norvil break help needed

hello again gents, being that its down time ive decided to try and make right all the minor issues my bike has. all in all its in very good shape, whoever rebuilt this bike before i owned it did a very professional job and made some great upgrades. The problem i need help with today is my brake ( i believe its norvil? ) when firm pressure is applied and held, the break works great. If pressure is slightly release but not completely, the lever loses pressure and collapses into the handlebar. You can imagine how this could be annoying while sitting at a stop sign on a slight incline! I have bled the brake, checked the connections for tightness, and inspected for any fluid loss along the way. Nothing has shown any issue? im very new to nortons ( only had this one six months ) and fairly new to being a mechanic ( 25 yrs old and most my experience is with dirtbikes ) so im out of ideas. any help is appreciated. attached is the pictures of my setup.







thought you might like a full view also

nortoneer850 said:

The problem i need help with today is my brake ( i believe its norvil? ) when firm pressure is applied and held, the break works great. If pressure is slightly release but not completely, the lever loses pressure and collapses into the handlebar. ]

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Hello nortoneer850.

Sounds like the master cylinder needs a new seal. You said no external leaks, so fluid is leaking across the seal. Assuming the bore is ok, someone can direct you to a seal kit for this master.

Cheers

nortoneer850 said:

The problem i need help with today is my brake ( i believe its norvil? ) when firm pressure is applied and held, the break works great. If pressure is slightly release but not completely, the lever loses pressure and collapses into the handlebar.

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The master cylinder assembly looks like a standard Lockheed Triumph unit, and I'd say that's where the problem is. I had a similar problem with a Triumph master cylinder caused by a faulty piston seal.

Master cylinder rebuild kits are available, but the cylinder could also be scored or corroded internally however, new cylinders or complete master cylinder barrel assemblies are available.

Lockheed service manual.
http://www.classicbike.biz/Triumph/Main ... Norton.pdf (25.52 MB)

The advice you had so far is good.....suspect the master cylinder seal.

And the master cylinder probably is a Triumph unit.

But to answer the implied question, no that is not a Norvil set up. It is an aftermarket brake with a modern floating disc and an adapter plate which has been used to mount a Lockheed race style caliper on the original Commando fork leg, in place of the original Lockheed road caliper. The caliper is a CP2696 universal, which is very much like the '70s caliper used in an original Norvil setup, differing by being able to be mounted either way round unlike the original handed parts and having 4 ribs instead of the original items 3!

It is a good caliper used in many classic race setups, there is some choice of pad, but an organic pad would be best for road use. the set up is better than an original Norton road brake, with the possible exception of that master cylinder. The Norvil disc also floated, but by a very different mechanism and it was cast iron, which some don't like because it is both heavy and prone to rust, however it has a better friction rating than stainless steel. I cannot see if your disc is stainless or cast, but most likely it is stainless, maybe you know.

The only thing that is not clear from you photo is if the pads sweep the pad track well.....meaning that it sort of looks like the whole pad may not be running on the metal surface of the disc. Hopefully you can see this easily enough yourself. Check that the pad surface is all above the disc and that worn pads won't end up wearing until they touch in the middle.

SteveA said:

But to answer the implied question, no that is not a Norvil set up.

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It looks like one of the kits as sold by The Norvil Motorcycle Co. (or Fair Spares in the US) so it could still be regarded as being a "Norvil" brake, just not the original factory Norvil brake.

http://www.norvilmotorcycle.co.uk/

L.A.B. said:

SteveA said:

But to answer the implied question, no that is not a Norvil set up.

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It looks like one of the kits as sold by The Norvil Motorcycle Co. (or Fair Spares in the US) so it could still be regarded as being a "Norvil" brake, just not the original factory Norvil brake.

http://www.norvilmotorcycle.co.uk/

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...point taken....it does differ slightly only in the radial hole pattern and the engraving on the supplied bracket, but that is catered for by supply date variations.

The also have a different view to me on the use of sintered pads, but on stainless they should be fine, potentially reducing the life of cast iron only.

Relatively unlikely that the stainless master cylinder barrel is damaged internally, but you just never know.

Might be an inferior m/c seal with a weak volute that collapses under change of pressure. It only takes a tiny bit of seal failure to allow all the fluid to bypass.

Definitely disconcerting on the road!

As a matter of safely, if nothing else, hydraulic seals should really be replaced every 2 years, if you have left the parts in su for five years or more, you really are pushing you luck

SteveA said:

...it does differ slightly only in the radial hole pattern and the engraving on the supplied bracket, but that is catered for by supply date variations.

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It would appear they sell, or have sold, discs with both hole patterns.

Wow everyone, thanks for the speedy replies and good information! The bike sat for ten years before I got my hand on it so I assumed I would run into problems like this. Hopefully I will have them all sorted by the time riding season is here.