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MG MGA - Brake System Maintenance

Hi All,

My 1600 has been back on the road for 12 years, including 2 years in storage, overall milage is about 50,000. Always used DOT 4 which has been changed each 2 years. Three years ago repacked the front discs and replaced each of the three flexible hoses.

There is no sign of any leaks (master cylinder, wheel cylinders or callipers), however as the system has been in service for 12 years I am keen to replace seals in both the master and wheel cylinders.

Am I doing unnecessary maintenance, given there are no visible loss of fluid.

Regards changing to DOT5, I am a convert having used DOT 5 about 20 years ago on a restored vehicle. However the cost here in AUS is about 5 times that of DOT3 or 4.


R J Goebel

Makes very good sense to me Russel. That was the first thing I did when I bought my current driver.

Regarding DOT 5 then there is a cost saving compared to DOT 4 using your figures! As the DOT 5 does not need to be changed every 2 years.
N McGurk

Surprise. You still need to flush the fluid every couple of years with DOT-5 as well. The stuff does not absorb water, but the system will still collect water by condensation in the master cylinder (among other devious channels). When water gets into a system with DOT-5 fluid the water will settle as drops or puddles in the lowest parts of the system. This can corrode low points in a steel pipe or and slave cylinder. With DOT-5 water damage in the cylinders shows up as pits in the cylinder walls, commonly in the lowest point of the cylinder wall.

Eve with flushing a quart of DOT-5 through the system ever 2 years it is still cheap insurance against future system failure.
Barney Gaylord

Yes Barney, I have heard that said, but I am not entirely convinced. In any case, even if you did feel the need to flush every couple of years you can always re-use the silicon fluid afterwards.
N McGurk


I'm also not convinced of the need to purge Silicon fluid regularly.

Silicon fluid does not absorb moisture like standard fluid, so unless you run without a lid on the master cylinder, there's no way for any moisture to get into the system at all, let alone settle in the lowest point of the cylinder.

dominic clancy

Neil & Barney,

Thanks, I'll get a kit for both wheel cylinders and the MC. Keep up the same brake system maintenance and should get another 10 years.

By the way, I remember an uncle of mine who was trained as an RAAF Aircraft fitter mechanic would always change brake seals at the same time as changing brake linings.

R J Goebel

I believe that Barney is correct about this one. I have used Silicon fluid for many years in my A and while it does not absorb water some water will collect in the system and need to be removed. I bleed the system every two years at the start of the driving season. It doesn't take that much fluid and when you think of the cost of brake parts it seems money well spent.
Keith Lowman

It's still recommended to flush the fluid, but that may be a general recommendation by manufacturers for all vehicles and climates. I flush my silicon-equipped systems every couple of years just to be on the safe side. After all, it's only a few dollars of fluid and 15 minutes of work. That said, I know a guy who ran silicon fluid for 20 years in his TC where the master cylinder is underneath the car and unsealed. He found no trace of water and no corrosion in the lines or wheel cylinders. He does live in a fairly dry area so that may have something to do with it, but he also drives thousands of miles per year in the car.

Theoretically silicon fluid will remain viable indefinitely. It's only the possibility of contaminants invading the system that require flushing. This includes water, dust, brass/iron and rubber. When you flush, do it with some force since water sitting in a silicon system will settle at the lowest points, so you need to force it out by pressure. Bleeding slowly may result in the water dropping back down where it was.

Just my methods and theories, others may disagree.
Steve Simmons

This thread was discussed between 07/03/2013 and 18/03/2013

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