Why would brakes lock up?

Yoniboi · Post by **Yoniboi** » Sun Nov 29, 2009 1:23 pm

I'm feeling a bit lost here as 18 months ago I bought a Nissin Radial master for the Spondon while it was in the workshop having the new loom made up. What I didn't know was that the machanic had ordered a Brembo race unit at the same time, so in the end the Spondon got the Brembo and the Nissin went in the parts bin.

Yesterday we fitted the Nissin to a mates Kawasaki, same bore, same DOT4, same everything and off he went after a brief test ride.

Today he phones me to tell me that 100km later the front brakes locked up altogther and although he didn't crash he sounded well pissed off and (maybe understandably) wants to fit the stock MC back tomorrow.

What I don't understand is WHY?

Do these things suffer from being in the parts bin for 18 months? Was it duff when I bought it? We filled the reservoir pretty full (he thought it was small and was worried about the level running low); Would that do it?

I haven't got a clue why it would do that???

ozzyfzr · Post by **ozzyfzr** » Sun Nov 29, 2009 3:34 pm

Certain brake fluids can attack the seals, this causes them to swell and it may block off the small bleed hole back into the reservoir. If this is blocked it holds residual pressure causing the brakes to lock on (no bleed down).
This may be the case!

When it was stored did it have bungs/red caps blanking all ports, it may have corroded internally due to brake fluid being Hydroscopic!!

Just a couple of suggestions
Regards
Ozzyfzr

Stig · Post by **Stig** » Sun Nov 29, 2009 7:01 pm

heard a similar thing to this before

It was the lever applying the slightest pressure on the piston in the MC and this caused the brakes to apply in the smallest of amount...not even enough to slow the wheel. This in turn heated the fluid, made it expand and then lock the wheel. When things cooled off, things went back to normal

It was the lever that was at fault in that particular case not allowing the piston in the MC to retract fully

check the lever and clearances around the piston in the master cylinder

davemfox2 · Post by **davemfox2** » Mon Nov 30, 2009 1:01 am

Stig wrote:heard a similar thing to this before

It was the lever applying the slightest pressure on the piston in the MC and this caused the brakes to apply in the smallest of amount...not even enough to slow the wheel. This in turn heated the fluid, made it expand and then lock the wheel. When things cooled off, things went back to normal

It was the lever that was at fault in that particular case not allowing the piston in the MC to retract fully

check the lever and clearances around the piston in the master cylinder

had the same hting happen to me a couple of years ago on my 400 gamma; was running a pattern lever which was slughtly different by about 1 mm, but enough

Dave