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johnnyrod

Brake Pistons Retracting Too Far

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I'm battling a bit with the brakes on my 1999 SV650, they're twin piston sliding Tokicos. The bikes has 40,000 miles on it but when inspected they look in good condition. I rebuilt them last summer with new seals etc. as there was too much lever travel and all round performance was poor. I'd also replaced the master cylinder seals the year before. Anyway this is a job I've done a load of times but this time I can't seem to reduce the lever travel. The system is well bled, and I've made sure I've got the air from the top banjo as well. The free play is perhaps a quarter of full travel, then the brakes go fairly firm. When you take the calipers off, you can see the pistons sucking back into them as the lever returns, this seems to be the reason for the lever travel, pushing the pads onto the disc before any real action happens.

 

This has been the case more or less since I rebuilt them, I was hoping some use would settle things a bit. Also I used red rubber grease on the pistons for the first time, normally I just use a bit of brake fluid. I've got braided lines from a double banjo at the top, and the pads are still looking pretty good. So, any advice would be gratefully received!

 

John

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Sounds like a problem with the master or reservoir link, since it should suck brake fluid from the reservoir instead of the line.

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Some seals will do this. The early Hinckley Triumphs would do that, too, giving long and inconsistent lever travel. If the seals are biting too hard or are a little stiff, they either have a stronger grip on the pistons or they are more eager to retract. You do need this function to prevent the brakes from sticking on, but as mentioned some have too much effect.

 

Did you use stock seals in the caliper?

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It only takes a minute movement to get a lot of lever travel. I seriously doubt you have any vacuum effect taking place, I'm pretty sure it's a result of the new seals retracting the pistons a hint more than they old ones. It's either that or you must have some air trapped inside. Try to zip tie the brake lever overnight as close to the throttle grip as possible, meaning fully applied. Turn the handlebars to the left and let it sit on the kickstand - the outer end of the brake lever needs to point upwards a bit for this to work. Any trapped air should escape within 24 hours doing this.

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