Odd thing happened yesterday with my disc brake

N0rt0nelectr@

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Day before yesterday I took my 74 Interstate out for a short ride. Had a great time with no issues. I hadn't ridden for almost 6 months due to some health issues. Got back to the garage and let it sit for an hour before rolling it into the garage. That's when I noticed that the brake lever went all the way to the bars! What the heck! Opened up the master cylinder and it was a little bit down but not by much. Let it sit over night and now I have brakes again! What is going on? Thoughts or ideas.
Thanks in advance for your help.
John in Teas
 

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It could be heat soak from sitting that hour and something within the spectrum of brake fade.
It might be a good time to change the fluid.

I have only had something like that once (on a scooter in Thailand) It lost its front brake in the back road mountains, the lever coming back to the bars, letting it sit and cool off and the brake returned to normal.
 

ashman

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Give the system a good flush out with new fluid and look for any signs of leaks, when sitting over time the moisture gets into the system, should be changed ever 3 years, after time and hard braking cause the fluid to boil so good idea to flush every 2 to 3 years.
 

Mart UK

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DOT4 absorbs water over time. Water boils at a lower temp than brake fluid. A spirited ride will generate enough heat to boil it. Once it's vapour, it compresses and you lose your brake. I change every 2 years and try to avoid directing water at the m/c or calliper when washing the bike.

By the time it had all cooled, the vapour may have escaped the system, or condensed back to recover your brake pressure.

Time to do a flush through with brand new fluid.
 

N0rt0nelectr@

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I was planning to change the fluid tomorrow as a just in case sort of thing. Installed a modified MC with a sleeve to a smaller size for extra stopping power, but that was about 3 years ago. Thanks for the tips. I will report back after the flush.

John in Texas
 
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It could be heat soak from sitting that hour and something within the spectrum of brake fade.
It might be a good time to change the fluid.

I have only had something like that once (on a scooter in Thailand) It lost its front brake in the back road mountains, the lever coming back to the bars, letting it sit and cool off and the brake returned to normal.
Rented a scooter in Thailand with NO front brake . Gone , missing . Took it back for a new scoot . Cost me $2 more for the day. $10 instead of $8.
 

Richard Tool

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Rented a scooter in Thailand with NO front brake . Gone , missing . Took it back for a new scoot . Cost me $2 more for the day. $10 instead of $8.
In some parts of the world being able to stop may be regarded as a frivolity...
 

N0rt0nelectr@

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I was planning to change the fluid tomorrow as a just in case sort of thing. Installed a modified MC with a sleeve to a smaller size for extra stopping power, but that was about 3 years ago. Thanks for the tips. I will report back after the flush.

John in Texas
OK, I drained the brake system and as I was doing so observed what looks like a small piece of rubber in the return passage of the master cylinder. Tried to use a dental pick to get it out but that didn't work. So on to plan B. I will take the master off and see if I can use some low air pressure to blow it out. Don't have a kit for the modified master cylinder. I will contact the dealer (Jim Noll) and see if he has kits for those.
John in Texas
 

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Rented a scooter in Thailand with NO front brake . Gone , missing . Took it back for a new scoot . Cost me $2 more for the day. $10 instead of $8.

I think my brake fade was the weight on the back. :D

1_1.jpg
 

ashman

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After time the rubber brake hose can swell up inside and stop your brakes from working, I found out the hard way, replaced with SS line, that was well over 30 years ago now, but now have a full Grimica front brake system, modern brakes with one finger stopping power if I want to use just one finger lol, it was the best investment when my stock front brake tried to kill me twice and injury from the second time, lesson learned new system while recovering from my first broken bone.

Ashley
 

Mart UK

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OK, I drained the brake system and as I was doing so observed what looks like a small piece of rubber in the return passage of the master cylinder. Tried to use a dental pick to get it out but that didn't work. So on to plan B. I will take the master off and see if I can use some low air pressure to blow it out. Don't have a kit for the modified master cylinder. I will contact the dealer (Jim Noll) and see if he has kits for those.
John in Texas
Good spot. But that may require dismantling, to replace where it came from.

If I can avoid it, I don't drain the system. I cover anything painted and use a clean cloth to soak up the old fluid in the reservoir (a syringe or Turkey baister would be better, if you have one). Once the reservoir is clean, fill with new fluid and do the lever / bleed nipple thing, until the new fluid comes through. I don't get airlocks that way.
 

N0rt0nelectr@

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After time the rubber brake hose can swell up inside and stop your brakes from working, I found out the hard way, replaced with SS line, that was well over 30 years ago now, but now have a full Grimica front brake system, modern brakes with one finger stopping power if I want to use just one finger lol, it was the best investment when my stock front brake tried to kill me twice and injury from the second time, lesson learned new system while recovering from my first broken bone.

Ashley
I have a SS brake hose that isn't that old, well about 5 years or so.
 

ashman

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After 38 years with the original stock brake set up with a few rebuilds and mods and disc replacement the stock brakes let me down in a big way lucky for me it was a only a minor injury to myself after 2 mishaps in a short period of time its was in my best interest to upgrade to modern brake system up front, all up at the time was under $600 for a full Grimica brake system and was one of the best upgrades I have done in 46 years of ownership, small price for what could have happen at a higher speed, my stock brake line swelled up over 30 years ago and was when I put the SS line on, before I upgraded to the new brake system I bought the MC reducing kit but I decided not to put it in , the Grimica system had the right size MC, racing calipa and 12" floating disc and new SS line and mounting bracket and was well worth the money than trying to save a old worn out stock system that wasn't really up to it from day one, yes it worked well for the first few years from new but slowly got worst over time and one day the stock system will let you down when you need it without warning as mind did.
My front brake is now up to modern day systems and stops as good as my modern Triumphs, well worth the just under $600 I spent for the upgrade and my life is well worth every cent, some will say its not original but my whole Norton isn't original since the early 80s and the roads are more dangerous now than back in the 70s.

Ashley
 

Larry S

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This is what I used for my brake issues.

I used this inexpensive pneumatic brake bleeder from Harbor Freight. It worked great. Basically you attach the suction tubing to the bleed nipple, using 90 psi air you pull the trigger, open the bleed nipple and vacuum brake fluid from the resivour and the air that is in the system. The main thing is to keep the resivour full so you don't pull in any air. Just keep on pulling fluid through and then do it some more. Solid pedal and lever.

Attachments​

 
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I have had sleeved MCs fail twice in exactly the same way you described - lever suddenly went to the bar/no front brake. The first time happened in the garage - was OK riding the day before, went out to ride - no front brake. Sent it off to be repaired by the original provider of the sleeved MC - who was a prominent supplier of them.

2nd time it failed I was riding and the brake worked normally at one stoplight - failed/no brake at the following stoplight. Exciting stuff!! :eek:

I removed the OEM sleeved MC/tossed it in the trash, bought the Brembo MC from CNW + the adapter plate to accept the Lucas switch gear. No problems since AND the brake feel/power improved dramatically over the sleeved MC (which was a noticeable improvement in feel - though obviously not in reliability- over the stock MC).

My takeaway note to self: " NEVER bet your life on a sleeved master cylinder!" ;)
 
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