ETZ leaking Brake Master Cylinder.

[nice2day]

One of the first things I did on the 250 rebuild was to restore the master cylinder and caliper. As usual I spent a lot of time and worked with extreme care and precision and bought all new moving parts. Well a few days ago I was bitterly disappointed to find the master cylinder still leaks....not only from the piston seal but from the reservoir tank as well. During the rebuild I did attempt to unscrew the plastic tank but it refused to move. I now regret not taking stronger action on this as it seems the seal at the bottom of its thread is leaking so the brake fluid constantly dribbles down the side of the unit... I did not expect this to leak!
As for the piston seal, I am very surprised it leaked. I was meticulous with fitting the parts. The piston certainly seals against pressure towards the caliper, feeling very solid with no leakage at all but like the header tank, the oil just slowly dribbles out of the piston seal at the lever end.
Anyway to save time I have managed to buy a new complete master cylinder for quite a reasonable price on Ebay...hopefully it will not leak but I am apprehensive all the same.
When I get time I will have another attempt to rebuild the old master cylinder with other new parts but here is a question: Are the plastic header tanks available to buy new?...I might have to damage the old one in my attempts to unscrew it and replace the O ring. If one is available I can make more drastic attempts on its removal ..Many thanks as usual.
Les

[Puffs]

Removed

[Blurredman]

Hi,

I have seen replacement reservoirs, on mz-b anyway.


As for the leaking piston.. They say the very old ones have piston rub against the bore on high mileage.

I recall rebuilding mine some years back and after a while the piston seal was leaking..... Looking at it it had become all twisted. Anyway I just purchased a replacement seal from e-Bay (some unknown brand I guess) and it's not leaked since.. I put it down to improper installation the first time..

[nice2day]

Thanks for your quick replies chaps.
Unfortunately I now have ANOTHER problem.....

I just fitted the new master cylinder and the oil floods out of the top hose fitting...no matter how much I tighten it...in fact it has screwed all the way in to the flange of the nut so I can see something is wrong. I have now had to drain it down and remove it which is always a big worry with brake fluid dripping everywhere and stripping my new paint off.

Anyway it looks like the threaded outlet hole has been cut too deep and the "cone" shape seal has been half drilled away so the brake hose fitting has nothing to seal against...Surely this not correct or do the later ones rely on a washer between the body and the end of the hose nut fitting?
Please click on photos to help view the faulty seal:

[nice2day]

By the way Puffs you could be right about the plastic reservoir not being NORMALLY removable as this new one appears to have some grey coloured glue to seal it. If I do manage to get the old one out I could re-seal the threads with JB Weld epoxy.

Les

PS: Since writing the above note, I have managed to remove the reservoir. Unfortunately the patient died in the operation ...well it ended up with a crack in it. To be honest, if I had tried it again I reckon I could have got it off without too much damage. It is threaded with a thin O ring at the TOP of the thread but a bit too thin to be effective IMO. The thread appeared to have been coated in a white sealant (unless this was extensive aluminium corrosion?) It is now all scraped clean and ready for a new plastic reservoir should I be able to buy one.

The rubber piston seal at the lever end I have to say is very weak in terms of being effective. It has no gator spring and the rubber is very soft which grips the piston very weakly.

Les

[Guesi]

https://www.guesi-motorradteile.de/inde ... 1/c/_/_/?_

https://www.guesi-motorradteile.de/inde ... 0/c/_/_/?_

https://www.guesi-motorradteile.de/inde ... 7/c/_/_/?_

These are the parts you need...

[nice2day]

Many thanks Guesi...I have already beaten you to it ..... I already checked out your shop this afternoon and put these items in the basket, plus a new SS piston...See attachment.
I will have to add the O ring too..
I will put the order in to you pretty soon.
Best regards and thanks again.
Les

[Puffs]

On the plastic reservoir it's clear then, and no doubt you saw that your original one, like mine, has no washer there. Aftermarket stuff might be different.

[nice2day]

Hi Puffs...It did have an O ring in place quite a thin one, around 2mm I reckon which gets pushed down out of site when fully screwed down. The trouble is that the O ring sits on the top of the start of the raised internal thread, there is not an actual machined shelf or lip, so is not supported all the way round and thus it can let the fluid pass by it. Using a fatter O ring will allow it to seal against the actual rim of the container and should seal a bit better...as long as it does not buckle or swell outwards which it might do . No, this master cylinder is cheaply made and designed, I reckon the threads still need to be sealed (suggestions please) to stop leakage as the design does not let the O ring work correctly.

Les

[Puffs]

What does the seller say on that?

Maybe there is place for a sealing copper washer.

[nice2day]

Hi Puffs I haven't bought one yet as I wanted to know what was going on with the new cylinder I bought on Ebay...no reply as yet.
Guesi is a seller of them as shown with links a few posts back. His O ring looks a little fatter I think. (this is not a personal comment )

PS: Proof that the tank design is prone to leaking oil is that hardly any "round type" master cylinders have any paint left on them


Les

[Puffs]

I didn't even know they were supposed to be painted...
But the lack of paint might also be due to the alloy/paint combination used. At any rate, I don't think mine leaks.

[nice2day]

Regarding the NEW master cylinder I bought as mentioned earlier on this thread:

The seller says "they are all manufactured this way" and he could send me a copper washer to seal the hose.
QUESTION Please:

Do you think this would be satisfactory? The original master cylinder has a cone shape at the bottom of the thread so the hose can bite into it and seal whereas his new ones seal supposedly against the hose end fitting with a washer...I am not sure if this is normal hydraulic engineering practice? I am not sure that this will work that well in terms of reliablity and sealing...what are your views please? Much appreciate a good answer as I have to accept this item or return it but there are not any alternatives available....
Maybe all the new ones ARE the same or am I being fobbed off???

Les

PS: After doing some searching maybe "DOWTY" type washers might be OK but I am still not convinced this is not a manufacturing fault, but I cannot compare other new replica round type master cylinders without actually buying another one from another seller.

[Puffs]

The issue is that it is constructed (slightly) different from how MZ (/Brembo?) designed it. Your current brake line might not be suitable for fitting with a washer - or maybe it will. Indeed, no washer on mine, but it might still work fine.

On fitting brake lines with copper washers, I just had a look downstairs, and modern Brembo does it, as does Nissin. So it is a viable approach.

[nice2day]

Many thanks Puffs, I can always rely on you for getting back with a good answer. I think the hose fitting is wide enough to accept a washer. The design of the unit looks externally identical but the actuating piston looks more modern with a different seal and also includes a gaiter arrangement so maybe these replicas are made by a company that makes other master cylinders and therefor have adopted a different (more modern?) seal arrangement. It certainly needs a washer but I have read that copper is not recommend so I was going to try to use a "Dowty" type seal...then again I do have suitable copper washers to hand so can you confirm the washers you saw were indeed copper ones please? Much obliged as always.

Les