Can I change the trim (showerhead, arm, flange, escutcheon, handle/knob and tub spout) without changing the valve in the wall?
Replacing the trim on an existing Moen tub/shower can be accomplished by first determining what kind of valve is in the wall. For many years Moen tub/shower valves have been manufactured using one of three valves. These valves are Standard, Posi-Temp and Moentrol. Although the look is similar, the trim is not necessarily interchangeable.
To determine if the trim can be changed without changing the valve in the wall, the first step is to identify what type you have. This chart(section) shows the differences.
Note:Posi-Temp trim and Moentrol trim are not interchangeable.
Figure 1 shows that the screw holes at the 5:00 and 7:00 position. This is a Standard valve that features a pull on/push off operation and turns left and right for hot and cold.
Figure 2 illustrates the pressure balanced valves. Models that have a lever or knob that rotate only are called Posi-Temp. This "cycling valve" handle is pointed towards the 6:00 position when off, rotates to the 3:00 position for cold, 12:00 for warm and 9:00 for full hot. If this is the way your Moen valve operates, any Posi-Temp trim will fit.
The other valve mentioned in Figure 2 is Moentrol. Moentrol is also pressure balanced and includes the pull on/push off volume control feature. The screw holes are at the 2:00 and 7:00 position. If your valve operates this way and has these screw hole locations, any Moentrol trim will fit.
A recent innovation now makes it possible to retrofit round Moentrol trim to standard valves. Service kit number 145058 (shown below) can be ordered to make the change.
Shower arms are usually threaded into an elbow behind the wall. Rotate the shower arm counterclockwise to remove. The new shower arm and shower head should be sealed using several wraps of thread seal tape. The shower arm flange is usually sealed by using Plumber's putty.
The final consideration is the tub spout. Moen makes two versions. The IPS (Iron Pipe Size) version (below left) is threaded and screws onto a ½" pipe that has male threads.
The other style is the slip fit tub spout (above right). It attaches to ½" copper tubing by slipping on and tightening with a hex wrench. Both tub spouts will have a cut out on the underside near the wall as shown above. If the cut out has a place to insert a hex wrench, you have a slip fit. If the cut out does not have the hex wrench opening, your spout is a threaded (IPS) version.