03 955i - spongy front brake (again)

[triple3john]

This bike has always had spongy front brakes,which is worse than on 3 previous Triumphs I've had with the same caliper design. I've fitted a radial caliper from a 675 Daytona which has an integral bleed nipple and fitted new Goodridge hose for the correct fit. The brake is still just as spongy even after bleeding with new fluid,it works fine but the lever comes back to the handlebar. I've now bought replacement discs and will have the calipers cleaned out. I'm at a loss as to what else can be done. I'm thinking of replacing the piston seals,although the brakes don't bind and I'm not sure if this is worthwhile. Any suggestions on whether to change the seals would be appreciated.

[01S3]

John,

My 01 was a bit like that, so I just pushed the pistons out of the calipers a bit, cleaned them all up (still in the calipers and attached to the brake lines) with WonderWheels and a toothbrush, and bolted them back on the bike, and they've been fine ever since.

If there's cack behind the seals, perhaps the seals won't let the pistons move freely and 'reset' themselves into a new position?
Have you tried removing a caliper, and putting something (a bit of wood etc) in between the opposing pistons to see if the lever feel improves with something of a different thickness to a brake disc in there? See if the pistons can creep out and then get themselves happily into a new position IYSWIM?

Alex

[triple3john]

Thanks,probably worth a try to clean as you suggest,as it's a cheap fix ! The issue must be to do with the caliper,as I've replaced the rest of the brake system or will have done when the front discs are swapped.

[01S3]

That's what I thought, and it worked for me!
I just think my pistons were a bit sticky, and couldn't creep out, so the lever couldn't get a fresh 'bite' to improve the travel.

Alex