Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Rear brake cylinders - watchpoint

Recently I changed the rear brake cylinders. Both of them had one piston stuck due to rust. As the other piston worked (although with some friction) I did have rear brakes, but inadequate. My car went through the Norwegian equivalent of MOT autumn 2020, so either it was not detected by then or they have seized in the time after. Then I helped a friend of mine change his, all four pistons completely rusted and stuck. Also through MOT with no comments autumn 2020. Later I have talked to the local Morgan mechanic here in Bergen. He has had several Morgans in for service this spring and all of them - with no exeption - has had defective cylinders to some degree or other. You might not notice it as most of the braking comes from the front (my friend certainly did not in spite of having no working rear brakes at all), but this is obviously not what it should be like. So gentlemen, check your rear brakes. Take the drum off, lift the rubber dust cover over the pistons, check for rust, brake fluid leak and that the pistons move freely. If it is ok, apply silicone grease under the dust cover and put it back. If not, ......
The cylinders on my car has surely been in there since 2004, God knows when they started to seize. I changed to silicone brake fluid three or four years ago. I know it is disputed, but at least it is not hygroscopic. No issues so far, but it will be interesting to see if rust develops or not in the future. I will certainly check after each ended season, when the car goes into winter storage.

I have had two changed in 8 years

Good post Robbie. On average when I was not using the car a lot the rear cylinders had to be changed every 2 years. They have been on for 4 years now as the car is used every day. BUT having found the brakes pulling a little in the wet. Inspection has shown that both front Callipers are in need of a re-build. The inboard pistons were seized on both sides. This was not apparent during braking in the dry.
To check I replaced the pads with some very worn ones then got a friend to pump the brakes it then was obvious.

Change the fluid every two years as a minimum. It makes a big difference.

And as Robbie says, remove the drums and check inside the rubbers. Annually is good. If not, when you change the brake fluid at two years.

My Roadster cylinders lasted almost 16 years doing this.

http://www.talkmorgan.com/ubbthreads.php/topics/612261/rear-wheel-cylinders-btr-axle#Post612261

Yes Dave, Even every 2 years in my case was not enough. When rebuilding the front callipers, there was a little water sitting at the back of the pistons. I can see why you would want to go to the Dot5 (am I right) that does not attract water, but that would mean a whole new system.

I use Motul RBF 700, still Dot4 and maybe a bit dearer than other brands, but having boiled brake fluid previously and lost braking, I havent had any problems since.

I’ve had to replace rear brake cylinders on a Classic Mini in less than a year.

I think there are several things that can happen …

1) A specialist and well respected classic brake refurbisher said that the seals swell slightly and if not used regularly then they will seize;

2) Fluid that gets past the seal to the outside, even a tiny amount, will absorb water and cause the rust under the boot then seizing through lack of use;

3) Components are simply not as good as they used to be!

I change fluids at no more than two years and often annually yet have still had problems. Over Winter I go in the garage weekly and give the all the pedals a good pressing. We had a problem getting my Son’s Elan going this Spring. We had to store it in a friend’s garage away from home for a few months and couldn’t do our usual pedal pressing. The clutch rusted onto the flywheel and pressure plate and I had to use a bit of brute force to jar it free!

Yes, DOT 5 silicone is hydrofobic. I was well aware of the controversy concerning silicone brake fluid, but I decided to take the plunge after the recommnedation of a friend of mine. He has an old Mercedes, an even older Nash, an MG TD, a Volvo PV and a +8, all changed to silicone, but no changes to the braking system. No issues at all. Of course it was done a VERY thorough job when flushing the old DOT 4 out and then changing to DOT 5, as it was done on my car (with his help). Besides, all the military vehicles in the Norwegian army use silicone, just because they are stored without use for extended periods of time. If I am not mistaken this is as a matter of fact a NATO standard. Correct me if I am wrong.
It is said that if DOT 4 and DOT 5 form a gel when mixed, but it does not seem to be true. We simply tried it in a glass. No gel, they just don't mix - like oil and water. And it is said that DOT 5 makes rubber parts like hoses and gaskets swell. If this is true or not, to what degree or if it has any practical importance I do not know, but as I said I have not heard of any issues.

The only time I had a completely new and dry braking system, when I rebuilt my BV8, I thought long and hard about using silicon fluid.

In the end, there were just enough stories of sticking cylinders, and spongy feel to put me off.

Maybe on a dry fill it would have been OK. but it was never adopted by manufacturers so far as I know.

I've been using dot 5.1 in my Roadster, until the last replacement, which has similar performance properties to silicon, but is conventional brake fluid.

Last time I had some 4.0 to use up so that went in.

From a sealed/unopened container hopefully?