About a month ago, I noticed a buzzing noise coming from the serp belt area of the car. At first I suspected the tensioner pulley, as these commonly fail. Just to be sure though, I stopped at Auto Zone and picked up a cheap mechanic's stethescope. Probing around, it took only a minute to determine the noise was the water pump.
This was not welcome news - I've never had much luck with water pumps. On this sideways V-8, room to work on anything in the belt area is very tight. There is little margin for error. But, I pressed on regardless. The factory service manual gave a pretty benign description of the job, making it sound almost easy. A posting at cadillacowners.com brought several responses that further boosted my confidence. So with some time off work, I dove in.
First step in the process is to clear some room. This means moving all the components on the right fender, including the A.I.R. filter, the AC accumulator, the washer fluid bottle, the bracket, and the fender brace. To move the accumulator, disconnect the clamp on the radiator support to free up the flexible pipe, and swing the entire unit up and out of the way. I wired mine to a circular bracket mounted on the intake manifold, behind the air cleaner.
Once these items are cleared, access to the water pump is very good. The next step is to drain the coolant, then loosen the three bolts holding the pulley to the pump. Using a half inch breaker bar, put downforce on the belt tensioner atop the engine. This locks the pulley so the bolts can be broken loose. On the DeVille, you can actually remove all three bolts and the pulley before removing the pump.
The 4100's water pump is a thin, flimsy item about 14 inches long by 3 inches wide, by about 1/4 inch thick. It's held on by 18 different bolts and nuts. Three of the bolts are large hex heads, two are Torx head, and the remainder are smaller bolt and nut/stud combinations. To keep mine in sequence, I started with the top center large hex head bolt, then loosened all the perimeter bolts in a clockwise sequence. When I arrived back at the first hex bolt, I removed each one, then lined them up in order on my work bench. In the center of the pump is one Torx head bolt and two small hex bolts. Here again, all went smoothly until I got to the last Torx bolt. It was frozen tight as a drum. I did everything I could think of to break it loose: shot WD 40 on it, heated it, but it wouldn't budge.
Before long my worst fears came true,and I stripped out the head of that bolt. THE LAST DAMN BOLT!!! Next step was to try an EZ-out. Still would not budge. With no options left, I drilled the head off the bolt, and removed the old pump.
Now I had a quandry. Because this bolt is right next to the water jacket outlet, I couldn't simply ignore it or a leak would be certain. I rented a right angle close quarters drill, drilled it slightly bigger and tried a larger EZ-out. Absolutely would not move. I didn't push it too hard because the last thing I wanted to do was break off a tempered steel EZ-out and then have to drill THAT out.
Now it was really getting dicey. My only option was to try and drill the bolt to the same size as the original, then tap new threads into it. The tough part was, this had to be done with near perfect accuracy, and I would get one shot to do it. Adding to the difficulty was the access. A high-pressure AC line was directly in the way of my drill, so I had to have the local hardware custom cut a carbide drill bit to a length of about three inches. If I missed the angle, or was off by as little as 1/8th of an inch, it would mean pulling the engine. Finally, and most disconcerting, the water jacket in the engine block runs in and then up, directly behind where I would be drilling. Go too deep, and this project would get much more expensive very quickly.
Needless to say, I was sweating bullets as I started drilling. Carefully and slowly, I ran the drill in to a point I had marked on the bit as the deepest point I dared to go. So far so good. Next was tapping the new threads. This also went amazingly smooth. Finally, I test fit the bolt - AND IT THREADED RIGHT IN! Well, sort of - because I couldn't drill as deep as the factory bolt, there were not enough threads to allow it to tighten down. So I had to shorten the Torx bolt by 3/8ths of an inch to make it work. But it worked! What a rush that was. Of course, I wasn't out of the woods yet. I still had to get the new pump on and running without leaks.
It didn't take long to discover the reason GM used the Torx design here. The pulley and belt ride very close to the pump at this point on the engine, and no standard bolt design other than Torx would allow enough clearance. Because I had destroyed one of my Torx bolts, I needed a replacement. This isn't a basic hardware store bolt. So I called the local Cadillac parts department. The guy there is very helpful. Even though I was talking about a silly 7 dollar part, he took the time to make sure he had the right one. As it turned out he had to order it, but put a rush on it to get it to me the next day. I'll be back to do business with him again.
Last night I was able to put everything back together, and to my utter amazement this job has been a success. I started the car - no buzzing, no leaks. I may have a few more gray hairs than last week, but that's the price of admission to driving (and repairing) an elderly Cadillac.
Well, I knew from the start this was a gamble. 
