulls it will be as good as it will be. A least for me, no of the "tricks" work. That's why I do it as in post #5 - I'm done in 10-15 minutes.

marshg246 said:

What do you think polished pistons will do for you? IMHO, if the pistons/seals are not leaking, then they are fine.

Click to expand...

The OEM chrome plated steel pistons had a surface finish that is/was as smooth as glass (so long as they weren't rusty!) Some of the new stainless steel pistons have a surface finish that makes the caliper seal 'hold onto' the piston when it should slide through. This holds the piston away from the pad, so when the lever is pulled to apply the brake, excess lever travel occurs to move the piston into contact with the pad (brake applied) Piston seal not leaking, just causing the piston to hang up in the caliper. Easily found if you hold a finger underneath the caliper touching the pad tang. Feel how much the pad is loose in the caliper and then squeeze the brake lever whilst still touching the pad tang, note how much the lever travels before the pad tang firms up. You might be surprised at how much lever travel is waisted just getting the pads to contact the disc.

dobba99 said:

The OEM chrome plated steel pistons had a surface finish that is/was as smooth as glass (so long as they weren't rusty!) Some of the new stainless steel pistons have a surface finish that makes the caliper seal 'hold onto' the piston when it should slide through. This holds the piston away from the pad, so when the lever is pulled to apply the brake, excess lever travel occurs to move the piston into contact with the pad (brake applied) Piston seal not leaking, just causing the piston to hang up in the caliper. Easily found if you hold a finger underneath the caliper touching the pad tang. Feel how much the pad is loose in the caliper and then squeeze the brake lever whilst still touching the pad tang, note how much the lever travels before the pad tang firms up. You might be surprised at how much lever travel is waisted just getting the pads to contact the disc.

Click to expand...

What you describe sounds exactly like the issue I had using some Girling copies of AP calipers.

I’m now wondering if it was the piston machining finish as you suggest?

Fast Eddie said:

What you describe sounds exactly like the issue I had using some Girling copies of AP calipers.

I’m now wondering if it was the piston machining finish as you suggest?

Click to expand...

Possible, I've dealt with caliper piston 'hang up' on bikes other than our commando calipers noteably a Fzr 1000 yamaha fitted with six pot calipers. the owner reported that although the brake worked fine, the feel through the lever wasn't to his liking. You could almost get the lever touching the bars if you squeezed hard enough (he said you would lock the wheel if you did that when riding along!) I had to exercise the pistons backwards and forwards in the caliper (using small G clamps) to get the pistons sliding smoothly in the seals and the lever feel to his liking (I think the bike had been stood for a while so the seals got stuck to the pistons)

All I can add to this discussion is don't polish up or reuse the original Norton - Lougheed caliper pistons . Buy stainless ones , they don't rust , pit or seize up . Not expensive .
Replace all rubber bits .
Use fresh brake fluid and flush it out every 2 or so years .
Enjoy .

Fast Eddie said:

What you describe sounds exactly like the issue I had using some Girling copies of AP calipers.

I’m now wondering if it was the piston machining finish as you suggest?

Click to expand...

Ironically the first time i made some stainless pistons (back in the mid 1980s) to replace ones was for some AP CP2195 calipers that the original anodised alloy pistons had suffered corrosion damage.

dobba99 said:

The OEM chrome plated steel pistons had a surface finish that is/was as smooth as glass (so long as they weren't rusty!) Some of the new stainless steel pistons have a surface finish that makes the caliper seal 'hold onto' the piston when it should slide through. This holds the piston away from the pad, so when the lever is pulled to apply the brake, excess lever travel occurs to move the piston into contact with the pad (brake applied) Piston seal not leaking, just causing the piston to hang up in the caliper. Easily found if you hold a finger underneath the caliper touching the pad tang. Feel how much the pad is loose in the caliper and then squeeze the brake lever whilst still touching the pad tang, note how much the lever travels before the pad tang firms up. You might be surprised at how much lever travel is waisted just getting the pads to contact the disc.

Click to expand...

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.