How to plumb a modern Master Cylinder into an old car?
Discussion
Hi, I have a MK5 Cortina based kit car (1982).
Standards discs at the front and standard drums at the back. Sporty!
I'm planning to fit a Mondeo MK5 master cylinder and servo. It has a 25mm dia cylinder which is ideal for any future upgrades and a larger servo to suit.
But I'm unsure how best to plumb it all up.
The Mondeo servo has two outlets, and I believe the Mondeo has a front/back/diagonal split (i.e., each master cylinder outlet controls one rear, and one front brake). This means that it pumps roughly the same volume of fluid out of each outlet.
I was planning on having a front / rear split since this is how my plumbing is already set up on my car.
This would mean that the master cylinder would need to pump more fluid to the front discs than the rear drums.
Is this even possible? Can the master cylinder pump different volumes, or do they both need to be the same? I'm not really clear if the two pistons have to have the same travel or not.
Standards discs at the front and standard drums at the back. Sporty!
I'm planning to fit a Mondeo MK5 master cylinder and servo. It has a 25mm dia cylinder which is ideal for any future upgrades and a larger servo to suit.
But I'm unsure how best to plumb it all up.
The Mondeo servo has two outlets, and I believe the Mondeo has a front/back/diagonal split (i.e., each master cylinder outlet controls one rear, and one front brake). This means that it pumps roughly the same volume of fluid out of each outlet.
I was planning on having a front / rear split since this is how my plumbing is already set up on my car.
This would mean that the master cylinder would need to pump more fluid to the front discs than the rear drums.
Is this even possible? Can the master cylinder pump different volumes, or do they both need to be the same? I'm not really clear if the two pistons have to have the same travel or not.
Why bother? Cortina Mk5 servo units are available: https://picclick.co.uk/Ford-Cortina-Mk3-Mk4-Mk5-Br...
I don't want the MK5 cortina m/c.
Their diameter is small leading to a squishy brake feel and no good for larger calipers which will soon be fitted. Squshiness just gets worse.
But with a larger cylinder the brakes become harder to use so you need a bigger servo.
This is why the 25mm Mondeo m/c with it's larger servo is the perfect size, and only cost me £20 for a 5 year old item. It also means I can get spare parts really cheap for quite a while yet.
Delivered with taxes etc I'd be lucky to get a Cortina one for under £200.
There are non for sale in the UK (Burton Power, Ford Tickover, eBay etc all come up with nothing). Your example was in Germany.
It used to be that when upgrading Cortina brakes people would fit Sierra m/c as they are 25mm, but good luck getting one of them these days.
It's easier to just upgrade to what's common now and enjoy the price benefit.
Just need to know whether my front/rear split would work.
Their diameter is small leading to a squishy brake feel and no good for larger calipers which will soon be fitted. Squshiness just gets worse.
But with a larger cylinder the brakes become harder to use so you need a bigger servo.
This is why the 25mm Mondeo m/c with it's larger servo is the perfect size, and only cost me £20 for a 5 year old item. It also means I can get spare parts really cheap for quite a while yet.
Delivered with taxes etc I'd be lucky to get a Cortina one for under £200.
There are non for sale in the UK (Burton Power, Ford Tickover, eBay etc all come up with nothing). Your example was in Germany.
It used to be that when upgrading Cortina brakes people would fit Sierra m/c as they are 25mm, but good luck getting one of them these days.
It's easier to just upgrade to what's common now and enjoy the price benefit.
Just need to know whether my front/rear split would work.
Normally on a kitcar or special, you'll have two different sized brake master cylinders, one for front, one for rear. You then use a balance bar arrangement to adjust the front/back effort.
Obviously production cars can sort all this out in design and testing and have these combined cylinders, then do the diagonal split for improved safety. If you do what you're suggesting, you'll have no way of balancing the front/rear effort aside from changing the callipers untill you find something that works. It doesn't sound like it'll work to me, tbh.
Obviously production cars can sort all this out in design and testing and have these combined cylinders, then do the diagonal split for improved safety. If you do what you're suggesting, you'll have no way of balancing the front/rear effort aside from changing the callipers untill you find something that works. It doesn't sound like it'll work to me, tbh.
montyjohn said:
Hi, I have a MK5 Cortina based kit car (1982).
Standards discs at the front and standard drums at the back. Sporty!
I'm planning to fit a Mondeo MK5 master cylinder and servo. It has a 25mm dia cylinder which is ideal for any future upgrades and a larger servo to suit.
But I'm unsure how best to plumb it all up.
The Mondeo servo has two outlets, and I believe the Mondeo has a front/back/diagonal split (i.e., each master cylinder outlet controls one rear, and one front brake). This means that it pumps roughly the same volume of fluid out of each outlet.
I was planning on having a front / rear split since this is how my plumbing is already set up on my car.
This would mean that the master cylinder would need to pump more fluid to the front discs than the rear drums.
Is this even possible? Can the master cylinder pump different volumes, or do they both need to be the same? I'm not really clear if the two pistons have to have the same travel or not.
The pressure will be the same at both outlets from the m/c and the quantity of fluid delivered wll be regulated by the brakes themselves resisting the fluid pressure, It'll be fine although you may need a pressure reduction valve for the rear brakes if one isn't already fitted.Standards discs at the front and standard drums at the back. Sporty!
I'm planning to fit a Mondeo MK5 master cylinder and servo. It has a 25mm dia cylinder which is ideal for any future upgrades and a larger servo to suit.
But I'm unsure how best to plumb it all up.
The Mondeo servo has two outlets, and I believe the Mondeo has a front/back/diagonal split (i.e., each master cylinder outlet controls one rear, and one front brake). This means that it pumps roughly the same volume of fluid out of each outlet.
I was planning on having a front / rear split since this is how my plumbing is already set up on my car.
This would mean that the master cylinder would need to pump more fluid to the front discs than the rear drums.
Is this even possible? Can the master cylinder pump different volumes, or do they both need to be the same? I'm not really clear if the two pistons have to have the same travel or not.
oakdale said:
the quantity of fluid delivered wll be regulated by the brakes themselves resisting the fluid pressure
I think this is the bit I don't understand.In my mind, the two pistons in the m/c are fixed to the same rod, therefore have to move the same volume of fluid.
Do they have a clever way of balancing themselves if one circuit needs way for fluid to achieve a certain pressure?
If so, then great, I can easily fit a restricter and happy days.
montyjohn said:
I think this is the bit I don't understand.
In my mind, the two pistons in the m/c are fixed to the same rod, therefore have to move the same volume of fluid.
Do they have a clever way of balancing themselves if one circuit needs way for fluid to achieve a certain pressure?
If so, then great, I can easily fit a restricter and happy days.
They're not fixed to the same rod, number one piston is pushed by the pushrod, the second piston is pushed by the fluid pressure in the no 1 circuit, so the pressure is always in balance.In my mind, the two pistons in the m/c are fixed to the same rod, therefore have to move the same volume of fluid.
Do they have a clever way of balancing themselves if one circuit needs way for fluid to achieve a certain pressure?
If so, then great, I can easily fit a restricter and happy days.
montyjohn said:
I think this is the bit I don't understand.
In my mind, the two pistons in the m/c are fixed to the same rod, therefore have to move the same volume of fluid.
Do they have a clever way of balancing themselves if one circuit needs way for fluid to achieve a certain pressure?
If so, then great, I can easily fit a restricter and happy days.
They usually use a floating piston so that the two circuits see equal pressure rather than equal volume iyswim. In my mind, the two pistons in the m/c are fixed to the same rod, therefore have to move the same volume of fluid.
Do they have a clever way of balancing themselves if one circuit needs way for fluid to achieve a certain pressure?
If so, then great, I can easily fit a restricter and happy days.
oakdale said:
They're not fixed to the same rod, number one piston is pushed by the pushrod, the second piston is pushed by the fluid pressure in the no 1 circuit, so the pressure is always in balance.
GreenV8S said:
They usually use a floating piston so that the two circuits see equal pressure rather than equal volume iyswim.
Ahhh that makes so much sense. Thanks guys, I'm with you now.montyjohn,
Better study hydraulics. Given a constant pressure on the pedal, a smaller M/cylinder transmits a greater pressure to the actuators, but yes, requires more travel to push the same volume of brake fluid. If that is what you mean by " a squishy brake feel". Most would perceive a harder pedal.
As M/cs get bigger, they will need more and more pedal pressure for the same on the actuators - dics or drum. A 1" M/c will move 5mls of fluid for each centimeter of travel, but will need two and half times MORE pedal pressure for the same braking effort! Non-servoed M/cs rarely go above 0.75" (19mm) and that's why Ford needed to fit a servo to a 1" master.
I've modified my car's brakes a lot from what it started out with, now larger caliper,vented discs at front and single piston discs at rear (from drums). I've found that a .75" master is fine, and although I was ready to fit a pressure controller valve to the rears, it just wasn't necessary. I suspect that a light 'special' (unless you plan an off-road behemoth) will be fine without the servo!
John
Better study hydraulics. Given a constant pressure on the pedal, a smaller M/cylinder transmits a greater pressure to the actuators, but yes, requires more travel to push the same volume of brake fluid. If that is what you mean by " a squishy brake feel". Most would perceive a harder pedal.
As M/cs get bigger, they will need more and more pedal pressure for the same on the actuators - dics or drum. A 1" M/c will move 5mls of fluid for each centimeter of travel, but will need two and half times MORE pedal pressure for the same braking effort! Non-servoed M/cs rarely go above 0.75" (19mm) and that's why Ford needed to fit a servo to a 1" master.
I've modified my car's brakes a lot from what it started out with, now larger caliper,vented discs at front and single piston discs at rear (from drums). I've found that a .75" master is fine, and although I was ready to fit a pressure controller valve to the rears, it just wasn't necessary. I suspect that a light 'special' (unless you plan an off-road behemoth) will be fine without the servo!
John
montyjohn said:
I think this is the bit I don't understand.
In my mind, the two pistons in the m/c are fixed to the same rod, therefore have to move the same volume of fluid.
Do they have a clever way of balancing themselves if one circuit needs way for fluid to achieve a certain pressure?
If so, then great, I can easily fit a restricter and happy days.
Modern cars the master cylinder will supply the abs unit and that likely has the valve's ect necessary to split the fluid correctlyIn my mind, the two pistons in the m/c are fixed to the same rod, therefore have to move the same volume of fluid.
Do they have a clever way of balancing themselves if one circuit needs way for fluid to achieve a certain pressure?
If so, then great, I can easily fit a restricter and happy days.
tapkaJohnD said:
montyjohn,
Better study hydraulics. Given a constant pressure on the pedal, a smaller M/cylinder transmits a greater pressure to the actuators, but yes, requires more travel to push the same volume of brake fluid. If that is what you mean by " a squishy brake feel". Most would perceive a harder pedal.
You've got that last bit in the quote above the wrong way round.Better study hydraulics. Given a constant pressure on the pedal, a smaller M/cylinder transmits a greater pressure to the actuators, but yes, requires more travel to push the same volume of brake fluid. If that is what you mean by " a squishy brake feel". Most would perceive a harder pedal.
A smaller m/c will make the brakes feel softer, not harder.
Yes you have more "leverage" as it where, but you won't have that firm feeling a large m/c will give you.
But your brakes will be rather effective with that small m/c in terms of braking force.
Think of it this way, an m/c of infinite diameter would be impossible to push. i.e. would feel very "hard". You would need an infinitely sized servo to match and your brakes would effectively be an on/off switch. Or the universe would explode. I'm not sure which would happen first.
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