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Old 10-12-2017, 10:47 PM   #1
Kilroy
 
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Squishy front brake

Ok y'all, this is seriously the LAST thing my CB350F needs. I rebuilt the master cylinder on it, replaced the lines, the caliper, the piston and everything. Literally the only thing that is stock is the housing for the master, which I cleaned out. I cannot get pressure. A buddy with a speed bleeder couldn't get it, so obviously I messed up somewhere. Who can I buy dinner/a six pack/just give money to to help me?
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Old 10-12-2017, 11:42 PM   #2
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Re: Squishy front brake

Break it apart and try to pressure each separate piece. Sometimes, the master won't pressure. Put some compressed air to the wheel caliper and check that. Sometimes, the piston seal won't slide in the groove if it was put together dry.
But checking each component separately is where to start.


Hard to properly rebuild an old master. There are cheap new ones on Ebay.
I'm here in Austin.
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Old 10-13-2017, 08:58 AM   #3
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Re: Squishy front brake

If the master cylinder bore was honed out to clean it, it may now be oversized where the replacement seals are not able to seal well enough to make solid pressure. If oversize seals are not available, then a replacement m/c is needed.

It is possible the system still has entrapped air. Replacing all the components can introduce alot of air. It is possible (though unlikely) that even using a pressure bleeder there is still a pocket of air in there. I can see a vacuum bleeder more readily leaving a pocket of air, but even those are usually very thorough.
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Old 10-13-2017, 09:59 AM   #4
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Re: Squishy front brake

Quote:
Originally Posted by mikes old virago View Post
Break it apart and try to pressure each separate piece. Sometimes, the master won't pressure. Put some compressed air to the wheel caliper and check that. Sometimes, the piston seal won't slide in the groove if it was put together dry.
But checking each component separately is where to start.


Hard to properly rebuild an old master. There are cheap new ones on Ebay.
I'm here in Austin.
Alrighty, I took apart the system and blew air through everything. Looks like all of my component parts are airtight, so I must've goofed up a connection or something, or my newly-rebuilt master is faulty. When the kid goes down for a nap I'll try re-assembly.
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Last edited by Kilroy; 10-13-2017 at 10:03 AM.
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Old 10-13-2017, 10:18 AM   #5
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Re: Squishy front brake

I would say you have air trapped in the system still, especially since you replaced so many components. A speed bleeder won't do anything to release an air bubble or air pocket. It just makes routine bleeding more convenient.

Something to try. Do a reverse bleed forcing fluid up from the caliper to the master. You can use a large syringe with a piece of tubing that fits tight around the caliper bleed screw. Make sure the master is full, then open the bleed screw and force fresh fluid up and through the line until it runs out of the master cylinder res. It you have a second set of hands have your helper steadily tap on the line all up and down it. This often helps release a bubble.

If you are getting partial pressure but not a firm feel it is almost always because there is still air in the system. You can bleed for hours the conventional style and never get the bubble out.
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Old 10-13-2017, 10:23 AM   #6
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Re: Squishy front brake

Alrighty, I'm willing to try it. I take it I can find the syringe et al at my local auto parts store?
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Old 10-13-2017, 12:17 PM   #7
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Re: Squishy front brake

Quote:
Originally Posted by Kilroy View Post
Alrighty, I'm willing to try it. I take it I can find the syringe et al at my local auto parts store?
maybe
Tractor Supply is where I got mine
https://www.tractorsupply.com/tsc/pr...p?cm_vc=-10005
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Old 10-13-2017, 12:31 PM   #8
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Re: Squishy front brake

Or you can try a Mityvac.
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Old 10-13-2017, 12:32 PM   #9
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Re: Squishy front brake

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Originally Posted by Liteitup View Post
maybe
Tractor Supply is where I got mine
https://www.tractorsupply.com/tsc/pr...p?cm_vc=-10005
Liteitup has shown exactly what you need on the syringe. You will still need some tubing to connect the tip of the syringe to the bleed nipple. Use clear tubing. You want to be able to see that you are forcing brake fluid up and no air bubbles .

Once you get it set up and connected, it is quick and easy to do. I am not a fan of using a vacuum bleeder in this situation--mostly personal preference based on my empirical success rates.

Edit: Your disc is good, right? No bends, warps, etc? You won't ever get a firm lever if you have disc that has an issue.
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Last edited by Johnf3; 10-13-2017 at 12:39 PM.
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Old 10-13-2017, 01:17 PM   #10
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Re: Squishy front brake

Quote:
Originally Posted by Johnf3 View Post
I would say you have air trapped in the system still, especially since you replaced so many components. A speed bleeder won't do anything to release an air bubble or air pocket. It just makes routine bleeding more convenient.

Something to try. Do a reverse bleed forcing fluid up from the caliper to the master. You can use a large syringe with a piece of tubing that fits tight around the caliper bleed screw. Make sure the master is full, then open the bleed screw and force fresh fluid up and through the line until it runs out of the master cylinder res. It you have a second set of hands have your helper steadily tap on the line all up and down it. This often helps release a bubble.

If you are getting partial pressure but not a firm feel it is almost always because there is still air in the system. You can bleed for hours the conventional style and never get the bubble out.

^^^^^^ THIS

Use two syringes... one like Johnf3 suggests and another to suck out accumulating fluid from the reservoir. There's an art and science to getting all the bubbles out of the pressuring syringe while slipping the clear hose over the bleed nipple while turning a small box end wrench just the right amount to allow flow while reciting Jabberwocky and then quickly turning said wrench again - shutting off the flow while not allowing any air to sneak by. I can make one jolly good mess doing all this but it's never failed me yet.
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Old 10-13-2017, 02:26 PM   #11
Kilroy
 
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Re: Squishy front brake

Thanks everyone. I'll try the syringe method I think.
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Old 10-16-2017, 08:38 AM   #12
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Re: Squishy front brake

After syringe method, if still soft, try tying the handle down to the grip overnight, sometimes that will force last little air out through the return port.
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Old 10-16-2017, 11:11 AM   #13
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Re: Squishy front brake

One time I put the wrong/old crush washers on, and got spongy brakes I couldn't bleed with speed bleeders, cracking the banjos, or reverse syringing. I can't remember exactly what sin I made...I think I did both at the same time actually....

Triumphs had an interesting problem, where the pistons were sticking to the piston seal, and the piston seal would haul back the pistons after braking. It caused long travel in the lever, which feels "spongy". That's probably not your problem though.
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