Topic: Ugh - rear brake master cylinder is toast and replacements are NLA

[tdskip]

Hope everyone is having a good week so far.

Hit a bit of a roadblock today on waking up the 1980 CB750F. With a rear brake master rebuild kit in hand I went to remove the circlip on the rear M/C only to find that it is completely rusted in place and I can't remove it. Bummer but no biggie, right, just get a new one. Well I've looked for replacement M/C but nothing is available. I saw some used ones on eBay but iffy that they won't have the same issue or have good bores.

Any ideas on sourcing?

Thanks!

[Kelly E]

Soak the MC in EvapoRust then it should come apart for inspection .

[tdskip]

Thanks for the response, let me give that a try.

[scottly]

Is Evaporust safe for aluminum?
I've managed to get very stuck rear MC snap-rings loose a couple of times. The trick is to get the clip free to rotate in it's groove, before attempting to remove with the proper snap-ring pliers. Lots of your favorite flavor of penetrating oil will help flush out the corrosion.

[Kelly E]

The EvapoRust won't hurt the aluminium, soak it overnight. If the paint is compromised you will have to repaint but good paint stays on. It won't hurt the rubber parts either. Clean the MC out with brake clean as best you can before you dunk it, oily stuff ruins the EvapoRust.

[ekpent]

 The circle clip may be just the beginning of the fun.  If the masters are like the F model bikes from 75-78 getting the piston out can be a real chore also. If you get that far I may have a tip to help.

[BenelliSEI]

Not sure about the later years, but my 1975 cb750F had the same issue. Previous owner tried to drill out the piston and totally FUBARED it (Fu*#ed Up Beyond All Recognition). NLA, but one from a Honda GL1000 bolted right up.

[Don R]

  I drilled a snap ring groove from the outside into it's edge and the snap ring that had no ends remaining just popped out. The 1/16" hole didn't hurt anything.  It was early and worth saving. 

[Bankerdanny]

I put an inexpensive Ebay rear master on my '76 750F last year. I had to fab up a bracket and a stop bolt to get it mounted so that it didn't rotate when the pedal pushed the piston up, but otherwise it was an easy job. If originality doesn't matter I would not be too concerned with fixing the original.