Master cylinder bore size?

[Djfan]

I need a new master cylinder for my 2001 2500 Ram. I don't know if I need a 1.25" or a 1.31". Google isn't helping me much. I don't have the original manual.

Any tips?

 

[JMcCoy]

I "believe" the smaller bore sizes are for the later 00-02 models with disk brake rears. The main difference is the smaller the bore the easier your pedal will be. I would go smaller no matter what.

 

[Ozymandias]

I "believe" the smaller bore sizes are for the later 00-02 models with disk brake rears. The main difference is the smaller the bore the easier your pedal will be. I would go smaller no matter what.

Not only, also the discs need less fluid but a way higher pressure for the Pistons.

So the force that the driver needs to apply to the pedal stays more or less equal.

We once mixed up these on another vehicle, used a disc MC on a drum vehicle - result was that the pedal fell to the bottom, wheel cylinders sucked up every drop that the small MC was able to deliver.
Lesson learned.