Marbles rolling around in the front of the engine????

I have a 98 SLS jimmy 4dr 4.3l vortec 4x4 w\AC. For some reason my truck eats belts. After the truck it at operating temp, and I shut it off, then start it back up the engine SQUEELS like a rabbit caught in a lawn mower, the ONLY way to cut the squeel is to rev the engine up to the redline, then the sound is gone and will NOT return no matter how long you drive until you shut it down again. It seems like maybe a bearing is off center and gets re-centered when I rev it up? Or maybe it's the belt..again, belts last about 2 weeks in this truck before the squeel comes back, the belts all look fine, belt dressing sometimes helps but not always.

Also, on what I think is a related note, the engine has a weird rattling sound. It's audible at idle, VERY audible (people walking by give me looks), it sounds EXACTLY like 10 marbles rolling around in an empty 5gallon plastic pail, to a T. The rattle remains even when driving however it's drowned out by the engine so I don't hear it much at all. It's coming definitely from the front of the engine in one of the pulleys. I can't tell which one because it sounds like it's coming from everywhere. I changed the tensioner and it did not help. Maybe it's the AC? Everything on the truck operates fine, but the sounds drive me crazy! Any ideaS? Similar experiences??

Have you tried wiggling and spinning the various pulleys with the belt off? I found a bad bearing once by doing that. It made the same noise as when it was running, only quieter. I was very glad to figure it out. So annoying.

Have you tried wiggling and spinning the various pulleys with the belt off? I found a bad bearing once by doing that. It made the same noise as when it was running, only quieter. I was very glad to figure it out. So annoying.

Yeah I tried that and couldn't find anything. The closest thing to something being weird was the AC pulling had a very very subtle feel of something, like it slightly rubbing on something in the tiniest of ways, but I think that was just the clutch inside it.

I would say the two problems are related. If there is a bad bearing (the ball bearing noise) there will be drag on the belt and it will have a tendency to slip (the squeal). It will get worse and you may get stuck. My idler melted down on the interstate a few years ago, but it was warning me for five days with a bearing noise, but I ignored it and I got stuck.

Base on how many belts you're eating up I assume you are carrying a spare belt at all times now?

If the AC was off (clutch disengaged) there shouldn't be much drag from the AC bearing. Is it possible it throws the belt slips when the AC clutches in? Remember the AC comes in even on defrost settings.

Once I found a bad bearing by spraying WD40 into the bearings while the engine was spinning the belt. The noise would suddenly change until the WD40 wore off. I don't know if I would red-line the engine just to get rid of the noise.

What mileage - what about the fixed idle pulley up top. Alternators sound like that so with the belt off spin it and grab the pulley and wiggle hard and see if the front or real bearing is loose. Then AC was covered above, Then water pump is next. The power steering pump has adjustment on the bracket and if thats off can eat belts. Also feel the pulleys and see if any messed up grooves that cut into the belt. The new diamond cut belts may be what you need - only about $5 more and they are crosshatch cut (diamond) not just the long grooves.

What happens to the belt, does it tear off, spin off, or does it burn? When you had the belt off, did you also try to pull and push each of the pullies, with exception, of course, to the crank pully?

If it can't be found by feeling the pullies when engine is off then how about putting on on of your old junker belts (or another new one) and start engine.

Soon you will see which pulley is not turning, binding, or smoking. If not then after the belt breaks or smokes and you turn it off the offending pulley can quickly be found as the hot one.

ps you may also use a temp gun, careful not to get caught up in fan, lol.

Well the rattle went from CONSTANTLY to now only showing up when the AC clutch engages so I think it's AC related. When idling, AC off, the clutch still turns on every 10-15 seconds, when it engages the marbles show up, then go away when it stops. Anyone else have this issue?

I thought they only ran when on ac or defrost.

I thought they only ran when on ac or defrost.

I thought so too but I think I read somewhere that the system has to cycle on and off now and then even if not in use to keep the system pressurized.

PS

Does anyone else find it ODD that it has to run when the truck is on defrost? I mean the AC runs when you have AC on yes, it's because it's basically a refridgerator that you run air through to give you nice cool air in the summer. But why the hell would I need it to be COOLING the air when I'm running my HOT air defrost to kill frost in the winter??

I think the ac runs in defrost to remove moisture. Just a guess.

I heard it was also to keep seals from going bad.

Glad to see you isolated the problem.

In every brand car and truck I have ever driven the AC always kicks in when the defrost is turned on, but the amount it cycles depends on the temperature setting of the dash knob. It will try to keep the temperature you set the knob for. In the newer vehicles it is an electric thermostat, not a cable controlling the heater hose valve. The more you keep the knob on the heat side the less the AC will kick in.

Like JOULES said I'm pretty sure its purpose is to remove moisture - for example in the summer when it's raining, the defroster with the AC running will evaporate the fog quicker than with the knob pointed toward the heat side. Who want it to blow warm air in the summer?

If you can't fix it soon, you can disconnect the wire to the fan clutch to keep it from kicking in temporarily.

Glad to see you isolated the problem.

In every brand car and truck I have ever driven the AC always kicks in when the defrost is turned on, but the amount it cycles depends on the temperature setting of the dash knob. It will try to keep the temperature you set the knob for. In the newer vehicles it is an electric thermostat, not a cable controlling the heater hose valve. The more you keep the knob on the heat side the less the AC will kick in.

Like JOULES said I'm pretty sure its purpose is to remove moisture - for example in the summer when it's raining, the defroster with the AC running will evaporate the fog quicker than with the knob pointed toward the heat side. Who want it to blow warm air in the summer?

If you can't fix it soon, you can disconnect the wire to the fan clutch to keep it from kicking in temporarily.

Where is the wire located? I'm not entirely sure if disconnecting it will help or not. There is still this re-ocurring squeel that comes and goes and I can make out some weird noise under there that is quieter than the marbles but it's most likely from the same area. Disconnecting the AC may help in way, but I have a feeling there is something wrong inside the AC pulley itself or the bearing it rides on. Will disconnecting the clutch wire for the winter jeopardize the AC's ability to work next summer?

The pulley bearing still spins even if the AC is not clutched in but with less stress. It looks like yopu can't wait this next spring. To buy a little more time I would disconnect the clucth. I just looked at mine, a 1999. Should be similar.

Standing in front of the engine compartment looking at the AC Compressor, there is a two wire jack right behind the pully at the "11 o'clock" position. My jack is mostly white with a blue tip -The blue tip has small (make that tiny) markings "+" and "-" . Remove that jack (without breaking the tabs hopefully) and the AC will not clutch in.

Is it safe? I don't think the compressor will suffer damage without cycling for a week or two. Longer than that I can't be certain. The internal seals need the liquid to cycle around to keep then from drying out, but I don't think they can dry out that fast.

The pulley bearing still spins even if the AC is not clutched in but with less stress. It looks like yopu can't wait this next spring. To buy a little more time I would disconnect the clucth. I just looked at mine, a 1999. Should be similar.

Standing in front of the engine compartment looking at the AC Compressor, there is a two wire jack right behind the pully at the "11 o'clock" position. My jack is mostly white with a blue tip -The blue tip has small (make that tiny) markings "+" and "-" . Remove that jack (without breaking the tabs hopefully) and the AC will not clutch in.

Is it safe? I don't think the compressor will suffer damage without cycling for a week or two. Longer than that I can't be certain. The internal seals need the liquid to cycle around to keep then from drying out, but I don't think they can dry out that fast.

Thanks for the post. I'll look into that and weigh the pro's and cons. In the end I might just end up having it looked at while in the city. The only problem I forsee is a shop going "You think it's from the AC too huh? hehehehehehe" because I'm sure an AC "fix" would be just to replace the comp at what I'm guessing will be about 700$ lol. What they NEED to do for these engines (and anything running AC) is supply a replacement bracket that someone can put in place of the AC if they decide its WAY to expensive to replace but need a pulley there.

There is one. I know there was a guy selling them on ebay a while back.
Not sure if hes still around but Im sure if you searched around the internet you could find them.