Why is my driveshaft hitting my gas tank??

[RenaissanceMan]

I'm either an idiot and missing something really obvious, or have an issue that I haven't completely figured out yet. about a week ago, I was getting a vibration from underneath the car at wot. Took a look underneath and discovered that the driveshaft was rubbing the bottom of the gas tank when the car was under load. The subframe bushings had never been changed out before, so I assumed that was the issue. I put in new subframe bushings, but the problem is still there. What the heck could be going on? The csb appears to be intact, and furthermore it is brand-new along with the entire drive shaft assembly. Here's a picture of my car suspended on jack stands underneath the subframe. Should I have this much of a gap from the bottom of the bushing to the bolt? I also posted a picture showing how close the drive shaft is to the gas tank. This doesn't look right to me.

[325isman]

Did you have drive shaft balanced before you installed it?

[RenaissanceMan]

Did you have drive shaft balanced before you installed it?

Yes, sure did.

[e30sh]

Did your problem start with the "brand new driveshaft" There is a little bit of offset built into the CSB. Was it installed backwards?

How do the motor mounts / tranny mounts look...could be a misalignment or even a bent driveshaft.

[RenaissanceMan]

Did your problem start with the "brand new driveshaft" There is a little bit of offset built into the CSB. Was it installed backwards?

How do the motor mounts / tranny mounts look...could be a misalignment or even a bent driveshaft.

Motor mounts and trans mounts look great. Car has been doing great since completing my S52 swap a couple months ago, and then the issue just started last week. The new driveshaft came pre-assembled with CSB and balanced from Driveline Service of Texas, and was installed at the same time as the S52, diff, and trans. Wasn't having any problems until now. I've been under the car trying to figure out if something is loose or failing, but am still drawing a blank. Everything is silky smooth until I floor the gas pedal and then I'm getting this somewhat violent sounding vibration that feels like it's coming from underneath the back seat...

[e30sh]

Have the 4 upper holes in the subframe where the diff mounts been slotted by chance?

There's a good write up on here somewhere about using muliple string bobs and a straight edge to verify drivetrain alignment.

[e30davie]

Im pretty sure the centre support bearing bracket can go on both ways, but only one way is correct as the bolts are offset from the centre of the shaft. i reckon if you got that wrong and bolted it up your driveshaft would not be straight and it might hit on things.