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Wed Mar 15, 2023 2:35 am

My NOS one for reference

Wed Mar 15, 2023 8:12 am

Cool
Any sign of seal 25?

Looking for a source for that lid rubber seal 24, if anyone has one

Wed Mar 15, 2023 10:35 am

Two gaskets stacked? Thats unusual.

Wed Mar 15, 2023 5:10 pm

I'm wondering if it's metal too since it's not black

Thu Mar 16, 2023 12:53 am

I wonder if this has something to do with helping to undo the cap. The aluminium caps are known to really freeze solid. Add brake fluid and moisture and a rubber seal. 2 layers of seals may help in reducing friction.

That NOS master cyl. must be one of the ultimate BD/WB collectibles ! It should be displayed at a museum !!! It is just so strikingly beautiful ( along with the design of the original ATE boxing) :!: :oops:

(total nerd mode).

Thu Mar 16, 2023 1:36 am

I think it looks cool too 🙂
What’s people’s advice to stop the lid seizing?

Thu Mar 16, 2023 2:23 am

100% agree, stunning, get that into a display case 8)

djfordmanjack wrote: I wonder if this has something to do with helping to undo the cap. The aluminium caps are known to really freeze solid. Add brake fluid and moisture and a rubber seal. 2 layers of seals may help in reducing friction.

That NOS master cyl. must be one of the ultimate BD/WB collectibles ! It should be displayed at a museum !!! It is just so strikingly beautiful ( along with the design of the original ATE boxing) :!: :oops:

(total nerd mode).

Thu Mar 16, 2023 2:32 am

In general I like to use Liqui Moly copper grease ( or any other brake caliper copper grease) just make sure you just put it only on the cap and cup threads, and under no circumstance, let it get into/ mix it with brake fluid ( alcoholic based DOT3)!
You can lube the rubber seal with any good conventional brake cup assembly paste ( I like to use og ATE).
Or you can do away with it all and used DOT 5.0 silicone brake fluid. I have done it many times and works great, but you have to make sure to either clean out/flush the entire system thoroughly from old DOT3 brake fluid, or assemble with all completely new brake parts ( cylinders, hoses and lines) to be safe.
It is great ! especially when using rare and precious NOS components, and on cars that are mostly garaged and rarely driven. From my own experience I have to say it is recommended to also replace DOT5.0 every 5 years or so, because, on an open circuit ( all our old master cylinders have a breather cap), dampness can and will get into the system as well, and with silicone, it will not mix with the brake fluid, but instead collect at the lowest points ( wheel cylinders). I like to use Harley Davidson DOT5.0 silicone.

RockStock wrote: I think it looks cool too 🙂
What’s people’s advice to stop the lid seizing?

Thu Mar 16, 2023 4:30 am

RockStock wrote: Cool
Any sign of seal 25?

nope, only the # 24 seal

Mon Feb 12, 2024 3:50 pm

Thank you both

RockStock wrote: Cool
Any sign of seal 25?

Maybe this is gasket 25…card
Part number 611 377
(Remains of rubber gasket 24 on the right?)

Tue Feb 13, 2024 2:35 am

that absolutely makes sense now. the cardboard will go between the cap and breather shield. When the shield and rubber sticks to the reservoir, the cap can still be undone.
From the looks of the crumbled pieces, it rather looks like rubberized cork than pure rubber, maybe. Both gaskets could be easily cut from Klingerit and rubber (cork) sheets.

Tue Feb 13, 2024 8:50 am

But the diagram doesn’t show it in that order?

Cover c/w splash guard 23
then
Rubber gasket 24
then
Card gasket 25

The splash guard (breather shield) doesn’t want to separate from my cap.

I also have a couple of caps with no splash guards. Makes me wonder if some came without splash guards.

Tue Feb 13, 2024 10:11 am

I realized before that the order of parts shown on the diagram was different. But even VW wasn't perfect all the time.
We have no way of knowing about ongoing improvements on the cap. whether they started w or w/o the shield and/or card gasket.

Using common sense, the cap must seal against the reservoir with a rubber seal, as it sees fluid splashing all the time. the cap needs to be vented anyways, as the m/c would not work otherwise ( in case of brake fluid loss, the reservoir has to provide new fluid into the m/c bore, which will not work against a vacuum on top). even with a breather shield inside the cap, eventually some fluid mist or drops will get up and between the actual cap and shield. The cap has to be sealed against the shield, or the fluid will not drain back in the reservoir, but drain around the rubber seal and bleed down through the cap threads, making an awful mess of the m/c and pedal pan underneath.

This is just talking from technical common sense. Not according to any VW literature.

I wonder if the breather shield is sealed/stuck/glued inside the cap, or maybe locked with a few peens? Or maybe just seized because of corrosion?

Tue Feb 13, 2024 10:25 am

Maybe the card gasket was simply replace with the rubber seal ?

I checked Mercedes parts catalogs for similar year, and although it has a different reservoir, it has a similar illustration and say that one is replacement for the other. parts 31 and 31a

https://www.niemoeller.de/de/ponton/w120-mercedes-180/B010/422601

edit, found these pics in my files (originally from TS ad). obviously an NOS cap kit. does not have the card gasket and shield separates from cap.