Is a different master cylinder needed?

[pipework]

Hay!! I'm about to convert my 318's rear axle to disc brakes. I was just wondering if I needed a master cylinder from a 2.5?? Can anyone help. Thanks.

[zaust]

Yes either a master with the rear out let or the less preferred way of a T price
guess what I have

[Brianmoooore]

Different master cylinder is ABS/non ABS - nothing to do with whether the rear brakes are disc or drum. No different MC required.

[pipework]

Different master cylinder is ABS/non ABS - nothing to do with whether the rear brakes are disc or drum. No different MC required.

So the internals are the same? Thanks for the info

[Brianmoooore]

A 325i without ABS uses exactly the same brake master cylinder (and rear pressure regulator) as a 318i without ABS, whether it has disc or drum rear brakes.
A 325i with ABS uses the same master cylinder as a 318i with ABS, which will have disc rear brakes anyway.
Each brake pipe to the front brakes on a non ABS car has its own port on the master cylinder, but an ABS equipped car has a single common pipe to the ABS pump for the front brakes, so only needs one port into the rear section of the cylinder.
I would have thought it much simpler for BMW just to fit a blanking plug on the spare port when building ABS equipped cars and use a common master cylinder on all models, but they chose to use two different versions instead.