Help!

I have been trying to fix this problem all summer with no luck!

The motor is 5 years old 1991 L98 396 SB stroker motor (running for 4) with maybe 4k on the motor at most. The water pump, alternator, harmonic balancer, and belt tensioner were all replaced at time of new motor. The only 2 pulleys that were left on the motor were the a/c (original ac) and the smog pump delete pulley.

The car has been dyno tuned and driven hard as well and the belt didn't move at all until end of last summer/beginning of this summer.

At first it appeared it was slipping off the smog pump delete pulley and I couldn't figure it out till I noticed the grooves on the pulley were worn so I replaced that and the belt did not fall off for about 5 drives. Then it started again and was (and still is) falling off at the a/c compressor pulley. I was reading online it could be due to the a/c compressor engaging or not engaging so I unplugged the a/c compressor (since it doesn't work anyway) to try and eliminate that as the issue....but no it still falls off on the a/c pulley after a 5 min drive.

I have tried the laser alignment tool to see where it could be off and that tool didn't help to much at all since the tool needed to be on metal grooves for the laser to go off ...the smog pump delete pulley is plastic. But checking the other pulleys they did not appear to be off.

Any ideas?

I'm sure its's something very dumb but I can't drive the car anymore at this point and the summers are short enough up here!

:will y:
Belt falling off A/C

 

Since all the spinning wheels are static, except you tensioner, I'd start there.

I bet if you swap in a new tensioner, you'd fix your problem.

 

Check the crank balancer, possibly seperated from the rubber inner ring and "walking" fore/aft?

Joel

 

I had serpentine belt problems, and eventually found that the bracket that holds the alternator had cracked and allowed the alternator to mis-align. I would check all brackets to make sure none of them have cracked or broken. Check the bolts on that air conditioning compressor bracket too. Best wishes, steve

 

..... How long since the belt was changed ? .....

 

I'm on my second one now....but I did notice when it's running the tensioner was hopping up and down a bit. Not sure if that's normal or not?

 

would I be able to see this without removal of the balancer itself?

 

My a/c bracket was cracked at the time of the new motor and I had that aluminum welded and it's still good. The bolts are super tight as well.

Originally the belt was falling off the smog pump delete pulley that had worn out and falling into the alternator...then shredding on the alternator blades.

Once the smog pump pulley was replaced it never fell off from there again and has moved down to the a/c...so I'm thinking the smog pump delete pulley/ bracket assembly is fine as well.

Maybe the tensioner has gone bad even though it was replaced before? ....but then again it was an autozone one...not sure if that could cause an issue?

Are there any other areas/brackets you looked at while you had your serpentine belt issue that I may not have checked?

Thanks!

 

Late last summer - August and then again maybe June this year (after a few drives) and then again early August 2017 and from then on I've only driven it around a few streets maybe 2 mile total trip to test to see if it stays on.


Latest test around the block starting in august 2017

test 1 - Fell off at A/C - not completely - put back into place
test 2 - Stayed on
test 3 - Fell off at A/C - not completely - put back into place

 

It looks like the back of the belt has grooves on it. The pulleys that the back of the belt contacts should be smooth. Sight along the front edge of the pulleys to see if they are in alignment. Use the shortest belt that will fit when the tensioner is at full tension.

 

Yes the photo appears that way but that was when the car was running. The grooves of the belt are on the right way.

 

Since you have done some engine work, I don't know if you are still using original brackets for accessories or not? I do know that my tensioner started making the same rattling noises you spoke of. I removed the tensioner and it was fine. What the tensioner rattling told me was that it had reached the limit of it's ability to tension the belt, and the belt was moving off of the pulleys. That was when I started to remove accessories, starting with the alternator. Don't have the car close by but from what I remember the alternator has a top bracket, that for me was till good. Taking the alternator off revealed what looked like a good bottom bracket, but looking closely I could see that it was cracked by a bolt hole boss. This allowed the bracket to flex, shortening belt effective length, and with the tensioner unable to take up the slack, the belt started to walk. I will see if I can plug in a couple of pictures. Since photobucket walked away I don't know if it will work or not. either way best wishes, steve

Well, looks like it worked? Here is a pic of the bracket I am talking about





At the end of the cotter pin is the crack I am talking about. That is all it took to make the belt not work.

 

I will check this out...thanks!

 

Wow....if that's all it took I will defiantly need to take a real good look at all brackets. Did you have any belt issue after that crack was fixed or did you get a new bracket?

 

If the brackets need to hold as tight a tolerance as others had mentioned my suspicion is this welded bracket. Welding can warp metal.

Also I doubt the bracket got heat treated afterward so it may have bent under load.

 

It seems that these brackets break quite often. Sparky at vettnuts sold me a used one. When you finally find the problem, let us all know please. As others have said, it is an alignment issue, but not easy to determine what is out of alignment.

 

There are at least 3 steel tube reinforcement braces for the alt. and AC brackets. These have to be installed or the brackets will break.

 

Started taking it apart tonight and noticed one of the a/c molting bolts was never installed. With that being said tho the car was fine like that for 4 years of driving roughly and hard dyno pulls etc. I would still like to order the bolt though. Anyone have any idea where to source the alternator bolts?

I will be taking the a/c compressor bracket off tomorrow and will keep you updated!

 

My thought is that it is unlikely that the last bolt was never installed. Never properly tightened perhaps. I think it worked lose and your AC is now flexing and possibly cracked. You are getting closer.

 

You may already know all of this, but getting at the bottom bolts on that AC bracket are easier, or at least i think easier, if you remove the right front wheel and then remove a small access panel in the fender liner. Then you can get to them with a straight shot. You do not need to disconnect refrigerant lines on the compressor.

Happy Saturday!