4.2L standard trans.

at exactly 53 mph to 75 i get a vibration, its not minor but not teeth jarring. only happens while foots on the gas pedal. happens in fourth and overdrive, just had intake manifold spacer replaced at dealershit. but it started doing this a few weeks before that was replaced, any ideas?

High gear/high speed vibration? Sounds like a U-joint or driveshaft balancing issue.

which u-joint typically goes out? now im just being lazy here

and as far as balancing goes on the drive shaft how would i go about fixing that?

It would sound more like a U-joint going than an unbalanced driveshaft. Just like an unbalanced tire, and unbalanced prop shouldn't vibrate only when the throttle gets mashed.

Check your engine and transmission mounts as well. If they are soft or cracked or broken, they need to be replaced.

^The engine/tranny mounts usually cause the shake/vibe at lower speeds, mostly at certain RPMs, and more frequently in lower gears... so if it only does it in 4th/at speed then I don't think so. My experience is based on a transversely mounted engine, but I assume it would be the same.

I'm with people on the U joint/shaft or other similar piece.

I second Rockos post. This doesn't mean I disagree entirely with anyone else's post, I just think you guys don't know how it feels like. I don't mean to throw acussations or anything like that, it's just from what you've said.

While Transmission and even engine mounts will produce slightly similar movements, there is absolutely no confusing the feeling of those and a worn universal joint, unbalanced shaft. The reason the "vibrating" (of the shaft, which gives it a lopey feeling because it's rotating instead of going back and forth) seems inconsistant is because of the way you feel it. The difference in time between rotations, or, rpm.

The most noticeable should be when the load it is under matches it's rpm. That doesn't sound like it makes a lick of sense to any of you motherlickers, but it's the best I can put it.

In example, you will feel it most when the shaft (not your engine / tacho. It is independant of that!!) is under low but some load, and equally low rpms. This doesn't mean it's actually wobbling any harder at these revolutions. It just seems like that because you can feel the independant revolutions of the rotation mass, instead of it wobbling at high revs where it feels like it's only wobbling a little bit. It's actually wobbling / vibrating to the same degree, just fast enough that the wobble is disguised.

...Except centripetal force has absolutely nothing to do with applied force to the driveshaft, unless it is severely distorting and somehow magically straightening itself back out when unloaded.

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