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67 GTX AC Belt issues

AR67GTX

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Having issues with belt squeal on my factory AC unit - I'm pretty sure it's coming from the alternator. Basically bring the revs up to 3300 - 3500 and the screeching starts. Hoping someone has some idea or trick I haven't stumbled on to.

Pretty much a factory setup except I think a 69 compressor. I've spent quite a bit of time aligning the pulleys including adjusting the pulley on the alternator, shimming the alternator mount - using straightedges and a length of 1/4" straight tubing laid in the pulley grooves. I decided the factory alternator mount with the long spacer was just too loose and bought a new one that is solid between the alternator lugs (no spacer tube). It was not a lot better but after doing some bushings and wrapping the bolt to tighten up all the looseness the alternator to mount was solid.

Mounting it to the block I found the whole alternator still tilting slightly in towards the crankshaft laying a straightedge on the alt pulley - just as the old mount did. So I put a couple of shim bolts behind the two inner bracket mount bolts and that seemed to put it pretty straight as one of the pictures below shows. I also pulled the alternator pulley out about 1/8 inch to get it lined up as close as possible with the crank and AC comp pulleys.

IMG_4960_zps1chun3b0.jpg




I bought a new set of belts from Quanta and applied CRC belt dressing to them and set the whole thing aside for a week and then installed them. They sent me 44" belts which puts the adjustment towards the far, outside end of the adjuster strap. That's what their charts showed for this year. I had 42" belts on it before and they adjusted towards the inside of the adjustment slot. I may drop another $70 and get some 42 inch belts from them if nothing else seems to work.

I replaced the alternator and pulley a couple of years ago and I'm wondering if it is somehow the issue. The belts seem to ride a bit high on it and the outside, wide edge of the new belts measures .380 vs .373 on the worn ones. the inside, narrow side is around .213 on both.

IMG_4962_zpsn0mr77rh.jpg


I've tighten the bezezzes out of the belts - probably about 1/4 deflection on top with finger pressure at mid-span. Hasn't seem to do any good except cut down on belt flap some. Finally resorted to thumbing through my shop manual (the instructions) and for some reason they have adjustment specs (deflection or torque) for every situation except a 383/440 with AC. Great.

Basically, I have a 3500 rpm - max 440 at this point. Above that and it's just a loud screech that sounds like everything is going to fly apart. Don't remember having this issue when I bought the car years ago and the one thing that has changed is the alternator and pulley so I'm suspicious of it.

Any body got any ideas or tricks to try - beyond getting some 42" belts, maybe look for a different alternator pulley, getting a longer piece of 1x2 for a pry bar to tension with?
 
Are the belts on Alt running the same Accessories ? Maybe a matched pair of belts would help if so. The front belt looks its running higher in the groove? I used a 2x4 under alt to floor jack to hold belt tight, didn't go crazy jacking up alt just enough. 1/4" deflection sounds about right to me.
 
How is the clutch on the compressor? I've had one start to go bad and that's exactly what mine started to act like before the clutch took a ****..
 
Thanks for the replies.

The AC belts both wrap around the crank, AC and alternator pullies and are both new and identical. They are Quanta reproduction fabric wrapped belts. I don't like running cog belts on vintage car but something I could try. I can probably try tightening a bit more but I'm sort of reluctant to get them too tight. I'm a long ways from a 4800 - 5000 rpm red line right now so I'm kind of doubtful just tightening them up as tight as I can will be the answer.

I haven't done anything with the AC clutch. I took it to a rebuild shop to put in a new seal about 15 years ago and inspect it when I rebuilt the whole system. I don't actually run it much - mostly just to circulate Freon/oil now and then. I haven't noticed any strange action with it like chattering or rough engagement. I also haven't tried running it out in the gears with the AC engaged just because - not much point in doing so.

Pretty sure it's the alternator slipping - you can sort of see the belts start to vibrate a bit just as the screech hits. It probably has the least belt contact. Other two belts are tight - idler on the water pump belt and PS belt is direct to the crank pulley so 180 deg engagement on it.
 
Quanta belts are the problem here. Big red flag waving. Good work on the pulley alignment!

Buy some good belts. Gates belts are generally harder and can squeal on some applications.

Also is you alternator overcharging or is your battery low? Generally not going to be the problem on a 2 belt system, but check that also when belts squeal.
 
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The car does charge a bit high based on my under-dash gages - around 14.5 V. But, it's always been that way, through alternator changes, voltage regulator changes - never varies. I probably need to compare the gage to a good multi-meter reading sometime. Replaced the battery about a year to 18 months ago and it's real strong.

Yeah - I don't think I really want to dump any more money on Quanta belts. I'll do a little research and see if I can find some good quality belts from Goodyear or Dayton or something like that and see if they work any better.

Thanks
 
Quanta belts are the problem here. Big red flag waving. Good work on the pulley alignment!

Buy some good belts. Gates belts are generally harder and can squeal on some applications.

Also is you alternator overcharging or is your battery low? Generally not going to be the problem on a 2 belt system, but check that also when belts squeal.
Quanta belts are for show poodles, if you want to drive your car they are well know to slip, stretch & fail.... Leave them for the trailer queens...

Gates are designed for real world service.... Goodyear makes a decent belt... Dayco... Not my choice... Known people who wear by them but I've had less than stellar results...
 
Thanks - anyone ever seen a good belt chart with various engine & year listings and actual belt dimensions. I think a 41 or 42" belt is what I need but seeing all sorts of figures.
 
I had issues with trying to drive on Quanta belts too, they flipped inside out.

Go to Rock Auto and get some good belts at a good price, <$10 each. I’ll bet the squeal goes away.
 
I'd look into getting a matched pair and get the correct size. What i wanted to ask was it squealing before you adjusted the mount/bracket? I'd go for a gates, continental or original mopar belt personally.
 
I've been doing allot of R134 A/C conversions on old Mopar's lately... I've asked a few parts guys for matched sets... They look at you like your nuts.. (And I deal with a parts house that doesn't sell to the public) Finally an old timer said Gates quit offering matched sets about 15 years ago...

I could tell you what belts I've been using but since I'm changing to a Sanden compressor it won't help you...
 
I have a new matched set of gates belts for a 383 A/C. They have those words printed on the cardboard sleeve. Pretty cool, from the mid 80’s. Was uncommon to see even back then.

I have a 58 Chrysler with factory A/C. The belts tensions are way different. The one belt is so loose it is doing nothing, the other is tight. I guess you could buy 6 belts and try them out to find the closest two.
 
Well, I'm learning some new stuff - didn't know matched sets of belts existed - thought it was typical to just buy 2 belts of the same size and manufacturer. But sounds like you're saying they don't exist anymore?

Yes, it was screeching before I started all of the realignment effort. I just installed a dual point distributor I rebuilt and reworked the mech advance on and was checking to see if I had finally cured my pinging issues by running the car a little. I typically drive it pretty conservative as it's a fully loaded, auto, air, PS, PB boat. Pinging is under control but I began to realize no matter how tight I got the belts they would screech and then one day looking at it in the driveway I managed to flip both older Quanta belts just running the rpm slowly up to about 3,000.
 
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Maybe go to a place that sells air compressor belts. Was told they use matching belts on multi belt compressors. That would be a last chance option.
 
Maybe go to a place that sells air compressor belts. Was told they use matching belts on multi belt compressors. That would be a last chance option.

Industrial belts are very different from automotive belts...

According to Gates new belts are so much more precisely made than back in the 70's theres no need for matched sets anymore.... In my experience Gates is full of ****...
 
Finally got some Gates XL belts and they are an improvement but still having a loud screech at higher rpm. However, they are much more stable than the Quanta belts and aren't flapping around like they are about ready to roll over any second. I tightened them up some more to where they are bow-string tight and need to try it again this weekend. I wanted to try a Gates green stripe belt but after a bunch of research I finally concluded their smallest width is 1/2" which is way too large for our pulleys.

My buddy with his 69 Hemi Roadrunner is having he same issues. Can't keep a belt on the car in spite of carefully aligning the pulleys and screeches all the time. He threw it off again last night winding the motor out coming home from a cruise night.

Not sure what it takes to keep belts on these old Mopars and quiet, other than maybe aftermarket pulleys.
 
Is the Hemi using Gates belts? If he actually spins that Hemi up like they are meant for an old trick that stopped the spitting of belts back in the day is to install a bolt through the bottom alternator bracket such that the back side of the belt rubs the bolt when ever the belt tries to grow..
It can be done by taking a 4” long bolt, heating and bending two 90 degree bends in it...
two nuts & two washers, bolt it through an unused area of the adjustment slot, swing the bolt head end of the bolt up so it nearly touches the belt close to the alternator pulley...

I know it sounds hokey, but it works...
 
I meant to add the Hemi guy says he's running a Quanta belt too but apparently left that out. I'll mention the bolt trick to him as he's getting pretty frustrated. This time he was hammering on the motor he said. Fortunately he was carrying a spare. It's only a 42" belt - you would think keeping it on the pulleys would not be an issue.
 
These freaking AC fan belts (dual belts) are driving me crazy. After tightening them (Rayco XL) really tight I went out and ran slowly through the gears - hit 3000 rpm in 1rst and sceeechhhh, then hit 2nd and at 3,000 rpm - screeeeechhhh until I let off. Drive down my neighborhood street at 25 mph and goose the throttle a little in 3rd and screeeeechhh! Looked at the belts again when I got home and I can see that one is not under quite as much tension as the other one - which is really tight. So much for the claim there is no need for matched belts because new production standards are so much more precise. Guess I'll try a set of Dayco top cog belts next but not expecting miracle. I never had this problem back in the 60s, 70s and 80s. I didn't even have this problem on the car when I bought it back around 2000. What is the deal?? I'm stuck with a 3,000 rpm max GTX.

Short of going to an aftermarket pulley system with serpentine belt (probably no room with AC) does anyone know a sure fire way to fix this? Pulleys are aligned as closely as I can possibly measure with rods and straight edges. I replaced the alternator a couple years ago and it came with a pulley - maybe an issue with the alternator pulley V-angles? The top of the belts ride about a 1/32" proud of the pulley v-grooves. I don't get it.
 
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