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Author Topic: brembo caliper problem  (Read 376 times)

Offline davrosxuk

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brembo caliper problem
« on: February 28, 2017, 02:18:08 PM »
Hello folks....I have swapped the front calipers on my gen 1 busa for brembo's and all has been well till I tried pushing the bike out of my shed....it was obvious the calipers were binding. I have taken them both off and they look as new....I can push the pistons in by hand although one is a bit harder to move than the others, it still moves ok.
When I pull the lever with the caliper off the wheel I can see the pistons move forward then backwards slightly so all seems good??? BUT when I put hem back on the wheel they don't release fully and the brakes bind.....any ideas?     PS. I have cleaned them with spray brake cleaner until they look new. The pistons have no marks at all on them. please help!!!!!

Offline Gary Evans

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Re: brembo caliper problem
« Reply #1 on: March 02, 2017, 04:28:15 PM »
Are you sure the new calipers are centered on the rotors and not offset?

Offline davrosxuk

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Re: brembo caliper problem
« Reply #2 on: March 03, 2017, 01:18:34 AM »
yes . I checked that first....they are both dead centre and the pistons are moving equal amounts both sides?????

Offline Gary Evans

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Re: brembo caliper problem
« Reply #3 on: March 03, 2017, 04:31:53 AM »
Was the master cylinder or brake lever changed?

Offline davrosxuk

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Re: brembo caliper problem
« Reply #4 on: March 03, 2017, 02:40:29 PM »
thanks for the replies gary.........no the master cylinder and lever have not been changed. This setup has been working fine till I parked the bike up a couple of months ago. There is no corrosion or dirt at all on the calipers and it has not seen the rain for years....that's what I cant understand, the calipers and pads look new and the pistons look to be moving backwards again ever so slightly when the caliper is off the disc but when I pump the brake with the caliper in place is isn't fully releasing for some reason

Offline Gary Evans

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Re: brembo caliper problem
« Reply #5 on: March 03, 2017, 03:18:06 PM »
The facts seem to be pointing towards a sticking piston/s. Retraction of the pistons is accomplished by distortion of the rectangular o-ring seal. When the piston moves the I.D. of the o-ring has some stiction griping the piston wall and slightly distorts when the brake is applied. When the brake is released that slight distortion is enough the retract the piston slightly. The force involved is very small and if the piston has any resistance it may not move and will cause drag on the brake pads. When brakes wear the pistons extend further and further. If new pads are installed without totally disassembling the caliper any grim on the exposed piston wall will be pushed back into the o-ring seal making movement more difficult. 
The right way to fix it would be to take the calipers apart, clean the piston walls and install new seals. The quicker cheaper approach would be to only take out the piston/s that exhibit any resistance to movement. You might even get away with only removing those pistons, cleaning them and reinstall with the same seals. If it doesn't work or leaks then you do it again the right way. With the front wheel off the ground you should be able to tell which brake pad/s are not retracting. 

Offline Rocketgeezer

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Re: brembo caliper problem
« Reply #6 on: March 03, 2017, 06:56:54 PM »
Mine are not Brembos there stock, but were doing the same thing, everything looked fine but when all bolted ready to go the front wheel would drag a bit, sometimes worse than others, calipers looked fine found no contamination, but I rebuilt the calipers, and new pads and the brake work like new money now no sticking
The older you get do you notice you start chickening out way before the bike does

Offline davrosxuk

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Re: brembo caliper problem
« Reply #7 on: March 04, 2017, 03:29:01 AM »
cheers fellas...Ive got the calipers off the bike now and later today I will split them and fully inspect the pistons and seals.