Morris Minor Owners Club

Yes that makes sense. Is Sprite caliper much less efficient? I currently don't have a servo so put up with a heavy pedal. Is the servo conversion easy?

.... and how about the clearance with the top trunnion with those wide tyres?

The total cross-sectional area of the pistons is virtually identical for the Spridget 2-pot and Metro 4-pot, so no real advantage from either. One benefit of a 4-pot caliper is that the pressure is applied more evenly across the pad, and it can be designed to have the pistons further out, so increasing the mechanical advantage and braking force for the same line pressure (without measuring I don't know if the Metro 4-pot does this in comparison to the Spridget).

Fitting a servo to a Minor is a bit of a fiddle, as the standard design feeds the rear brakes directly from the master cylinder, and for a servo this line has to be extended to the front, so that the output from the servo can feed both front and rear brakes. A good place for the servo is near the engine bay floor on the RH side, opposite the distributor. It's near the brake lines and away from the exhaust system.

With discs on a Minor I would recommend fitting servo, if for no other reason than it avoids the nasty surprise when jumping out of a 'modern' into the Minor that the brakes don't work! They do of course, but with Spridget/Metro discs the pedal pressure is higher, particularly than on a 1098 Minor - the difference between discs and the earlier 803/948 brake pressures is much less.

I have marina discs on one of mine since the 80s but fitted the smaller master cylinder so the pedal pressure isn't too bad. It gives great confidence when stopping from high speed .