International Lancia Forums

We have three different diameters for the wheel brake cilinders on S1 / S2 Fulvia coupe.

- big piston (54mm), at the front of S1, total surface area for the 4 pistons is 9200 mm2
- small piston (33mm) at the rear of S1 and S2, total surface area for 4 pistons is 3400 mm2

At the front of S2 we have a small and a medium size piston. The combined surface area of the 4 small and 4 medium pistons is the same as for the 4 pcs big piston. This is logical as the weight distribution of S2 is not much different from S1. If we subtract the 3400 mm2 from the 9200 mm2, we have 5700 mm2 total surface area for the 4 medium ones. Or a diameter of appr. 43 mm for each piston.
Thus

- medium piston (43 mm) at the front of S2, total surface area for 4 pistons is 5700 mm2.

The surface area of the 18mm master brake cilinder is 250 mm2

If used with Dunlop brakes:

chamber 1 drives 9200 mm2 at the front. With its surface area of 250 mm2 and stroke of 22mm is can drive the 4 pistons for 0,6 mm each.
chamber 2 drives 3400 mm2 at the rear. With stroke of 10 mm it can drive the rear pistons for 0,75 mm.

If you use the S2 Girling brakes:

chamber 1 drives 8 small pistons thus 6800 mm2. This is less than the 9200 mm2 it was designed for. So you are ok.

chamber 2 drives 4 medium pistons or 5700 mm2. This is a lot more than the 3400 it was designed for.

In your case the solution might be to use one hose per calliper. Connect the small en medium cilinders so that you arrive at the total surface area the master brake cilinder was designed for.

I think the front / rear separate circuits as on the S1 is safer than the front / mixed separation as on S2. If a piece of steel wire wraps around a front wheel it cuts through the hose(s). On S1 you only loose the front circuit. On S2 you loose front and rear circuits.

Thanks Huib for the advice´s. Will think about it and choose.

Get well soon and all the best to you.

Andreas

Up Date;
Back on the wheels
reflector with new surface

regards
Andreas

reflctor ass.

Very nice to see it coming together after all that hard work and time

Hi Andreas

Did you decide anything on the brakes?

I made a mistake on the calculations for the master brake cylinder.

On S1 the first plunger has to provide the fluid for not only the front brakes but also for the rear as it pushes the second plunger.
So, the situation is actually worse as in my calculations.

If you use the S2 callipers with an S1 master brake cylinder, it is perhaps an idea to connect the bigger cylinders at the front to the first chamber (counting from the fire wall) and combine with the rear ones. Connect the small ones at the front to the second chamber. You then have the surface area's the same as for the original Dunlop brakes.

Hi Huib,

i changed the masterzylinder from first to second series. So everything should work well.
Undepent on this thanks for that also info for the other Lancisti in the forum to be on the save side.

regards Andreas

Update :
Ass.and installation of the engine and gearbox is done.
Some problems with the bonnet depent of the carburators occured but solved it by " lowering" the gearbox and the engine by
shorten the rubber´s of the mounting. Moreover a small modification of the intake manifold.

regards Andreas

Superb!

Thanks Charles
Step by step and week by week with the target to finsh it at the end. A long way but i am sure now with a good end at least.