I've got a Spohn TQ arm, Moser 12 bolt, Spohn DS. Rear tires are new. Vibration wise everything seems fine until about 65mph and then I get some nasty vibration. It seems to get a lot better under WOT. When I used the angle finder the DS was about 0.5 and the rear mounting area 1.5 so this should give me a pinion angle of -1.0 right? I really need to get rid of this vibration if anyone has any ideas that would be great.

 

If you are with in 1 degree your phasing should be good. I know you have new tires but I would get them re-balanced.

 

This is one of the main reasons I got new tires. I made sure they balanced them when they were installed. I also use a tq wrench when I put the lugs on and everything. I installed the Moser 12 bolt, Spohn sway bar, Spohn drive shaft, Spohn LCA relocation brackets basically all at the same time and I think that is when my vibration problem started. Ofcourse I went from 3.42 gears to 3.90 and that could've made a previous problem worse. After a while of running like this one of my tq arm bolts came out and the stock tq arm bent. So now I've got an adjustable Spohn tq arm (none trans mount) and new rear tires balanced hoping that would fix the problem and it doesn't seem to have. The main thing I am wondering is does it seem like my pinion angle numbers make sense and did I do the math right? DS = 0.5, TQ ARM Mount Location = 1.5, so 0.5-1.5 = -1.0 and that is where it should be right? I also just installed new rear shocks and it didn't make a difference not that I expected it would.

 

I know you had the Spohn driveshaft installed but this sounds like a DS problem.
My stocker would vibrate at around those speeds until I replaced the DS with a 1LE piece....it may or may not be the problem but you might check out the driveshaft. I would think spohn would have it balanced right on but its something to check out.

 

Ya I know it was the first thing I kind of suspected but I called Spohn and they told me it couldn't be the driveshaft and that it was computer balanced. I still think it could be my pinion angle.

 

Your pinion angle is definitely either -1 or +1 degree, we can't tell from the info you've give. If the angle of the DS to pinion makes a \/ downward, then you're set, at -1. Otherwise, you're at +1. Go ahead and set the angle to zero, if you just want to elliminate that as a problem.

Is the 12-bolt new, or used?

Dave

 

I got it new. Moser 12 bolt 3 chnl abs, c-clip elimination, 33 spline, 3.90 gear. I will try to give more info on my pinion angle settings. I put the angle finder on the bottom of the driveshaft and got 0.5, I then put the angle finder on the bottom of the torque arm flat part right where it mounts to the Moser rear with the 2 bottom bolts as that runs parallel with the pinion. When I took the readings and set it all 4 wheels were on a concret block that was the same size.

 

Another thing I just want to add since I just tried it an hour or so ago but when I take the car out of gear at speed the vibration stays the same or possibly even becomes a little worse.

 

Walk thru this http://www.go-fast.org/z28/pinionangle.html for me and that'll tell what the angle is.

I have heard of the odd rear axle just having a vibration from parts being out of tolerance. Not sure I've heard of any issue with Moser though. I've run my car up on jack stands, with the rear wheels removed, to make sure it wasn't a wheel problem. You could try that, just be careful...

Dave

 

When you did that did you just let the rear suspension hang down or did you put the jackstands under the axle tubes or something?

 

Jackstands under the axle tubes....

 

my guess is something wrong with the driveshaft

 

Well guys I am still fighting this issue and I want to get it fixed before this summer. I've messed with the pinion angle up and down and it can't be that. I've taken the driveshaft to a local shop and had them re-balance it and that did nothing. I've made sure the wheels are centered front to back, I am pretty sure they are centered side to side with an adjustable panhard but I need to find a good way to measure that if anyone has any ideas on the best way to do that let me know please. At this point the only things left I can think of to check is the driveshaft length, maybe it is too long and I still need to check that for sure with the rear at drive height but I doubt that is it I'm sure Spohn knows what length I needed. The only other thing I can think of is something in the rear end. Moser sets the backlash and I never checked it and I don't really know anything about rear end internals so maybe someone can tell me if this could cause a serious vibration?? If it can I'll take it to a shop and have that checked ASAP. If anyone can give me some ideas that'd be great, I've been fighting this problem for YEARS now and am about to give in and take it to a shop and we all know how hit and miss that can go with a vibration issue but I really want it fixed before the summer! Let me go over what I can be fairly sure it isn't at this point real quick as they've been checked and are suposedly OK. rims/tires are balanced/new, driveshaft was rebalanced and no change, pinion angle has been changed over and over and doesn't do much to the vibration, tires measure equal front to back of car, I think housing is fairly centered side to side. Beyond these things I'd like ideas. Also there seems to be no play where the driveshaft goes into tranny, I can a mechanic check that and he said it seemed fine. Please help

 

try this as someone else suggested to me

put the rear of the car on jackstands
remove the rear wheels
remove the rear coil springs
put a jack under the center of the rear and lift the rear end until you hit the bumpstops.
you want to pay close attention to the DS as if it's too long it will bottom out in the tranny as you lift the rear. If it's starts to bottom out, stop jacking and take new measurements for the DS to be shortened.

I find it funny that your problem sounds exactly as what I'm dealing with except mine is a moser 9in and my DS (1LE) appears to be too short. I'm guessing if a DS is too long or short you get the same vibrations???

 

Maybe your rotors are out of balance..