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Discussion Starter #1
Hi guys,

I think one of my calipers is seized. The pistons won't move when I'm pumping the brake lever. The other caliper operates perfectly.

I rebuilt both calipers with new rubber seals, but I think I need to replace the pistons on the seized caliper. The pistons are on order from Bike bandit. Basically what I'm asking is, have I missed anything? Will the new pistons fix the problem or is there something else that could be causing the pistons not to move?

When I'm bleeding the brakes the brake fluid does come through, so I'm pretty sure the Master is fine. Also, the pistons do pulse a little when the lever is pulled but they just don't seem to come out. I inspected the caliper bores as well and they seem in pristine condition. The pistons themselves do look a little used and they fitted a little too snugly for my liking when I was replacing them.

Any ideas guys and gals?

Al.
 

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Sorry, I'm not going to be much help. [:I]

I never rebuilt the calipers on my F1, and I did over 200,000km on it. I'm sure they needed rebuilding by then, but they still worked pretty well.

I think the problem with mine was more to do with the dust seals than the actual pistons though. The only thing I can suggest (which i gather you've already done) is to pull the pistons out and give them a thorough cleaning. Other than that, I would get some new pistons, or go to a brake specialist and get their opinion.
 

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Discussion Starter #4
Thanks lads. I have new pistons on order from Bike Bandit (excellent website/service). Should be arriving tomorrow.

I pretty much know what I'm doing when it comes to brakes. I've rebuilt the calipers before. I just needed to know if there was anything I'm missing. As I said the right caliper is working fine, so I'm confident that my rebuilding procedure (under the watchful eye of the trusty Haynes manual) is doing the job.

Thanks for the concern though.

I'll let you know how the brakes are when I get the new pistons in.

Thanks again,
Al.
 

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I rebuild mine once a year and had something similar the first year i did it, i cleaned them up so good it made them almost too clean and made the piston stick to the 2 seals on the caliper (packing and seal) after pulling them out again i realised that the new seals are meant to be a snug fit but not stuck so after using a little brake fluid and coating the pistons with it they moved in and out smoothly and helped bed the seals in better.

Might be worth trying it to see if that helps.

Russ
 

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Discussion Starter #6
Yeah, I always "lubricate" new seals and the pistons with brake fluid. Anyway, the new pistons went in without a poblem. I now have two fully working calipers. She'll stop on a penny now.

The brake lever still feels a little soft though. I think I need to bleed the master cylinder. The calipers are both bled fully of air but seeing as the master cylinder doesn't have a bleed nipple, I'm going to have to bleed at the banjo joint bolt.

Al.
 

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now that i have time to reply, i was going to say time to replace the pistons. but you already did that, so im glad you got it to work.
 
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