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Discussion Starter #1
hi Guys
in a earlier posting i had mentioned that i had gotten a long -in -the -garage bb for a small outlay
the final thing i had to attack was the brakes
the fluid had been sitting for about 10 years
what happens is that
the water vapour in the fluid starts to attack the steel in the calipers ( yes they are cast steel not alloy )
the fluid coagulates and becomes a goo especially in the different master cylinders
the relief valves at the back and front become embedded and stuck
the pistons freeze onto the seals
the slider pins dry out and freeze up
the cross pins seize in the holes

the dcbs system is probably the best analogue system you can find ( eg pre abs )

when its in full order its very good at sharing the braking force as a primitive anti skid device

but its complex with long hose runs and lots of nice places for goo and bits to accumulate
when its far gone a flush is of no use as the good will not move out
the only way to do it ( and i found out the hard way ) is to take off all the masters and relief valves and clean them out
particular attention needs to be paid to the zamak spacer that collects goo and the tiny tiny relief holes that get blocked
also the nylon filter and anti return valve on the side of the fork mounted mater cylinder needs to be removed ( not easy ) and cleaned

the proportion valves need to be cleaned and rinsed very carefully
the 2nd master cylinder needs to be reassembled very very carefully and the c clip has to click into place
no click means its not fully seated and will release under pressure --- not good

if you do that then you have a fighting chance to get the cbs working again
for the flushing the factory procedure is ok but you will need a device to create a partial vacuum in the system to coax the fluid to come to the nipples
i call it " sucking the nipple " sounds rude but it isnt
i use a large syringe with flex hose to create the vacuum and when fluid starts to dribble out i then start to pump the appropriate lever to force the fluid through
usually i let the bike sit overnight once flushed and then do a quick second flush the next day to force out any recalcitrant bubbles

then i do several km of stop and go runs with repetitive braking to bed everything in and get resistance and bite in the levers
have fun
paul
 

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Good words Paul
the 2nd master cylinder needs to be reassembled very very carefully and the c clip has to click into place
no click means its not fully seated and will release under pressure --- not good
Non engineering nerds might not know that the internal circlip used has one 'sharp' and one rounded edge. The internal groove in the cylinder is also similarly shaped.
So if the circlip doesn't snap into place turn it over and try again and it will almost certainly snap into place.
 

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Discussion Starter #3
in fact the face plate it seats against has an annular groove that traps the tangs if its fully home so its difficult to unclip
big of a b--er to release it..
 

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Yep.Remember to keep your brake and clutch fluid clean everyone or you too can be a big tub of goo.

I'm so glad I don't have linked brakes anymore.
 

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Discussion Starter #5
question
the system is now bled and seemingly " water tight " so to speak but the pdeal is spongy
if i pump is 2 times is hardens up
is that an issue?
i am wondering if i have residual air in the pipe work from the 2Nd master to the back caliper that wont flush out ??
paul
 

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I found a cheap vacumn sucking device in the form of a manual sucker bottle for lawn mower oil. Get the right hose diameter and it is very good at pulling the brake through. Far cheaper than specific brake vacumn pumps which are quite dear.
 

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There will be some air in there cbrpaul if you have a spongy pedal. This can be a pain to get out.
Steps to take.
1. Disconnect the secondary cylinder where it attaches to the caliper. If you have another pair of hands handy (a helper) you can bleed the rear caliper by pumping the secondary push rod the air will eventually come out. If alone leave the bleed nipple open (with tube on going into a jar) and just pump the secondary cylinder a few times. Chances are that when you first pump the secondary you will not feel any/much fluid resistance. When you feel fluid resistance (it is very noticeable) stop pumping.

2. The other 'trick' is to disconnect the rear caliper and hang it in the relevant position (one for each nipple) where the nipple is at the highest point, this ensures the air finds its way out.
 

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Discussion Starter #8
hi Duck
thanks for the info which i followed with the help of my lad
i have now got 99 pct of the recalcitrant air out of the rear system
so its about as good as ill get
strangely enough the residual bubbles came out of the rear cylinder nipple and not the mid
so pretty much good for the road
got a bagster with backpack coming in later in the week ( bought 2nd in germany of eBay small ads ) and a small carrier for bagage on the tail
then off we go…
have fun
paul
 
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