Topic: 1972 CB 750 front brake master cylinder

[beemerbum]

I'm probably not the first here to encounter a brake master where the piston seems seized in the bore. I would very much like to save it and using Honda parts, rebuild it Any suggestions on how to free it up would be appreciated

[bryanj]

You need to push it inwards to remove the wire circlip, rubber boot and eared circlip(usually realy awkward) then you can use a drift to tap the piston out from the banjo bolt end see if it cleans up and worth the seal kit

[scottly]

The "grease gun" trick for calipers, where you thread the end of a grease gun tube into the caliper to pump the piston out, also works for master cylinders. Attach the end of the gun to the banjo bolt fitting on the MC. Nothing can withstand the power of the gun.

[Maraakate]

If it's truly that seized in there how is the rest of the cylinder?  When they are that far gone I'd imagine that it's so nasty in there once you get it out that it would be a safety hazard to continue using it.

With that said, have you tried spraying a liberal amount of penetrating oil in there and trying to work it back and forth a few times?  Might take an hour or so of playing around to get it to work its way out.

[bryanj]

The nightmare part is removing the "eared" circlip which can take literaly hours. Now Dave Silver sells a repro master that costs not much more than a seal kit.

[754]

New master's are fairly cheap but look a bit different  than stock.
 If you need another stock one, I have a about 10 cores, probably 2/3 will be good, I have the circlip tool to open them up.to inspect.

[beemerbum]

The nightmare part is removing the "eared" circlip which can take literaly hours. Now Dave Silver sells a repro master that costs not much more than a seal kit.

Motion Pro sells c-clip pliers with extended tips, seemingly just for that purpose

[ekpent]

I bought a pair of those once from I think Z1 Enterprises and the very first time I used them the tip broke off. Should be in the pissed off thread ! 

[bryanj]

They may do, but that doesnt help when the ears on the circlip break off due to the corrosion in the groove.
Ive been doing these a long time and in all honesty in most mome workshops i rekon its 50/50 as to it comming out, correct tools or not.
Last time i did some o stripped out 10 in 30 mins BUT that was in a comercial workshop using a propane cutting torch(not to cut into them)

[beemerbum]

I bought a pair of those once from I think Z1 Enterprises and the very first time I used them the tip broke off. Should be in the pissed off thread ! 

A good long soak in Blaster took care of the problem once the fershluginer c clip was out (it put up quite the fight), the air compressor blew that piston about 50 feet. Slight hone and new parts kit we are good to go. Now on to the caliper

[Johnie]

I have used the Motion Pro circlip tool on numerous MC and never had the tip break. Still a good idea to let it sit overnight in PB Blaster
before you work it.

[ekpent]

They may do, but that doesnt help when the ears on the circlip break off due to the corrosion in the groove.
Ive been doing these a long time and in all honesty in most mome workshops i rekon its 50/50 as to it comming out, correct tools or not.
Last time i did some o stripped out 10 in 30 mins BUT that was in a comercial workshop using a propane cutting torch(not to cut into them)

Yes those rusty ears can become pretty fragile and its frustrating when one breaks off.  A 'soft' vice helps a lot when working on these.