Master cylinder check valve

I thought it might be worth explaining the function of the check valve in the standard master cylinder that seems to cause much consternation hereabouts. It is actually a reasonably clever and useful one-way valve (with an override) to aid bleeding in a motorcycle installation. In normal use, the valve allows high flow from the master cylinder to the caliper, and in practical terms offers no restriction as the brakes are applied. When the brakes come off, the valve can lift off its seat momentarily to allow high pressure to decay, but then the small orifice helps restrict flow back to the cylinder, which can be of benefit when bleeding the brakes for example, when you are trying to encourage a flow from the reservoir to the bleed-screw.
The valve is not absolutely necessary, as many brake systems manage perfectly well without them. If you feel the imaginary restriction when applying the brakes is the cause of all your braking woes, the valve could be removed, though it may be an idea to replace it with a ring of the same flange thickness to maintain return spring pre-load.

Hope this helps!

Cheers, Jon.

According to one forum member, piercing that valve will not only stop your bike in 10 feet or less, it will eliminate erectile dysfunction, cure baldness and remove unsightly warts.

So I understand... :roll:

JimC said:

According to one forum member, piercing that valve will not only stop your bike in 10 feet or less, it will eliminate erectile dysfunction, cure baldness and remove unsightly warts.

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It may do all of the above and on top of all those things it may even cause rapid weight loss the resulting brake scares the s##t out of you.

toppy said:

JimC said:

According to one forum member, piercing that valve will not only stop your bike in 10 feet or less, it will eliminate erectile dysfunction, cure baldness and remove unsightly warts.

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It may do all of the above and on top of all those things it may even cause rapid weight loss the resulting brake scares the s##t out of you.

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One thing it will not do is make any difference in the performance of the stock Norton front disk brake.

It also makes it more likely that the brake puck will get pushed back into the caliper when cornering aggressively resulting in a unpredictable lever height. Jim

I incorrectly stated that punching a hole in the master cylinder check valve would not change the performance of the Norton disk brake. I believe Jim Comstock has identified a performance modifier.

I'm sure there are forum members who qualify as experts on the subject of hydraulic brakes. If I were to seek an expert's definitive answer as to the efficacy of punching a hole in the Norton master cylinder check valve, I would contact Mike Morris at Vintage Brake. Personally, a rudimentary understanding of physics is enough for me.

This may be of some help:

dud dear rude dude hobot hole has nothing to do with any check valve *only* the front brake restrictor hole that is labeled as a valve in parts book. It is completely open plain hole in rubber surround so same restricted flow in as out. Chalk and cheese comparison for misdirected obnoxiousness. Fact of the matter is apparently only me and one Texan knows difference of just restriction removed vs restriction removed *plus* ratio" increased. This hole is so tiny and in center of bore that is does hinder bubbles on brake bleeding but completely different physics why than a check valve, my Cdo's never had. Ms Peel had all the features of all the upgraded resleeves, done my Rick and Mary mom pop shop plus RGM lever on a 110 tire minus the 1.6 lb lighter Heinz rotor spin, so I know what that's all about yet with just a hobot hole in plain jane Trixie, squeals at any speed, lockup possible around 70 so have let off all the rest of the way down so now no need or desire for better life saver and can keep Trixie part numbered only. Hole was quite good enough I drooped plans to upgrade Trixie with Peels hand me down brake soon as possible bit minus the lightened rotor Gerry The Oil Guy took with him on his death. At least you bring Gerry back to mind and maybe above will convince someone to try just a hot nail and get back to us.



The 'valve' restriction is in the left more end item here with a hard plastic spreader that may look like a check valve to some but has 3 opens to pass fluid freely so only retained as part of return spring tension stack. Try it ya may like it but new mc sales could sag if word gets out.

hobot said:

The 'valve' restriction is in the left more end item here with a hard plastic spreader that may look like a check valve to some but has 3 opens to pass fluid freely so only retained as part of return spring tension stack. Try it ya may like it but new mc sales could sag if word gets out.

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Tried it,
It makes the brake application quicker and the initial lever feel is lighter.
It in no way makes the brake more powerful in a stop from speed. It also made the lever position a bit unpredictable on the track. Jim

Hobot,

Don't you realize what you are attempting defies a basic law of physics? Even in Arkansas or Texas.

Ok comnoz what do the resleeved mc's use instead that make them check valved predicable. Everyone but hobot seems to use brakes hard while leaned racing around in public so I guess I just don't know what I'm missing out on. My panic tests are going straight into pu truck sides, dumfounded deer cluster or cattle crossing just over a crest so racer needs don't fit my conditions. No extra power just opening a hole but my strong grip became effective while prior freaked me out enough I got another UFO like mc for Peel so I could use the Lockheed on Trixie but didn't want to after so now a useless spare.

Btw in what way did the lack of restriction make brake unpredictable so I can try sense for it before surprised?

hobot said:

Ok comnoz what do the resleeved mc's use instead that make them check valved predicable. Everyone but hobot seems to use brakes hard while leaned racing around in public so I guess I just don't know what I'm missing out on. My panic tests are going straight into pu truck sides, dumfounded deer cluster or cattle crossing just over a crest so racer needs don't fit my conditions. No extra power just opening a hole but my strong grip became effective while prior freaked me out enough I got another UFO like mc for Peel so I could use the Lockheed on Trixie but didn't want to after so now a useless spare.

Btw in what way did the lack of restriction make brake unpredictable so I can try sense for it before surprised?

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They don't use anything -I wouldn't use one of them either. Jim

Comnoz you have confused me now. Ya state the Norton brake w/o the restriction or a check valve is more unpredictable yet the upgrades don't use them either, hm. Can't have it both ways. Upredicable brakes I've tried either self energized out of control, delayed full effect to over compensate for or hung then released for fork dives and too many times lock up on leans d/t something on surface but those were modern cycle brakes with 25-27:1 ratos not Lockheed which basically just didn't want to stop with the restriction. So if ya can what was your sense of dislike w/o constrictor or check valve? I like it of course though others may not so just order up a standard upgrade. Trixie is test to resist what I did and doing to Peel and to give me good comparison of what various upgrade are doing but i'm not adverse to modifying stock parts like they did in their hey day. What ever the physics I stop better and as a scared pilot that's all I need to know. My 27:1 dual rotor cycle is a handful to brake well on THE Gravel and touchy to panic grab on tarmac so some skill with 2 finger dangers. I'm sort of shopping for gizmo that can record pull down and take off events to pass around. Any suggestions pm please.

Well I tried both on the track and on the street to make a Norton brake both powerful and with a firm predictable pull. I never got it there. Once I got the master right, the caliper and rotor couldn't take the heat.

A bigger rotor and better caliper and master was what it took for mountain passes. Jim

well ok then unknow lever position in racer lean counts and i just tame myself down to stay within factory brake limits with help of a hole but peel is meant to risk so in same camp with non norton everything>

KEYBORAD SUDDENLY DOING WEIRD THINGS ON FORUM BUT OK IN EMAIL FOR MORE MYSTERY>

Dedicated to JimC which much as he rubs me raw I'd have same reaction if not living it. So more brake mysteries, stoppie-ing a Commando is something I'd like to master. Gave up completely on factory brake and isolastics hole or no hole. Peel though could pull down so much better than my SV650 when I hopped on SuVee same day d/t Peel flat tire I'd be shocked pulling stopies to slow for unknown over crests on SV that were mere easy routine commuting pull downs on Peel. SHOCKED THE SHIT OUT OF ME JIMMYC. I'm no stoppie expert but about every brake for a gas pump I'd nail SuVee brake to stoppie and plunk down and got pulled off corner school leaning limits of Ninga brake so was not prepared for Peel throwing my butt over bars rather than having seat rise slap my butt. Comnoz says he can stoppie his though I think that has something to do with the extra weigh his packing in big fairing though his muscular frame may nullfify that. I asked how he avoided flying over bars to be told his knees are braced on the big fairing ends so I'm gonna to follow suit on Peel. The HUGE difference is when ya stopie ya aint stopping as hard as Peel which was impoosible to stoppie to only ride front locked for bike lengths, so long people ran out waving arms to warn me, more than once, trying and trying to find right amount of feahter not to lock up but still couldn't brake as hard as on tap because I could not hold myself down in saddle strong enough so definitely better slowing than any modern I've scared myself on. I think I know why but JimC would not believe it.

I'm as sensitive as anyone on being believed but that's secondary to actually living it and some of Peels sport bike squid squadron spanking involved out braking them down hills into super sharp narrow 90's switch backs and down hill racing is half the time in Ozarks so one of my desires is to start a Pikes Peak down hill run through Peel may be only entrant. There is more to deadly slowing that just lever power and tire patch so think more like slamming on brakes in a car than poor ole topple overs. Evenyous might take this as BS bragging and permanent public record foolery but the wilder ones should perk up as I ain't selling anything but flying hi til ya die. How many of you'd pick a isolastic Commando to throw down guanlet and slap pilot faces on computerized wonder rockets. I am getting the sense that what matters so much to other cycles don't apply to one wierd Combat but I already knew that from reactions in real life so catch up as can. For the manics left have I ever mentioned ya may not know what ya missing out on?

hobot said:

Comnoz says he can stoppie his though I think that has something to do with the extra weigh his packing in big fairing .

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Plus the fact that my Commando is raised about 3 inches .... Jim

AH HA higher CoG definitely stiffles G forces tolerated to stay levelish on acceleration and deceleration. Maybe in another thread could review where/how you gained 3" and why. I abhore stoppies and wheelies so Peel should act like a long fork front leg chopper dog dragged into a vetanarian clinic. I may hit what's in front but by gosh it will be levelish dead on like a man not toppling ass over head. Btw hope none of ya ever have to do it but in a pinch with nothing to loss but life and limb freaking out on both brakes locks to toss sideways like flat tracker into turns stops better than anything except hitting something. Does take some forced practice though to prevent rear leading the way which lowers slowing too drastically. Btw comnoz I awoke today with question on your statement you removed the Lockheed mc cylinder restriction and didn't like it d/t lever return randomness, so ask did ya remove the whole restrictor valve w/o compensating of the return spring slack or just punch hole in it?

Hi,
goes the check valve all into the spring?
Please, a picture.
Thank you.
Piero