belt slap
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More Turbo
Joined: Nov 2010
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belt slap
Im working with the 7.3 IDI. Today after putting in new glow plugs i was under the hood and noticed my alernator belt slaping alot. I have tightened it all the way almost and its the correct length. The belt is accualy hitting the pulley on the vacum pump. Got new belts from the Napa to replace it. I think it was labeled wrong from the store when i bought it in a pinch. Anybody have any advice to keep the slap from occuring? I know hte slap comes out after bringing the rpms's off idle. Just worried at idle of ripping through the belt
Lead Driver
Joined: Dec 2006
Posts: 6,496
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From: So. Jersey
I used an idler pulley/bearing assembly from a Dodge 93-96 5.2l truck. A piece of 2" wide 1/4" thick flat stock about 4" long and tapped a hole in one end to receive the idler mount bolt and bolted it to it. Then simply welded the other end to the bottom of the upper alternator bracket. The pictures below is self explanatory.
Postmaster
Joined: Apr 2008
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Yup, you need an idler - I got one from a Mustang (plastic pulley), and I did my brackets a bit different (puts the idler right next to the water pump pulley), but it still works pretty good. Bubblegum has a nearly identical setup to mine as far as idler location goes, but her pulley is a steel one from TSC - also works nice, no belt slap there either. IMHO these trucks should have had idlers on them from the factory. But if your belt slaps so bad it hits the vac pump pulley, maybe you still need to tighten it a bit more? Factory length for the alt belt is 57" by the way, and the alternator bracket allows for some huge adjustments even if you got a bit longer belt.
Posting Guru
Joined: Dec 2005
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From: Peterborough, Ontario
Or.....don't look when the engines running and the hood open. Out of the trucks here none have had an idler added to them.
Huh, just thinking, that all totalled up I think my trucks would be over a million miles on them. I'll have to check it out and tally them up when I get a chance!
Huh, just thinking, that all totalled up I think my trucks would be over a million miles on them. I'll have to check it out and tally them up when I get a chance!
Senior User
Joined: Nov 2010
Posts: 273
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From: in the shadows
Greywynd, how fast do you drive? I was told by the person who installed my idler thing a while back that they are good not only for idle, but also when the engine is revving up, which would be very good for me because I pretty much only know two positions of the gas pedal - foot off it, and foot on it to the floor 
Postmaster
Joined: Jun 2009
Posts: 3,420
Likes: 1
From: Maryland
when i rev up my motor the belt slap stops i dont want to over tighten the alt cause i blew up one by doing that gawd it was liek a gunshot when the alt locked up cause the bearings blew apart
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Postmaster
Joined: Apr 2008
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Yeah, I told her the same thing, that belts only slap at idle, but if it makes her sleep better at night then sure, the idler helps at high speeds too She does indeed drive like she's qualifying for NASCAR tho, I think the only thing that saves her is the fact her truck is 2wd dually (and so it is fairly low and wide) - I honestly have no idea how she didn't roll her old K5 Blazer (tall and narrow) coming around a corner at gazillion miles an hour... lol
And I know about the alternator self-destructing due to overtightened belt, but your belt ain't so loose it's hitting the vac pump pulley now, is it? It was the OP whom I was suggesting to tighten their belt some first, cause even if the belt is too long hitting that other pulley still ain't right.
She does indeed drive like she's qualifying for NASCAR tho, I think the only thing that saves her is the fact her truck is 2wd dually (and so it is fairly low and wide) - I honestly have no idea how she didn't roll her old K5 Blazer (tall and narrow) coming around a corner at gazillion miles an hour... lolAnd I know about the alternator self-destructing due to overtightened belt, but your belt ain't so loose it's hitting the vac pump pulley now, is it? It was the OP whom I was suggesting to tighten their belt some first, cause even if the belt is too long hitting that other pulley still ain't right.
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Postmaster
Joined: Jun 2009
Posts: 3,420
Likes: 1
From: Maryland
Yeah, I told her the same thing, that belts only slap at idle, but if it makes her sleep better at night then sure, the idler helps at high speeds too She does indeed drive like she's qualifying for NASCAR tho, I think the only thing that saves her is the fact her truck is 2wd dually (and so it is fairly low and wide) - I honestly have no idea how she didn't roll her old K5 Blazer (tall and narrow) coming around a corner at gazillion miles an hour... lol
And I know about the alternator self-destructing due to overtightened belt, but your belt ain't so loose it's hitting the vac pump pulley now, is it? It was the OP whom I was suggesting to tighten their belt some first, cause even if the belt is too long hitting that other pulley still ain't right.
She does indeed drive like she's qualifying for NASCAR tho, I think the only thing that saves her is the fact her truck is 2wd dually (and so it is fairly low and wide) - I honestly have no idea how she didn't roll her old K5 Blazer (tall and narrow) coming around a corner at gazillion miles an hour... lolAnd I know about the alternator self-destructing due to overtightened belt, but your belt ain't so loose it's hitting the vac pump pulley now, is it? It was the OP whom I was suggesting to tighten their belt some first, cause even if the belt is too long hitting that other pulley still ain't right.
Lead Driver
Joined: Dec 2006
Posts: 6,496
Likes: 94
From: So. Jersey
? Belt slap really isn't a problem as much as just annoying. YOUR system on the other hand has been plagued with misaligning and failing tensioners, one belt system so when it breaks your done unlike a multi belt system I can afford one or two broken belts and keep driving. Or upon component failure like an A/C compressor bearing I just take that belt off and keep driving. You can't do that so really you shouldn't be to excited about the serp system.
Cargo Master
Joined: Feb 2010
Posts: 3,493
Likes: 3
From: NY
Thats true, but I've done work on mine and replaced vacuum, idler, and another pulley too (I think) and never had any trouble with the pulleys not aligning. My tension works pretty good too. My belt did come off while I was driving once and it was kinda hard to turn but other than that is ok to drive without the belt. Truck didn't shut off or anything.
Lead Driver
Joined: Dec 2006
Posts: 6,496
Likes: 94
From: So. Jersey
Thats true, but I've done work on mine and replaced vacuum, idler, and another pulley too (I think) and never had any trouble with the pulleys not aligning. My tension works pretty good too. My belt did come off while I was driving once and it was kinda hard to turn but other than that is ok to drive without the belt. Truck didn't shut off or anything.
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