Author Topic: Front Brake Piston Issue  (Read 252 times)

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Offline John Sperger

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Front Brake Piston Issue
« on: July 11, 2018, 11:23:32 pm »
Hello Everyone,

I'm stumped. It's a 99 C10 with 133,000, runs great. The front brakes needed to be rebuilt so I purchased Murph's front end kit. The throttle side went on great, bled the air, no issues. The left side however is another story. I have two issues 1) I can't bled all the air out of the line and 2) the smaller piston won't move when the lever is pressed (however if I clamp the larger piston the smaller one will move but as long as the larger piston is un clamped it won't move).

So regarding the #1 issue, I've bled and bled this thing, over 24 ounces of fluid. I even tried the rope around the lever for 12+ hours, nothing. When is dissembled the caliper I removed the brake line and totally cleaned the entire caliper. I just took it off again and I don't see any particles or dirt inside the caliper, it looks fine. I have not soaked it overnight (not sure what to use there).

I think the problem could be around the new orings inside each piston. I'm wondering if the larger piston slides easier than the bottom one thus only allowing the larger piston to move and not the lower one. Since these are new orings I'm not sure what to do for a fix. It does seem like the smaller piston takes more effort to push out of the caliper but I wonder if that's the air in the line.

When I do take the pistons out of the calipers there is fluid behind the piston, so I know some fluid is there.

Thoughts anyone? I'm not planning to replace with different calipers or anything like that, the stock system works for me. Oh and the brake lines are original, yes... I know they should be replaced but they appear fine and in good shape.

TIA.
John
John   COG #8131   Ripon, WI  '99 Concours

Offline Mcfly

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Re: Front Brake Piston Issue
« Reply #1 on: July 11, 2018, 11:56:55 pm »
Things I've had ruin my brake rebuild experiences:

1) The simplest of screw ups, the inner seal flipped when putting them back in the caliper.
It's a finicky and tedious process that was fixed with Castrol Red Rubber Grease.  It makes
putting the pistons back in the calipers a breeze.

2)  Bleeding the 3 line system can be a challenge, and I needed a pnuematic bleeder
to get it done right (same with bleeding out the clutch line).  Switch to SS 2 line made
bleeding A LOT easier.

3)  Cleaning... I've tried to rush through cleaning everything, and I ended up with a
stuck rear piston.  Make sure everything is as clean as possible, then clean it more.   ;D
Brake crud on the piston wall will stick a caliper piston.

When bleeding newly rebuilt calipers, bleed them, then take the caliper off, and slowly rotate
it about as you tap it with a rubber mallet... Loosens up and stuck air bubbles.

Hope this helps!
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Offline SteveJ.

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Re: Front Brake Piston Issue
« Reply #2 on: July 12, 2018, 12:34:18 am »
There could be gunk in the recesses that hold the seals, forcing a tighter fit. I clean mine out gently using a pick
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Offline Bud

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Re: Front Brake Piston Issue
« Reply #3 on: July 12, 2018, 09:00:50 am »
I had an issue bleeding the brakes on my silverwing project.  I finally used the reverse bleed method and got them bled out.  Get a syringe and some tubing and force brake fluid through the bleeder screw.  You might use a bit of thread sealing tape on the threads of the bleeder screw.  Try it.  It works.

Offline John Sperger

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Re: Front Brake Piston Issue
« Reply #4 on: July 12, 2018, 12:41:22 pm »
Bud - how did you know when you had all the air out with this method? I've seen other posts on this as air wants to travel North not South.

Thanks others for the comments! I'm re-reading them all!
John   COG #8131   Ripon, WI  '99 Concours

Offline WillyP

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Re: Front Brake Piston Issue
« Reply #5 on: July 12, 2018, 03:59:19 pm »
You need to bleed the air out of the caliper, at the caliper, first. Don't scrimp or cheap out at this step, take your time, work slowly, and work at it until every speck of air is out.
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Offline Bud

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Re: Front Brake Piston Issue
« Reply #6 on: July 12, 2018, 08:01:28 pm »
Bud - how did you know when you had all the air out with this method? I've seen other posts on this as air wants to travel North not South.

Thanks others for the comments! I'm re-reading them all!
This should give you the general idea. 
https://www.youtube.com/watch?v=6UCNWfA7dVs
If you have a helper, you can have them watch the master fill up and remove the excess fluid, as well as alerting you to the lack of new bubbles appearing as you fill. You can still bleed them as you always have after doing this to confirm you have no bubbles coming out at the bleeder.  I tend to use this method when dealing with an empty system that is being stubborn.  When all the air is gone the lever will have a nice firm feel when you squeeze it.  Air in the system will contribute to a spongy feel when squeezing the brake lever.  Hope that helps!
« Last Edit: July 12, 2018, 08:06:08 pm by Bud »