Master cylinder disassembly

You’ll recall that the end plug to the brake master cylinder would not come out.  In the interim the workbench was built and the tool chest installed.  Even with the shop vise in place it still would not move.  Nor is the work optional. Remember I said that Green essentially had no brakes when I last drove him in 1980s.   The end plug has to come out so that the brake lines can be rebuilt.

Seven decades of ignoring maintenance has clearly taken their toll.  So how does one “thaw” frozen steel parts?  A propane torch and a gentle touch (mostly the former).  Steel expands when it is heated, so a couple of minutes invoking the blue flame and with the good offices of a pipe wrench, and it broke loose.

With the end plug removed it was a simple matter to remove the spring and various caps and seals.

So here is what it looks like in an exploded view on the work bench.

 

2017apr08-6

Well, it’s a beginning.  I have not yet ordered the rebuild kit, which will supply new gaskets and seals. Most of the metal parts will go back into place.

One of the key parts is visible at the bottom.  The piston holds the primary seal, a cap, at one end and the secondary seal, a ring, around the other.  It is cast aluminum.  I took a small wire brush to it to ensure corroded grit would not get back into the brake lines.  I think it cleaned up rather well.  In doing so I noticed a number cast into one side of the piston shaft:  24887.  I assume it is a part number, though the service manual does not say.

My chief concern is the master-cylinder bore.  Having had no preventative care and having sat unmoving since at least 1987, the real problem is the inevitable corrosion along the walls where the rubber seals trapped moisture in the system. You can see a spot of that bright red-orange gunk on the cylinder wall just as the piston was removed.  The other image shows the bore after I scraped the walls with a flat screwdriver to see what would come loose, and brushed it with a small steel brush.

Those small pits are a problem.  The bore can be honed a bit to take off surface scoring, but the pits will not allow the seals to fully seat against the walls, allowing a small bit of leakage that over time will weaken the brakes.  I plan to borrow a hone, but can take off less than the thickness of a sheet of tissue paper.  To much, and the piston seals won’t handle the pressure and brake fluid will leak past them.  The cylinder will be ruined and I buy a new one.  Since my goal is to bring Green back into running order with as much original equipment as I can manage, I will be really careful.

 

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