This has been buggin me since I first started driving the car.
At first, I thought I had a u-joint angle issue that was causing this.
(and I still might) vibration @ about 70mph. Put in an adjustable upper control arm to change the pinion angle a bit, but vibration is still there.
At 70 in 5th gear (vibration @ speed --not RPM) I grab the shifter at the bottom, near the boot----no vibes at all
. Now I'm thinking tires.
So something else is buggin me as well. I have not been able to get even 10" of vacuum at idle, since day one of installing this engine. (GMPP 454 HO). And I have read from other people that they are getting up to 20" on this same motor. I cannot find any leaks on the engine on the outside---perhaps there is one on the inside??
Would this make the car "buck" at idle in gear??? This thing has a violent lurching at idle. Once power is applied it goes away. None of my other manual trannys have ever done this to this extreme. Even the 79 chev with a 454 moves pretty smooth even in granny at idle.
Initial timing is at about 8*, the engine idles smoothly enough when just hangin' out, but as soon as the clutch is engaged, it is just like your 10 yr old is trying to get your attention by jerking the rocking chair.
Could a bad joint angle cause this???? Or is there something else a bit skewed somewhere. The car drives okay, and is not high strung at all in traffic----except when I want to idle in gear.