Wednesday, June 22, 2016

Master of Puppets

Now that the transmission's done, I'm going to start working my way through the rest of the car's systems to replace or renovate whatever I can.  First up: the braking system, specifically the master cylinder.

In the older Midgets and Sprites, the master cylinder is a single unit that has two bores sharing a common fluid supply.  For early cars with drum brakes, it's a 7/8" bore; for cars with disc brakes, it's a 3/4" bore.  I've got the right one for my car, but the bores were pretty pitted.  I bet that's why I always had a little brake fluid seeping from the unit way back when it was a functional car.

I bought a brake cylinder hone and did some work, and I think I cleaned things up enough to work.  I mic'd the bores and they came out at 3.77" instead of 3.75".  I think 2 hundredths of an inch won't matter.  The important thing is that the bores are smooth.  It's hard to see in this picture, but there's just one little spot in each bore that I think isn't a big deal.

Time to reassemble... All new parts, except for the original top and cap and screws and pistons.

First thing is the springs and the check valve for the brake line.  The check valve keeps just a little pressure in the brake line to keep you from having to mash the pedal to engage the brakes.  It's not the same as in the drum brake unit but it's there... at least, it was in what I took apart, so it goes back.  The thing is, the new springs are not quite the same as the originals.  The new springs are tapered at each end and the originals are tapered at one end, which allows the check valve to fit the other end.  So after a bit of digging, I learned it's ok to widen the end of the spring to make the check valve fit.  So I did.


Now, time to fit the new seal on the pistons, and assemble the springs and pistons in the bores.  A little brake fluid does the trick to lubricate the rubber and the bore.  The order of fitment is the spring (with check valve in the brake bore), a rubber seal, a washer, and then the piston with its seal.  The piston goes in with the hole in it facing out (where the pushrod will go).



Then, the gasket and the front plate.  The plate goes with the flat part up and the gasket matches.


Finally, the top and its gasket, and the cap, and that's the way it is.

Next, I plan to clean up the pedal box (it was pretty good, so I don't even think I'll repaint it) and work on the calipers and rear wheel cylinders.  I bought a rebuild kit for the calipers, which I have done before but given the time it's been sitting will probably need redoing.  I bought a clutch slave cylinder because they're so cheap.  I may just buy new rear wheel cylinders but we'll see.  They might be ok and just need new seals.  Once they're done, I'll need new brake lines and hoses, and that's the braking system in the bag.

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