To try to fix the problem of burning brake fluid in the engine, I've started overhauling the brake system components. As it's the easiest to get at, I've started with the master cylinder. Following the instructions in the manual (and the paper that came with the overhaul kit), I've got as far as pulling the piston out of the body of the cylinder. The instructions say it should just pull out, although to be aware that the o-ring could slip into the circlip ring and make it tight. However, I can't budge whatever it is that's stopping the piston from coming out. The piston itself moves freely within the bore, but once it comes up against the "stop" at the open end, that's it - not even a little movement that suggests it will come. I've been trying with padded (so as not to damage the surface of the piston) pliers, but still can't get anything. There's what appears to be a blue ring that was just below the circlip, and doesn't move with the piston, that I can't identify from the manual instructions, and it almost appears to be this that's stopping the piston coming out. This ring is stopping me from seeing the o-ring beyond it.



Has anyone come across this before and can make suggestions on how I can overcome it?

 

Stuart , you have the worst type of master cylinder to o/haul , because of it's design , with the External Piston , it is a snug fit in the booster and needs to form an air tight seal between booster and master cyl .

Because of the very fine tolerance , for the above reason , that blue plug virtually welds itself to the body of the master cyl . In most cases the blue plug was destroyed in order to remove the piston , it didn't really matter as the repair kits had a new plug in it . You can no longer buy that plug , so you now would need to make your own .

or you can ....

Try spraying an anti rust solution in and around that plug , tap the body upside down , and more spray and tapping , it will eventually start to give way , once it moves you can then give it a good tug and it will pop out .Caution is needed when inspecting the cylinder bore ,it pits and wears easily .

They were really designed as a throw away unit , ( if they are still available , better to get a new one ) if not you need to have it re-sleeved and kit by a brake shop . I would also give them the booster at the same time , if as you say "burning brake fluid in the engine" the seals inside the booster will be badly swollen and deteriorated , those seals and rubbers are not compatible with brake fluid .

Good luck with that

 

Thanks MasterSid. Yes, I had read that the parts were an interference fit, but still hoped I would be able to move them. Over night I tried leaving penetration oil on top of the plug, hoping that it might make its way between that and the bore, but still no sign of movement this morning. I also wonder whether the o-ring may have swollen, just to make the situation worse.
Rather than waste any more time trying to get this out, I'll be ordering a complete replacement Master Cylinder assembly, as well as a complete Servo assembly. They will at least help me get the car back on the road a bit quicker. Maybe some time in the future I'll go back to opening up the original parts, just to see what condition they're in inside.

 

Given the circumstance , replacement would be the best option in this case .

Good luck with that Stuart ,

Sid

PS , you probably know this , but .........

you need to BENCH BLEED the Master Cyl before you bolt it back up .

 

Hello Stuart1960,
You were reading the writings of an idiot. The only parts that are an interference fit are the flexible seals.

With cylinders where the internal parts are really stuck, I use a 10,000 psi grease gun to pump the inner parts out. Normally any cylinder I have to do that to has a corroded bore and needs to be re sleeved. The sleeves used in this operation are Stainless Steel and in my opinion, the resulting cylinder is better than the original unit. Accordingly, I would opt to have the original unit repaired rather than buy a new unit.

Regards,

Brent

 

Just took mine apart. I was able to clamp the piston in a well padded vise and gradually slide-hammer the blue plug out.

 

rbr, how did you grip the blue plug to be able to use the slide-hammer?

 

Stuart-
I clamped the piston in the vise (heavily padded) and used the m/c body "like" a slide hammer...
it gradually worked the plug out.

 

Got it, thanks. To save time, I've bought a complete cylinder that I've now installed (together with a new servo/slave cylinder).
I'll be keeping the old cylinders with the aim of eventually refurbishing them for spares, so I'll give your method a try when I get to it.