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Infinite Front Brake Problems

Avery_74cb360

Veteran Member
Joined
Jun 22, 2022
Total Posts
1,079
Total likes
5
Location
West Liberty, Ohio, United States
So I got my 1974 CB360G running over the past few weeks. When i went to take it out of the driveway, the front brake locked up. Steve helped me take apart the caliper carry arm, cleaned it up and reinstalled it, but that wasn’t the issue apparently. The piston was stuck, so i flushed it out with the master cylinder.
Since the master cylinder was in bad shape, Steve had me get a new one from ebay. Here is the link: https://www.ebay.com/itm/262581136299
I bought new steel lines from common motor to go with the new master cylinder. I got them all today, but when i went to put them on the new master cylinder, the bolt for it appears to be slightly too small. I can’t use the original banjo bolts, because they are too big. So i used the bolt and washers that came with it, and tried to flush the air out of the system. However, it leaks from the master cylinder because the bolt is too small. What do i do? Do i have to re-thread the master to fit the original sized banjo bolts? Do i need another new master cylinder?
Furthermore, when i went to put the piston back in the caliper after cleaning it all up, it got stuck and i cannot get it back out. My plan was to flush it out with fluid again, but as you can see that’s not going to happen.
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Stuck piston
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Stock size banjo bolt on the left, master cylinder and its bolt on the right


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I use a compressor with a rubber tip blow gun in the banjo bolt hole. WARNING! cover it with a heavy rag, and keep your face away.
 
I have used the master I suggested with good results.....

Please explain HOW the original banjo bolt to that master is suddenly too small.....

The picture seems to suggest that you attempted to use a banjo bolt with the wrong pitch threading or cross-threaded the correct one........

As always, you may phone.....
 
I have used the master I suggested with good results.....

Please explain HOW the original banjo bolt to that master is suddenly too small.....

The picture seems to suggest that you attempted to use a banjo bolt with the wrong pitch threading or cross-threaded the correct one........

As always, you may phone.....

I tried to phone earlier but i must have missed you
I’m not sure why it’s too small. The original banjo bolts do not thread into that master cylinder. The bolt that came with it seems to have a little more wiggle room, but it does have the o-ring thing in its washers so i thought it wouldn’t be a problem. I’ll try it again tomorrow when i have time to be with the bike. Maybe i just didn’t tighten up the bolt enough i’m not sure.


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It seems like the master cylinder is okay now, i just tightened the crap out of the bolt and it doesn’t leak out anymore.
I saw to purge the air from the lines you stick the end into the master and pump it until you see no bubbles. I did that, there was a steady stream that comes out when the lever is squeezed. But it doesn’t seem like the fluid gets to the caliper. Maybe it does, but when i open the bleeder screw nothing comes out. Maybe it just needs to be fuller? I pumped it for quite some time.
Still don’t have the piston out. I just finished trying the air compressor. I tried duct tape around it to act as a seal for the air but it isn’t tight enough. Fluid sprayed out when i did it though so i guess that’s a good sign that the fluid does get there


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Just double-checking: have you added any fluid to the reservoir? The level can drop substantially when bleeding and pushing out the caliper piston.
 
Reservoir is full. I’m not sure if i understand how the disc brake works itself. When the lever is squeezed, a small amount of fluid travels down to the caliper, and when it’s let go, does the fluid return back to the top so the piston goes back to normal position?
How did the piston get pushed out with the fluid in the first place? Why won’t that work again?


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You could heavily tape up the side holes on the banjo bolt and put it in then use the bleeder for air pressure.

If you are confident that the piston seal groove was completely cleaned out (so the new seal is not too tight), then just squeeze the piston all the way in and proceed with reassembly.
 
Piston can get pushed out without the rotor in place. That is another way to remove your piston, just squeeze the lever with the caliper off the rotor and get ready for a brake fluid shower.
 
Yeah that’s what i thought, that’s how i got it out in the first place. I don’t know why the piston isn’t moving now though, no matter how much i squeeze the lever
Would a penetrating oil do anything? I got some today but i don’t want to damage anything


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(Avery_74cb360:) How did the piston get pushed out with the fluid in the first place? Why won’t that work again?


My explanation may not be perfect, but my understanding is that the square o-ring on the caliper piston has enough spring to it that it will return the caliper piston to its original position, provided that it is only pushed a small distance. The fluid then returns to the reservoir. This is usually the case when the caliper is installed on the bike. When you remove the caliper, it's possible to push the piston further and it will start to slip relative to the o-ring and eventually it will come out. The reservoir drops as this occurs. As ballbearian mentioned, that will be messy, so I'd put a small pail underneath to catch the piston and the fluid.

If it's not moving the piston, I'd recommend checking that fluid will come out at the bleeder screw when it's opened and you pump the master cylinder.
 
Yes that is exactly what i’m confused about. Fluid comes out of the brake line when i was purging the system of air. However, i take it out of the master, put it in the caliper, and it’s like there’s no fluid there, nothing exits the bleeder screw. Maybe it was just gunned up? The air compressor would have fixed that so i could put it on the line again and try it


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I read your posts again and see that you have no fluid at the bleeder screw. Is that still true if you remove the bleeder entirely? If so, what about removing the steel line from the caliper and checking that fluid gets that far?
 
Air is compressible but not fluid. It has too much air in it now to move the caliper. If you would bleed out the air and fill with fluid it will come on out. What a waste, what a mess!

If you have a new seal in it, or not, just compress the piston back in and carry on.
 
There is no more steel line at the caliper. The lines i got are stainless steel from common motor, the lower line runs straight to the caliper so there is not messing with a hard line.
I can take the bleeder out and check that.
My thought was that maybe since the piston is out pretty far, there is a lot of space for it to fill with fluid. Maybe the bleeder ain’t bleeding and the piston isn’t moving because it just needs filled up more


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Air is compressible but not fluid. It has too much air in it now to move the caliper. If you would bleed out the air and fill with fluid it will come on out. What a waste, what a mess!

If you have a new seal in it, or not, just compress the piston back in and carry on.

I was told originally to just push it in more instead of taking it out. I put a block of wood on it and hit it like i was told, but not too forcefully of course. It didn’t really move, it seems to be at the slightest angle so i don’t know if it’ll go any further in


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Air is compressible but not fluid. It has too much air in it now to move the caliper. If you would bleed out the air and fill with fluid it will come on out. What a waste, what a mess!

If you have a new seal in it, or not, just compress the piston back in and carry on.

That's good advice. Often you can push it in by hand, provided you're only up against air. Should be easier if it's not connected to the brake line.
 
That’s what i was saying, i even tried hitting it in. I just went back out to look at it. Pressing super hard, i can feel it budge in just a little, and then come out. O ring sticking? I can’t take it out to lubricante it so it’s not having a fun time


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That’s what i was saying, i even tried hitting it in. I just went back out to look at it. Pressing super hard, i can feel it budge in just a little, and then come out. O ring sticking? I can’t take it out to lubricante it so it’s not having a fun time


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Did you lube the front edge of the piston and the o-ring with brake fluid before pushing the piston into the caliper like I suggested?
 
Well, you'll need to either fill up the caliper with fluid by repeated bleeding or find a piece of rubber hose or something to put around the blow gun attachment (or whatever way you have to exert air pressure) to better seal up the air leak into the caliper to blow out the piston (remember, aim it toward a thick towel or something else soft and away from anything it can damage, like you)
 
Well, you'll need to either fill up the caliper with fluid by repeated bleeding or find a piece of rubber hose or something to put around the blow gun attachment (or whatever way you have to exert air pressure) to better seal up the air leak into the caliper to blow out the piston (remember, aim it toward a thick towel or something else soft and away from anything it can damage, like you)

I might have to fill it up that might be my only choice unless i buy a different air compressor attachment. I tried different kinds of tape and lots of things but couldn’t get it sealed


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If you must, you must. I don't own an air compressor and I found myself in a very similar situation with my 360. It is messy, but it will hopefully help you make progress.

IMGP1504.jpg
 
^^^And that is a great idea. So glad I only have one bike with hydraulics (and it needs some work too)
 
You know what i was thinking about doing that exact thing, i bought more brake fluid just in case today. With the old leaky master it’ll be even less fun, i’ll consider it a last resort


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If it is cockeyed, at an angle it will get stuck. smack it on the high side to get it straight in the bore or it won't come out or in, it's jammed.
 
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Funny, auto censor didn't like my terminology.

Only because you hyphenated the word - I personally edited the censor list to allow the use of many terms when included in a single word, like petcock but not pet **** or pet-****. I fixed the one above
 
Finally got the piston in after getting it stuck another time. Put that plastic o ring in and then the brake pad. How snug should that pad be fitting? I needed some force to put it in it didn’t just fall in, it won’t come out with my hand either

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The pad should move pretty freely, so there must be some corrosion or burrs in the part of the caliper where it fits. Make sure the guide pin at the top is clean and the groove in the pad is also
 
What is the discoloration around the edge of the brake pad? Kinda looks like red paint or possibly rust. Might be helpful to clean up the outer edge of the pad to see if it slips into the caliper a little more smoothly.
 
I think it’s just something with the flash on my phone, it’s not discolored looking at it right now. I’ll clean up the pad more, but i don’t know how i’m going to get it back out to do so


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It can't possibly be in there as tightly as the piston was. You could pump the piston out a little to push the pad out enough to get a grip on it, just don't push the piston too far out
 
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Had to push the piston most of the way for it to pop out, but i got it. I cleaned it up with some 100 grit and then 220 grit, much better than it was. It slides in a lot easier now, if i had to guess that is what got stuck in the first place from how it looked. Double checking everything before throwing it on the bike: the piston isn’t supposed to be flush down there right? I used the c clamp i bought to get it as far as it would go
This looks much better doesnt it
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Also, isn’t this carry arm adjuster screw thing supposed to have a nut to go with it? I had that one to the right in the bag of stuff i took off of the front brake, but it will not go on much at all
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That nut looks suspiciously larger wrench size than it should, IIRC the nut is a 10mm wrench size (6mm thread). Ace Hardware has metric nuts, take the screw with you to make sure it fits. I'd forgotten the red line is the wear indicator, that's what was showing in the earlier picture. The piston will come out of the caliper the distance it needs to once assembled and you finish bleeding it, then apply full braking pressure at the lever.
 
Okay, i have no ace hardwares near me but i’ll see what i can do. I put the calipers back on the bike and i’m very relieved, i can wiggle the swing arm just slightly, nothing is sticking anymore. Think we’re close!


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Okay, i have no ace hardwares near me but i’ll see what i can do. I put the calipers back on the bike and i’m very relieved, i can wiggle the swing arm just slightly, nothing is sticking anymore. Think we’re close!


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Good, glad things are finally going better. You're learning a crapload of stuff in all this, it will be invaluable to you in the future.

Tractor Supply also has metric nuts and bolts if there's one of them near you, even Home Depot or Lowe's if need be but they might make you buy a package of 3 or 5 to get one.
 
I’ve definitely learned so much doing this, if i could do this everyday for the rest of my life i would
We’re going out for dinner for my early birthday tonight i’ll be able to stop in and get that nut[emoji106] I would run to lowes real quick but i bought a few things there and they didn’t work out


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I’ve definitely learned so much doing this, if i could do this everyday for the rest of my life i would

I'm glad you're enjoying learning, many would have bailed by now considering some of the struggles you've had. However, though wrenching on bikes is an incredible amount of fun when you first start doing it and everything is new and a great learning process... once you do it for a living, trust me, it becomes as drudgerous as any other job. Especially if you ride and wrench on your own stuff too, I did that for 20 years and finally had enough of it.
 
As much fun as any of it has been, i much rather would have missed out on some learning and got more time riding haha. If the non stop rain here clears up tomorrow hopefully i’ll be able to take the bike out for a ride. Either way i’m sure you guys will get an update, wether it be 10 feet down the driveway again or not


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