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Discussion Starter · #1 ·
I've encountered my first hurdle when I was reassembling my '78 CX500(because the PO partially disassembled it); a seized master cylinder. I haven't checked yet, but I'm sure the caliper is probably seized too, but one part at a time!



I soaked it in SeaFoam Deep Creep and put the heat to it, still stuck.



Can anyone suggest a method to unstick the cylinder? OR, can anyone suggest a suitable replacement (other model or later CX)?



As you all know, the '78 has the round reservoir. I looked on Ebay, no '78s available at the moment, several are available from later model CX's (rectangular reservoir). It looks like several other models have master cylinders that are similar, most notably mid-late 70's GL1000's and CB models.
 

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There are rubber pieces in there that heat will destroy. An ultrasonic cleaner may help. I think you may be better off picking up a new MC though. There are several threads on here with links to differing one's on ebay and other retailers.

Unsticking calipers takes a lot of patience and can be done with the help of a c-clamp alternating with pressure. Good luck.
 

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Discussion Starter · #4 ·
Ah ha, thanks!
 

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I have never tried to unstick a MC, or even worked on the round type. But does the lever not want to pull in? Or has it pulled in and stuck? If the lever is stuck in the extended position, you might be able to remove the dust cover from the piston and use a small drift to gently tap at the end of the piston. You just want to jar things loose, not drive the piston all the way in immediately. This I would think would be a lot easier with the MC in a vise on the bench, but you could probably do it on the bike.



Without seeing it, can you access any of the grooves in the piston thru the banjo hole? If you can, this might allow you to retract the piston from the above bumping. I would take the "C" clip out first before I started doing this. It may even be a straight shot from the banjo hole to the piston where you could drive the piston out with a thin drift.



The caliper may be a challenge too. Ideally, you would force the piston out with hydraulic pressure generated by the MC. If you don't have a working MC, that isn't an option. It is sometimes possible to remove the caliper and apply 100 psi compressed air to the banjo hole and cause the piston to pop out. Do this with a towel around the entire caliper and fingers out of the way in case it comes out suddenly. And it will. The other option is to block off the banjo hole and replace the bleeder screw with a Zerk fitting. Then apply a grease gun and force the piston out with grease. The MC and the grease gun supply several thousand psi of force, compared to 100 or so with air.



As Linny mentioned, you do have rubber pieces that too much heat can affect, but if you are replacing the cups and O rings in the MC, that may also help. I wouldn't wait long after heat application before trying to move the piston, you don't want to bond the parts with melted rubber. Also you may want to try acetone and ATF in a 50/50 mix. That is supposedly the best penetrant and releaser.
 

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Ok just a simple question, have you removed the circlip holding the piston in place?




I just finished refurbishing mine and well, no way it can seaze solid, there is no metal on metal, rubber seals on metal yes...but if you forget the clip...
...it ain't gonna move.



I also did my calipers, yes the easiest is to use the MC but if that does not work and by the way, if the MC is buggered, you find water/sludge in there, be prepared to replace the pistons like I did, the get pitted inside and it destroys the seal in the caliper, like a pitted front fork and seals.



I placed my caliper in a vice, took a vice grip and worked it out, you'll damage the piston as the metal is soft but mine were buggered anyway so...




Now I have a full brand new system, every seal and part that wears is replaced...just have to test her now..




PS



I forgot, there is a steel washer behind the circlip so if you removed the clip, the washer could be the one rusted into the alu MC...sorry forgot about that.
 

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Ok just a simple question, have you removed the circlip holding the piston in place?




I just finished refurbishing mine and well, no way it can seaze solid, there is no metal on metal, rubber seals on metal yes...but if you forget the clip...
...it ain't gonna move.



I also did my calipers, yes the easiest is to use the MC but if that does not work and by the way, if the MC is buggered, you find water/sludge in there, be prepared to replace the pistons like I did, the get pitted inside and it destroys the seal in the caliper, like a pitted front fork and seals.



I placed my caliper in a vice, took a vice grip and worked it out, you'll damage the piston as the metal is soft but mine were buggered anyway so...




Now I have a full brand new system, every seal and part that wears is replaced...just have to test her now..


I forgot, there is a steel washer behind the circlip so if you removed the clip, the washer could be the one rusted into the alu MC...sorry forgot about that.


I went through three until I found one that was exact for my restoration that was either rebuilt at some time in its life &/or the PO's system was maintained very well. If you'll notice my signature I needed one of those four screw ones that fit with the proper angle on a Custom's bars so it was a fight finding an original one that was in great shape.



I had one that was so frozen not even a 3 lb sledge hammer with a pin punch from the backside could get the piston out of it despite weeks of penetrating lubricant of all types - including Kroil. I got one of the others apart but the interior was so corroded it wasn't funny. Brakes are very important to me, even more so than tires, so I wasn't going to settle for anything substandard. I've got a spare kit for it and will rebuild the MC the next time I change the brake fluid which I may need to do next year as according to Old Okie the caliper seal boot is showing some tiny rubber deterioration.



Regardless the new DOT 5.1 (not to be confused with DOT-5) was far easier to bleed and will likely be changed on at least an every two year basis. In theory it will last a heck of a lot longer than 3 or 4 but how hard is it to change, especially considering it is totally compatible with our system? You can actually mix it right in with 3 or 4.



My choice of moving up to the newest fluid was not based on its far higher boiling points but the fact that it has about half the viscosity of 3 or 4 thus will respond quicker on apply and especially release due to the small return hole we have in our MCs.



Stuff costs a fortune compared to common 3/4 but is quickly becoming the standard so the price will eventually decline. Don't expect to find it at the common auto parts stores yet, you'll have to hit a bike shop to find it on the shelf - most any have it.



Do your own research and I think you'll come to the same conclusions that I came to.
 

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Ye what can happen is water can penetrate the MC and oxidise the piston and port, then you screwed, this if the bike has been left to rot, if however it has been standing undercover just not used then it should not lockup as the piston floats inside the port, rubber seal seals it.



Either way, I'm going to test mine, if the braking is poor then I'll resleave the MC with a S/S sleave as everything else is brand new but the port can pit from oxidation.
 

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Ye what can happen is water can penetrate the MC and oxidise the piston and port, then you screwed, this if the bike has been left to rot, if however it has been standing undercover just not used then it should not lockup as the piston floats inside the port, rubber seal seals it.



Either way, I'm going to test mine, if the braking is poor then I'll resleave the MC with a S/S sleave as everything else is brand new but the port can pit from oxidation.
 

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Discussion Starter · #10 ·
Ok just a simple question, have you removed the circlip holding the piston in place?




I just finished refurbishing mine and well, no way it can seaze solid, there is no metal on metal, rubber seals on metal yes...but if you forget the clip...
...it ain't gonna move.



I also did my calipers, yes the easiest is to use the MC but if that does not work and by the way, if the MC is buggered, you find water/sludge in there, be prepared to replace the pistons like I did, the get pitted inside and it destroys the seal in the caliper, like a pitted front fork and seals.



I placed my caliper in a vice, took a vice grip and worked it out, you'll damage the piston as the metal is soft but mine were buggered anyway so...




Now I have a full brand new system, every seal and part that wears is replaced...just have to test her now..




PS



I forgot, there is a steel washer behind the circlip so if you removed the clip, the washer could be the one rusted into the alu MC...sorry forgot about that.




No, I'll remove the circlip when I have a moment, thanks
 

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Discussion Starter · #11 ·
Ye what can happen is water can penetrate the MC and oxidise the piston and port, then you screwed, this if the bike has been left to rot, if however it has been standing undercover just not used then it should not lockup as the piston floats inside the port, rubber seal seals it.



Either way, I'm going to test mine, if the braking is poor then I'll resleave the MC with a S/S sleave as everything else is brand new but the port can pit from oxidation.




I think mine will not be fixable, PO partially disassembled the bike; drained and brake fluid and took off the MC and caliper then it sat for 25+ years without fluid in the system (I was told it was mostly stored inside, but who knows).
 

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With the circlip removed you should be able to stick a down in the banjo bolt side if it's straight and give it a few taps with a hammer. Since it's wood it won't hurt anything.
 
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