TOPIC:

I'm just back from three weeks holiday in Greece, while there I had to use the Apache 125 that I keep in Athens with no front brake!
On arrival I removed the cover from the bike to find that the front brake master cylinder piston was almost siezed in the bore. I say almost because it wasn't totally seized, the brake could be applied with alot of finger pressure on the lever but would only release very slowly. I could use it only in an emergency!!
This has happened before about three or four years ago, on that occassion I managed to get the piston out of the bore easily, I could see nothing wrong so put it back together with the same seals and have had no further problems until now. This time it's not going to be so easy to get the piston out, I didn't have the tools to do the job in Greece so I've brought the master cyclinder back with me and will attempt to find out what's going on in due course.

Anyone got any theories on what's happening? The bike sits in the hot sun without use sometimes for months!
I did manage push the piston fully down the bore while on holiday, the bore seemed fine, no marks or corrosion, no leaks. The piston then stayed in that position for four days, on the fifth day it must have relaxed for some reason and the spring suddenly managed to return it to the top! It was still unusable though.

I spent most of the three weeks on the island of Naxos, we stayed at a remote place called Moutsouna which is only accessable via single track roads through the mountains with some almost shear drops right of the edge of the roads. It was fun but I didn't need the rear brake fade!!!!

I've also brought the seat back with me as after 13 years of Hellas it's in a sorry state and needs recovering. Can anyone recomend somewhere for the job?

Hi Valdez,
Normally you can’t expect your calliper piston to grow bigger and seize, though I did have a KLR Kawasaki with pistons in Nissin callipers made of some sort of thermoset material that expanded, I made new pistons in stainless steel to cure it.
I have seen a gummy stuff on the outside of a piston, which when cleaned off was as good as new.
I have seen square section piston seals when old rollover in the grooves jamming the piston
Is your calliper like the Nordie calliper with a plastic insert for the cylinder bore? If the plastic insert was worn perhaps the piston could tilt slightly and jam?
Nordie brake seal kits include the plastic insert.
That should give you something to think about
John

Hi John,

Thanks alot for your input. The problem is not with the piston in the calliper it's the piston in the handlebar mounted master cylinder that's gone tight. I checked the calliper and piston, these parts are fine, fully operational.
The master cylinder is the same part as fitted to the Nordwest although the calliper is different.
I'm begining to think its more likely to be the seals causing the problem rather than the piston. The really wierd thing is that this happened before, I could find nothing wrong and on reassembly everything was fine. I'm thinking that maybe the seals could dry out! The bike spends months parked in the heat with the handlebar turned right hand side up. Could the seal be drying out, no lubrication therfore making it very tight in the bore??? It's on the bench now in the garage, I'll go and leave it soaking in brake fluid to see if it helps it loosen up!!

15 MINUTES LATER....

Just come in from the garage, the assembly has been on the bench since I got back on Monday morning. I tried to move the piston down the bore using the lever, it's all still assembled. It needed alot of force on the lever to shift it but once moved it freed up immediately!! It's now working fine, free and easy not tight at all, it's like nothing was ever wrong!!! Amazing!
I'll take it apart over the weekend and see if there's any clue's as to what's happening!!
Leigh

Hi Leigh,
I cooked the the newly replaced seals in in a rear caliper, but think it is possibly the master cylinder that was sticking, but as I don't have spare seals yet, "Uncle Bob please get my spares package sorted out" have not stripped it for a look see.
Fortunatly I hardly use a back brake, I don't fancy riding without the front though
John

Hi John,
I've just taken the piston out of the bore and it's definately the rear seal causing the problem. There are no marks, scratches or corosion on the piston or bore. I wiped the aft seal and cylinder dry, then tried to reassemble (just to see), it was so tight that I'm sure the seal becoming dry is the problem!!

The same problem with the rear brake would be harder to spot so I can see how the rear caliper could become cooked.
Leigh

Hi Leigh,
I'm sure our hot and dry climates don't help not good for rubber or plastics
My bikes are inside and under dust sheets but we can have 40c + at the hottest time of the year, rarely drops below 30c
Good excuse for getting inside and having a cold beer
John