TA/B/C Brake Master Cylinder Restoration

When I last ran my TA (in 1965 - doesn't time fly!), the master cylinder was in a poor state so I bought a new Lockheed unit. But it never got fitted because I "retired" the car soon afterwards as the wooden body frame was giving way. As part of the restoration, started some two years ago, I replaced the very corroded but probably original MC with the new unit. This replacement included a new heat shield unit from Moss (top left in the attached photo), and plating and blackening of the knuckle shaft at the same time.

However, having thought about it for some time, I decided to replace the rubber seals as I intend to use silicone brake fluid. I understand from others that swelling of rubber parts is different for silicone than for conventional brake fluid. It appears to be essential to start with new dry rubber parts if changing to silicone.

So I bought an MC repair kit from the MG Octagon Car Club and set about the refurbishment (on the kitchen table, when my better half was out, should you ask). The overhaul is very easy with a decent pair of circlip pliers (I used Draper, under 10, with several combination of ends). It was just as well that I pulled it apart because the very thin metal washer inside had largely corroded away in storage - see lower washer in the photo. No metal washer came with the repair kit, and no suppliers appear to offer this part in their lists. So on an inspiration I hacked apart what was left of my old MC, and to my amazement out came a similar washer in excellent condition - see upper washer in photo. The rest is straightforward. Just keep everything clean, soak each item in whatever brake fluid you intend to use, and it should go together easily. Apart from the circular seal over the piston, which takes some persuasion. I didn't remove the threaded section of the MC, nor did I have to hone the internal bore as the latter was still smooth and clear. I had bought a simple hone for an electric drill from Frost some time ago for use on my wheel brake cylinders which I could have used here, but there was no need.

Care has to be taken to ensure the holes in the piston end are clear and clean, and also for the tiny relief hole further in than the main entry port from the outer reservoir can.

I should mention two things. Firstly, Octagon sells a complete brass replacement MC but I have no further knowledge of this unit. Secondly, some owners have experienced trouble with silicone brake fluid, which in a few cases appears to swell the circular washer at the cylinder end enough to stop the relief hole being fully cleared. Solutions appears to be to skim a few thou off the internal piston, or to back off the brake pedal a tad to give slightly more clearance.

I hope this helps anyone contemplating what appears at first sight to be a difficult repair, but please bear in mind the usual caveats on responsibility (not mine) and safety (yours). Happy MG motoring.

Ian Linton, TA3120, East Sussex 21 May 2005