Finally did some calculation to know which cylinders I have to order:
M= 710kg
Static F/R weight ratio= 63:37 [FONT=&quot]Found here[/FONT]
Dynamic @ 1g approx. 50% rear axle weight transferred to front. Found here
Didn't include the CG Height for simplicity :yum:

Approximate Coefficients of Friction(COF):
Tyres: Concrete (dry) Rubber= 1,0
Brakepads: FERODO Premier = 0,29 (50m @[FONT=&quot]53,4kg/m2,100-to-0 km/h for a focus)[/FONT]

[FONT=&quot]Diameter Brakes (puntoconv.):[/FONT]
[FONT=&quot]Font piston diameter = 54mm[/FONT]
[FONT=&quot]Rear piston diameter = 31mm[/FONT]

Details of the box:
Pedal pivot ratio = 5:1
Pedal travel = 266mm (Calculated with 55deg angle and 275mm height)

->Deceleration= 1 g=> 710kg*9,81m/s2=6.965,1N
Static F/R ratio applied: FF=4.388,013N FR=2.577,087N
Dynamic F/R ratio applied: FF=5.676,56N FR=1.288,54N

Force at pads with coefficient of friction (Fw = µD*FN)
5676.56N = 0.29*Fbrake
FF-Brake=19.574,33N

1288.54N = 0.29*Fbrake
FR-Brake=4.443,25N

Brake cylinder/Piston sizes:
0,625mm Front = 0,625*0,0254=0,015875m
Rear 2 possibilities:
0.700mm Rear = 0,700*0,0254=0,01778m
0,750mm Rear = 0,750*0,0254=0,01905m

Area front cylinder= π*(0,015875m/2)2=0,0001979m2
Area rear cylinder= π*(0,01778m /2)2=0,0002483m2
Area rear cylinder= π*(0,01905m /2)2=0,0002850m2

Area front piston= π*(0.054m/2)2=0,002290m2
Area rear piston= π*(0.031m /2)2=0,0007548m2

Hydraulic Pressure (P=F/A)
F front piston =19.574,33N/2= 9.787,165N per piston
P=9.787,165N/0,002290m2= 4.273.871,179Pa
-> total pressure front = 8.547.742,358Pa

F Rear piston =4443,25N/2= 2221,625N per piston
P=2221,625N /0,0007548m2= 2.943.329,359Pa
-> total pressure rear = 5.886.658,718Pa

Hydraulic Pressure to force at pivot (P=F/A)
F front cylinder at pivot (0.625)= 8.547.742,358Pa*0,0001979m2= 1.691,598N
F rear cylinder at pivot (0.750) = 5.886.658,718Pa*0,0002850m2= 1.677,698N
F rear cylinder at pivot (0.700) = 5.886.658,718Pa*0,0002483m2= 1.461,657N

Force differences f/r have to be as close as possible for the balance bar to be almost straight.
At high braking like this situation rear force can be reduced with the proportion valve, however it doesn’t lower pedal force needed since it’s a reducer….right?

Pedal pivot ratio = 5:1
Actual pedal force req. for 1G deceleration (with 0.625 and 0.750 cylinders), which is the power needed to lock the wheels, if the assumptions of the COF of 1.0 for the tires, the weight and it’s shift of 50% are indeed correct and if the COF of the ferodo test is applicable to the seicento (and of course if I haven’t made a mistake :yum=

(1.691,598N+1.677,698N)/5= 673.86N -> 68.715KG (with 0.750)
(1.691,598N+1.461,657N)/5= 630.65N -> 64.308KG (with 0.700)

Just for reference what 1G of brake power is:


So if all the assumptions and the mathematics are correct it’s a nasty push needed for a full lock…
So I think my math isn’t quite correct somewhere :yum:

But apparently I’m better off with a 0.750 as rear cylinder for a nice straight balance bar as starting position.
Possible Pedal travel length is approx. 26cm, what the actual is going to be is another calculation. But since I can only choose between these 3 types (0.625, 0.700, 0.750), I will see it in real life and not bother calculating that If in fact there will be plenty of stroke left, I can always downsize the cylinders even more to reduce the amount of force needed at the pedals.

Rethinking the amount of force needed:
68.715KG isn't really a huge push :yum: I came to that conclusion referring to experience in the gym doing a leg press/squat, however 70kg there isn't really 70kg doing the press, since you're lifting yourself also

Some progress has been made!

First off, brake booster is out :yum:


Initially made some holes in the box to mount it to the floor and positioned it somewhat to the front to cope with the pulling force on the box floor:


However ran into a speed bump... The holes of the box are directly inline with the chassis beams... So began the search and making of a proper positioned adapter plate. And here's the successful result :


Showing the repositioning when temporally mounted :


Some grinding needed here and there to cope with the angles of the floor:




And after a lot of measuring and manufacturing... It's in!! :


That's it so far!
Now it's time to give it all a lick of paint and it's shine
...and of course... well everything

I'll keep you guys updated!

I'd put a plate on the other side (the underneath) to prevent the bolts tearing through.

fingers99 said:

I'd put a plate on the other side (the underneath) to prevent the bolts tearing through.

Click to expand...

Yep, that's exactly what I'm going to do. The picture showing the little washers was just for test fitting. Way to small indeed to handle the forces, many thanks for the input though! much appreciated

It looks really good.

Some progress made!, gearbox is ready to go in. Cleaned and painted (heat resistant).
All orange parts are powdercoated by myself :

lxfusion said:

All orange parts are powdercoated by myself :

Click to expand...

I take it the other half was out when you popped them in the oven!

All the parts where indeed been removed! :yum:, after sandblasting I hardend the powder with a heat gun paintstripper, works perfect

Ah, you didn't get that bit: "other half" means wife, girlfriend............

But I think it melts at something like 220C, which is (long time since I used anything other than a microwave!) within the range of a domestic oven.

fingers99 said:

I take it the other half was out when you popped them in the oven!
Ah, you didn't get that bit: "other half" means wife, girlfriend............

Click to expand...

Hahaha, finally get it (thought you where talking about the gearbox itself, stupid me ) Speaking of which, how about delarue his other half, must been away for sure when this happend, haha :yum: (couldn't be that healthy I think ):

delarue said:

Click to expand...

It's a bit like me baking my headlights in the oven .

Thanks

X

Update: The heatgun paintstipper methode sucks, the finished powdercoat chips off way too easy... Heatgun makes it look nice, but I think it doesn't bake the coat well enough. I think an oven is a must for DIY powdercoating!

I wonder if the issue is the part cooling too rapidly?

One thing I used to do years ago was to mix epoxy adhesive with powder paint pigment, smear it on whatever I wanted to coat, and put it in a pre-heated oven. Gives an appearance rather like vitreous (stove) enamel.

The cooling problem could indeed be very true, since the part itself doesn't get so hot throughout the core, which could result in a faster cool down!