Accessory Belt Issue....... Help! *******UPDATE******

My car runs the stock pulley & belt setup. I’ve had the car for 12 years, and never had a belt issue, nor replaced a belt up until last fall when it threw the water pump / alt. belt on what was the last pass of last year. I figured it was just time, as the belt was who knows how old. I replaced the belt and it saw a few street miles last fall before tearing the top end down to have the heads worked on over the winter. All recently went back together once again with the bracketry and pulley setup no different than it has been since I’ve owned the car. I am completely confident that the belt was tight.

Today I pulled it out of the garage and took it for a short drive to put gas in it for the upcoming race weekend. I cracked into the secondaries once and felt and heard a rap under the hood. Pulled over........ yep, belt gone.

Anyone have any ideas on why the same setup that was rock solid for 50 years would suddenly start throwing belts? Alternator is solid as a rock. Water pump is solid and spins evenly. All pulleys appear to be in good repair. Could I be tightening the belt too much??

Probably due to changes in belt manufacturing, may be wider than originally used. If you are not already using deep groove pulleys, a cheap way out is to match up an old air pump belt. They were narrower than a standard drive belt and will sit deeper in the pulleys.

Stealth change out the belt to a dayco top cog belt.

My hemi would snap or throw belts until I changed to dayco. No problems since going on 8 years.

Mike

Check the basics. Are the pulleys excessively worn or cracked? You should check the pulley wear against a gauge - if you don't have one PM me and I will send you one - vendors give them away for free.

And check for pulley alignment - something may have moved.

I had this same problem. Had the belt on my car for years shifting at 6700rpms, hitting the rev limiter occasionally with no problems. Changing oil one day and noticed the bottom was missing some chunks. I put and new belt on of the same part number. First time out shifting it came off. I checked pulleys, mounts and tried a few different brands of belts, nothing worked, if I hit the rev limiter it would come off. Never did figure it out, I changed over to serpentine belt.

I had the same issue at a race last year,everything looked good, but kept throwing belts. The lower pulley ,factory single belt had cracked at the mounting bolts.Could not notice any wabble,so I go out for a first round ,dial 11.10 to his 9.90. As I shift into 2nd the car made an inmediate left turn heading straight for the guardrail,luckily I steered away and did a figure eight on two wheels and barely missed the opposite wall,The good news the other guy missed inches tee boning me.The pulley broke off the bolts cut the radiator hose so clean it looked surgical. Long story but please check your stamped pulleys for cracks.I will no longer use a stamped pulley on anything race.

switch to one of our serpentine belt kits and no more problems.

There is always a reason things start to fail, the hard part is figuring out what is causing the failures
Now get to work

I'd be looking at a misalignment of at least 1
of the pulleys.. a belt just doesnt fly off
on its own... could be even a bent belt usually
caused by a pulley misalignment
Try putting a straight edge on each one

Check the crank thrust

X2. And Gates belts are like plastic, always squealing. Add a Dayco Top Cog as said above if thrust ect check out.

Thanks for the tips guys! I’ll be out in the garage today going over this list. Hope I get it figured out.

The 15470 belt worked best for my alternator and 15440 for power steering on my hemi.


15 means 15mm or 7/16 and the 47 or 44 is length of belt.


I bet just changing to this belt will fix your problem it did on mine.

Good luck

Mike

Had a similar problem with mine. I lowered my alternator mounting position 10" to make room for turbo clearance. This left a very long span between the A.C. compressor and alternator. The belt passed VERY close to the water pump belt adjuster/idler pulley on its way by. There were witness marks on top of the A.C. clutch after it tossed a belt. I think it was "flapping" up and down enough to get out of the groove. Solution: I made a small 90 degree guard which is mounted under the water pump idler bracket bolt. It doesn't touch under normal operation, but it keeps the belt from flapping up enough to get out of the groove.

UPDATE:

I couldn’t find a local distributor of Dayco, so I went with a Gates belt, one size narrower than the book calls for. Then I also made an adjustment to the bracketry; although it looked straight, when I put a straightedge across the pulleys the alternator was a little proud of the crank and pump. So I moved it back slightly and reassembled.

Well, Either I fixed the alignment, the narrower belt worked, or (most likely) it was just a freak deal from the get-go, because I made 3 full passes on Sunday with no issues whatsoever.

Car went a new best as well, 11.321 @ 117.89; but that’s for another thread.....

NICE!

Glad you got it sorted out. Congrats on your new best!!

nice catch

good deal.

Glad to hear you got it squared away

Make real sure the crank pulley bolts are all good and tight. I actually started to hear a faint knocking noise that made me think my converter bolts were loose. Ended up being the crank pulley bolts were just a little loose. I did not throw my belt but I was only street driving when it happened. Good luck with it. Ron