Morris Minor Owners Club

So, most of us know that the Brake Master Cylinder for some reason or other, changed internal bore from 7/8" to 13/16" in 1962. A whole 1/16" difference....

My car is a '55, but I know has had all sorts of bits changed over the years including having latter, post '62, 8" brakes on the front.

Is there an external part number or other way to identify if I have the original or latter Master Cylinder?

Or do I have to take it apart and vernier gauge the bore/piston?

Here is a Genuine Lockheed 13/16" master cylinder with the markings visible:-
https://www.ebay.co.uk/itm/304175233218 ... SwlLhhXZyI
The after market master cylinders are not so marked.

The earlier master cylinders have not been generally available for many years. I remember having to fit the later type to my 948cc car a LONG time ago. If I had to guess, I would think it most unlikely that your car still has its original master cylinder after all this time

The 1/16" I.D. may not seem very much but it does allow for a higher pressure on the wheel cylinders. The down side is possibly a very slightly longer pedal travel.

Thanks guys.
I'm just thinking that I changed all the wheel cylinders earlier in the year and it got me thinking about the Master.
I'm assuming it's been untouched since the car was last 'restored' in 2009, but whether the original was left in at that point, or it was replaced, possibly from the car that donated other bits, I've no idea.
I believe the Donor car was a 1967 E Reg, just because some of the door glass had the Reg etched in.

I do feel the brake pedal travels a bit far on the first press, so I was wondering if the seals might be a bit worn.
It's been bleed within an inch of it's life after the other work.....
As seal kits are available for both bores, it just got me wondering about how to identify them.

philthehill wrote: ↑Sat Dec 04, 2021 12:02 pm The 1/16" I.D. may not seem very much but it does allow for a higher pressure on the wheel cylinders. The down side is possibly a very slightly longer pedal travel.

Wouldn't a bigger bore mean less pedal travel? The piston in the MC won't have to move as far to displace the same amount of fluid? Or have I missed something?

geoberni wrote: ↑Sat Dec 04, 2021 4:07 pm I'm assuming it's been untouched since the car was last 'restored' in 2009, but whether the original was left in at that point, or it was replaced, possibly from the car that donated other bits, I've no idea.

If it was replaced in 2009 its the bigger bore type...

https://www.morrisminorspares.com/brake ... ed-p829360

The bore size of the master cylinder was reduced from 7/8" to 13/16" - not increased.
The master cylinder piston will have to travel further to displace the amount of brake fluid.
The reduction in the master cylinder bore diameter by 1/16" will allow the master cylinder to exert an increase in fluid pressure on the wheel cylinders pistons for the same pressure applied at the brake pedal provided that the wheel cylinders have not been increased in bore size.

So, coming back to this, the Master Cylinder is now out and stripped down. It is the original 7/8th.

It had been leaking for a while, there was/is a shallow puddle of brake fluid laying in the Longitudinal member which houses the Master Cylinder. I've stuffed it with paper towel to soak it up.
Aside from having been leaking, the actual Master Cylinder looks OK , with no damage to the Bore.

The internals were not secured with the type of Circlip I was expecting, having seen the manual and several videos.
Perhaps changed after a past refurbishment.


What is the correct way of fixing the Return Spring to the Pedal?

Can I just confirm it's supposed to be a Clevis Pin with 2 holes, and I assume the Spring would go through the outermost hole, with the Split pin in the inner one?

Whoever refurbished Basil years ago decided to fit a Metric Bolt, with Nylock and a home made sort of tab washer to take the spring

You can see here the grime inside the Rubber End where the piston had been leaking, the tab washer and the Clirclip.
The end of the Push Rod is caked in the old fluid grime, but should clean up with some wire wool.
Note - I've edited this just to correct a typo I spotted, some 10.5 hours after posting, and also after Phil's reply some 4 hours ago.
I have no idea how the time limits are working on the edit function....

As regards the circlip - the circlip can be either the square section wire clip with the two forward protruding tangs or like the circlip in the photo above - so long as the circlip is a good fit inside the master cylinder groove there is no cause for concern.
The split pin should go through the inner hole of the clevis pin and the spring through the outer hole. The other end of the spring should fit through the small bracket attached to the bottom of the chassis leg.

philthehill wrote: ↑Thu Jan 27, 2022 8:40 am

Thanks Phil
Yes the circlip was a good fit so I'm not concerned about it, I was just a little surprised to see it was that type.
Funny thing was, my Mrs tends to include some 'odd little items' amongst my Christmas presents each year, and in 2019 one of her little extras was an 'interesting looking pliers' she had seen on a market stall and had no idea what they were for.
Something out of one of those '£1 each' type of bins....

So I finally had a use for the Circlip Pliers she brought

I still have to get the final rubber 'Valve Washer' from the far end of Cylinder.

Any suggestions other than a bit of bent wire?

As to cleaning up the remains of the old brake fluid, I'm thinking some warm slightly soapy water, scrubbed with a large bottle brush. There do not appear to be any natural drainage points in that section, which probably explains why I found the shallow puddle of manky fluid.
I think a scrub and then soak up before drying out with warm air.

Would it be worth drilling a small drain hole to the rear of that section and plugging with a Rubber Grommet afterwards...?

I'll be wax treating both members before replacing the gearbox cover.

Any thoughts on using Red Grease on the rubber bits?
I know it's well advised for the Wheel Cylinders, but would a thin smear be advisable on the Main and Secondary Cups, instead of wetting with brake fluid which is what the manual says...

Just bumping this up the list of active topics since nobody has come back to it after 24 hours...

The correct type of grease - red rubber grease, with "for use on brake cylinder components" on the tin, is reportedly nothing more than more viscous brake fluid anyway, so yes, use the brake grease I would say.

This is what I use:

https://www.ebay.co.uk/itm/284457657321 ... SwCFFhRxG6