Odd vibration problems???

[Guest mattrp]

Ever since I performed the v8 conversion on my car I have had an odd vibration. It come through the shifter handle and can be felt through the floor of the car. It is stronger during acceleration, BUT, it occurs in a lesser way by simply revving the motor with the clutch pushed in, so a good portion of it is in the motor. I have only two ideas, because this motor before, and now after the rebuild still has it

 

1. The harmonic blancer/crank pulley are out of whack (the crank pulley wobbles a little, and I have an electric fan so that cant be the cause)

2. The tranny mount has tension on it becuase of a slight shift in the engine position during installation (just a little bit though, no huge pushing required to bolt it up or anything like that)

 

I know I still need to tie down my diff, and do the mustache bar mod, but the alignment is pretty good right now. I just really hate this vibration. Oh yeah, its worse when the car is hot, better on cold mornings.

 

Any ideas????

 

Matt

72 500Z

[SpeedRacer]

Some of it may may be your driveline angle. Stop over at Pete's web site http://alteredz.com/drivelinemods.htm and check out the info he has on this - it's really well documented and I think it will help.

 

The harmonic blancer/crank pulley not running true is a bad thing. Even if it not causing the vibration it will be effecting the engine and belt(s). Stock harmonic blancers can come apart at high revs and that is really bad. They're not cheap but you might want to consider a fluid damper from some like Summit Racing http://www.summitracing.com/

[pparaska]

If you have the vibration with the car sitting still with it out of gear, I'd go for the flywheel and/or harmonic balancer. I had a girlfriend in highschool that had a SBC from a junkyard put in their 68 327 Camaro once. Had a vibration all the time. Turns out the old redneck mechanic had gotten a 400 and didn't put a 400 flywheel on it and used the one from the 327. Of course, he wouldn't believe me (the mechanic) when I showed him books that pointed out that the engine had a 400 harmonic balancer on it. I was just some dumb highschool kid, so what could I know. Yes, I ended up getting a new 400 flywheel for it and installing it. Vibration was gone.

[awd92gsx]

See? I can use the search function

 

I was going to post that I have a strange engine vibration when I decided to check out the search feature...I notice the same symptom: the crank pulley wobbles a little

 

I thought the 350 was internally balanced and didn't think it would cause a vibration, but, I suppose if it's out of balance itself it could huh?

[MikeJTR]

Because you feel the vibrations when the car is not moving, the vibrations are probably not related to driveshaft angles.

Often, vibrations are caused by using stiff transmission mounts, such as the polyurethane transmission mounts. These send normal vibrations through the unibody. It's often best to use the factory transmission mounts because most aftermarket replacement rubber mounts are stiffer than stock.

Also, the exhaust system can sometimes cause vibrations. It helps to supprt the exhaust pipes near the rear of the transmission mounts. If you look at many full-size cars, a bracket runs from the back of the transmission to the exhaust system.

[awd92gsx]

The part number that JTR recommends is no longer available through GM (or so my Wholesale GM guy tells me, so I had no choice but to go aftermarket on the mounts.

[Guest 305240]

I've got a 350 in my Jag. The engine was vibrating a little, then I noticed the harmonic balancer was wobbling. The rubber in the damper was letting it seperate. I had visions of it comming loose and destroying a whole bunch of stuff. I replaced it with a good JY one and the vibration is gone.