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A senior moment.

An overdue replacement of the front brake master cylinder piston & seals is underway on the 375/2C. So the smaller size master cylinder, but the design is the same as on a 350.

I had to completely overhaul the one on the Spanish barn find 2C that became the "Forgotten Error" hill climber two years ago, but I can't remember now if the plastic 'reservoir' detaches from the master cylinder body. The two screws and steel disc are out, as is the piston, but before I dunk the cylinder in the ultrasonic bath I thought I removed the 'clear' plastic reservoir part, when doing that one, to let the cleaning process reach the parts better.

Am I mistaken? If not, remind me how it comes off.

It does come off - but it can be a bl@@dy tight fit!

you can remove it , as i have done to get at the tiny return hole as it was blocked, i cant recall if they were allen bolts or phillips screws holding it on as previouse , it was stubborn, hope this helps. muller.

Allen bolts IIRC.

After getting out the two allen screws, you can try to get a thin knife, like for cleaning patatoes, between the plasic reservoir and the body of the master cilinder.

To mount it again first get the allens in before pressing the reservoir into the body. If it is pressesd in you cannot turn it any more. I use a vice to press them in. Normaly you should change the sealing that comes with a compete sealing set.

This is a 13 mm pump for clipons (I guesss the reservoir is about the same as yours)

Aha! I did try briefly with a knife, but didn't want to use too much force. That must have been how I did the other one but it wasn't so tight. A bit of gentle heat from hot water on the cylinder body might assist perhaps. They are allen (socket head) screws, which came out easily.

I mustn't grumble too much as it last needed a new master cylinder piston about 25 years ago. I treated it to stainless caliper pistons and new seals in 2012, but I'll probably put new caliper seals in again while I'm at it.

I think I used a good soaking of penetrating oil to 'wet' the seal, followed by judicious use of a strap wrench to get some initial movement.

Well it just yielded to immersion of the cylinder body in hot water in a shallow dish, followed by judicious use of a thin but blunt knife.
That's a good tip about lining up with the screws before pushing it home on reassembly.

I was a bit surprised that the one caliper piston was also sticking. So reluctant to come out that I had to resort to the compressor. Once removed the pistons look fine but time for new seals I think.

Crikey. That shows how long it's been since this caliper was completely stripped down. The ball under the bleed nipple has gone rusty round the middle! I'm guessing it's just a 6mm ball bearing? The threads on three of the caliper bolts were rather rusty on the area not used. All those years of exposure to road salt occasionally I suppose. They cleaned up OK with a quick run down the thread of a die.

I too had corroded ball bearings under the bleed nipples and can only assume the brake fluid also contained moisture.And I had to phrase that very carefully!
John

I´ve just restored a pair of calipers.
These ball valves often are rusty because most of them have passed a lot of years without the rubber cap. You can be lucky if you can get them out without braking the valves.
If you use stop female screws (nuts?) you don´t need that special washers to block the nuts.
The large screw is a special one and you won´t find it in any ctlalogue. For those who have the posibility to make them, here are the dates. The 10mm diatance washer between caliper and fork ist 4 mm.
The lower screw has a special thread, I only could find them black an had to shorten them.
Maybe it helps anybody

ciao
norbert

Interesting. I've just double checked the lower screw on mine (250 2C with Paioli forks ) and it seems to be M10 x 30.

Well I now have a properly functioning front brake again. Grimeca systems on Morinis are pretty easy to fill and bleed, but a Mityvac makes it a breeze.

The front wheel is now spinning beautifully freely and the brake works very well (I ought to treat it to new pads really but these will do for now). So freely, that it has shown up a slight whirr from the speedo drive. Hopefully, having the wheel out and applying a small dab of suitable grease in the right place will sort that out.