340 belt throwing

[challenged-one]

Hi guys.  I have a 70 Challenger with 340, 4 speed, power steering and a/c.  My problem is the fan belt that runs around the crank pulley, water pump and power steering pump doesn't stay on.  It used to stay on just fine and now the dang thing never stays on and the problem has only gotten worse.  I first thought it would be a belt alignment issue. It looked like it lined up good, but could maybe use a little improvement. I put a new belt on and that didn't help. Then I did a little shimming on the power steering pump bracket and I thought it was cured, every thing seemed fine.  Then it started doing it again.  Thinking maybe my shimming didn't help, I took out the shims and again tried a new belt without success.  The power steering pump had a little leak, so I replaced that, hoping it would also have been part of my belt problem.  Wrong again!  The water pump pulley spins freely with now slop at all.  I checked the crank pulley bolts and they are tight, they were a little loose though.  When it's running I see no obvious alignment issues or pulley wabble etc.  The problem has progressed and sometimes the belt comes off within seconds of starting the engine.  Could it be a harmonic balancer problem?  Any ideas?   

[Jim]

It looked like it lined up good, but could maybe use a little improvement.

Don't just eyeball it. Get out a straight edge. You might be surprised to find how far out of whack you really are. Doesn't take much. Stick cars love to throw belts.

[MEK-Dangerfield]

Are you sure you have the belt tight enough? I slip a big pry-bar down along side of the power steering pump to move it as far to the drivers side as possible before I tighten the bolt.

[Moparal]

Are you sure you are recieving a 3/8th groove belt?  Now adays they try to give you mm belts which are not the same v shape and depth as the originals and can walk up the side of a pully. I had this happen before. Depends on the brand sometimes. Those top cog belts are known to sling off a 3/8ths belt pully system. They have all those little notches on top of the belt. 

It also seems that sm blk mopar pump brackets were known to flex way back when.  It is obvious something is off or maybe the pump/steering box isnt flowing right and dragging some on the hydraulics

[Bullitt-]

My problem is the fan belt that runs around the crank pulley, water pump and power steering pump doesn't stay on. 

On my 340 these are two different belts...Power steering is one.. Alternator & water pump another both going to one of two grooves on the crank...every small block I've ever seen was like this. 

[challenged-one]

This belt is just around the crank, water pump and power steering.  The other 2 belts go around the crank, a/c and alternator. 

The belt is not 3/8", it's closer to 7/16".  I'll get a 3/8" and try it.  I checked the last belt that I took off and it is a 3/8" though and I had the prob with that one too.  It did seem to get worse when I put this last one on though, so I'll make sure to get a 3/8".

It's very tight, I do the same pry bar trick. 

I'll spend some more time on the alignment and try a straight edge. 

Just changed the power steering pump and that made no difference. 

It just seems weird to me that this problem has gotten worse over time.  Seems to me an alignment issue would be consistent.  Seems like such a simple thing, but it's been frustrating the heck outta me.  Hmmm

[Aussie Challenger]

Don't just eyeball it. Get out a straight edge. You might be surprised to find how far out of whack you really are. Doesn't take much. Stick cars love to throw belts.

  Also check the bracket that holds the pump and make sure that it is not bent or distorted, if the pump is in the wrong plane it will throw the belt.
  I also thought that the power steering belt went straight to the crank pulley, if there is a long distance the belt can get a whip up and throw off. This is one of the reasons this belt is kept isolated and short. My '70 Challenger has the short belt.   

[472 R/T SE]

I don't know which power steering pumps had it or if it had to do with the brackets but with my last 340 car there was a hole that's square shaped.  Perfect for a ratchet end to fit for tightening belts.

A buddy showed me that, said that's what the hole was for. 

[Aussie Challenger]

  Some had the square hole some didn't, it is a good idea to use it though or be very careful not to dent the stamped reservoir.