T140 front brake bleading problems

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The motorcycle stood for 15 years after a rebuild, but the owner could not get the brake correctly bled. A small amount of fluid could be forced through the bleed screw. Loosening of the lower steel pipe banjo allowed the fluid to exit as normal. Later I removed the caliper and stripped it to find the piston seals in bad shape. Is there anything else which could cause the pistons not to return in the caliper?
 

L.A.B.

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Is there anything else which could cause the pistons not to return in the caliper?
Check the master cylinder barrel assembly isn't over-adjusted (screwed too far into the casting see AP Lockheed manual, link, below) or a blockage but I suggest you also strip the master cylinder and check it for corrosion as the bike has been standing for several years. Preferably renew any old rubber hoses.

http://www.classicbike.biz/Triumph/.../Lockheed_Hydraulic_Brakes_Triumph_Norton.pdf
 

Fast Eddie

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When I did mine recently I was pulling my hair out and getting nowhere. Then I noticed the pistons were not moving beyond the elasticity of the seals with each ‘pump’. The pistons moved out, but then just moved in again cos of the seals.

I clamped one piston closed and pumped out the other, then pumped out the second one. It worked a treat.

I later discovered that the ‘tang’ on the brake lever that pushes on the piston in the master cylinder had been filed down, probably by a PO who didn’t know how to adjust the master cycl as mentioned by LAB. I think this reduced the amount of travel on the piston, contributing to the seal issue.

A new lever has restored correct lever travel and feel and all is good in the shed again!
 
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Re;"The motorcycle stood for 15 years after a rebuild, but the owner could not get the brake correctly bled. A small amount of fluid could be forced through the bleed screw. Loosening of the lower steel pipe banjo allowed the fluid to exit as normal. Later I removed the caliper and stripped it to find the piston seals in bad shape. Is there anything else which could cause the pistons not to return in the caliper?"
After 15 years I would renew the master cylinder rubber seal- in fact overhaul the whole braking system as a safely mater of course.
 
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