mk1-forum.net

I need a new brake master cylinder for a 1959 Mini which has been upgraded with the later front twin leading shoe brakes (15/16, 0.9375" bore wheel cylinders) but has the early rear wheel cylinders (5/8, 0.625" bore).
Minispares now do the flat top clutch master cylinder (GMC 153). Originally the top of this master cylinder would have had either a removable union or a small hexagonal nut shape machined into it, but neither of these options are easily available. This new flat top looks much more period correct than the later cone shaped top versions, and is the correct bore size (0.75") to suit the early Mk1 850 brake systems. This cylinder also has the original size small base foot
Details in links below:-
"The GMC153 is the early 0.75" BORE BRAKE MASTER originally used on 1959 minis to approx 1963 with single front wheel cylinder per wheel drum brakes and most 997 Cooper with booster valve and 7" disc brakes. Also fits Austin A40 Farina Mk2."

From Minispares:
The (GMC153) 'flat' top brake master cylinder (0.75") is £150.76 inc VAT.
https://www.minispares.com/gmc153-tin-t ... -0-75-bore
The (GMC171ORIGINAL) 'cone shape' top brake master cylinder (0.70") is £111.60 inc VAT
https://www.minispares.com/gmc171origin ... ginal-type

I believe the early larger bore master cylinder will reduce the pedal travel but will require more effort. Any thoughts are welcome on the choice of master cylinders, bearing in mind the combination of later/early brakes and wheel cylinder sizes fitted as mentioned above. ie. Will any differences in pedal travel or braking effort be significant on an early 850 Mini?

If the bore of your current master cyl is corroded and therefore the need for a replacement, Past Parts will re-sleeve the cylinder part for you in, that dreaded word, so I'll say it quietly......., stainless. With a new set of seals, they'll bring it back to new. Seemingly, they are VERY competitive too.

They've done my friends corroded .75"bore servo to like new.

Forgot to say earlier, but the early 'double ended' master cylinders with the big unscrewable nut at the top end are simplicity itself to sleeve and the honed finish .75" bore size is a SAE standard hydraulic cylinder size to boot!

Yes Peter, it came back like new, pleased with service of Past Parts.

Looks like it would be worth putting a link to Past Parts in the 'Recommended Parts Suppliers / Useful Web links' section of the forum, if they are not already listed?

Edit: Past Parts now added to Parts Suppliers / Useful Web links listing for reference:-
viewtopic.php?t=40238

Past Parts:-
https://www.pastparts.co.uk/services-products/

Past Parts Brake Master Cylinder Resleeving video:-
https://www.youtube.com/watch?v=X36_uEwgjSI

Call me a bit nerdy but I love seeing these old machine shop fitters turning out this sort of work.....

Me too Peter. From a bygone age before we ended up a consumer, throwaway society