Sorry,but driveshaft angle DOES matter. It comes into the total called "working angle." It's more important on a lower car. If you tranny is down 2.5 in the back, and the car is lowered, the rear end will higher in the car, which means the driveshaft will have to be about level. So since the tranny goes down, and the driveshaft doesn't continue down at the same angle, you put more "working angle" in the u-joint. Exceeding working angle even if the angles are parallel. The aussie has excellent points.Axle run out is another good one that feels like driveshaft problems.The 69 we're building has a very low number on the tilt because of working angle. The faster the driveshaft turns, the less angle you want. 3.5 deg, I think the max is 4k drivesaft speed.

 

ya. you're right. i'm wrong. with a tailshaft of 2 down and DS of 2 down as well that u-joint is straight and the rear one is not. that has to vibrate.

but still, pinion needs to come up a bit

 

The drive shaft is a steel 3.5" i think,maybe 3". We bought it through American driveline, the only thing that puzzles me is that it only has weight tabs on one end of the DS. ALl other DS if looked at around the house has one on both ends. But getting the DS down to get balanced tommarrow, but they say they can only balance to 2400rpms, they said that is all anyone can balance it to, is that correct?

The car has a grab-a-track 5 leafspring in the rear, with track bars. SO i dont think much axle wrap is happening, plus the car is putting 584hp to the flywheel, and 540 tq.

cprstreetmachine you exactly correct about it getting above the trans, giving the DS a positive angle. Thats why i suggested the 9", giving the pinion a lower stance for adjustments.

 

i'm not sure about their balancer speed but there are balancers that run at actual speed. the harmonic thing is a calculation that the DS guys would know about even if they cant balance at high revs.

did you think about engine speed when the vibe starts and does it pass or get worse?

 

gold! see the second half on critical speed and see if any makes sense or exactly half critical speed matches the engine revs you experienced the problem at.

http://www.markwilliams.com/driveshafttech.aspx

 

Sorry, wasn't picking on you Kali. Just wanted to make it clear. Especially for guys doing swaps like T56 under a stock tunnel. You may be able to get the angles equal and opposite, but the working angle will be horrible, and can still vibrate.

Awesome link Aussie, thanx. Tagging that one,too.

 

One quik thing Kalli

You said that as a car accellerates the rear end will rotate down.. Are you sure? as the tires rotate forward the housing should rotate up! equal and opposite reaction to the forward movement of the tires.

 

The housing does rotate up...and yeah Kalli does know that

-Gun

 

CPR and Monster: no offense taken anyone. Didn't mean to sound snappy. I deserve to be slapped around for what I've said above :-)

 

No, didn't think that. Just didn't want you thinking I was picking on ya.