Drive belt alignment

I own a 1991 Ford F-150 XL with the 5.0 V-8. The problem I am having is the serpentine drive belt keeps jumping one rib off of the crank pulley. Thus, that lone rib of the belt continually runs on the edge of the crank pulley damaging the belt. I replaced the belt tensioner in vain, and have thoroughly inspected the alignment of pulleys. Nothing appears out of alignment, but I cannot overcome this problem. I talked with another Ford truck owner and he told me he has had the same problem for three years (No gumption)! Has anyone else encountered this problem? Does anyone have an idea of what is going on? Please help.

Just a suggestion. I wonder if one of your pulleys is bent?

I had a similar problem with a buick Lesabre. Turned out the water pump was going. Bearings in the water pump made the pully wobble ever so slightly. It was enough to make the belt edge closer to falling off.

You might have to take your belt off and try wobbling your pulleys.

Oh my god that last sentence sounded bad. lol

Hi I'm not sure how old this post is, but I've got the same problem and I dont see any wobbly pulley's.
I just changed the serpentine belt (mechanic did it for me) and it's failing again after only 75 miles.
The mechanic has just rebuilt the engine 300 miles ago.
He said yesterday when he changed the belt that he could see no reason why it had failed.
I've looked at it and from what I can tell the pulleys all look like they line up. I've slacked the tightener and there isn't any noticable wobble in the ones I tried.
What's happening seems like the ribs are separating on the belt.

Please does someone have some suggestions?

Oh by the way... it's a 98 F250 with a Triton 5.4 in it.

Hi I'm not sure how old this post is, but I've got the same problem and I dont see any wobbly pulley's.
I just changed the serpentine belt (mechanic did it for me) and it's failing again after only 75 miles.
The mechanic has just rebuilt the engine 300 miles ago.
He said yesterday when he changed the belt that he could see no reason why it had failed.
I've looked at it and from what I can tell the pulleys all look like they line up. I've slacked the tightener and there isn't any noticable wobble in the ones I tried.
What's happening seems like the ribs are separating on the belt.

Please does someone have some suggestions?

Oh by the way... it's a 98 F250 with a Triton 5.4 in it.


This may sound extremely novice or unprofessional, but I SHIMMED the crank pulley just enough to put the pulley in the correct distance for the drive belt to ride without tearing the belt to pieces. Again, this may be exremely unprofessional, but this truck to me is just a "worker", not my priceless object of affection. This was roughly six or seven thousand miles ago(I don't drive it that much), and I have not had a problem since. I do not see any wobble or misalignment out of the crank pulley, and again this has solved my problem. Let me know what you think, or what your mechanic suggests in the future.
Thanks

Hey Chitown,
Actually I went back to the mechanic and we found that the power steering pump pulley was a hair to far out. I've only put about 130 miles on it but so far the belt still looks like new.
I actually had a fella tell me about shimming this morning just before I went to the mechanics, but I figured since the mech. put the motor back together I would let him solve his alignment problem and he did.
Thanks for replying,
DF