Master cylinder sizing.

[diamondnik]

Last week I looked at the car's original master cylinder, it is also stamped 23/20. I assumed that number pertained to something else, but now I see that my original 318ti MC was stepped as well (Canadian market Ti). I wonder what the relationship is between front and rear line pressure, and how it changes when increasing only front piston size...

[e36 323ti]

Originally Posted by diamondnik

Last week I looked at the car's original master cylinder, it is also stamped 23/20. I assumed that number pertained to something else, but now I see that my original 318ti MC was stepped as well (Canadian market Ti). I wonder what the relationship is between front and rear line pressure, and how it changes when increasing only front piston size...

I have asked ATE for an explanation. I hope they respond....

Assuming our latest discoveries are correct (i.e. Ø=23.81/20.64mm) a stock 318ti/323ti has a static front bias of 66.59%. Replacing the stock master cylinder with one with diameters Ø=25.4/20.64mm (e36 m3 3.0 MC) the bias changes to 63.65% - i.e. the static front bias is moved approx. 3% to the rear.

The e36 m3 3.0 (assuming Ø=25.4/20.64mm) has a static front bias of 61.21%...

With e46 330i disc (325mm) and caliper (Ø=57mm) up front, stock ti' rear and m3 MC the static front bias of a ti' is 68.92%...
With e46 330i disc (325mm) and caliper (Ø=57mm) up front, stock ti' disc rear but caliper Ø=38mm rear and m3 MC the static front bias of a ti' is 63.97%...

[e36 323ti]

Originally Posted by e36 323ti

I have asked ATE for an explanation. I hope they respond....

Got an answer from ATE today. They verified that the data given in he North American pages are correct. I.e. the e36 m3 master cylinder is stepped.

They also confirmed that the master cylinder which we have in our ti's is stepped, even though this cannot be read from the data sheets!

They also said that in Europe it was common to only give the leading bore in the data sheets. However, they promised to change their practice such that both diameters for all master cylinders hereafter should be readable from the data sheets.