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MG MGB Technical - Master cylinders

Hi Guys. Im a new member and nearly nearing the end of a home restoration. I didn't intend to take it as far as I have but I've really enjoyed it. I've removed the master cylinders now because they looked horrible with peeling paint and thoroughly cleaned them with a wire wheel etc. Looked really good and shiny but surface rust is appearing now so I wondered what ideas to finish them off as I believe painting isn't a good idea with brake fluid etc etc I haven't rebuilt them yet but I don't want to buy new ones any ideas ?
H c Jones

There are solvent resistant coatings available that can be applied to the master cylinders, preventing future rusting and not damaged by contact with brake fluid. One is called Gun Kote and is available in the UK. They do require the part to be baked after coating. (I use an air brush to apply the coating, and use an old toaster oven to bake them--outside, as the fumes are not good for your health.) There may be other solvent resistant coatings suitable for home/hobbyist use and a web search may turn them up. I applied Gun Kote to the clutch master cylinder of my daughter's car over ten years ago and it still looks new.

Les
Les Bengtson

If you don't want to buy new, you could always use silicone brake fluid which doesn't strip paint. Although silicone does get some bad press.
75^110:3:26^36:5:28^15:1:3^18:0:2^127:1:5^5:0:1

The master cylinders were never painted. I just used aerosol clear lacquer, and the glycol-based brake fluid hasn't affected it.
Paul Hunt

Thanks I've got a good idea now however I've noticed today a few pin holes in the top of th brake cylinder probably me getting to aggressive with the wire brush wheel. I'm guessing I can't have any air leaks ? If that's the case any ideas how I could deal with this l don't really want to use a new plastic type ?
H c Jones

Which master cylinder do you have and for what year. You note it is the "brake cylinder". Both my 68 and my 79 have a plastic reservoir on top of the cast iron body. Thus, I do not understand what your are questioning. Yes, the reservoir is "open to the air" and only the cast iron part of the system is a sealed system--when the brake/clutch pedal is depressed. The reservoir would develope a vacuum if it was not vented and the system would not be able to cope with worn brake shoes/worn throw out bearing and driven plate.

It might be possible to seal any holes with a small amount of solder. But, until I understand what your are asking, it is hard to offer solutions.

As for the master cylinders not being painted, Paul is perfectly correct. All of mine have been plated rather than painted. But, the poor quality of the plating has resulted in damage to the substrate over the years which required bead blasting and a proper finish applied after the blasting.

Les
Les Bengtson

Les

UK models didn't get dual circuit brakes until around 1976/7. The single circuit master cylinder had a metal reservoir, like the clutch, only bigger.

I had a similar problem with mine about twenty years ago, but original style replacements were still available at that time. I noticed the problem while bleeding the brakes with my Eezi-bleed. It was spraying a jet of fluid all over the front wing.

I'm not sure how easy it would be to fix. New old stock items do crop up on Ebay occasionally.
Dave O'Neill 2

I can't believe you've got holes in the wall of the reservoir, have you? It's pretty thick metal. If you have I would think it is scrap. Or do you mean in the cap? The cap has an air hole in it anyway, so a couple of tiny extras won't make any difference.
Mike Howlett

Hi Guys

Yes I have pin holes in the top of the cylinder guess the metals pretty thin and all my "refurbing" has made it worse its definitely has small pins holes and when I blow through it you can feel the air escaping plus last night I filled it with some fluid and turned it upside down and it leaked out so.............I may have to but new style plastic ones :(


H c Jones

One of mine developed pin-holes on top as well, discovered when I used an EeziBleed and it went everywhere!

The 'ventilation' aspect doesn't matter, the caps are ventilated anyway, they have to be so fluid expansion when the brakes are being used can expel air, if it didn't the fluid would pressurise and the brakes would bind.

The original clutch at least tin can masters are available again from some sources e.g. Leacy and Brown & Gammons.
Paul Hunt

Thanks Paul

Don't think its worth risking its an awkward job fitting them so i'll go with modern replacements I think - it was just that they looked so good once cleaned and polished up
H c Jones

Hi, how about soldering the holes. It would be seen but close to original colour or silver paint maybe? What is the condition of the bores are they worn or pitted? I have had a couple of master cylinders stainless steel lined rather than replaced with new non original. Some places will tell you it cannot be done because they cannot drill down through the reservoir due to the bridge in the reservoir. Or very expensive as they have to sweat the cast bore out of the reservoir to drill and resolder back in. It is actually very easy to do drill from the bottom through the reservoir and both sides of the cast bore up into the upper reservoir. Then solder a small plate over the hole in the bottom of the reservoir which can’t be seen when fitted to the car.
K Stuckey

Well thanks for the all advice, I will just go with the more modern ones as I want reliability and although the originals are nice I'm not 100% into keeping it totally original.
H c Jones

This thread was discussed between 07/11/2015 and 09/11/2015

MG MGB Technical index

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