BMR Sales2

iTrader: (40)

It does sound like the pinion angle is too far negative with how you are explaining the issue. It makes it seem that when the pinion climbs under load (while accelerating) you are close to where the pinion angle wants to be but as soon you let off the gas and the pinion falls out of the range of what it wants. Basically you just need to bring the nose of the rear end up a little and you should be good. Do you remember how you came up with the pinion angle measurement? The driveshaft and the front of the rear end should meet up in the shape of a "V". Take the measurement off the rear of the driveshaft and bottom of the torque arm bracket and those two numbers added together should be in the -2 to -3 range.

Sam Strano

iTrader: (41)

I've been down this road before when someone swears the angle is "right" and they have a hellacious vibration. In fact I had to fix a car that showed up here one day having just left a shop that makes and installed adjustable torque arms in the Philly area (not central PA). The car vibrated like hell, I looked under the car and could see it had way too much nose down pinion angle. I tweaked it twice pulling a little more out each time. I didn't measure it because it was "measured" before and was a disaster that this guy stopped by my shop for me to rescue him.

You can have too much pinion angle and I submit you do. I had a 1997 GMC truck bone stock. Ate 3 rear axles, shook so badly a can of soda would come out of the cup holder. It was a mess. You know what fixed it? A shim under the trans mount to change the pinion angle. There are millions of those trucks around, had lots of friends with them, nobody had that issue. The truck wasn't lifted or anything, it was 100% bone stock down to the paper air filter. I happened to be talking to a tech friend of mine while in Denver CO (I'm from PA). He took it in and fixed it in 10 minutes after over year of warranty work, 3 rear axles, one of which was rebuilt twice, 2 driveshafts, different tires. And it was simply a little pinion angle.

2JAWZ

iTrader: (1)

Well as I said I will leave it to the pros. Tired of stressing with it. I figured I could handle it but,, I was wrong. I appreciate all the time and help for sure though.

jblankenship

iTrader: (5)

The angle of the driveshaft has nothing to do with driveline angle. The crank pulley and rear end yoke need to be opposing opposite parallel angles.

BMR Sales2

iTrader: (40)

Not a problem, if there is anything else we can ever help out with just let us know.

This is just another way to measure and get the correct pinion angle. You can also figure it out using the measurements of the driveshaft angle and the and angle of the rear end. Here is a link that Midwest Chassis has that explains it very well.

http://www.midwestchassis.com/upload...nion_angle.pdf

Cferrel4

My vibration does not rattle the car to death, doesn't matter if your accelerating, cruise or coasting. Just when the car hits around 60-65 mph you can hear and feel in the seat a rotational noise. I could make the same drive each day and it may or may not happen each time either.

The more I think about this, I think that the pinion angle might be ever so slightly off.

To date and for anyone else tuning in, I have 4 new struts, mounts and shocks, lowered the car 1.25", 4 new BFgoodrich supersport AS tires, pan hard bar, tubular lower control arms (older bushings had separated), new transmission mount, polyurethane torque arm mount.

I purchased a digital angle finder and am going to try and source an adjustable torque arm from a friend for trial & error. Going to have to get the car on a lift in the spring that I can drive it onto or an alignment machine where it can sit up higher so I can get underneath it easier to measure it while the vehicle is at ride height. My 2 post lift with its arms will not give me that benefit.

Alas, I must wait another 2 months before I get it out and to it. The salt is thick on roads and every car has become 2 tone from mid way down. Not going to do that to this firebird.

jblankenship

iTrader: (5)

Bmr's method makes no mention of the crank/trans output angle. You can not set drive line angle by the driveshaft and pinion yoke only. Even the link the mentioned describes that it must be equal opposing angles at the trans and yoke. The driveshaft does not matter. Pinion angle is only half of the drive line angle. Also the bottom of the torque arm bracket is not equal in angle to the yoke. And yes I have a bmr torque arm.

BMR Sales2

iTrader: (40)

We are talking about pinion angle not drive line angle. On most 4th gens the crank/trans output angle is gonna to be a fixed angle unless the engine/trans has been moved up or down. You can definitely measure the pinion angle with driveshaft angle and and the angle of the rear end. If the angles of the output shaft and the driveshaft and the driveshaft and the pinion are equal and opposite the pinion angle is 0 which generally will create a vibration in the car as it it doesn't compensate for pinion climb. The base range of -2 to -3 compensates for the pinion climb and allows the drive line angle to be 0 under load ensuring that there are no vibrations. I know this how we as well as Madman have always measured pinion angle. I have adjusted many torque arms this way and have had very few issues getting them to be vibration free so I can't imagine I have just been lucky all those times.

jblankenship

iTrader: (5)

Ok, if trans output angle has nothing to do with it, how do you know what -2 or 3 is? Just based on the driveshaft and pinion? That's funny. We are talking about drive line angle. The drive line angle is what is causing the vibration because its wrong. In order to set the pinion angle at -2 you first need to know where drive line angle is zero, then turn the front of the pinion down 2 degrees. Just because the motor and trans are fixed doesn't mean you don't need to find the angle. Just because you set the rear ujoint angle at 2 or 3 does not mean the angle at the ujoint at the trans will be the same. As a matter of fact when these cars are lowered in the rear a lot of times the driveshaft runs uphill to the pinion and guess what. The pinion and driveshaft don't look like a V. In fact just the opposite. It can also be run in broken w configuration. Again, this is why the driveshaft does not matter when setting drive line angle. Setting the "pinion angle" based just on the pinion and driveshaft is doing nothing more than blindly setting the rear ujoint angle which does nothing to cancel out vibrations.

jblankenship

iTrader: (5)

I went back and read your post again. If you set the rear pinion(ujoint) angle like you say under load the pinion and driveshaft will be inline. That would the be an angle of zero on the rear ujoint. But now what is the angle of the front joint. If its not zero it will vibrate because they are not opposing angles that can cancel. Ujoints don't move in circles. They move in an elliptical pattern and must cancel each other out.

jblankenship

iTrader: (5)

Here is what happens when they are not opposing equal angles.

leadfoot4

iTrader: (1)

VERY INTERESTING video!!

SteenH

Really hoping I didn't create myself an issue by making my own motor mounts which actually raise the engine abit. Have yet to fiddle with the angle yet considering my DS is too long. We'll see

RevGTO

iTrader: (12)

Although the rotational noise tends to indicate a driveline issue, don't neglect tires as a possible cause. I took the 17" wheels off my M6 car, put new tires on them, and installed them on my DD A4 car. I had an almost identical vibration to yours above 60 that smoothed out over 70. Had them rebalanced and found a couple were off and the net effect was that the vibration began earlier - at just over 50mph. Like yours, it didn't always happen consistently even at the same speeds and same roads. Finally had them road force balanced and that improved it greatly, but didn't completely cure it. In the end, I put my 16's back on with different tires and it's fine. The 17's seem fine on the M6 car. Go figure.

jblankenship

iTrader: (5)

This problem is easy to solve as well. To determine wheels/tires vs driveline put the rear axle on jackstands and run the car up to the vibration speed. If it's there it rules out the front wheels. Next remove the rear wheels and put one lug nut back on to hold the rotor on. Run it back up to the vibration speed, if it's gone it was the wheels/tires. If it's still there it's the driveline.

RevGTO

iTrader: (12)

Yep, good to be schooled on an old technique

Cferrel4

16" factory rims that are straight, Tires are brand new and were road forced balanced after the initial balance just for good measure. I know the tires are not the issue.

Cferrel4

Thought I would issue a quick update on this Bird. Took it out, vibration was still there after sitting all winter. I have not have any luck finding an adjustable torque arm to try.

I did purchase an early 2000 Trans AM WS6 wrecked roller with 56k miles on the original factory suspension which was still intact for $300 shipped. The rest of the car was stripped out. So I stripped the chasis. Sold the posi unit for $100, 6 speed pedals for 60$ & rear disc backing plates for $60. I still have a mint T-Top headliner, sun visors, power steering rack, buckles and hood hinges to sell so I should get all my money back.

I transferred over the larger front and rear sway bars and bushings since that should not affect my vibration. I also just went through and installed those springs from the WS6 which I believe should be the 1LE springs which should work with the original torque arm. The bird definitely sits up higher. I am going to drive it home after work today and take it on the highway and see if my vibration is gone.

If the vibration is gone, then I am going to sell these lowering springs and call it a day. My wife drives it more then me and I think the 1LE springs with bigger sway bars will suffice for her handling needs on the street to work, wegmans and around town.

If the vibration is still there, then I am going to keep the springs and open up the rear differential.

I will post up later how I make up.

Cferrel4

Drove it about 100 miles this weekend. Vibration & noise are still there, but only when coasting down from highway speeds. When accelerating the noise is gone.

Hopefully going to open up the rear differential to inspect it and change the fluid if it gets slow enough here at work today.

clg82

iTrader: (2)

you lost me at "my wife drives it more than me"