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Discussion Starter #1
I'm trying to replace the front brakes on my CB450. I got a new front caliper, and new lines and new pads. I made sure there was no air in the line. Tightened the bleed valve and the front lever is super spongey. It builds up a little bit of pressure but then that pressure drops off after a few seconds. So, I thought maybe there was a leak with the master cylinder. I replaced that, but the problem still persists.

All connections are tight. And with the new master cylinder the problem is exactly the same. It builds up a little bit of pressure then drops off.

I'm thinking there might be a problem in the caliper, but I don't know what to look for.
 

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New caliper... new master.. new pads.. new lines.....
when did u change the master?
And what do you mean "spongy"
Maybe your rotor is getting "soft"
 

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Discussion Starter #3
I don't think the rotor is the problem here. The new master cylinder arrived in the mail two days ago. By spongey I mean lever feel, it doesn't build up to 100% pressure.

Let me make it clear that front brakes barely work. They are at about 10% strength.


If there is air in there I'm not sure where it is, because the line at the bleeder valve does not have any bubbles at all when opening it.

I used the banjo bolts that came with the kits, and they worked fine on all my other motorcycles. I re-used one banjo bolt but I cleaned it out with brake fluid before putting it back on.

Really stumped on this one!
 

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How did you bleed the brakes (gravity or vacuum)? Have you removed the caliper to see if the piston is extending properly?
 

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The banjo fittings can trap air in the hollow ring around the bolt. The one at the master cylinder can be cleared of air by tilting the reservoir so the fitting is lower, then slow squeeze, hold several seconds, quick release. The others, you have to evaluate the line position relative to the fitting, to see if the air will be drawn back into the mc. Sometimes, you have to crack the bolt loose a bit while the lever is squeezed, to squirt a bit of fluid and air past the seals, then tighten it again while there is still some pressure. Very messy, and you have to make sure the fluid doesn't get on any paint or polished surfaces.
 

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Discussion Starter #6
I loosened the caliper slightly and squeezed the lever and saw that the piston was extending. Don't know how to confirm that it is extending properly.

It's possible that the problem is coming from a banjo bolt, but that seems like it would be an odd thing to happen twice - remember I switched out the old master cylinder with a new one, but the problem is exactly the same.
 

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Good enough for me - my thought would be that you might have had some kind of problem with the piston seal. Did you gravity bleed it? I've never been able to get a fully empty brake line to not-squishy without a vacuum pump (I just have one of the little hand pumps from Harbor Freight, but it does the trick).
 

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Put lid or cover on master cylinder. Unbolt master from handle bar. Tilt master cylinder so lever is elevated. Gently pull lever, release slowly. Repeat two or three times. Mount master back onto handle and pull brake lever. Better but not great, repeat.

Not better? Unbolt caliper and move it so you can see it while pumping brake lever. Check fluid level in master while mounted on handle bars... 75% filled is good for this. Replace master cylinder cover. Unbolt master as before and pump lever watching caliper piston move out. Two or three pumps. Hold or prop up master in tilted position. Squeeze caliper piston back into caliper slowly. Repeat. Caution you can pump the piston out of the caliper or pump the master dry. Avoid. This is a variation on a reverse bleed.
 

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You have air in the brake line. Guarantee it.

The best and easiest way to do this is by reverse bleeding.

Instead of filling the brake fluid on top, you would use a syringe and inject the brake fluid through from the bleed valve.



This method lets physics do the work for you since air bubbles will always rise as the fluid pushes through.
 

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Discussion Starter #11
Did not set any gap between rotor and pad. I'll keep that in mind though.

What I've done is cable tie the brake lever down for the night, and will tackle it again tomorrow. I'll try Boomer's steps with the mc, if that's a no go then I'm going to have to consider a reverse bleed.

I am still not entirely convinced its air in the line because I've also tried using a mity vac (at like 15-20 psi). If there was air in the line, wouldn't the mityvac be able to pull it out?
 

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15-20 psi? How open was your bleed screw? Mine rarely gets above 5 psi if the thing is open enough to pull a meaningful amount of fluid through, unless I’m furiously He-Man’ing the pump :D
 

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Rotor going "soft" was me being sarcastic...
It was the only part in the equation that was NOT replaced... and having a solid piece of steel "fail".. is kinda "rare"...I
 

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Discussion Starter #14
The mityvac has an attachment so it's not a hose directly on the bleed valve. I build up pressure on the mity vac first, and then crack open the bleed valve.
 

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Discussion Starter #15
Good joke :D The funniest ones are the ones you have to explain :D
 

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I'm familiar with the pump, yeah. I see what you're saying. Out of curiosity, what's your bleeding technique? Like start to finish, on a fresh brake line and caliper, I fill the master, hook up the hand pump hose to the bleed screw, open it up, and then pump until the master cylinder gets low and then refill, then repeat until I'm only getting fizz in vacuum line rather than whole air bubbles, then lock the bleed screw at the end. I burn through about a whole 12 oz. container of DOT3 on a single front brake line.

You're on all new components, so I can't imagine anything's sticking, and it doesn't sound like you have any obvious leaks, so I'm down to there still being air in the lines.
 

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Discussion Starter #17
Initially I don't like to use the mityvac because sometimes it draws air into the lines from the side of the hose, making it difficult to tell if the system is free of air.

So, what I do is:

1) tighten down all the banjo bolts
2) fill the master cylinder,
3) attach a hose to the bleed valve and position a bottle underneath it so that the hose end is below the master cylinder.

4) I pump the lever about ten times to build up some pressure, keep the brake lever held down and crack open the bleed valve,
5) before it runs out of pressure I'll close the bleed valve, and release the brake lever
6) I repeat this until there is no air in the line at all, not even fizz

7) I then crack open the bleeder valve, and pump the lever so that I can see fluid moving through the line with no bubbles at all.

This has always worked in the past for all the other times I've done it. Just not working at all on this one!
 

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Complete speculation, but I'm wondering if there's a point in the line where it goes high and has a bubble there that applying pressure from the lever side isn't clearing, just passing fluid under. I can't say if there's anything wrong with your way, but maybe give the alternate bleeding procedure a try and see if it helps.
 

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Sheesh you guys really like to complicate things don't ya? LOL

Seriously the reverse bleeding method is by far the easiest way to do this to be sure that there will be no air bubbles in the brake line.
It's basic physics here. Air bubbles will always rise and cannot go downward easily to be bled out from the bottom bleed valve. By injecting brake fluid from the bottom up you are forcing all the air bubbles to rise and they will come out through the master cylinder.

Trust me it's very easy this way. I can completely bleed and refill my brake line without any air trapped in it in 30 minutes or less with this method.

Here's how I would do it

1. Empty the master cylinder of all fluid. Leave it open
2. Attach a syringe to a tube which is then attached to the bleed valve on the caliper. I bought a syringe used for injecting turkey and used some silicone tubing that I got from the local hardware store.
3. Fill syringe with brake fluid while tapping on the tubing to make sure that any air bubbles will rise and not get trapped in the line.
4. Loosing the bleed valve just enough to allow fluid to be injected through.
5. Slowly inject the fluid in watching the master cylinder the whole time to make sure you aren't overfilling it.
6. Once the master cylinder is starting to fill with fluid, watch for air bubbles escaping.
7. Once it's half full, tighten the bleed valve and now slowly pump the brake lever.
 

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Try either one! :D I just don't have a syringe on hand and the mityvac has worked every time for me, so that's my particular poison haha. But I think either could work! We're on the same page in terms of the bleeding being the prime suspect, to be fair.
 
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