WMS 4-pot brake kits

[Keri-WMS]

Im not 100% on the 300mm yet sorry, plus i will have to shift my brembo's. Don't have the £500+ yet

No problem, just see how it goes...

Im going down the workshop saturday afternoon so ill look for that wheel for you

Thanks! (Don't worry too much as I have in theory got a wheel, just waiting for the chap to get the tyre taken off and sent to me.)

HOWEVER! Does anyone have an old (so it's original) lower ball joint and it's bolt for the Mk1 / GT going spare? I need one to see how deep I can go on a 298.5mm setup! If I'm really lucky I can get the rotor/disc moved a LONG way inboard which will turn straight into clearance for wheels (or keep the same wheel clearance but with a 298.5x32 rotor instead of a 298.5x20.5 one!

Fingers crossed.

[Acki]

It's not quite that simple - the bigger the pistons are the softer the pedal (all other factors being equal), basic physics/engineering sadly.

That's not fully correct.

You push the pedal till all brake pads lay on the disc.
After this you will get pressure in the system.
All what happens now, is that brake lines/pipes, brake calipers (!) etc. will deform.
This you feel in the pedal (it's soft etc.).

Master brake piston size -> the lift you have to make till the pressure can raise.

Main problem: When you change the piston size of the brake too much you will raise the force on the brake pad and this force is important for your deceleration.

This raised force will also deform the caliper more - soft pedal.
vice versa: good caliper -> hard pedal :-)

And now I have one question Kerz, what Piston size the Uno 4pot calipers had which I bought, years ago?
I hope this winter I can install them...
I will also update the rear brake system (better looking), and I have to do some calcs - but calipers are ~550km far away from me

[Keri-WMS]

That's not fully correct.

You push the pedal till all brake pads lay on the disc.
After this you will get pressure in the system.
All what happens now, is that brake lines/pipes, brake calipers (!) etc. will deform.
This you feel in the pedal (it's soft etc.).

Master brake piston size -> the lift you have to make till the pressure can raise.

Main problem: When you change the piston size of the brake too much you will raise the force on the brake pad and this force is important for your deceleration.

This raised force will also deform the caliper more - soft pedal.
vice versa: good caliper -> hard pedal :-)

And now I have one question Kerz, what Piston size the Uno 4pot calipers had which I bought, years ago?
I hope this winter I can install them...
I will also update the rear brake system (better looking), and I have to do some calcs - but calipers are ~550km far away from me

Hi Martin! Blimey, you bought your kit five years ago and haven't fitted it yet?

You had 1.38/1.38" pistons, for the Uno.

I know what you're saying in that the pads don't move far once they touch the disc, but:

- The tiny bit they do move from rest to touching the disc moves the pistons.
- Once they touch the disc, any compression of the pad moves the pistons.
- Any flex in the caliper moves the pistons (all calipers flex a bit).

So all the above will move the pistons, so piston size makes a difference to these.

- Brake lines, master cyl mountings/bulkhead flex etc are all things that give you a soft pedal but are not affected by the caliper piston size. That said, if you have smaller pistons you'll need more pressure in the fluid, and these "in-car" parts will all flex more!

Of course more force will flex the caliper more, and that is only combatted by getter more leverage (bigger discs) or a stiffer caliper.

The best thing to do is fit the largest discs you can within the wheels (unless they get too heavy), then match the front > rear bias (or at least match the upgrade piston area to the original calipers), then make everything as stiff as possible (stiff calipers, braided lines, master-cyl stopper/braces etc).

[Acki]

Are that 5 years now? Uff... okay... and you are sure?
This winter the brake will be installed - I will make a highway test when I'm sure that the brake is a good one
Bolts on one caliper are rusty - never seen any water
This winter they will installed

You nearly wrote the same like me - I think. pressure = force / area. pressure is the same like before (when caliper is as stiff as the "old ones").
But the area is the piston area, but you have to calulate the real "brake torque" about the middle dia of the brake and with the area and friction value of the brake pad. It's some work to have all values, but it's a simple calculation to know that all parts can work well together.

The problem about the piston size - the size of the standard piston is 48mm (or what ever you have) but the force is double because the pistons moves the caliper (that both side of the disc "brake").

Little bit difficult to explain, will show are small example in the next days

I want to install the light Barchetta alu calipers in the rear with 240mm Cinquecento discs. But when the cylinder is too big I have to much brake power on the rear...

[Yelfig]

Don't know if Uno has adjustable proportioning as the punto has but if not you can get an aftermarket one to regulate the pressure at the rear brakes...

[Yelfig]

proportioning valves I mean (where is the edit button when you need it..)

[Keri-WMS]

You nearly wrote the same like me - I think. pressure = force / area. pressure is the same like before (when caliper is as stiff as the "old ones").
But the area is the piston area, but you have to calulate the real "brake torque" about the middle dia of the brake and with the area and friction value of the brake pad. It's some work to have all values, but it's a simple calculation to know that all parts can work well together.

The problem about the piston size - the size of the standard piston is 48mm (or what ever you have) but the force is double because the pistons moves the caliper (that both side of the disc "brake").

Little bit difficult to explain, will show are small example in the next days .

I do know what you mean! I'll put it another way:

A Punto 48mm single piston sliding caliper has the same EFFECTIVE piston area as an opposed piston caliper with two 48mm pistons (one on either side of the disc).

This is because say for instance the pads move or compress 1mm each. The 2-piston caliper displaces 1mm x 48mm diameter of fluid per piston - as there are two pistons that totals 2mm x 48mm diameter.


Now with a sliding 1-piston caliper the same is true, 1mm per pad. What happens can be thought of as two stages, easier to understand:

1 - Inner pad moves with the piston = 1.0mm x 48mm dia.
2 - Outer pad moves with the CALIPER 1.0mm. The inner piston has to move another 1.0mm to take up the "slack".


So in a 1-piston caliper the piston travel/volume shifted is 1x piston x 2mm = 2mm. In a 2-piston caliper it's 2x piston x 1mm = 2mm.

Hope that makes sense!!!

[clarkster]

all this talk of stiffening the system up, i wonder how much stiffness is lost when you have to use caliper mounting brackets between the hubs and the calipers, given that the factory calipers just bolt straight to the hub casting???

[Keri-WMS]

The WMS bracket lugs are probably stronger than the Fiat strut lugs, while Fiat used cast iron or steel, it's REALLY thin!

Also this part doesn't affect how the caliper behaves in terms of stiffness - don't forget a sliding (OEM) caliper has effectively no side-side mountings anyway.

Also if you're worried about adding an extra componant, that's actually not the case.

OEM = Carrier + caliper
WMS = Bracket + caliper

Hope that makes sense!

[Keri-WMS]

Latest news - it would appear we can do kits for the (new) Fiat 500.

Lower models: 284x22
Higher models/Abarth: 298.5x28

Just need to get my mitts on a car to get the brake lines sorted / confirmed.