I'm trying to track down a nasty vibration I have in my 72. I've had this vibration since I finished the car and can't figure it out. Like most common vibrations, it's at 60mph and speed-related not engine-related. Faster than 60mph, it's fine. But right at 2800, especially upon deceleration, the vibration is nasty.
I've narrowed it down to the driveshaft/pinion angle. The rear end is stock and the u-joints are new. A local shop told me my u-joints were incorrect, causing the shakes. "Which others ones am I gonna use?"
The rear end is at 0º and the driveshaft is 5º. I've searched and heard a lot of differing opinions on what degree is best. Having the driveshaft balanced is an option, but I'd rather do that last.
taz3
14th-July-2007, 07:35 PM
You do see that loose bolt right!:D
supr78nova
14th-July-2007, 07:36 PM
I am assuming you took this picture before you started driving the car around and had this problem. If not, try tightening the lower bolt on the u-joint strap in the picture.
Bscman
14th-July-2007, 08:17 PM
The rear end is at 0º and the driveshaft is 5º. I've searched and heard a lot of differing opinions on what degree is best. Having the driveshaft balanced is an option, but I'd rather do that last.
What about the crank/trans...what angle is it at?
And as everyone else mentioned...tighten that bolt! IIRC, no more than 17ft lbs as over-tightening will distort the caps and screw things up. A little blue loctite is a good idea as well ;)
the FLYER
14th-July-2007, 09:06 PM
are those factory straps ???
if they're new you better confirm ya even have the correct ones. there are two different straps available if i'm not mistaken for a passenger car... a bigger unit for trucks. maybe my eyes are decieving me but that appears to be the wrong strap (for a different diameter bearing cap on the joint)
confirm the strap is correct, tighten and try it again... see what ya find ;)
teddisnoke
15th-July-2007, 02:17 AM
Heres another idea. Your driveshaft may not only be out of balance, but out of round. It does not take much. Have the driveshaft shop check the runout as well as balance. It could have a slight bend that will produce a vibration. Had a friend who discoverd this in his car after chasing alot of other things that turned out to not be the culprit.
FunkyNova66
15th-July-2007, 03:03 AM
Definately tighten up that u-bolt strap. Geezus....:eek:
johnnynogood
17th-July-2007, 01:44 AM
I'm pretty sure this is the correct u-joint retainer. I was unable to tighten it completely, but put some washers and got it snug.
The vibration continues!
Snugging the fit helped somewhat, but the I can't shake the shakes. Next culprit: driveshaft balance.
novaBRO
17th-July-2007, 01:53 AM
i had a 79 trans am that had a similiar problem. turned out to be a bent rim:eek: the vibration occured @ 75MPH and then dissapeared.
Bscman
17th-July-2007, 02:03 AM
I'm pretty sure this is the correct u-joint retainer. I was unable to tighten it completely, but put some washers and got it snug.
The vibration continues!
Snugging the fit helped somewhat, but the I can't shake the shakes. Next culprit: driveshaft balance.
If it's the correct strap for the U-Joint you shouldn't need to shim it with washers to get it to fit right.
I wouldn't try anything else until you get that issue squared away.
U-Joints are not 1 size fits all, there are a few different sizes out there...so it could still be an issue, and could be why that strap won't tighten down all the way.
Also, to ask again (maybe you missed it) your rear end is at 0* and driveshaft is sloping down at 5*, but what angle is the trans output shaft?
johnnynogood
17th-July-2007, 01:58 PM
One of the actual bolts that bolts into the rear end would mysteriously bottom-out, thus not allowing complete tightness. There must've been some dirt in the holes (I had to clean them out when I got the car). So that's why I had to put a couple washers between the bolt and retainer.
I checked a few different straps just in case and the ones I have, although not factory, were the only ones that registered for GM cars 67-up. There were ones for trucks, but they were way too big.
The transmission is at 0º from the pan. I wasn't sure of how to accurately measure from the tailshaft itself (TH-350). This may help, give-or-take a degree:
If it's the correct strap for the U-Joint you shouldn't need to shim it with washers to get it to fit right.
I wouldn't try anything else until you get that issue squared away.
U-Joints are not 1 size fits all, there are a few different sizes out there...so it could still be an issue, and could be why that strap won't tighten down all the way.
Also, to ask again (maybe you missed it) your rear end is at 0* and driveshaft is sloping down at 5*, but what angle is the trans output shaft?
I agree with Bscman. You can't tell anything with that strap like it is. Fix that first, then see what happens.