Why is my Moen universal shower faucet leaking at the union

Nothing the problem is with the tap contact moen help line

The nuts used for capping off the sprayer attachment will bottom out and not seal. Unless there is tape or thread compound on the nut, it can spray a tiny jet up under the faucet when the faucet is activated. If there is clearly water leaking from above that, then the o ring for the spigot may be failing and need replacing. If this is the case, it will only leak when the faucet is activated. There is always the possibility of a crack in the casting of the faucet body; hope not:)

I'm not aware of any problems with non moen replacement parts being the cause for a water hammer problem. Start with the simplest and cheapest correction which is using a moen replacement cartridge. If the water hammer persists then you may have to install a water hammer arrester in the plumbing system. This is basically a shock absorber in the plumbing system to stop the effect of water hammer. An arrester will cost you around $10 to $15 at your local plumbing supply shop. If you are not comfortable soldering copper then you will want to hire a licensed plumber to complete the work for you.

I had the same type of problem with an older toilet in my house. It developed a water hammer when it shut off after filling the tank. I replaced the fill valve with a generic universal replacement for about $10 and it stopped. Again sometimes the simplest fix will work. Let me know how it works out.

The exact procedure to remove the old cartridge is with a plastic removal tool.With replacement cartridge you have to buy this plastic removal tool.Also there is same metal removal tool available.With the help of this tool you can easily remove the old cartridge.
Moen Cartridge Replacement Instructions

Moen shower faucet cartridge replacement is a project that will take some time to get done right. When is it time to replace a Moen cartridge? If you are like most people, you won't want to replace your old Moen cartridge until your old cartridge is starting to show its age.

Replacement is necessary, usually, once the old faucet starts to drip. Thankfully Moen faucet cartridge replacement is not difficult. However, if you are uncomfortable with doing the repair yourself, do not hesitate to call a professional plumber to do the job for you. This will guarantee that the job is done right.

If you follow these Moen faucet cartridge replacement instructions you will be able to replace your old cartridge by yourself. First of all, as with any plumbing repair, make sure that the water supply is turned off. Open the faucet to remove water pressure from the lines and let the remaining water drain from the pipes. You will then need to remove the faucet's handle by removing the decorative cover and removing the retaining screw. This will allow you to remove the handle.

Once the handle has been removed, work on releasing the splash plate from the wall. Generally there will be one or two screws to remove and the plate should release from the wall easily. From here the process begins to get a little trickier. Insert a shower stem socket onto the faucet valve's retaining nut and release the nut. Your Moen cartridge removal will be complete once you grab the cartridge with a pair of pliers and pull straight out to remove the old cartridge.

Clean any surfaces that you have access to and replace with the new cartridge. Follow all of the previous instructions in reverse order to re-assemble your shower faucet. Check to make sure that all the connections are tight before turning the water back on and testing the system out.
Now in your case the broken/cracked while removing the old cartridge so try this procedure carefully to get the stuck -up old cartridge out.
TAPPING the Threads into the Cartridge:
Carefully  hold one tab on the cartridge tight against the brass lip on the faucet body with needle nose and try  to drive the 1/2" tap into the smaller bore of the cartridge. It will take  about 15 minutes to slowly work the tap in all the way (maybe 3 turns?). Then  back out the tap... remove needle nose. [remember to turn the tap 1/4 turn back, for each 1/2 turn forward ... this clears the metal particles from the tap and makes the next 1/2 turn forward go smoother].

Next, assemble a 1/2" x 4" threaded rod, so it had threads all the way to the two jam nuts on one end)... If you use a bolt, get one with threads all the way up to the head. you may find it hard to find - so try a carriage bolt and spin a nut all the way up to the head .... continue: 

next on the bolt goes a 1/2 nut (this is the "jacking nut") and a flat washer so the jacking nut can spin easily against the next piece, a 1/2 drive socket (7/8" ) with the square hole toward the washer and jam nuts ( bolt head ).
The open end of the socket faces the brass body of faucet and rests on the round brass lip... having the same inside diameter. This allows a space for the cartridge to be pulled into ( a cavity). Thread the bolt into the tapped cartridge and snug it up so the 7/8" socket is aligned with and resting against the brass body. If the cartridge spins smooth, the threaded rod is GREAT. You can just work with the 1/2" rod and use needle nose (or similar) to stop the  cartridge from spinning, to get the rod threaded into the tapped threads in the cartridge... then, slip on the socket, washer and nuts.

Now snug it up tighter. Check socket alignment. Then begin turning the jacking nut ( the "extra" nut) until it contacts the flat washer and 7/8" socket. Now, as you continue to tighten the jacking nut, it will pull the 1/2 bolt (threaded rod) away from the faucet... and the cartridge will come along too. [You have to prevent the 1/2 rod from spinning while tightening the jacking nut. put a wrench on the bolt head.]
This procedure is bit lengthy and requires some appropriate tools,but this will release the stuck cartridge out.
Thanks. keep updated for any more query.you can rate this solution and show your appreciation.

check all solder,threaded,joint's.i'm pretty sure that model has shut off's to the left and right of center.check those as well.water will travel in some strange way's,yes alway's down but it will follow some strange path's. p.s.take a look /check your shower arm.

Call moen and give them your model no. they will send you a new cartridge free of charge. if you can't wait local stores like lowes will have them. Turn off your main water shut off valve and take off handle, then with some pliers take off brass ring, the cartridge will pull out. First notice the notch it rests in and notice where the hot water adjustment disc is. Assemble the new one the same way, put some vasolene on orings and reassemble. hope this helps.

yes it is a cartridge replacement,the cartridge is,should be all that you need to replace.you did not list what kind of faucet. so here is a few number's. some bath/shower valves' take#1225-(plastic) this is also use'd in some kitchen,lav, model's.two handle faucet's#1224,the "posi-temp"#1222 is a tub shower only,there are cartridge puller's available,and recomened them,one is made by moen,another by brass craft,i have pulled cartridge's with out,so it is up to you.hope this help's.

A stem is a cartridge in a real old valve. You have pulled retainer clip, you can try to pull it out with pliers, but you might need a moen cartrigde puller.

I took the parts to the Menards in town. Luckily I found the guy that knows it all! He showed me the rubber gasket( that holds the ball) to purchase as well as recommended that the 2 small rubber gaskets that were in there to be replaced as well while I had it open to avoid doing this in the future. I got home and replaced them and no leaks:) Thanks:)

the cartridge if defective,replace it and your leak will stop.