Master cylinder disassembly

[keithtraffic]

I have had some issues with the front brake on my 550 so have had to look at the master cylinder.

Unfortunately (as commonly seems to be the case) the internal circlip was badly rusted but have managed to remove that. I was then expecting the whole internal assembly, piston, cup spring etc to simply come out or at least come out with a gentle push from hose connector end, but it seems locked in place.

Should they simply and easily come out or have I missed something else which needs to be removed first? is it possible that perhaps the washer under the circlip has rusted and this is causing the problem? If so how much pressure is it safe to apply to help it out (I have already applied some easing fluid which help release the circlip)

Thanks for any help - would like to get the bike roadworthy again very soon!

[Trigger]

Have you removed the ring clip that holds the rubber dust cover ? If you have then it is the washer that is holding tight.

[keithtraffic]

Yes - that was almost rusted through so will need to get a new one and a new boot - any idea how much force a can safely apply to break the washer free?

[Bryanj]

Use a long bolt through the outlet hole and tap with hammer, piston and all seals/clips are in a rebuild kit

[keithtraffic]

Thanks - that worked fine.

One (hopefully) last question for now....

The reservoir has two small holes at the bottom (see picture). The one on the left is clear and goes through into the bore of the master cylinder body but the one on the right seems to be a blind hole or is very firmly blocked. Should it be clear or is it not really a hole with any purpose? If it should be clear how do I clear it (I have tried a very fine piece of wire but if it is blocked the wire can't shift the blockage!). [ Guests cannot view attachments ]

[Nurse Julie]

Yes, it should be a free route through. Don't enlargen the hole when trying to clean it out....all sorts of problems will occur.

[SumpMagnet]

I feel your pain! Having just been through the same with my 750. Geting the rear one apart was even worse than the front... as you can't tp out hte piston

[keithtraffic]

Thanks All - just managed to clear the hole (it helped to really know that it should be free route through!). I used a small piece of steel wire (about 0.4mm dia) and with a bit of pressure that cleared whatever was blocking it.

Just waiting now for delivery of the rebuild kit and then hopefully all will be OK again!

[keithtraffic]

So, Master Cylinder re-furb kit has arrived, but putting it all back together is not going smoothly!

Everything in the kit looks pretty much identical except the Secondary Cup - this came already fitted to the Piston, but it looks slightly different to the original with the end of the cup being more flared. (see Picture). Overall at the very ends it is about 2mm larger in diameter.

Although softer than the original I just can't seem to get it into the Master Cylinder Body!!

Has anyone any experience of this - is it possible its the wrong kit? (although purchased from David Silver against the right bike model!). I maybe could just force it in (say using a vice) but this seems a bit extreme.

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[mike the bike]

It will go in easier if you lubricate it with brake fluid.

[keithtraffic]

I did give it a good coating of fluid but it still seems too tight - should I force it in?

[K2-K6]

I know it's only from the photo,  but it looks wrong to me.

The parallel part of the seal looks bigger than the bore compared to original.  That section would not normally compress so it could be giving the problem.

The flare part of the seal will squeeze tight against the bore size but not the straight section.

Have you got a vernier caliper to give you a basic check of that straight section compared to the bore size?

[Trigger]

Could we have a picture of the side of the mater cylinder as, you may not have a SOHC one fitted 

[Nurse Julie]

Just looked at your intro photo and that's not a Honda SOHC/4 master cylinder you have fitted, unless you have changed it since that photo.

[keithtraffic]

Hi All,

Thanks for all the input.

First to dimensions - here they are. The critical diameters are identical (even though the pictures might suggest otherwise), although there is some slight difference in the lengths. The parallel part of the seal is about 13.5mm dia so should fit in the bore without a problem. It is also comparable with the first part of the original one, before it expands out). Just as an experiment to test this I turned the piston around and put it into the cylinder the wrong way round, so that I was not pushing 'against' the flare and it does go in OK!

I have looked at several different rebuild kits supposedly for the 550 and some show the 'flared' secondary cup but others (notably cmnsl) show a cup which is the same as the one I have removed - can they both be correct? I have also seen at least one suggestion that there are two different sizes of kit and one of them is wrong but don't know if this is really the case.

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As to the question - is this really a 550 master cylinder, here are some more pictures. Carefully comparing these with the workshop manual and other pictures on line I would conclude that it is but am happy for more expert opinion - This is how the bike came to me, but of course it is possible someone has changed it in the past.

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