I'm going to swallow my pride and ask a question that exposes my ignorance. I have seen lots of serpentine belt discussions lately, and I don't understand the advantage of having *everything* fail when a single belt fails. Isn't it advantageous to keep individual components on their owns belts so they continue to function when a separate belt (and component) fails?
I don't think that's an ignorant question at all--it's fair to ask. You're right, it seems counter-intuitive to put all your eggs in one basket. And it's true, you lose that one belt and you lose everything. But, there are some disadvantages to V-belts.
Serpentine belts are far less prone to slippage. They have a lot more surface area in contact with the pulley. With V-belts, all belt routing must be convex (for the most part). This puts a limit on how much "wrap-around" you can get on an individual pulley. So, to overcome this, you must add tension. To get enough grip with a modest amount of tension, they came up with the V-groove. This jams the belt between two angled surfaces. This nets you more normal force and more frictional force with a given amount of belt tension. But, it also makes the system very sensitive to belt stretch. It's all in the geometry, but basically any little increase in belt length makes you give up a decent amount of available frictional force.
This sensitivity to proper adjustment makes V-belts prone to failure. If they stretch even the slightest amount, they slip often, wear faster, get even more out of adjustment, and fail. Serpentine belts have been proven to be far more reliable in the long run.
With the need to stay convex, you end up needing multiple belts for the various systems. Each belt must have its own plane to operate in, and the stack-up of these planes takes up space. Not to mention, needing to change only the rear-most belt always warrants a heavy sigh from the guy with the wrenches.
Another consideration is accessory mounting. With a serpentine, every single accessory gets a nice, simple, solid mounting. I like this. The brackets are simpler and easier to deal with. With V-belts, each accessory gets a weird bracket, weird bolts and arrangements, or odd solutions for adjustability. Serpentines also simplify the tensioning, as one tensioner should do the job for the whole system. You never have to adjust, check, or tend to the tension of the system as long as the tensioner is functioning.
Also, I don't mind losing everything at once. If the water pump loses its belt, I like the fact that I'll lose steering and alternator at the same time. That makes belt failure more obvious, and I'm therefore less likely to overheat my engine. My one exception to this line of thinking is when you have hydroboost brakes that operate off the power steering pump. I'm not a fan of having that fail unexpectedly. Losing steering and brakes at the same time in a large vehicle really stinks. Been there and done that.
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