I just recently replaced the sepentine belt on my 1991 F150. As I watched the belt checking it for proper roatation I noticed that it had walked one rib off the crankshaft pulley and stayed there. I placed it back in proper position thinking I had misaligned it and watched it walk itself right back off the crank. I replaced the belt tensoner as I noticed it jumping up and down as the belt turned. This did not solve the problem. I am at a complete loss at this point as to what to check for. The belt lines up just fine across all the pulleys until it goes arounf the water pump pulley. At this point it looks as if the belt is pulled forward across the water pump pulley and then one rib off the crankshaft pulley. From the crank to the smog pump it lines back up and runs straight. Any ideas as to what I am missing?

 

I had that problem a couple years ago with my '88 F-150 with the 300 6 cylinder. Come to find out, my water pump bearing was loose actually quite loose. I don't know why it took me so long to notice it. I would check the bearings of everything driven off the belt for looseness.

 

i had a simmilar problem on my 460. bought an ac delete pulley didnt help so i used some big flat washers to allow the pulley to be moved a small ammount to align belt

 

oh yea the washers allowed the bracket for the delete pully to be moved a small ammount

 

Ok...I will check the water pump out and see if there is a problem...only about 3 or 4 years on it but really that dont mean it hasnt tanked...

 

Well I went ahead and changed out the water pump...new one not rebuilt...it seemed to solve the problem for abot 2 minutes then the belt jumped the one rib again. Having a feeling that Im gona have to pull the balancer but not sure.

 

I've seen the power steering pulleys "walk" on their shafts, causing misalignment. It's easy to check the p/s pulley - the nose of the pulley should be flush with the pump shaft. If it isn't, its simple to thread a bolt (5/16" fine thread?)w/ washer into the shaft to pull the pulley into place.

It could also be a bad balancer - look at the rubber ring that joins the inner and outer sections.

 

Well if anyone is still reading this...I changed the water pump which was leaking come to find out...and I also pushed the power steering pump pulley on the final .010 of a inch and then changed out my balancer...the belt will now hold for round abot 5 minutes and squeal the entire time then "jump" one rib forward and stop squealing...the only issue that I have possibly noticed is the fact that the balancer pretty much came right off with very little pressure and I was able to put it back on to with in about .06 of a inch or so by hand. Dont know if I should try a repair sleeve for the crank or try a new belt as this one might be worn at this point or what. Any ideas at this point would help

 

I'm having a similar problem. My belt does not squeal but it rolls up on the back lip of the power steering pump pulley. I've concluded that the tensioner arm may have a twist in it. The face of the tensioner pulley is not parallel to the power steering pump and is leaning in the direction that would aim the belt to the back side of the power steering pump pulley. I would look at the alignment of the pulley that is upstream of the one where the belt is jumping over.

 

Did you ever resolve this problem. I have the same problem on my Dad's 1990 E-250 5.0L. Wondering if its the tensioner and/or idle pulley. The plastic idler pulley on the tensioner looks like its seen better days... plastic looks prety thin. I can faintly see the pulley's structural ribbing.

Curious how the folks on this thread fixed this problem.

-Glenn

 

Yes I did resolve this. It turned out that the ps pump shaft was a bit too long so I put washers between the pump and mounting bracket and havent had a problem with it since.