OK, I have searched but I can't find a post with similar issues so here goes..
I have an 88 IROC conv. with a Moser 9", a Tremec TKO, Spohn suspension stuff, etc.. When I first started on the car I installed a set of Eibach pros but didn't like the stance (the rear was too high) so I cut a coil out of the rears to set the car where I liked it. At that time I set the pinion angle at -1
but incorrectly as I measured the pinion against the driveshaft. Most recently I set the pinion at -1 against the crankshaft - this resulted in a big vibration at about 70 mph that continued (and got worse) when I put the trans in neutral. I figured that since I had recently installed the Moser that the car was severely out of alignment - not the case. What I did have was
extreme working angles on the driveshaft - 6 deg. in front and 5 deg in the rear. In addition, my driveshaft points UP from the trans tailshaft to the rear pinion. If I adjust the pinion to -5, I get driveshaft working angles of 2.5 and 1.5 front to rear. The vibration is greatly reduced.

I want to keep the stance - it looks great, so putting stock springs in the rear is not an option. I autoX the car and it handles like a go-kart. Shimming the rear of the trans up 1" at the rear mount is attractive but not currently possible in that the TKO has the large mounts for putting the shifter in the different positions. My plan is to modify the trans tunnel when I install the roll bar this winter. I will cut the necessary clearance in the trans tunnel and then reweld "a cap" - it should be invisible.

Has anyone else run into this problem? I want to avoid shooting myself in the foot as I only have a few toes left.

 

ive got a similar setup and ive noticed the same thing, the trans is just very tall and the tunnel is not high enough to get the propper angles with a lowered car, tunnel mods would probably help, but if you are using the stock center console i think it could cause issues

 

Thanks. I'll be doing this in a month or two, I really want the correct angles. I'm running fairly stiff suspension members and I really feel the driveshaft vibrations. I'll post pictures when I get into it.