| Brake problems
Following the 3 DNFs at Cadwell due to brake failure here is what I have found so far, bearing in mind that at the meeting I changed the disc, pads, fluid and mastercylinder.
This morning I have been Checking for cause of the brake problems and I think I may be onto something.
I suspect that a major part of the problem is the change to a better disc, firstly I ran a SPS iron fully
floater which is what I had on when I crashed, after that I changed to a modern semi floater off my 748RS
front end. Trouble is both discs are a nominal 5mm thick making them 1mm thicker than the standard 600SS
disc, in itself this should not be a problem as the narrowest point of the calliper is 7.5mm wide giving
the newer disc 2.5mm of clearance, however this is only true if the disc is aligned dead centre of the
calliper, now looking at how the pistons are protruding from my calliper there is a 2.5mm difference with
the outer pistons stuck out the futhest, which suggests the disc was running near enough up against the
inner edge of the calliper.
With the self aligning aspect of the the fully floater this is not so obvious
and also less of a problem, but changing to the semi floater after the crash probably made things worse as
shown by how many laps I did in race 2 compared to race 1.
I have checked the speedo spacer I made and it is exactly the same width as the original speedo drive so
its not that.
Attention then turned to the spindle retainer that clamps inside the bottom of the left fork
leg, in the time I have owned the bike I have never disturbed this, on inspection it was found to be
protruding 1.5mm on the inside of the fork leg which in turn moves the front wheel and the disc 1.5 mm
futher away from the calliper mount, not a issue with the original narrower disc but may well be with the
thicker 5mm discs especially the semi floating one and as things got hotter and expanded clearances would have been futher reduced maybe to the point where the disc was continually rubbing the calliper causing the brake fluid to overheat.
Currently ony a suspicion/theory but it is something I can easily alter.
It may also be the cause of my original new brake pads glazing over on Saturday evening practice as the thicker pads would certainly had clearance issues on the Saturday afternoon untimed practice, especially the inner pad, but again the fully floating disc would have helped mask it.
Interested to hear Paynep (Paul Paynes) and Fil2's views  |