Brake Pad Wear
From Citroen-SM-wiki
Rear pads should not wear out quickly.
If they do, then it is time for a test of your hydraulic pressure. As the
rear pads are fed from the suspension, they always have the "same" feed pressure. But
if your pressure regulator spring is getting tired, the up limit on pressure
will be down and this limits the front brake pressure and changes the brake balance.
In my opinion it is worth putting a additional 1mm shim ring into the regulator on any car with 75000 miles or more if you do not/are not able to measure the pressure.
The shim ring is over the spring in the return housing of the regulator.
If you can measure the pressure and it is ok, then rear pad wear is either caused by that 2 hundredweight full tool kit you always carry in the boot(trunk) or your brake distribution trolly is moved out of adjustment. I have posted that fix before.
If your brakes on the SM are not really really sharp, check out the pressure.
(From http://autos.groups.yahoo.com/group/Sport-Maserati-L/message/76, by Andrew)