1988 Chevy C3500 Keeps throwing belt?

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  #1  
Old 12-24-10, 11:07 AM
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1988 Chevy C3500 Keeps throwing belt?

Okay, bought this 1988 Chevy C3500 Ext cab, 2 wheel drive, 454cui, w/ ac. It keeps throwing the belt, I have changed the idler pulley, water pump, tention assembly (all needed changed), and 4-5 belts. At first it was coming apart right before the last rib. It would tear maybe a foot down the inside of the belt and pop off.

rrr^r

Now everything looks good except at the new tentioner pulley where it hangs of the front, maybe a 14 inch.

Front Pulley Motor
Belt
fff pppp mmm
fff bbbb mmm

I am not sure what to do now. It kinda looks like the tention pulley is either too narrow, or not sticking forward enough. Is there a way to adjust it out? Could they ave given me the wrong tentoiner assembly, maybe one with a different size pulley?

Thank you,
Jeff
 
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  #2  
Old 12-24-10, 02:40 PM
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shim pulley?
yes, they will sell you all kinds of wrong parts. the only way to have a perfectly right part is to take one off your truck and bring it with you to compare.
belts are prolly wrong size either. when i need to go out and buy a belt, i do not even hope anymore to have it right from the 1st try.
also, sounds like belt is slipping somewhere. this will cause overheating and separation.
 
  #3  
Old 12-24-10, 08:01 PM
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Shim pulley?? Not sure what you're asking, It's the tension pulley where it looks like it is slipping at now.


I haven't really had problems with getting wrong parts in the past, I was just thinking maybe there might be another tension assemby that is almost identicle, except for the pulley size, and or how far the pulley sits forward. The pulley does look like it is the same width as the belt, it just hangs off the front of the tension pulley after/while it is running.
Do you mean overheating and separation in the belt?
 
  #4  
Old 12-25-10, 12:15 PM
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i just had idler pulley replaced on my V8. it's bolt mounted to the engine block. the only other pulley i have is tensioner pulley. it is bolt mounted to the tensioner body. basically, both can have washers("shims") installed behind the bearing, to scoot pulley forward a bit. i assumed pulley is not forward enough and belt is overhanging it.

if you have V-belt, and V in pulley is not mating well with the belt, you will not have total contact, but end up with high points. it may slip on those and overheat with separating the belt along. for 88, i somehow doubt what you are buying as "new" now is exact match.

now, sounds like you have ribbed belt, not V-belt: was coming apart right before the last rib doesn't it sound like groves on pulley are not matching ribs on belt, cutting it in a half at the last rib?

also, one of the pulleys is possible not perpendicular to the belt run anymore. once again, for 88, as there's a lot of downward directed force on tensioner, head or block material simply can give eventually slanting the center bolt. makes sense? idler pulley i had to replace - bearing went wrong - clearly showed about 3 inches long strip of shiny metal(it's black otherwise) on the OUTSIDE of pulley itself. so, it was not running true, but at the angle to the belt run.

basically, what i'm saying, if pulley is off even by a little bit, comparing to the general belt run, it will put pressure on the belt across it, one direction or the other. so, if it does not sit exactly in the belt run path, or is slightly narrower, or wider, or is slanted - you got the point.
 
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Old 12-25-10, 01:16 PM
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possible that the outer ring/pulley on the crankshaft balancer has slipped & moved forward or back.
causing the belt missalignment
 
  #6  
Old 12-25-10, 08:14 PM
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Well the tension pulley, and idler pulley are both smooth, the rest of the pulleys are ribbed as is the belt. The belt ligns up fine with everything when I first put it on, it is just after running the motor that it hangs off the tension pulley. Now this belt has popped off 3 or 4 times, could that have warped or twisted it some how, making it slip off the tension pulley?
I may have to find some washers and shim it, and see if that works first. ty

newtofta, it only has one pulley on the crankshaft.


Here's the tension assebly & pulley:


And this is what the belt looks like:
 

Last edited by daddyzaring; 12-25-10 at 08:55 PM.
  #7  
Old 12-26-10, 04:40 AM
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You say it is running off the tensioner pulley?? Could it be the idler pulley assembly is incorrect? Have you compared it to the original? Is it sitting perfectly parallel to the front of the engine? If it is cantered at all, it will run the belt sideways and begin it's trip over the edge of the first ribbed pulley edge (knife) and begin shredding.
 
  #8  
Old 12-26-10, 10:57 AM
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the pulley part of the crankshaft balancer is mounted to the inner part with a rubber compound sleeve.
over time this joint can fail & cause the pulley to move in or out.
i have seen it happen many times-on various make engines
 
  #9  
Old 12-26-10, 05:02 PM
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"The belt ligns up fine with everything when I first put it on, it is just after running the motor that it hangs off the tension pulley. Now this belt has popped off 3 or 4 times, could that have warped or twisted it some how, making it slip off the tension pulley?"
Unsure what you mean: I would think the back (non-grooved side) of the belt would run against the tensioner pulley, not over it. Is this the way it is routed?
 
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