front brakes not fully freeing off

[Jeremy R65]

Hi all.  I'm sure this must have been addressed here before, but I could not find it. I have a 1980 R65 with twin ATE disc brakes.  A couple of years ago I stripped the calipers, fitted new pistons, seals and rubbers, carefully assembling with lashings of red rubber grease. Brakes worked fine and freed off fully. The bike has not been used much since, but recently the brakes do not release fully and are dragging a bit too much. I picked up the hint a while ago about the small hole in the reservoir and I have prodded about with fine wire and that is apparently clear. Made no difference.  The lower brake lines were 1980 originals so I wondered if they were breaking up inside.  New Goodridge hoses made no difference.  So, any suggestions as to the likely cause and what I should do next please? Jeremy

[Tony Smith]

It could be a lot of causes and in order to be sure that I cured the problem I would pull the master cylinder apart and clean thoroughly, including polishing the bore. If I had the slightest doubt as to the condition of the piston I would obtain a kit for it - they are cheap compared to the alternative.

You have already replaced the lower hoses - if the upper hose is more than a few years old I would replace it as well.

Split the calipers and clean everything, polish the pistons and the bores, again if there is any loss of suppleness in the seals I would replace them. If the seals are OK, don't sweat too much looking for the "correct" square section o-ring between the calliper halves, I've been using suitably sized round section O-rings for 30 years and am yet to have one cause a problem.


If I were to guess what your problem is I would say that a period of inactivity has allowed some moisture to do mischief, which the clean and polish program will eliminate.