Another pinion angle question: Here's my situation, '97 Z28, M6, Adjustable frame mounted torque arm, adjustable track bar and control arms, Ford 9" rear with a 3" Chrome-molly drive-shaft. I get horrible drive-shaft vibrations at anywhere from 50mph to 100mph depending on where the pinion angle is at. My tranny output measures about 4 degrees down. Where should my pinion angle be set? 4 degrees up? The vibrations change with the slightest pinion angle adjustment (come in at different speeds), but are always present. I don't think it's the d.s. itself, I've had it balaced less than a year ago. Please help.

 

For street driving most guys set the pinion angle to -1 (if your tranny out put shaft is 4 degrees down, your differential yoke should be 3 degree up). This puts everything in plane and minimizes U-joint wear. Do a search on pinion angle.

 

Are you measuring the tranny output shaft or the driveshaft?

A 4deg "down" (\) on a driveshaft, combined with a 3deg "up" (/) on the pinion shaft nets you a 7deg pinion angle, and thats way too much. You want the difference between the two angles to be -1 to -2deg.

"up" and "down" mean different things to different people. The important thing is that when you move the angle finder from the DS to the pinion shaft housing, the little pointer should only have moved 1 to 2 deg, and the yoke end of the pinion shaft should be pointing slightly "down" relative to the DS, so that as the yoke end of the pinion shaft rises under maximum load, you have a straight line through the pinion shaft and the DS.

 

That is the measurement off of the tranny output shaft and the pinion shaft with the car jacked up at all 4 corners (stands under the front A-arms and under the rear axle) I removed the d.s., put the angle finder on the tranny output shaft, got a reading of -4. I then tried adjusting my rear pinion angle to bring it up to +3 or 4. I ended up getting it to about +2 or 3. It cut the vibrations in half or more. There is now a much less intense vibration at around 55mph and up. I think allot of the vibes I am feeling is due to my chassis mounted torque arm versus the stock torque arm. The solid heims and polyurethane bushings and probably transferring allot more vibration into the cab.

 

If ya measure at the pinion yoke it should read a - negative/down 2* for stock. If ya want more hook go more.

MADMAN:
Okay guys here are the facts.

The object of pinion angle is to raise the pinion yoke under load, which in turn loads the chassis and plants the rear tires. The pinion is set in relation to the ground which is what we are racing on. The driveshaft is not a factor in this equation because for 1 the driveshaft doesnt plant the tires and 2 that is why we run ujoints. It doesnt matter where the motor is in height , whether it is higher or lower than the pinion. The pinion is going to rotate up due to the torque of the pinion trying to rotate over the ring gear, which in turn will lift the body and plant the tires. This is called antisquat!(considering the other misconception is that the car squats on launch) You arent trying to remove driveline mis alignment you are trying to get the car to "PLANT" the tires at the hit.

All I can say to the naysayers is measure it your way then run the car. Then try it my way and see which is faster!



The way I have been doing it for years

 

At this point, I'm not even worried about trying to set the angle so that it plants the tires better, all I'm trying to do is get rid of the vibrations.

 

If it's set right and in line it shouldn't have a vibration from that.Run 150 with 6*.
Is the rear square in the car?

 

Yes it is square.

 

The "stock" angle is 2* so if it is close to that it's not out of spect and ya need to look somewhere else.

 

Are you sure the DS is balanced? U-joints in good shape? When did the vibration start? IOW , what was the last thing you did before the vibration started?

Rich

 

The vibrations started when I put in my adjustable torque arm, this is why I am 99% sure it is pinion angle related. With my stock torque arm in place, I had a tiny vibration when coasting at highway speeds, but nothing like I have now. That vibration was probably due to a slight driveshaft inbalance or the pinion angle being marginally off because of the lower pinion output of the 9" rear-end.

 

I have had the same problem on my car. After swapping out the stock rearend with absolutely no vibrations for a 12 Bolt, I have had horrible vibration issues from about 65mph and up. The more I give it gas though, the less the vibration is so it has to be driveline related. I have tried setting the pinion angle different but nothing has seemed to help unless I am measuring the angle wrong. My next step is to jsut replaced the driveshaft since I need a bigger one anyways.

 

What you appear to be doing is trying to verify that the tranny output shaft and the pinion shaft are parallel to each other. That is a critical element to making a drivetrain with 2 "U-joints" work without vibration. But its not clear to me what the angles are that you are getting. Its hard to visualize what you are describing, in terms of "+" and "-".

Are you saying that when you put the angle finder on the tranny output shaft, the finder shows -4deg, and then when you move the angle finder back to the pinion shaft, the pointer swings 7 or 8deg degrees and is now at +3 to +4? That would make the angle between the tranny output shaft and the pinion shaft 7 to 8deg, and that kind of departure from the shafts not being parallel is going to cause major problems with the u-joints, including non-linear motion translation = vibration.

The 9-inch rear is a problem, with regard to the pinion shaft location. It sits 3/4" lower than the stock 10-bolt or a 12-bolt, and it is not located in the "center" between the two wheels, it is offset to one side. This makes driveshaft setup much more critical than on the stock configuration.

If I've misunderstood what you are trying to do, run it by me one more time in the hope that I can get it through my thick skull

 

Yes that is exactly what I am saying. If you were to draw a perfectly horizontal line under the car, my rear tranny output is pointing down 4 degrees from that line, and my pinion is pointing up about 3 or 4 degrees from that line, making an overall angle diff. of 7 or 8 degrees. I have tried adjusting the pinion everywhere from down 4 degrees to up 4 degrees and I have the least vibrations at up 3 or 4 degrees. I realize that the 9-inch pinion output is slightly lower and to the side but there are plenty of people who have done 9-inch swaps without having vibration issues. Like I mentioned, I barely have any vibration with my stock torque arm installed and the 9-inch. Could it be that the vibrations aren't being transfered through the car as much because of the soft rubber mount that it slides into. I am also going to try out my stock driveshaft but if I remember correctly it has a balance issue.

 

Then it sounds like they are parallel. If I draw a line from the tranny input shaft, through the output shaft, it will be pointing down 4deg from horizontal.

If I draw a line through the pinion shaft, it will be pointing 4deg up above horizontal in the front, and down 4deg from horizontal, when the line through the pinion shaft emerges form the rear of the differential housing.

Now you need to drop the the nose of the pinion shaft a degree or two, so that when the system is under heavy load, the nose of the pinion shaft will torque up to the same 4deg above the horizontal line.

If that's not what you are saying, I don't think we can resolve it without an actual sketch.