Help me choose a master cylinder
Discussion
Hi, I'm re-building a kit car based on Cortina MK5 running gear.
I don't have a master cylinder or any bracketry for it so looking to buy a m/c and make a new bracket.
Problem is I don't know what size m/c to go with.
In the future I'm likely to upgrade the front brakes, but not sure what with yet and really want to get the thing working in stock form for now to determine a baseline.
I want to ditch the servo setup to improve brake feel (does this create an MOT issue?).
Also I'd would rather go dual circuit (again, would this be an MOT requirement).
Given the above, I want a pick a m/c that comes in a variety of diameters, and has some really cheap yet likely questionable eBay specials so i can experiment with sizes a bit before buying a quality one once I'm happy with the set up.
I've been told that early non servo Capri used 19mm dia so I was going to start there.
I couldn't actually find any non-servo Capri m/c's, so tempted to go with TRIUMPH GT6 MK3 which seem a bit more common https://www.ebay.co.uk/itm/265720846542?hash=item3... which I believe used 0.7" but if I find there's too much travel, I'd need to source a bigger m/c and then I'd likely have to fab up new brackets etc as I expect the shafts are all different lengths, bolt patterns etc.
Is the a m/c, that comes in different diameters but everything else is the same so easy to swap, and plentiful so I can get cheap knock-offs for now?
I don't have a master cylinder or any bracketry for it so looking to buy a m/c and make a new bracket.
Problem is I don't know what size m/c to go with.
In the future I'm likely to upgrade the front brakes, but not sure what with yet and really want to get the thing working in stock form for now to determine a baseline.
I want to ditch the servo setup to improve brake feel (does this create an MOT issue?).
Also I'd would rather go dual circuit (again, would this be an MOT requirement).
Given the above, I want a pick a m/c that comes in a variety of diameters, and has some really cheap yet likely questionable eBay specials so i can experiment with sizes a bit before buying a quality one once I'm happy with the set up.
I've been told that early non servo Capri used 19mm dia so I was going to start there.
I couldn't actually find any non-servo Capri m/c's, so tempted to go with TRIUMPH GT6 MK3 which seem a bit more common https://www.ebay.co.uk/itm/265720846542?hash=item3... which I believe used 0.7" but if I find there's too much travel, I'd need to source a bigger m/c and then I'd likely have to fab up new brackets etc as I expect the shafts are all different lengths, bolt patterns etc.
Is the a m/c, that comes in different diameters but everything else is the same so easy to swap, and plentiful so I can get cheap knock-offs for now?
No requirement for a servo as far as MOT (or even IVA) is concerned. No issue with dual master cylinders either, per se.
Almost certainly you will need to re-work the pedal to give a different pedal ratio than you currently have. Typical non-servo pedal ratio is around 6.25:1 although they do vary.
You could do worse than look at what you'd find on similar kits tbh. Maybe Westfield or similar setups. Our Westy has a dual-circuit master and originally had M16 front calipers (Cortina) and rear drum brakes from an Escort. Over the years, I replaced the M16 calipers with some WiIlwood 4 pots (same piston area) and fitted discs to the rear, but was careful to retain the same brake balance, so have kept the original master cylinder.
From experience, I'd suggest either copying a setup that you know works (as above) or do some calculations.
On my latest build, I started out with a setup that passed an MOT brake test but frankly felt dangerous given how hard I had to press the pedal, but unsurprisingly, it failed the IVA. Not by that much really, but even had it passed, I'd never have left it like that.
On examination realised I had the wrong pedal ratio (I'd bought a secondhand pedalbox and never even asked the ratio - idiot) and given the results at test, I decided to go overboard so replaced the pedalbox, removed the MX5 brakes, went up 50% on front caliper piston area, much bigger diameter discs, at the back I also went +40% piston area and even bigger on discs diameter (mid-rear engine car). This gives super brakes in both feel and performance. I did manage to keep the original master cylinders though (dual master setup on Wildwood pedalbox)
All that to say, trial and error is not the way to go! It gets expensive.
Almost certainly you will need to re-work the pedal to give a different pedal ratio than you currently have. Typical non-servo pedal ratio is around 6.25:1 although they do vary.
You could do worse than look at what you'd find on similar kits tbh. Maybe Westfield or similar setups. Our Westy has a dual-circuit master and originally had M16 front calipers (Cortina) and rear drum brakes from an Escort. Over the years, I replaced the M16 calipers with some WiIlwood 4 pots (same piston area) and fitted discs to the rear, but was careful to retain the same brake balance, so have kept the original master cylinder.
From experience, I'd suggest either copying a setup that you know works (as above) or do some calculations.
On my latest build, I started out with a setup that passed an MOT brake test but frankly felt dangerous given how hard I had to press the pedal, but unsurprisingly, it failed the IVA. Not by that much really, but even had it passed, I'd never have left it like that.
On examination realised I had the wrong pedal ratio (I'd bought a secondhand pedalbox and never even asked the ratio - idiot) and given the results at test, I decided to go overboard so replaced the pedalbox, removed the MX5 brakes, went up 50% on front caliper piston area, much bigger diameter discs, at the back I also went +40% piston area and even bigger on discs diameter (mid-rear engine car). This gives super brakes in both feel and performance. I did manage to keep the original master cylinders though (dual master setup on Wildwood pedalbox)
All that to say, trial and error is not the way to go! It gets expensive.
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