Bad vibration when not under thrust
Thread Starter
Instructor
Joined: Nov 2012
Posts: 114
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From: KINGSPORT TENNESSEE
Bad vibration when not under thrust
1972 468 medium to large cam 4 speed 3.55 rear. Driveline is tight! Runs like a sewing machineunder thrust. When car catches up with engine, or i back off gas, feels like an 8 lb sledge beating against the differential. Car surges bad. Replaced motor mounts, got worse. Replaced differential with 3,000 mile unit, no change, less than 1/2" playin driveline. Cam too big for 4-speed?? Or what? Help! WAS A LITTLE BETTER WHEN CARB WAS LEANER AND TIMING WAS LESS. IDLE A 800 NOW,BEFORE 1,000. QUICKFUEL SS 850 CARB.
Last edited by VETTEWITHLEGS; Jun 8, 2015 at 12:40 AM.
Melting Slicks
Joined: Apr 2009
Posts: 2,632
Likes: 112
From: Great Plains Iowa
The 454's have an externally balanced vibration damper and flexplate so if you're using 427" parts it WILL vibrate something awful. And are you sure your transmission mount isn't broken? If in doubt jack up on the transmission and if it lifts off the crossmember it IS broken.
Thread Starter
Instructor
Joined: Nov 2012
Posts: 114
Likes: 0
From: KINGSPORT TENNESSEE
Replaceddiff chunck with new (3kmile) unit. No slack anywhere. Surgegotmbetter but not gone. Everything points to a cam too big for 4 speed with my gears. Old - 3.55 new 3.70 need @ 4.11 or 4.56. Or just change cam. Power band seems to start at 2500 rpm's.
