I have a small vibration in my car between 60-65. I just changed wheels but its still there. its in the steering wheel, and can feel it in my right foot. Here is what i have. 39 ford mustang 2 front 8 in ford rear with parallel leafs. if you can follow my description. The car is raised in the rear on jackstands. trans is 1deg down, pointing down toward the rear. driveshaft is 6 deg up, pointing up toward the rear. rear pinion is 3 deg down, pointing down toward the front of the car. I hope this all makes since!!!!!
Is the driveshaft in-phase (spiders acting 90 degrees from each other)? Has it been balanced? Start with the easy stuff.
I had it shortened by a driveshaft shop and i believe they did balance it. and the spiders are in phase. my rear is 4 deg off from where it should be but dont know if thats enough to hurt
the pinion should be tilted downward about 3 to 5 degrees with the car at ride height ...this allows the pinion to raise when under acceleration. the pinion should never go over a straight line with the drive shaft. Is the shaft to long? As the shaft raises it could be bottoming out in the transmission.
the drive shaft doesnt look too long. does the rear pinion angle need to be the same angle as the transmission?
from what i understand trans points down x # of degrees the pinion points up same # degrees. thats how i set mine up seems to be ok.
Up or down at the pinion...needs to cancel out what is degreed at the trans...if trans is @ 3 degrees then pinion needs 3 degrees UP or DOWN within a couple degrees either way...yours should be OK on the plane you checked...is the engine trans straight in the frame and rear axle square in frame? I need to add...AT RIDE HEIGHT....you mentioned you're up on stands in the rear.....and am guessing the stands are under the axle?
rdr, yes it is under the axle. everthing is square. i have driven this car 14k miles like it is. and the vibration isnt huge, but it is enough to bug me at highway speed. mine checked 4 degrees out. I know its not really bad but neither is the vibration. just anoying.
run it in the air with the wheels off. It still could be your wheels. A drivelive vibration usually has a higher frequency and a wheel vibration.
http://www.iedls.com/Education-Zone.asp http://www.vibratesoftware.com/html_help/html/Diagnosis/Propshaft/Propshaft_Angles.htm
Had my front tires re-balanced. again, and still have vibration. I re angled my rear axle per steve-cooks link to empire. That should all be good. I raised the car up on jack stands( at ride height) and ran it up to 80mph. everything seems smooth with the rear of the car. I am trying another set of fronts in a few days to eliminate a tire issue. or to prove one.
Driveshaft angle means nothing, the driveshaft just joins the trans to the rear...its angle means absolutely nothing. The important angles are the trans and the rear end. If the trans is 3 degrees down then the rearend must be three degrees UP not down. If you were to draw an imaginary line through the trans, and an imaginary line through the rearend, the lines need to be parallel to each other. The only exception to this rule is when you need to compensate for lear spring flex or wrap up when the car is under power. The rearend should be tilted down a couple of degrees IN RELATION TO THE TRANS. Lets pretend the angle of the trans is 3 degrees down ... now set the rear so the imaginary lines are parallel which means the rear is three degrees UP.... now from the 3 degrees UP you can drop the rear 2 degrees down. End result is the trans ends up 3 degrees down the rear ends up 1 degree up but under power the leaf springs flex and allow the rear to move up 2 degrees or so which brings the rearend back to the 3 degrees up so the planes (or imaginary lines) are equal as they should be. Wow, this message even confuses me and I wrote it. Hope this helps. I stand by my comment regarding driveshaft angle meaning nothing...in cases of street rods it means nothing, in the case of a 4x4 pickup that is being raised a large amount, the driveshaft angle does become a problem because of the extreme angle in relation to the trans and the rearend. If your trans is 1 degree down then you rear should be 1 degree up for the trans and rear to be on the same plane. You now need to drop the angle of your rear down 2 degrees from plane. Meaning your rear should be 1 down and it should come up to 1 up when power is being applied. Sounds to me like you are out 2 degrees...easily fixed using shims. One other thing you might want to look into, I have found that factory GM rally wheels can be horribly out of round (don't know what you are running, just using this as an example). I mean out of round up and down and out of round wobble. Might want to check you wheels for runout if you are running steel wheels. This can also happen when running aluminum wheels that are two piece and welded together (as opposed to one piece cast aluminum wheels that are machined on a lathe). Good luck
I think it has a sense. I am having hard time also the same as your problem. Specially when I am the trans, it suddenly down.
Just to add to the stew! It's often recommended, to have u-joints flexing thru ~3 degrees, just to keep from brinnelling the same-spot on their yoke pins, via needle bearing contact. Said to help insure that grease is pumped around too. Helps to imagine a vertical plane, where pinion offset lives, in addition to the horizontal plane, where his angles are depicted.
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