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hi folks,my 63coupe(300hp 4spd.)has a moderate to severe vibration from 35 mph and up,new u joints,driveshaft hi-speed balanced, ran it on a hoist and everything seems to run true,installed a used diff.assem.as it seemed to feel like a pinion growl vibration.At70mph it is a steady dronevibration and also shows up more under hard acceleration.the corvette tech suggested that the rear spring is weak and halfshaft angles are going up to far resulting in the wrong u joint- shaft geometry, causing vibration when car squats down under load and at higher speeds,any advice on this theory or other possible causes? thanks........ian
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Re: 63 vibration
Ian -
Vibration that is more severe under hard acceleration is often caused by worn-out bushings or a loose bolt where the front differential mounting bracket attaches to the frame crossmember. You might also check the transmission mount to see if it has separated. -
Re: 63 vibration
I once had a bad vibration when one of the segments of my clutch decided to leave it's designed position.
ArtComment
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Re: 63 vibration
all the bushings,clutch etc.are new(frame off)but that doesn't mean there isn't a problem.......i'll keep looking.......ianComment
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Re: 63 vibration
Mine was new also, had maybe 500 miles on it!!!
ArtComment
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Re: 63 vibration
Ian:
Will your car vibrate standing still and revving the engine? If it won't, you can rule out everything forward of, and including. the clutch. If it vibrates, I would first look at the fan blade. A bent blade will make a droning vibration. Check by disconnecting the appropriate belt. A clutch might make a heavier vibration as opposed to a buzzing vibration. If the engine was rebuilt with new pistions, was it balanced before re-assembly. Many aftermarket pistons are far enough off on weight to upset engine balance.
Your problem actually sounds more like an exhaust system grounded. Engine roll on acceleration could ground a pipe harder, making the vibration worse.
I don't think it's your half-shaft angles. You could shim you rear spring with washers at the spring bolt about an inch or inch and a half to check this out if you like. If you ran the drivetrain on a hoist at the suspect speed, wouldn't this problem show up with the axles hanging in air. Wouldn't rebound angle of the joints be close to the jounce angle?
Is it possible that whoever put in the half shaft joints that they damaged the axle flanges. It's easy to do. This could cause binding in the joints.
Maybe there's something here you can use.
MikeComment
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Re: 63 front spring
Check this area closely. Are you using stock rubber cushions at the differential nose? ...I've heard that some aftermarket poly cushions are too thin and can cause this vibration even when new, by allowing the U-joint trunnion to contact the fiberglass or the differnetial-mounted bracket to touch the frame. It's also possible that the holes in the differential-mounted bracket are elongated, allowing the bracket to be slightly off the correct angle even though the bracket is now tight.Comment
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Re: 63 vibration
good ideas to check,my engine was in fact totally balanced including clutch,i found the fan clutch causing some vibration earlier in my checks,i agree i don't think its the halfshaft angle but i am going to double up on the spring cushions for the time it takes to try this .the front engine mounts also might be suspect as they were of offshore origin!thanks for your ideas........ianComment
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Re: 63 vibration
My SWC had a driveline vibration that drove me batty for years- all new u-joints, motor and trans mounts, every new rubber bushing in the suspension, overhaul the trailing arms, balance the driveshafts, overhaul the trans and diff- no expense left unspent. The final fix was to put a thicker pinion snubber rubber in to change the pinion angle slightly. Man, it's as smooth as silk now! Mine is SN 4037, built Nov '62. When was yours built? I know an old guy that was a Chevy tech in '63 and he says that was a common problem on passenger cars, too, in that era.Comment
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