My car is gonna shake itself to death...

Got my aluminum shaft and had the u-joint replaced with a spicer unit. I also had them balance the shaft as well. They confirmed that the shaft is not bent and that the yoke is good.

Now when travelling at highway speeds the vibration starts at 65-70mhp or so mph and gets progressively worse. The shifter shakes extremelly bad beyond this speed.

If I put the trans in neutral (5 speed) the vibration is still really bad until it slows to less than 70mph (120kph or so). The bearings in the 9bolt rear were just replaced in October 2002. The tranny has been professionaly rebuilt and I installed a new bushing in the tailshaft as well.

Oh, I have a prothane poly trans mount from spohn as well as torque arm mount..

I need opinions. I have a couple of guesses and am open to more...

1. Improper balance job - don't think it's this, these guys come highly recommended.
Also, the vibration is also there with my stock steel shaft - just MUCH less noticable. I'm guessing this is due to the steel shafts added weight.

2. Bent outputshaft in tranny/tranny problem
3. Wheel bearings (got this in the archives)-they are original.
4. Posi cone clutch-unit problem (also got this in the archives)

Help.

Thanks

 

Steve,
I'm experiencing similar problems with my car. The main difference is that I had a steel driveshaft and the vibration was very harsh at 70 mph. Now I have an aluminum one from an LS1 and the vibration starts at about 70 and get progressively worse with speed. I had swapped in 4.10s and a T56 when I noticed this problem. Although I had noticed vibrations before at higher speeds when I had 3.42s. But I guess that makes sense with the increase in driveline speed with the 4.10s.
I have replace the axle bearings already. I did notice that my driveshaft can move inside the tail of the transmission. I can wiggle it up and down about .040". I'm gonna try to change the tail housing bushing, but i'm not too optimistic since you said that didn't work for you. Sorry I couldn't be of more help but if I get anywhere I'll let you know.

 

Make sure your tires aren't out of round or flat spotted.

 

Thanks for the info Chris. I changed the bushing and it totally got rid of a 'whine' sound I'd get during periods of 'float' (not on the gas but not completely off it either) at highway speeds.

I heard someone actually mention that it may be the posi units. I have 3.45 9bolt.

I still don't think it is the rear either. I have a strong feeling it's the damn driveshaft and the balancing just wasn't done at high enough speeds...

 

Definitely isn't the tires. Mine are about 5 years old now (rears) and they are getting quite smooth in the middle of them - some areas more smooth than others but the vibration is definitely coming from the driveline directly under the seats. You can feel it right in the shifter pretty bad.

I don't know about your car but mine gets worse when I let off the gas completely at high speed. Maybe this is the key...


hmmm

 

My trans tends to whine under load. I'm not sure if the bushing will fix that. I would say that my vibration is slightly worse when I'm off the gas. I have run my car on jack stands with the wheels off, so I know that it is not the tires.
I've never heard of a posi unit causing a vibration, but I'm not too familiar with the 9-bolts. If you talk to driveshaft manufacturers they tend to say that OEM driveshafts aren't good at high speeds. My driveshaft has .014" of runout at the rear and .025" at the trans. I'm debating whether I should try a driveshaft from someone like Denny's Driveshaft or Island Empire. Not sure if I want to drop $350 for nothing.

 

one possiblity is the yoke on the rear end(the pinion yoke) is out of balance/off center, you may want to see if you can find a shop that can(or see if yours will) balance the shaft with the rear end yoke bolted to the driveshaft, this is not uncommon and a often overlooked problem