MY99TAWS6

iTrader: (3)

Ok have bmr torque arm and its adjustable of course.I had some wicked vibration problems past 70mph and so going over things more carefully.Buddy went and shimmed up my 4l80 trans so trans was straight.He used couple of pretty big shims.

I took out the shims as been reading the fourth gens are supposed to have down angle on the trans .
So no measured my driveshaft from passenger side car is on ramps but only in back.front is on ground.
So driveshaft measured from passenger side is negative 3 degrees down.
Rear end is negative 5 degrees down.
So here is the problem. In bmr instructions it says to subtract the rear from driveshaft.
Ok but not good at negative numbers!
So negative 5 subtract negative 3 should be negative two ?
But then in bmr video they show negative 5 and negative 2 driveshaft and they say to add them and the guy says that gives negative seven.! Then they go to adjust the arm and say they now have negative two but they don't give the new numbers.

So what the heck. Checked spohn site and they said to subtract the rear from driveshaft and to check on drivers side.
Umi think says same thing.
i have spohn in my 96z and don't seem to vibration issues but forget how I set it.

So I want zero right now same as stock basically. To get zero do I set my bmr arm to negative 3 rear and negative 3 driveshaft would give me zero?
Or do I set it to positive 3 rear and negative 3 driveshaft to get zero.Help! Please help this stuff is giving me a huge headache.

Badazz 97 TA

iTrader: (18)

the guy in the video messed up his math. you are correct with the -5--3=-2

MY99TAWS6

iTrader: (3)

Hmm ..talked to bmr and they have changed their instructions to now say the same as video.To add the two angles together. So negative 5 plus negative 2 is negative 7 .
All I can say is my car seems to have big vibrations at negative 5 rear end and negative 3 driveshaft so going to adjust it and do my own experimenting.
Here is what the new bmr written instuctions say

Load the rear axle by either setting the car on the ground or letting the car rest on jack stands positioned under the rear axle.

Place the angle finder on the driveshaft and record the angle. The driveshaft angle is negative if it slopes downward towards the rear of the car. The driveshaft angle is positive if it slopes upward towards the rear of the car.

Now place the angle finder on the rear end torque arm mounting plate and record the angle. The rear end angle is negative if it slopes downward towards the front of the car. The rear end angle is positive if it slopes upward towards the front of the car.

Add the two measurements. This is your pinion angle. (Example: -2 rear end angle plus -1 driveshaft angle = -3 degrees)

Turn adjuster to achieve the desired angle.

As a starting point, most F-Bodies seem to like the following initial settings: Automatics: 1-2 degrees negative Manuals

This would agree with what was said in the video.
But wish they would have shown both rear and driveshaft final angles.

BMR Suspension

iTrader: (6)

I re-wrote the instructions a couple of years ago to try to avoid this confusion.....maybe I should re-write them again...

Two problems here:
1) The 2 numbers need to be added together. This avoids the problem of subtracting a negative.
2) You cannot measure the pinion angle with the rear tires on ramps and the front tires on the ground. This will transfer a bunch of weight from the rear to the front. The front and rear suspensions need to be compressed the normal amount when you take your measurements.

I wish that there was only one way to measure pinion angle. I have researched this and it seems like every "expert" that has written a chassis/suspension book uses a different definition for what angle is positive and what angle is negative.

A good starting point is to adjust your torque arm so that the differential is pointing down by 2 degrees. Then take your measurements and add them together. That should get you really close. Follow the instructions after that and you should get it right.

BMR Suspension

iTrader: (6)

Actually, the video is correct now. The way that the positive/negative angles are defined, the 2 numbers need to be added together.

Here is the text from the video:

BMR supplies a magnetic angle finder. So find a nice flat spot and mount your angle finder on it. The driveshaft angle is negative if it slopes downward towards the rear of the car. The driveshaft angle is positive if it slopes upward towards the rear of the car. A negative 2 is what I’m reading on this angle finder.

Same way with the mounting bracket. This is where BMR suggests that you take your pinion angle reading from. The rear end angle is negative if it slopes downward towards the front of the car. The rear end angle is positive if it slopes upward towards the front of the car. And right now we’re at negative 5 degrees. For an automatic transmission car, we’re shooting for between negative 2 and 3 degrees. And that’s at a factory ride height.

Now we’re going to make our calculations for pinion angle based on the BMR suggested method which is taking the rear end number, which is a negative 5, and adding it to the driveshaft angle, which is a negative 2, and that gives us a negative 7. We were shooting for a negative 2, so we’re going to make a quick adjustment on the barrel nut.