NubWS6

All, I have a vibration in my drivetrain that I just can’t seem to chase down. The car has been lowered 1.5 inches and I thought my vibration was a combination of bad pinion angle and aluminum driveshaft that the previous owner put in. So I got a custom steel shaft made and bought the BMR tranny mount with adjustable torque arm mount and the BMR torque arm with the adjustable trunions on the rear. Finally got my pinion angle corrected from -5 to -2. And the vibration went from a harmonic vibration, meaning it got worse then better with a harmonic rotational frequency. Now it just vibrates all the time in a steady vibration at 37 Mph and again at 47mph. So far I have replaced my tranny with a performabuilt stage 2, torque converter, all wheel bearing, all suspension bushings, front and rear shocks, front and rear springs, driveshaft, and u joints.

i am thinking that since it went from rotational harmonic vibration to a straight vibration that the pinion angle was part of it but does anyone have any ideas? I am thinking of changing the front slip yolk and tail shaft bushing in the tranny. Anyone know how many splines are in the slip yolk? Mine has one of those weights/balancer on it and someone suggested that the rubber in that was bad? And this point I have around 6k replacing **** and I can’t figure it out...I have had 2 speed shops look at it, the local drag racer guy down the street from me and I can’t tell you how many “racer” friends and I am at the end of my rope.

thanks in advance for any thoughts

vorteciroc

What type of vehicle? I am guessing a 1993-2002 F-body...
What model transmission is being used? 4L60E... Solid/ Poly/ or Rubber mount? ...27 spline output-shaft the 80 series units have 32 splines.
What type of rear suspension? Torque arm? Are the lower control arms parallel to the ground or on an angle from lowering the car???
What type of differential? 10 Bolt? Does the rear suspension have any Heim-Joint/ Rod-End type components instead of Poly or Rubber?
Please give us both of the drive-shaft angles... one at the transmission and one at the differential. New Universal joints?
Where the Drive-Shaft angles set with the vehicle FLAT (IE on a frame-machine) ? How were the angles established?
Is the new Drive-Shaft balanced? Did you say the transmission end yolk has a balancing weight on it from the old drive-shaft?
Does your vehicle have any wheel-hop problems/ worn-out rear suspension shocks and/ or springs? When does the vibration occur?

NubWS6

Hmm, and here I thought I gave good data.

It is a 2001 Pontiac Firebird WS.6 with a 4L60E from Performabuilt Stage 2 with a 1200 rpm converter (manufacturer escapes me at the moment) with the BMR Torque Arm Relocation Cross Member and a poly bushing.
It is the stock 10 bolt rear carrier with 3.73 gears and the BMR adjustable torque arm. It has the non adjustable BMR rear control arms and non adjustable BMR panhard bar with poly bushings.
I dont have the angles of the driveshaft, I had those corrected by the local speed shop and they tell me they are at -2 per the factory specs, and it is a new steel shaft made and balanced by Fleet Pride here in Rochester, NY, with new universal joints and yes it has a balancing weight on the slip yolk end on it that was stock.
I believe the driveshaft angle was set on just a standard drive on lift, not on a frame machine.
There is no wheel hop and all the suspension parts have been replaced, including all 4 springs (BMR lowering springs), front struts (KYB Adjustable), rear shocks (KYB Adjustable), ball joints, outer rear axle bearings, tie rod ends, all new poly a-frame bushings, all front & rear sway bar bushings and pins, bump stops, etc...as i stated i have spent around 6k replacing suspension parts and every other rotating part on the car. including new tires (Nitto) and rims (18x9 front and rear).

At this point the only 3 items I haven't replaced are the factory slip yolk and the transmission tail shaft bushing (both will be done in the next 2 weeks) and the rear end (carrier bearings and pinion bearing) but there is zero noise from the rear end.

MaroonMonsterLS1

Somebody has to be that guy...tire balance

Jays_SSZ28

iTrader: (2)

How did they adjust the pinion angle on a car that has no adjustable suspension parts?

I'm surprised at how many people don't know how and where to measure the pinion angle. Most people adjust the u-joint working angle and think they're adjusting pinion angle.

vorteciroc

His torque arm (Single upper control arm) is adjustable for setting pinion angle.

performabuilt

iTrader: (25)

I do not know the material of the mounts you have however in my own experience if the are poly urethan you are bound to have some degree of vibration sometimes it real bad other times not so much, GM made mushy expensive liquid filled mounts for good reason. Just my thoughts ,

Jays_SSZ28

iTrader: (2)

I missed that part. Would still surprise me if they did it properly.

NubWS6

All suspension bushings are Energy Suspension Parts Polyurethane.

And I wouldn't be surprised if they didn't set it correctly either cause the guy said something about having to shim the tailshaft of the transmission...and your probably right all they set was the driveshaft working angles, not the actual angle of the rear end. I learned something as well today. I always assumed pinion angle and drive shaft working angle were the same...they are not.

I guess the only way to do something right is to do it yourself so I will work on checking all these angles myself.

MaroonMonsterLS1

Pinion angle is a direct reference to the driveshaft.
The differential (and the pinion obviously) will try to rotate UP when power is applied.
When power is applied, you want to have the driveshaft straight with the differential.
That's why you set the relative angle between driveshaft and pinion at -2 or -3 degrees...because that's how much the pinion will rotate up.

NubWS6

Ok, this might be a dumb question, but can you do this without a frame machine? How do you get the car level? There is no spot that I can think of to put a level on... Or does it just have to be level relative to its stance on the ground? So I can put blocks under the wheels and let it back down to sit on the blocks to load the suspension and still allow me room to get under it?? My garage has a 3" slope rear to front for drainage, do I have to take that into account as well? or does it not really matter cause your figuring all the angles relative to each other so the slope doesn't really matter?

Jays_SSZ28

iTrader: (2)

It doesn't need to be level and you don't need a frame machine. The suspension needs to be loaded.
Each angle is relative to the others as you said.

vorteciroc

If you have not set the driveshaft angles before, or are simply inexperienced...

I would recommend having the vehicle flat, so that you will have an easier time reading the magnetic angle finder and not make a mistake.

Otherwise as stated... as long as the vehicle weight is on the suspension, you are good to go.

MaroonMonsterLS1

I mean...ideally you would have the car level. weight distribution and whatnot...but I wouldn't want to set up the car with it on a big 'ol hill haha
The easiest way is a 4 post lift.
next would be to drive the front up onto some cheap ramps and jack up the rear...make sure you set the rear end down on the jackstands so the axle is resting on them...not the chassis.