SSWS6

I had Synergy Motorsports install a BMR adjustable torque arm and trans conversion crossmember and I checked the pinion angle today and it was set a 0. Is that correct for a lowered vehicle? The car rides fine and there are no noticable vibrations but wouldn't -1 or -2 be better and help out more at the drag strip? The car has BMR 1" lowering springs if that matters.

BMR Suspension

iTrader: (6)

I would first try it the way it is but a 1 1/2 degree to 2 degree negative pinion angle is preferred.

Black02SLPSS

iTrader: (5)

Im having the same problem. I have a UMI piece, but after reviewing their instructions and BMR's video on how to set it im just confused. UMI says to add the driveshaft angle to the pinion angle and that will get you your "true" pinion angle, while BMR is saying you need to subract the two. So im a little confused as to what to do. Ill get it up on jacks again and give measurements and maybe someone can tell me if im close or not

vjo90rs8

iTrader: (9)

Here is what I do....

1. Drive the rear of the car up a pair of Rhino ramps
2. Put angle finder on bottom of driveshaft and remember that angle (depending on which side of the angle finder you put against the driveshaft will determine which angle is being read)
3. Put the angle finder on the flat part of the torque arm where is attaches to the rear end. Record that angle.
4. Pinion Angle1 = (driveshaft angle1 - torque arm angle1)

On my car I read 84* (angle1) on the driveshaft and 86*(angle1) on the torque arm. 84* on the angle finder is actually +6* from the ground(angle2) because the rear of my car is at and upward angle due to the ramps (90-84), and 86* translates to 4* (angle2). In this case you would subtract the two angles
Pinion Angle2 = (torque arm angle2 - driveshaft angle2)

Both equations are the same
Pinion Angle1=Pinion Angle2 because you are hiding the 90* shift in the equations.
Pinion Angle2=(90-torque arm angle1) - (90-driveshaft angle1)
Pinion Angle2=DS angle1 - TAangle1

If you had the car at ground level you might rear 90*/0* at the driveshaft and 2* at the torque arm (on angle finder).

0-2=-2 BMR tells you to subtract the two angles from the angle finder.

Again, if you car is at ground level and the drive is parallel to the ground that angle is 0*, you obviously know that you want your pinion to be slightly facing the ground (negative angle). So when you read 2* on the angle finder you know that that is actually -2* with reference to the ground.

0+(-2) = -2 UMI tells you to add the two actual angles only using the angle finder as a reference.

I hope I got all this right, let me read it again...yup, sounds good

Black02SLPSS

iTrader: (5)

Good write up. My car sits at a 3degree angle normally. That is with finding a flat spot with the center console out of the car. I put the angle finder on the bracket that holds your airbad module in place and took a reading from that, then replicated it when i jacked the car up. Is that the wrong thing to do or should i just make it completely level all around?

leadfoot4

iTrader: (1)

"Again, if you car is at ground level and the drive is parallel to the ground that angle is 0*, you obviously know that you want your pinion to be slightly facing the ground (negative angle). So when you read 2* on the angle finder you know that that is actually -2* with reference to the ground."

Vjo,
I understand what you're saying here, but you might want to rethink this. The pinion angle also takes into account the angle of the transmission tailshaft, which is in the same plane as the crankshaft. Most engines have a slight rearward tilt, and from what I've seen, this is why the videos say to key off the driveshaft in order to get your initial angle.

I'd been messin' around for quite a while, trying to trouble shoot a vibration in my Z-28, and it wasn't until I watched the video a couple of times that I understood how to work the pinion angle out. At one time, simply out of frustration, I did as you describe. I put the level (digital) on the torque arm mount on the rear end, and went -2 degrees from there. Still had the vibration. Went .5 degrees down from the driveshaft angle, and the car is now smoother than it's been in a long time.

junior28570

iTrader: (22)

I'm not sure (yes or no) your method will produce the same results. The car should be level and loaded (with the driver or same weight in the seat). Being on ramps will move the weight and the susp. angles. It's possible but should be verified once you have your settings.

SSWS6

Thanks for the info all. I was only checking the angle at the TA. I will also check the angle at the driveshaft and subtract.

junior28570

iTrader: (22)

[QUOTE=leadfoot4;9221351
Vjo,
I understand what you're saying here, but you might want to rethink this. The pinion angle also takes into account the angle of the transmission tailshaft, which is in the same plane as the crankshaft. Most engines have a slight rearward tilt, and from what I've seen, this is why the videos say to key off the driveshaft in order to get your initial angle.
[/QUOTE]

The plane in which the crank and tailshaft reside is irrelevant if you know the drive shaft angle (the "crank plane" portion of the formula would be required by design engineers in determing "where can we put the axle and how much roll do we need to create X angle").

It really is simple geometry; "Pinion angle simply refers to the angle of the differential’s pinion in relation to the driveshaft." ..Car and Driver.

Here's an example .. if I were to put my drive shaft DIRECTLY beneath my engine .. level to the earth and measured, I could easily match the plane of the crank and tailshaft. Clearly, this would have not net me 0 pinion angle.

2 measurements; 1) pinion (angled down) .. 2) drive shaft (angled up, toward the engine)

Good luck all

vjo90rs8

iTrader: (9)

Not saying that my method is absolutely perfect but I can honestly say that there is not way I could sit in the drivers seat and measure the torque arm and driveshaft angles in my garage on a flat surface at the same time, lol. If you have a lift that is great but I am a simple man with simple tools and the method works great for me.
Again, if you can accurately measure the driveshaft angle then you shouldn't have to worry about anything else but the torque arm angle.
Also, yes, being on ramps will shift weight alittle but the relevant suspension angle should not change with respect to eachother. Pinion angle on ramps should be equal to pinion angle at ground level, probably within a tenth of a degree.

leadfoot4

iTrader: (1)

I pretty much agree with this, and in using different words, intended to say the same thing....

At one point, I removed the driveshaft, took an angular measurement off the tranny output shaft, and then adjusted the torque arm to match this angle. The idea was to establish "zero" angle as a baseline. This did not work, as it placed the pinion quite a bit "positive".

The only way I was able to eliminate the vibration my car had was to use the "driveshaft to torque arm difference" method

junior28570

iTrader: (22)

vjo .. I agree, being on ramps SHOULDN'T have that much effect. Knowing the rear will have less weight on it, I would lean toward putting a tad bit (.5 max) angle on the pinion than if it were flat. I don't have 200lbs of anything to put in my seat so I can read protractors either but .. a friend or a coupe small girlfriends would work too I'm no different than you on this, simple man doing simple things with simple tools

leadfoot .. we completely agree. If you were building a car from scratch, the crank/tailshaft plane would be relevant. You would want to have enough rake in the motor placement so you wouldn't have to put too much roll in your axle to accomplish X pinion angle (among other considerations) ... THAT was my main point. For a street car application, the motor rake (crank/tailshaft plane) is set by GM, nothing you can (or would) do about it anyway