Alright, I've got a pretty serious vibration going on from about 60mph and faster. I recently installed a moser 9", UMI adjustable torque arm with the relocation bracket that locates the torque arm off the transmission, and poly motor and trans mounts. The pinion angle is set at -2 to -3 degress, I rebalanced the driveshaft as well as all 4 wheels. I just cant figure out what is causing this vibration. I know the engine and trans mounts as well as the torque arm relocation bracket are all going to cause more vibrations, but I am talking the car is fine from 0-60, then at 60 on I get this HORRENDOUS vibration that pretty much rattles your teeth out. I avoid driving on the freway now because I am afraid it is going to tear something up. Is there something I am missing? I sure hope so because I would really like to get this fixed... I have since reinstalled a stock rubber trans mount which made no difference at all, so I cant see it being a mount issue.

The only thing left that I can think of being wrong with it is the angle of the lower control arms. My car is lowered (DMS Springs Koni Shocks), and the lower control arms have a pretty bad angle going upward to the rear axle. I am going to have relocation brackets installed on thursday and I am going to have the shop that is installing them check everything. What else can be causing this vibration?

 

Rear end may not be assembled right

 

is it in the front or rear?
thats allot of pinion angle IMO.

 

The steering wheel does not shake at all, it feels like it is coming from the rear.

 

Check both angles, front and rear driveshaft angles
must be near equal or you will get a lot of driveline
vibration. Worse as absolute angles increase as well.
Trans pan should be parallel to pumpkin (TA flat) at
some particular load-point, the rest being compromises
about it. With hard linkage mounts (poly or rod) you
may not need as much pinion angle as you have dialed
in. Back it off (nose up) and see if it gets better. If it
gets better but starts to cost you hook, may want to
try shimming up the trans tail instead for the same
result to driveline angle difference, but not pinion.

Shims under the tail mount compensate for a down
pinion angle, shims between crossmember and body
will compensate for an up angle (not likely to need
that).

The 9" is a heavy piece and anything that "kicks" it
is going to bump the body more than before. I'd check
runout on both tires, see that there is no significant
wobble at the wheels (balanced for weight != perfect
roundness, axle not-bent, wheel not perfectly hub
centered and so on). Cinder block and a stick would
do for that, just look for min/max variation of a close
spacing as your "inidcator".

 

my best bet is the pinion angle

 

I got alot of vibration over 100 after my TA relocation and lowering. I was thinking about getting a adjustable TA and try messing with the pinion angle.

 

I just fixed the same problem on my car by adjusting my pinion angle. Thanks to the lastest edition of GM high tech.

 

The GM High tech with sams car on the front?? Is that columbus ohio you are from?

 

Thanks for all the advice, I'll work on it tonight and let you know how it goes.

 

i had the same problem with my moser 9 inch. 1 drive home from the track and it fell apart. on the way out it made a crazy vibration noise.check to see if you have play where the driveline and pinion meet. my pinion was falling out and killed the whole center section.

 

I did check that, everything is solid.

 

im having the same over 60 it gets real bad but under 60 is fine i hate it.

ive turned rotors, balanced tires, swaped out for differant rims and tires, new rear u joint

 

I have to check my tool box to see what car is on the cover. I am from Columbus Ohio,I think a few of us may come to Cincy to get some racing action this weekend or in a few weekends.

 

I will post this for everyone to read,this fixed my car!

I had a bad viberation over 60+,at 120 I thought my car was going to fly apart. I checked the tires,balance on the driveshaft,gears,bearings,u-joints,brakes etc. In the latest issue of GM hightech there is two articles about Madman suspension on a 9 sec LT1 car and a gear swap on a f body(get this book if you dont all ready have it!). I was setting my pinion angle incorrectly.


YOU WILL NEED A MAGNETIC ANGLE FINDER

1)I started by putting my car on a level drive on lift
2)I checked my engine angle(I found my engine was higher in the rear,due to my energy suspension trans mount. It had a 1/8" spacer that I removed to get the engine closer to being level)
3) I adjusted my panhard bar to center the rearend(be careful using the quarter panel in case the car has ever been wrecked).I think GM's tolerence was .5",mine is within 1/8"
4)I set the LCA's to angle from the rearend up to the body at 1.8*(I have relocation brackets b/c my car is lowered @ an inch) I would try to get them between 1.5 and 2 degrees
5)I measured the driveshaft angle it was -3* from the trans down to the rearend.
6)I measured the pinion angle from the tq arm bracket on my moser 9" and it was at 1*(nose down)
7) I took my -3*(DS angle)and subtracted 1*pinion angle and found I had -4*(-3*-1=-4*)
8) I adjusted my Spohn tq arm and moved my pinion angle to 0* and remeasured the driveshaft and it was at -2.5(angled down from the trans to the rearend). That gave me -2.5* of pinion angle and no more viberation! I have had the car at 130+ and smooth as new.


Anyone can feel free to add any steps,If you feel I missed anything. I would like to know if anyone else tries this.

 

Alright I was measuring angles tonight underneath the car and I set the pinion angle equal to the angle of the driveshaft. When I measured the angle of the transmission in relation to the driveshaft, the driveshaft is actually angled up towards the rear end from the transmission. I am going to shim the rear of the trans to try to get it at least level with the driveshaft if I cant get it so that the driveshaft is angled down to the rear axle. Would an upward angle from the transmission to the rear axle be a bad thing? I attached a picture of what it looks like. From what you are all explaining, the driveshaft should be angled downward to the rear axle and not upward? I will shim and we shall see.

 

Is the article called Mad ET's in the new GMhighTech. Has a Maroon TA pullin the wheels.

EDIT: Nevermind its prob the next article called (PUTTING YOUR REAR IN GEAR)

 

Its both of those articles,great reads!

 

Is your car lowered? How much? or was the back jacked up?

 

Car is lowered, DMS springs, I couldnt tell you exactly how much its lowered. I shimmed the transmission and put the poly mount back in because it was thicker and it actually got rid of most of my vibration. Still have some vibration tho. I think messing with the pinion angle some more will get rid of it. I do not have a lift I can use, so I just put the jack under the rear axle and jacked it up from there.