Lethaldosage423

Some time this year i am going to be pulling the trigger and purchasing the Air ride air bag system from American Muscle.
I was going to get coilovers but the roads here are rough and my driveway has a nasty curb. Air bags just seem like the better option, i can run it at a good height while driving and air up to get into my driveway ect.. I am probably never going to track it. (maybe occasionally at the drag strip but no full tracks)

My concern now is the pinion angle. A few months ago i purchased a Whiteline upper control arm from AM. installed it per the instructions (I'm a mechanic btw) and every time i got on the freeway i had an unbearably annoying whine coming from the diff.

I have the TORSEN 3:73 rear end and I'm told its kind of noisy to begin with. I ended up putting the stock arm back on. Since I've had the car (Brand new) I've always had a faint whine at 70+ mph cruising, it goes away as soon as i step on it. I'm told this is normal for the diff but as soon as i installed the whiteline arm, the noise was much louder and it drove me crazy for the 100 miles i had it on.
i wondered if it was due to the harder bushings causing more noise transfer. but i was always concerned about the pinion angle. I installed it on a drive on lift so the rear axle had the weight of the vehicle on it.

So with the bags ill be getting the pan hard bar to center the axle, lower control arm relocation brackets, and adjustable lower control arms. and id like to put my whiteline uca back on.

my concern is setting up the pinion angle. If i install the arms with the car in the air, tighten the bolts to barley snug, put the car straight on the drive on lift and tighten everything to the specified torque, will my angle be correct?

(I understand that all the angles will change if i air up/down. i plan to set the bags to daily driver height and torque everything then)
will my pinion angle be correct if i do this or will i need to do some measuring and math?

I appreciate any help.
-Chris

UPRSharad

How did American Muscle suggest to adjust it? I'm sure their techs will have an opinion.

I daily drive my 2011 5.0 on full UPR Suspension and Air Lift Performance bags. I set my pinion angle at my normal drive height, and that way it is ideal 99.9% of the time. Pinion angle is less critical while creeping over speed bumps or aired out in a parking lot.

Norm Peterson

If the pinion angle is far enough off, you'll get a fairly heavy vibration. Been there.

Your noise - gear whine in particular - is a bushing issue. Firmer bushings will transmit more of however much noise is present in the diff, and the UCA attaches more directly to where this noise is generated than the LCAs do (the tube to pumpkin joints are probably good for a little isolation and the axle tubes probably do not "sing" at the same frequencies that the pumpkin casting does).

I have no idea about Torsens and noise, though with a few more gears it seems like there might be more if the two rear tires aren't turning at precisely identical rpms. Did the noise change if you drove along and slowly swept the steering from left to right and back? At some point the wheel rpms should match exactly and none of the helix gears should be turning.


Norm

jpplaw

Agree with the above. Harder bushings and anything tubular will amplify and transmit noise. Pinion angle being off will cause horrible vibration.

S stang

Adjustable uper controll arm if set right should not be noises if done right

Norm Peterson

Firm bushings will still transmit more gear noise even if you get the setting perfect.


Norm

JFitz

Norm, perhaps you know this - I'm lowering about 1.75/1.5 inches (rear/front). Do I need to adjust pinion angle?

I guess my question is...how low is too low?

Norm Peterson

No real idea since I'm not lowered and don't have much interest in drag racing (where people seem to be excessively concerned with pinion angle settings), and it sort of depends on whether you're still running the OE LCAs an UCA or if you've swapped any of them out for something with firmer bushings or rod ends. Firmer control arm ends do not require as much PA because they will deform less under acceleration loads, which is what the PA setting is intended to accommodate in the first place.

Too low without correcting PA will give you a heavy vibration, this much I do know from a different car (also a link-type suspension, hence the side view geometry was generally similar to the S197) that would throw that vibration at me if there was too much passenger weight in the back seat but which was stock-smooth otherwise. Car was lowered only minimally, maybe half an inch, and the OE LCAs were fitted with poly/poly bushings (appropriately tweaked to minimize the amount of "bind" in roll).


Norm

JFitz

OK, well thanks for the info, as always.

moosestang

Does your shaftmasters have a CV joint or two U-joints? Pinion angle is much more critical when dealing with u-joints, at leas as far as vibration is concerned.