Of wayward V-belts...

Driving home today in my C900, I accelerated hard out of the toll booths to get ahead of a semi before the lanes bottlenecked. Right at the redline in 2nd I heard something that sounded like I ran over a piece of road debris, but the pavement was clean. Quick scan of the gauges once I got into third and past the truck, no signs of anything amiss. Steering felt a little odd, but otherwise all OK. Pulled off at the next exit to look and sure enough the P/S and A/C belts were off. The former was popped inside out and worn a bit thinner than it had been, while the latter was shredded. I can only guess that, since my A/C is non-functional at the moment, I may not have tightened the belt back up the last time I was working on it, and the high RPMs caused it to abbrade and shred itself. The P/S belt runs inside the A/C (A/C is outermost, then P/S, then dual alternator and water pump belts) - did the A/C belt flailing around knock the P/S belt off and turn it inside out? All the belts were new this year. In any case, it was weird. Just glad it didn't take out the alternator belts in the process. I drove home with no power steering, which really wasn't too bad - probably be a lot easier with stock diameter tires instead of the 205s on the Super Aeros, though.

I don't have an answer for you but I sympathize. I will hazard a guess that you are correct  that the ac belt  was the culprit. My f 150 turns the power steering belt  inside out regularly.  I just leave it  and make certain that it is tight.  I also carry an extra belt and wrenches. 

In reply to pilotbraden :

New belts - a replacement and a spare - for each of the affected accessories have already been ordered. Tools are already in the car (it's a 30-year old Saab, so...).

V belts don't like high RPMs and high loads. They also don't like being too loose, or overly tight. 

Try shutting the AC off when turning lots of RPMs.

If they are flipping, they are probably too tight. 

In reply to Toyman01 (Moderately Supportive Dude) :

A/C was off - since the compressor clutch is bad it's not being used at the moment. Interesting that being too tight could contribute to the belt flipping. I try not to overdo it with belt tension, but perhaps I did. With the belts up against the firewall, it's a bit awkward to get a feel for how tight they are when adjusting.

In reply to 02Pilot :

You might try changing to a cogged v belt. That may solve the problem. Check your pulley alignment. If that is off, you will never get it to work. 

Thanks Toyman I will not tighten the belt so much next time. 

In reply to Toyman01 (Moderately Supportive Dude) :

These were cogged Continental belts. Cogs aren't as deep as some (IIRC Dayco belts are deeper) but they aren't flat. Alignment is good as far as I can tell - with the way everything mounts there's not much room for it to go wrong (A/C and P/S pump are rigid mounts, alternator has brand new bushings).

Went out this morning for a more thorough inspection. Turns out one of the two alternator belts was also flipped over. Got that back the way it should be and reinstalled the P/S belt for the moment. When the new ones show up I'll swap them in.

Related question: what's the purpose of dual belts for the alternator and water pump? Is it just redundancy for critical systems?

In reply to 02Pilot :

A belt is only rated for so much hp before it starts to slip. With V belts, if you need more hp, you just add another belt. With micro v belts they get wider. 

For instance, my air compressor has 2 belts on it. 

My 16" lathe has 3. 

In reply to Toyman01 (Moderately Supportive Dude) :

But if it's down to the power rating, why are there two for the alternator and water pump, but single belts for the P/S pump and A/C compressor? Is the demand of the accessory part of the equation?

And for the record, this is a NA 16v pumping out a beastly 125hp when it was new - I don't think it's taxing the belts too much. Hell, my 2002 with a modified engine puts out more power, runs to a higher redline (often), and runs a single belt. It's never thrown it off or flipped it over.

The surface area of the pulley is also critical to transmitting power. The AC compressor and power steering pulleys are large with lots of surface area. Alternators, on the other hand, have tiny pulleys with less contact patch.

In reply to Toyman01 (Moderately Supportive Dude) :

I hadn't thought about that but it makes sense. Thanks for the clarification.

The biggest HP drag on the belt drive is usually the mechanical fan, if it has one. 

I don't fully understand why belts flip over, but all my experience over the years has been that V-belts are relatively picky bastards and switching to serpentine belts was one of the best things that ever happened to cars. 

In reply to Vigo (Forum Supporter) :

No mechanical fan. The car in question is my Saab 900, so the engine is the wrong way around. I have thought more than once about replacing the mechanical fan on my 2002 with an electric more than once. Engine Masters did a couple of episodes on accessory and fan drag - I think I need to go back and watch those.