Think my master cylinder has had it. '97M2. Gone all spongy last night. My system has dot5 silicone fluid so what happens if I change to a dot 4 replacement. What's best to use.
Can't afford a new one cause I've just been layed off.
Pete

nothing as long as you bleed it so its all dot 4 now.

Why change to a different fluid?
Tis just as cheap to replace with the original spec fluid and doesn't risk any incompatability problems

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2001 X1 2009 1125CR 2006 Uly X3 2010 Uly a fully Maz'd S1 and a 1991 RS1200 Westwind.

Flush the system through with DOT5! It's cheap enough at H/D. If it still feels spongy - Call for seal advice etc

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Sept 2017. Email will find me.

Not true - it can affect the seals depending on what the O-rings are made of.

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Sept 2017. Email will find me.

I was thinking of a second hand cylinder and keeping the silicone fluid. Was the seals in the master cylinder I'm worried about. I changed to a X1 master cylinder that had dot4 in it and just wondered if the silicone done for it as well.
Pete

I recently used a master cylinder repair kit on a later model and although it was fiddly
to do it wasn't difficult - see my post a couple of weeks back in this forum. It was about £15 if I recall correctly - if you strip your MC you can check the bore and the seals to see if you have a problem before buying.
This episode has well and truly taught me that silicone fluid must be changed frequently ,as although it isn't hygroscopic, water will find it's way into the system and will give corrosion troubles etc. The only advantage I can see with silicone fluid is that it doesn't strip paint if you spill it and I think that's why HD used it - to look after the finish on their wurlitzers!
From what I have learnt there is no way I would try to change fluid without a system stripdown, wash out with alcohol and new line and seals throughout.
As a side issue - some seals rely on the DOT 4 to swell them to produce a good fit and maybe exposing a previously used 4 item to silicone might cause this to be lost?

Please bear in mind that on a 97 bike with an OEM PM front caliper, the original M/C will be 5/8" bore. An X1 with a NISSIN caliper, IIRC, will have a 1/2" M/C which may result in an increasing lever travel for any given braking effort. I'm uncertain what the real world effect will be, however of using a 1/2" M/C with a PM caliper.

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Try doing this to yer fueller...........