How to open terrible master cylinder?

Why they designed them so poorly never ceases to baffle me. The only thing I know has ever worked for me is a vice and impact driver. Just wondering if anyone knew any tricks?

 

Anti seize was never a dealer thought I guess.. I just replace them with an oversized radial type, but you can cut a slot into messed up screw heads with a small dremmel cutoff disc for use of a higher torque flathead screwdriver. But if they are too corroded inside this may snap heads off...and leave the master somewhat useless. That's why I just swap them out to newer radial style that has the reservoir separate.

 

Guessing you are talking about the front brake or the clutch master? Penetrating oil for sure, then I use a 1/4 bit with a 1/4 wrench on it. I tap the bit with a hammer as I turn the wench. I have great success with this, better than with the impact screw driver.

 

Easiest thing is to just drill the countersunk heads off.
Then with the cover off there is enough screw sticking out to work the vise grips.

 

I drilled mine to. Terrible feeling drilling on your master cylinder and thinking about metal shavings in your brake fluid.

 

We drilled it, still can't get the screws out. Had to use a hose clamp to keep it on. Works for now, but not too happy with it.

 

Sounds to me like it needs to come off of the bike and be rebuilt. If the cover screws were corroded that badly, then the internals aren't in great shape either.
That will also give you the opportunity to use penetrating oil and maybe some heat on the screw stubs to try and get them out.

 

Metal corrodes, and multiple metals touching corrodes even worse, in bolt and threaded cavity scenarios there is no room for the metals to expand as they corrode resulting in extensive pressure in the cavity essentially cementing it in tighter. 30+ years of this being allowed, most often results in a snapped bolt, I've seen this happen more often than not. I give the guys some respect for their efforts in believing that they can fix it, (and at times it can be) but when you deal with the one most important safety item you have on a bike, (front brake is 70% of your stopping power) cutting corners just don't seem to be a rout I'm willing to take for a daily rider. I understand keeping it and fixing it if its to be an all original restoration, but again...there are used and reproduction parts all over. I guess weigh your options angst where you want to go with the bike.

Post a pic of it....