• Hi everyone,

    As you all know, Coffee (Dean) passed away a couple of years ago. I am Dean's ex-wife's husband and happen to have spent my career in tech. Over the years, I occasionally helped Dean with various tech issues.

    When he passed, I worked with his kids to gather the necessary credentials to keep this site running. Since then (and for however long they worked with Coffee), Woodschick and Dirtdame have been maintaining the site and covering the costs. Without their hard work and financial support, CafeHusky would have been lost.

    Over the past couple of weeks, I’ve been working to migrate the site to a free cloud compute instance so that Woodschick and Dirtdame no longer have to fund it. At the same time, I’ve updated the site to a current version of XenForo (the discussion software it runs on). The previous version was outdated and no longer supported.

    Unfortunately, the new software version doesn’t support importing the old site’s styles, so for now, you’ll see the XenForo default style. This may change over time.

    Coffee didn’t document the work he did on the site, so I’ve been digging through the old setup to understand how everything was running. There may still be things I’ve missed. One known issue is that email functionality is not yet working on the new site, but I hope to resolve this over time.

    Thanks for your patience and support!

Brembo front brake holding pressure?

ray_ray

ray_ray

Mini-Sponsor
The front brake on my 08 WR250 will almost lock the wheel from rolling after using it only a few times on a ride. This just popped up from nowhere a couple days back.

I've verified the brake floats on its pins as expected, verified both pistons move in and out when not on the bike, and changed out the fluid ... No real dirt on the outside around the pistons and I sprayed them really well with WD40 ... No real help really ...

Do these things have some sort of relieve valve that allows the pressure to be release when the lever is released?
 
I can think of 3 possibilities-
1-too much fluid in reservoir
2- brake pistons binding in caliper
3- kink in brake line- creating somewhat of a check valve effect
there is no relief valve.
 
HUSKYnXJnWI said:
I can think of 3 possibilities-
1-too much fluid in reservoir
2- brake pistons binding in caliper
3- kink in brake line- creating somewhat of a check valve effect
there is no relief valve.
Click to expand...

#1 - checked OK
#2 - maybe but I can move both pistons and when I press them all the way inwards, the lever can be used to move both pistons outward.

#3 - might have some traction ... My cable is a little bent in a couple places...
Is there an easy way to check to verify that the brake line is not the issue?
 
I don't know of a way to check the brake lines for this, short of pressure sensors to measure pressure in the lines, but if such a tester existed it would be money. I can't think of a home test. Best I have is the probability- that physical kinks you can see visually can produce this problem.
When you pull the lever you have the strength of your hand, leverage (mechanical and hydrological) to your advantage in creating positive pressure to flow through the brake lines (and kinks/problem areas/ and overcome a sticky piston in the caliper). The reverse of this is simply releasing the lever- which largely is a vacuum (negative pressure) to return to normal. A Kink can create enough resistance (like a check valve) to not allow the system to go back to "zero".
 
HUSKYnXJnWI said:
I don't know of a way to check the brake lines for this, short of pressure sensors to measure pressure in the lines, but if such a tester existed it would be money. I can't think of a home test. Best I have is the probability- that physical kinks you can see visually can produce this problem.
When you pull the lever you have the strength of your hand, leverage (mechanical and hydrological) to your advantage in creating positive pressure to flow through the brake lines (and kinks/problem areas/ and overcome a sticky piston in the caliper). The reverse of this is simply releasing the lever- which largely is a vacuum (negative pressure) to return to normal. A Kink can create enough resistance (like a check valve) to not allow the system to go back to "zero".
Click to expand...

I think I will look at the entire system off the bike next .... I'll check if I can see pressure being retained on the pads after the lever is released...
 
Does this make any sense:

If the brake line is causing the issue and I have the problem re-produced on my bike ... Will wiggling the brake line (at the kink) remove the additional pressure and make the brakes release?
 
ray_ray said:
#2 - maybe but I can move both pistons and when I press them all the way inwards, the lever can be used to move both pistons outward.
Click to expand...

Still could be warn and hanging where the high wear position is. You sure you don't have to much fluid int he resi?
 
Motosportz said:
Still could be warn and hanging where the high wear position is. You sure you don't have to much fluid int he resi?
Click to expand...

I've ran the fluid level up and down and no real change ... I might try changing the pads tomorrow also ...They aren't worn out but look all gnarled up ...

After I took the caliper off the bike and was just compressing the pads together and watching the action of the pistons, I think I could see the pistons releasing slightly when I released the lever... So the brake line is still on the table along with the pads as a cause ...
 
I checked this also .. No help :(
Freaky said:
Have you got enough free play in the lever?
Click to expand...

After playing with the brake line small kinks, I noticed the master cylinder fluid was all blurry looking again so I pumped more fluid out the bleed hole and the brake started working as expected again :). I managed to get some air in my brake lines also but I'll deal with that later ..

Thanks for help here ...
 
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