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My 1976 Sport has wire wheels and twin discs. It has a 16mm diameter Grimeca master cylinder with single outlet. Today the lever locked up such that the lever was solid but not operating the piston. On investigation there appears to be a separate component that transfers the force from the adjuster bolt on the lever to the piston itself. This had become dislodged and was no longer acting on the piston. The component in question is about 1 inch long is rounded at one end where it seats onto the piston and is cupped at the other end to receive the lever adjuster bolt. The only thing keeping it axial alignment with the piston appears to be a rubber seal / bellows. Is this the correct arrangement or is there a bit missing? I can’t find any drawings either blue book or parts list that shows this detail. I noted that the piston was sticking in the bore so I’ll be giving the master cylinder a thorough clean and a new seal kit so hopefully that will sort it but as found the arrangement seems odd. Any info / advice gratefully received.

Hi there,
no, that's exactly how it should be. It's a vulnerable area though, with no real protection from road dirt so it pays to occasionally remove the lever and the cupped part and grease everything.
DD

Hi Dom,
Not good having solid lever and no brake!!, Some other ideas I had, I wonder if you either have non standard brake lever or the adjuster is too far out so that the force isn't applied linearly. Hopefully a clean and overhaul will sort it
Take care.
Mark

Thanks both for the replies. Reassuring to know I do have the bits I need to put it back together. Still think the design is poor. I suspect the sticking piston along with a badly adjusted brake lever screw caused the bit in between to drop out of position.
I’ll be keeping a close eye on it in future!

Yep, correct adjustment and regular maintenance is key. Any design will fail without these.

Fair comment, a thorough clean of the master cylinder was required. Rusty crud had accumulated at the spring end eventually resulting in a sticking piston. Old brake fluid purged from the system, lever adjusting screw set and locked, front brake restored!

Hi,
Glad it was easily sorted!
For us in 2022 easy to be critical of the design but in
1975 when introduced it was pretty much state of the art for hydraulic disk brakes.
Of course the brakes can now be replaced with up to date equipment
as can the suspension, electrical systems etc.

take care
Mark

mbmm350s wrote: ↑11 May 2022 06:19 For us in 2022 easy to be critical of the design but in
1975 when introduced it was pretty much state of the art for hydraulic disk brakes.

Not forgetting, they're also damned sight better than the Scarab systems fitted to contemporary MV-Agustas!

mbmm350s wrote: ↑11 May 2022 06:19 Of course the brakes can now be replaced with up to date equipment
as can the suspension, electrical systems etc.

Very true, but as I've approached each replacement, I've found myself at a crossroads: to load my bike with generic after-market parts or to keep it intrinsically the same. I prefer the latter and with some patience and scouting around, most OEM things can be found either new, NOS, rebuilt or rebuildable.
Additionally, when replacing things like front reservoirs with cheap items off the 'bay, I believe many of these parts are basically single-use and when new seals are eventually required, there might be problems sourcing the right type. (Maybe not.)
Any subsequent owners will also have to rely on a previous owner noting down the exact replacement part used in each case.

We're so lucky that many parts on our bikes are not Morini-specific. My NOS Bosch starter-relay came from a snowmobile place in Oregon!
Happy days.
DD

Hi hphilbo +
Can I ask how to fit a a new seal kit in my Grimeca brake master cylinder ? I can't see any way to pull the piston out- no holes to remove a circle in the recess... ?
Many thanks in advance

Hi
Doug at MDINA says it just pulls out...no circlip...I have ordered a 16mm seal kit with rubber outer cover...we shall see...
Matt

Hi All
I’ve changed the rubber seals on my Grimeca master cylinder but it still leaks where the lever pushes the piston and I can’t get the brake to work while it does.
I hadn’t used this Grimeca master cylinder before and the Brembo I removed (ex Laverda) will easily work if I put it back. I have cleaned the piston barrel fairly well but not sure how to definitely do this…Any ideas on how I can make the Grimeca work? What can go wrong other than seals?

Maybe the cylinder bore is damaged-Scored by grit etc that got in when the bellows wasn't fitted? The cylinder is simple so the fault should be visible with a magnifying glass etc. Or you were unlucky refitting it and damaged the seal. On another bike I found someone had fitted a seal in reverse so it would never pressurise the system!

Thanks Steve- I think it must be damaged bore. I hadn't used it before and can't remember why it was replaced now...I'll replace it with another - actually wonder if I can use a modern/new one not Grimeca. I would love confirmation of the size of the bolt that holds the hose on so I know what size to get when I replace. The piston bore is 16mm on the Grimeca but I'm not sure of the size of bolt- 13mm spanner...

The majority are a 10mm thread (unless you buy one for an American or British bike when they can be 3/8" UNF) The 10mm thread can be 1mm pitch or 1.25 so get a master cylinder with the banjo bolt supplied. (most come with it any way)
It's sometimes harder when sourcing a replacement to identify the bore size of the master cylinder-not all of them quote it, just say it's meant for whatever model/make. One advantage of a replacement is they often come with a brake light switch too.
Pay attention to the angle of the cylinder relative to the handlebar too. I.e for clip ons or touring bars.

Thanks Steve- I think it must be damaged bore. I hadn't used it before and can't remember why it was replaced now...I'll replace it with another - actually wonder if I can use a modern/new one not Grimeca. I would love confirmation of the size of the bolt that holds the hose on so I know what size to get when I replace. The piston bore is 16mm on the Grimeca and just need to get the correct size of the bolt that holds the hose to the master cylinder end...
update: I've bought another master cylinder from Doug at MdinaItalia and await arrival- hopefully this'll solve issue!