what am i over looking
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Joined: Mar 2003
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From: mohave valley
what am i over looking
i have a 70 truck with a 302 two barrel and auto trans. starts right up. good/even compression. after it starts and warms up i have a really bad vibration around 900-1400 rpm, the motor that is. runs great. ive rebuilt the carb, then rebuilt another carb and tried it. converted to petronics elec. ing. and then added msd 6a. fuel pressure is good. distributor seems fine. timing is good. replaced wires and plugs. vacumn is good. i have tried just about everything i know to do. anyone have any suggestions. what am i over looking. thanks in advance
Post Fiend
Joined: Feb 2000
Posts: 5,130
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From: Brea CA
what am i over looking
Hi, that rpm range is right around the fundamental frequency if your engine is out of balance. Has any engine work been done like changing the flywheel/flexplate or damper? Also could be your torque converter going out, they'll vibrate right around there too.
Barry
Barry
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From: mohave valley
what am i over looking
no engine work. the truck had 90,000 miles when i bought it, two years ago. i noticed the problem right away. ive put 15,000 miles and it hasnt changed. my first feeling was something to do with the torque converter. just by the way it felt when i sat in the vech. and could feel the vibration. i have thought of disconecting the torque converter and starting the engine to see if it goes away. do you have any other, and or, better ways to check this out.
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Joined: Aug 2001
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From: Wimberley, TX
what am i over looking
This is a long shot, but a friend of mine had that problem on a GM engine. It turned out to be a broken crankshaft.
He noticed one day when changing the belts that the crankshaft pulley had some wobble to it. All the bolts were
tight on the pulley and the main bolt in center of the crank was tight too, but you could move the pulley and crank end around.
It was broke just inside the front main journal and the break was irregular enough that it still drove the front of the shaft.
Hope that's not your problem but you might check just to eliminate it.
He noticed one day when changing the belts that the crankshaft pulley had some wobble to it. All the bolts were
tight on the pulley and the main bolt in center of the crank was tight too, but you could move the pulley and crank end around.
It was broke just inside the front main journal and the break was irregular enough that it still drove the front of the shaft.
Hope that's not your problem but you might check just to eliminate it.
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From: mohave valley
what am i over looking
its not bad when its cold. but when it gets fully warmed up is when it starts doing it. at first i thought it might of been a flat camshaft lope. but i checked and there all good. i checked for a vacumn leak, but couldnt find one, so a ran a vacumn check and the vacumn is good and steady. like i said, it runs great and smooth. just shakes around 800-900 rpm. last thing i have to check is maybe a bad motor mount.
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