I recently put a new Moser 9" in my 87 firebird and I thought everything bolted up fine until I went to tighten things up (front and rear up on jack stands). I went to jack up the rear end and get the suspension in the compressed position so I could tighten all the bolts. This is when I found that the rear end of the car came off the jack stands before the suspension fully compresses and the car has about 5" of wheel well clearance? Dont get me wrong the suspension moves just not as much as it should.

I have all after market parts:
hotckis control arms
hotckis panhard bar
hotckis sway bar
hotckis rear springs
spohn cross member mounted torque arm
spohn sway bar instalation kit for 3" axle tubes
spohn lower control arm relocation brackets
kyb agx shocks

The car sat fine with the old GM 10 bolt rear end and this set up. Due to the new 9" it seems that the torque arm is more forward in the car on the shackel spohn uses on the tranny crossmember but that does not effect anything.

I have unbolted one thing at a time and tried jacking up the rear end to try to find if a part is binding:
torque arm
shocks
panhard bar
put control arms back to the original location

With each part unbolted one at a time I had the same result, car sitting like a truck. The only time the suspension fully compressed was when I took the springs out? I also tries two different sets of springs hotchkis and OEM, both had the same result. Also when I put the car back on the ground the car sat normal?? At this time I thought that may be I was caused by not having a sway bar hooked up yet, allowing the rear to not equaly raise on each side causing some sort of bind. But I just installed spohns kit to put my sway bar on the 9" and still the same result?

What do you guys think? Is there something wrong here? I know that my suspension always compressed with a jack on the last rear end. Any ideas, I am so confussed.

I forgot one thing. I also checked to make sure that the drive shaft was not to long and bottoming out on the output shaft but what I found is also confussing. When the suspension is hanging the drive shaft is deepest into the tranny. When I jack up the rear end the drive shaft pulls away from the tranny. Is this correct or is this part of my problem?

And the pinion angle is at -1

 

I had kinda the same problem but I dont think I had a 5" rise. Was more like 3". The only thing I could figure out was that the spring perches on the new housing are just a bit taller from the axle centerline, combined with the larger diameter axle tube which helped compound the problem. My fix? I removed the upper spring isolaters and cut 3/4 of a coil from the top of the spring. Then I slid some heater hose over the top spring coil. It went back to the ride height I had it at with the stock 10 bolt. Hope this helps.

Mec

 

When you have the car up on 4 jackstands the front hangs over the stands like a kid on the other end of a teeter totter making the rear of the car lighter than if the front wheels were on the ground.
Just bolt it up, torque everything and put it on the ground. Take it for a test drive and when you get back look at the stance. It should be normal.

 

AL SS590 M6,

I have lowered my car of all 4 jack stands and it settled to normal ride height like you said . But I still thought something was wrong or binding my 10 bolt never did this. I guess I am over thinking this one.