I blew my top, rear MC problem

[TommyT]

while working on freeing up a seized rear master cylinder from a 91 K75 RT the top or the plug (?) that the brake fluid hose connects to the master cylinder popped off. It has a O ring that I can not seem to get to go back in the bore while installing the plug. The O ring either slides down to the bottom when I put the O ring in the groove in the bore and then push the plug into the bore or if I put the oil ring on the plug it rolls to the top of the plug and it will not fit into the bore. in both cases the brake leaks out bore. it seems like the O ring is too thick to fit properly, I do have to stretch it a little to get on the plug.

I can't figure it out, how to get the O ring to stay in the groove while inserting the plug back in the MC. The MC is good I did install a rebuild kit. I hate to give up on it. Should I just epoxy, glue the plug into the bore and go from there?

[Martin]

Would silicone grease or rubber grease help.
Regards Martin.

[TommyT]

Would silicone grease or rubber grease help.
Regards Martin.

I tried that while trying to stuffing the O ring into the bore with a very little screw driver while pushing down on the plug while it was on the plug. No go.

[Laitch]

The MC is good I did install a rebuild kit. I hate to give up on it. Should I just epoxy, glue the plug into the bore and go from there?

You installed a rebuild kit into it but then it seized. That isn't a hopeful scenario. Do you know why it seized?

You might need a new o-ring after its explosive exercise. Does the ring fit into the plug or the bore? You might try fitting the o-ring wherever it goes, sticking the plug into the freezer for an hour or two, then removing it, applying bearing glue on the cylinder's contact surface then inserting the plug, rubber-banding it into place to let it expand and cure, and hoping for the best.

It might be time to replace the unit with the Chinese version that's been adapted for the purpose. Many members have had excellent results using this product that supports totalitarian labor exploitation; those results can be yours, too. Read all about it here.

[TommyT]

You installed a rebuild kit into it but then it seized. That isn't a hopeful scenario. Do you know why it seized?

You might need a new o-ring after its explosive exercise. Does the ring fit into the plug or the bore? You might try fitting the o-ring wherever it goes, sticking the plug into the freezer for an hour or two, then removing it, applying bearing glue on the cylinder's contact surface then inserting the plug, rubber-banding it into place to let it expand and cure, and hoping for the best.

It might be time to replace the unit with the Chinese version that's been adapted for the purpose. Many members have had excellent results using this product that supports totalitarian labor exploitation; those results can be yours, too. Read all about it here.

It was seized, I freed it up, installed the rebuild kit everything seem great until I tried to put the plug (what the right name for it?) back in. The O ring seems to have been designed to be in the bore at the mid way point in a slight groove and then the plug is inserted.  The O ring does not slip on the plug without stretching it to slide it on. That seems wrong, too tight.  So I don't think the freezer will help. I really wonder how the factory install them and I even wonder why it was not just glued on without the oil ring. Was it to allow the movement, spin around around the bore of the feeder hose? I actually used a grease gun screwed into rear of the MC to free the frozen piston after a couple of my other free the piston efforts that I have used in the past failed.  I think ideal might be it, the plug seem to have some marks like maybe glue was used on it to hold the o ring before inserting the plug into the bore.

Yes the Chinese version now seems like a good choice but I seem to want to keep exploiting German labor, since I am from that heritage. I guess it is time to shift to exploiting a different labor force.

[Laitch]

The O ring does not slip on the plug without stretching it to slide it on. That seems wrong, too tight.  So I don't think the freezer will help.

Freezing the plug will temporarily shrink its diameter so the o-ring should slip over it more easily. Regardless, expanding your exploitation horizons is a worthy goal, instead.