Thread: keep losing alt drive belt at 7000 rpm need help

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i keep losing my alt drive belt at 7000 rpm, it does not break but comes off

Need to know what type of car. Otherwise, just replace it and tighten well.

Sounds like you either need serpentine or you need to underdrive your alternator. A smaller crank pully would probably be the best way because belt speeds would be lower. A larger alternator pulley would just decrease alternator speed while belt speed remains constant.

I HAVE A 1969 CAMARO DROP TOP, 327 30 OVER.
ALL NEW BELTS BILLET PULLYS, ALL LINED UP
ONLY P/S BELT AND ALT W/P BELT. IT HAPPENS
AT 7000 RPM. WHILE DRIVING. SUPER T-10 TRANS
POSI 373. ALL NEW SUPENSION, FRONT AND REAR SWAY BARS
ALUM HEADS HOLLEY 750CFM 4150 CARB. MSD IGN
ALUM DRIVE LINE, ALL NEW MOUNTS. NEW EDELBROCK LONG
WATER PUMP NEW. NEW COMPOSIT FAN
NEED HELP
THANKS MARIO

Originally posted by 76GMC1500
Sounds like you either need serpentine or you need to underdrive your alternator. A smaller crank pully would probably be the best way because belt speeds would be lower. A larger alternator pulley would just decrease alternator speed while belt speed remains constant.

If it's not a stock set up, or if a bracket is bent, maybe it's not aligned right. (All pulleys on the same plane)?

I had the same problem when I ran a eight inch balancer pulley. Since I changed to a 4 inch pulley, all is well

Try a 4" deep pulley

http://www.powermastermotorsports.co...cessories.html

Definately an alignment problem............7000 is a lot of RPM for any engine, the undersize crank pulley will help, but watch your charging.

Go with "Techinspector1's ' suggestions!
Especially the "spring loaded Idler"!
After making sure to follow step one! First!
If they aren't straight, they aren't goin' to stay on!

There may be a simpler solution. My '77 'Vette used to do the same thing (but at about 5500 rpm). It was just the cheapo Auto Zone belt stretching like a rubber band! Bought a good Gates belt at NAPA and it never happened again.

Just in case we're overlooking the obvious.

That's true Sinisterv6:
ALSO!
There used to be a belt manufactor (Gates?) that had "SS wire" in their belts rather than the "poly/nylon" cords..
I haven't had a need for them lately, so I don't know if they are still being manufactured!
Plus, the "notched" belts conform better than the "solid" belts do at high speeds!

I HAD THE SAME PROBLEM ON A 63 VETTE AND A 76 TRANSAM
I GOT A 2 GROOVE PULLEY AND PUT A SHORT BELT FROM THE CRANK TO THE WATERPUMP AND ANOTHER FROM THE WATERPUMP TO THE ALT.

Shift at 6900

Go with Tech, Smart guy that one, the force is with him strong.

Otto

Pulley alignment, or belt too long (it does not take much, at 7G), or stretching. Actually, at 7000, a tiny bit of any of these thing is too much.

Must've used some kind of new fangled johnson rod