Thread: Throwing belts

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Good morning all,
I just came back from a shakedown run, and when I run the car hard and shift manually, it throws the alternator belt. If I leave it in drive and nail it all seems ok. I just put a new March alternator bracket on last week, and the alternator seems to be held rather well. It only is doing this if I shift manually, over 5500 RPM. The engine is a 355 in a 71 Nova. Any help is greatly appreciated.

Tiny

Did it throw belts before you changed the bracket ? If so is it the same belt , once a belt is throwen it wants to keep doing it. If not it sounds like a miss alignment of the alternater. Carlg

Tiny,

I agree with crush, it sounds like the pullys are not perfectly aligned, or possibly at high rpm the alternator bracket is coming out of alignment.

I suggest that you watch the belt and pullys while reving the engine to see what happens. Also make sure the adjustment is not too loose or too tight.

Pat

You don't want to check alignment while the engine is at high RPM!!!! If it throws the belt then.......

Make sure you are not in line with the fan or the belts.

If you can, without a belt on lay something long on the two pulleys, like a yard stick or a piece of rod. This magnifies the alignment. The chunk of yard stick that sticks up and away should be reeeeeeal perpendicular with the front of the engine.

The next question is, do you have the belt tight enough? Those manual shifts change engine rpm suddenly which causes the belt to change from driving the alternator to the alternator breifly trying to drive the engine... If the belt is loose enough this pitches the belt.

Originally posted by kcress
You don't want to check alignment while the engine is at high RPM!!!! If it throws the belt then.......

Make sure you are not in line with the fan or the belts.

U R RIGHT! good point. Proper caution should be exhibited. Stand back, wear safety glasses, keep your hands away from moving parts

Pat

That used to be a problem when you could order a crate 327 375 horse long block and bolt on your 2x4 mainfold then the rest of the stuff from your old motor. too many rpm for the pully sizes. the fix was to go to a smaller crank pulley and slow everything down. you may not charge at idle.

Thanks for the quick replies, I will check alignment of the pulleys. I had used the same belt again, so I will get a new belt and try this as well. May also try a thinner belt to set more in the pulley. As a last resort I may switch to the serpentine system, I have heard this is much more stable and less prone to throw belts. Thanks again.

You might want to try a spring loaded idler adjuster,this will take up the slack when you drop RPM's on shifting.

Oh yeah, that a good idea too.