On my 850 when i apply the front brake the braking action is pulsing. It is particularly noticeable at slow speeds and coming to a stop. The lever doesn't seem to pulse, just the braking action. I notice when spinning the front wheel there is a minor grabbing each time the same part of the disc goes through the calliper, this is the same part of the disc that grabs when slowing down on the road. Obviously the disc is either very slightly out of shape or thicker in one section I think. Any ideas from the panel on the problem or what to do about it. If the disc has to be shaved do I have to worry about re chroming it and what is too thin for this standard Norton disc and brake assembly.
Grabbing front disc brake
- Thread starter nnnrh
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concours said:
So why did they chrome the disc?
Fast Eddie
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To make them look pretty!phil yates said:
They do look a bit naff when un chromed and left out in the rain etc, they rust straight away.
Chrome stops this.
But it is not as good a friction surface.
concours
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phil yates said:
As stated, purely aesthetic. An iron rotor rusts after 30 minutes in the rain, the next day the brown rust gets sprayed on the entire side of the bike, and is a SOB to remove. The Japanese bikes used stainless, not quite as bad as chrome, but still a significant trade off in friction coefficient from the iron rotors.
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My front brake did the same thing. In normal use the chrome wears off the disc but doesn't wear off uniformly. So eventually the disc will get bald spots where there is no chrome which I believe causes the pulsing action of the brake. Over time the chrome completely wore off my brake disc and now the brake works pretty well. If you don't want to wait you could always have the disc blanchard ground to remove the chrome.
Thank you gents, the inside of my disc does have a rust patch but this is not the part of the disc that grabs. I guess it must be slightly warped. Secondly is there a minimum thickness discs can be ground to. My wives car seems to need new discs every so often as the service people tell me they are too thin for any more grinding????
Fast Eddie
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Sensible decision. Let us know if it cures the issue or not.nnnrh said:
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I vote with Glen as likely replacement rotor either still has most its chrome on or has rusted to need resurfacing and for sure its rail road wheel robust thickness is way over kill to handle the heat distortion most of us could even develop to worry about. If not concerned too much with a factory issue only concours look might also have it hole lightened a pound or more off its ~6.5 lb flywheel for distinctly better sense of fork suspension and sooner easier tire squeal slowing with less squeezing to avoid lock up. There is type rotor grinding that does not leave the parallel spiral machine lines that's known to lower friction on pads, blanchard grinding IIRC.
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nnnrh said:
Is that "wive's cars"
Or "wife's car"?
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Forum had discussion to realize there is no listed minimal decision thickness on Norton rotors so its your call or shop how much ya can get away with but very common with only issues ever reported being those with bad weight saving holes job added. I live both my Commando brakers better than my modern dually as more controllable to avoid lock up w/o any pulsing in any of em.
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hobot said:
pete.v suggested to me that a larger disc and new calliper would be effective without changing much else (I already have a S/S re-sleeved MC).
Like nnnrh, I am reluctant to dump the Norton calliper as I like the look of it and it matches the rear. Taking off the chrome might be the way to go for me. For my riding, the front brake is not all that bad as is. I might change my mind in an emergency stop.
Tell me hobot
My original Combat had a brake where the lever could only be pulled in half an inch then dead stop. In other words no feel at all.
But my MkIII has a lot more lever movement and progressive feel. Why would this be?
The best Norton front brake I ever had was the single leading shoe drum on my 61 Dominator 99. I've had Commando drum and disc brakes. Previous Combat had a Lockheed racing calliper. But none had/has the same bite as did my Dominator.
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Don't know why your Combat had such short lever travel and still some brake effect. Only 3 things can shorten lever stroke, mechanical and hydraulic blockage or rather bad ratio between size of master cylinder bore/stroke vs calipers. IIRC Combats have ~17:1 while modern 25-27:1. If ya increase rotor OD then need to redo caliper slider mount by adapter or welding. Also as rotor dia. goes up the width of its friction band goes down so Lockheed single caliper puck would over hang it, like it does on my next Ms Peel brake. I remember my P!! drum brake was better than my two factory Combat brakes UNTIL I poked out the end of rubber restriction valve by red hot 6 penny nail. That didn't get any leverage advantage but boy howdy tire grip sure became my limiting factor to point I'm still pissed off I finally tried forum wisdom fitting 100 size after years of 'confidence' on 110. Only one fella in Texas I know of tried my mod and complained he still had to use same amount of pressure to get about 1/3 shorter more confident stoppage, sheeze. I like the sculpted and fairly light Lockheed caliper so on Peel will see what happens with it over hanging 1/4" beyond the narrower wave rotor friction band. I seriously believe that the main benefit of the sleeved down "up-graded" master cylinders is none of them have any restriction built in. I seek no better braking just better tire on my otherwise factory Trixie and Peel's custom deal is mainly to reduce sprung and spun mass. I hate braking so time to time force myself into cyclic fear states practicing pull downs till I cry Uncle louder than poor ole tire.
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hobot said:
Thank you hobot.
That is very interesting stuff.
I know your preferred method of stopping is to hit trees (and deer etc) rather than wearing out brake pads.
And they are extremely effective techniques.
I just assumed the short lever movement on my 72 Combat was normal. I never tried any other as no one I knew had a Combat, or any Commando for that matter.
The Norton front brake is equipped with ABS (anti lock). You can't lock the front wheel no matter what you do.
I can't fit a larger disc without a different calliper or mounting, that is obvious. I didn't like the look of my Lockheed calliper fitted to my last Combat. It was grey in colour and to be honest, on its own it made no improvement to braking that I could notice.
So perhaps I will stay with what I have (maybe remove the chrome) and stay an honest mile behind the car in front, and never venture past a cross street to eliminate attack from the side. The enemy is everywhere.
Modern double disc brakes are extraordinarily powerful. My Commando will never match that, but I can live with what I have, maybe finding small improvements.
I don't suppose very soft pads would make any difference?
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