https://www.mevspares.co.uk/BRAKE-MASTE ... CLONE.html
There have been delays in receiving new parts, due to Australia Post. In the attached photo are the new plunger/rod assembly and the latest support sleeve from New Zealand. The sleeve is a really good fit on the plunger (loose) but was found to be a 0.0025-in. interference fit in both bores in the master cylinder bodies. On tightening the three setscrews the plunger locked up – to the extent that the master cylinder had to be dismantled, during which the plastic support was damaged. Waiting on a slimmed new one. This illustrates very well your comment about the two sleeve bores being perfectly in alignment and not loaded in any direction.
I have been having a look at the worn brake shoe support dimples in the back plate. With the brake shoes located in wheel cylinder and adjuster slots and the web of the shoe against the dimple, the brake lining is not at a right angle to the back face of the backplate, even noticeable at a casual look!
It is my proposal to drill holes in the dimple that accept 5 mm KLIK-thread inserts, like a pop-rivet but with a 5 mm thread into which a setscrew can be freely threaded. The riveted inserts will be counter sunk into the back plate and an in-hex head Allen screw with locking nut will be used for adjusting the brake shoe position. The procedure will be to install the brake drum, fully tighten the brake adjuster, lightly contact the brake shoe web with the setscrew and tighten the locking nut. Then adjust the brakes as normal. Should work! Such worked on tractors, many years ago, we used to spot weld a nut to the back plate.
This problem has caught me out on two of the last three m/c rebuilds. Neil Moore and I had several long conversations, so here are the bullet points:Hi Michael,
I am at the resto show at the moment so have copied Scott and Neil who should be able to comment. I have had similar problems with the master cylinder but not exactly the same.
I concur with the adjustable dimple. I used set squares to get the shoes running parallel and true.
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The NZ-supplied small seal for the rod is NOT the same profile as the original seal. Check the one you have against an original.
The white nylon spreader can clamp the replacement small seal to the rod.
Also possible: the original washer placed over the seal and spreader can clamp the incorrect seal to the rod.
About a year ago over the course of a few weeks, I did 8 rebuilds of one master trying different combinations of seals and spreaders.
Neil did send a couple of original profile seals and that solved the sticking problem, although on one master, I did re-use the original nitrile spreader after continued sticking problems with the nylon replacement.
To me, the correct solution is buy the kit offered by MEV in the UK that has the correctly shaped seal and I'm guessing, the original style nitrile spreader.
Open to corrections and learning more.
Cheers,
Scott