i have a mk1 fiesta 957cc with no servo & standard master cylinder.

Problem is i'm about to fit 4x4 sierra brakes and i've been told by someone at work that the master won't be able to shift the required amount of fluid to move the bigger pistons as it has been designed with small brakes in mind?

Is this technically true or just BS?

Please Help!

 

True.

How close is it on your scenario. I dont know. But for safety sake Id consider getting the XR4's master cylinder as well.

 

I'd run into problems then though - i think - due to the sierra having a servo and me not as where it joins the pedel will be totally different..

 

Without seeing both the cylinders. I'd (guess) not actually. You may find the ed that clips to the pedal linkage isthe same shape. You may need to shim the cylinder away from the bulkhead though. You could always fit the servo as well if that would help. You just need to run a vacuum from the inlet manifold onto it. Not difficult.