? about pinion angle

[rallye455]

I have a GM A Body (72 442) and am doing a body off resto and purchased a Moser Fab 9 housing for it. I have the bare frame stripped and bolted the rear in today and the face of the housing is tilted back at 87.7 degrees. Can anyone tell me what the angle of their housing is?

[68protouring454]

alittle confusing, but it sounds like you have 2.7 degrees of pinion angle and the pinion is pointing up, which it should point down 2-3 degrees
do you have adjustable uppers? there jig may be off alittle needing adjustable uppers

[The WidowMaker]

it all really depends... 87.7 to what? the ground? the frame? the tranny?

throw all that out the window. set your pinion equal to your tranny in degrees whether the same or opposite. then measure you driveshaft and fiqure your working angles. you need to set it all up so your working angles are as close to 1 as possible (without being less than one) and are within .5* of each other. a perfect setup would have a front working angle of 1 and a rear of 1.5 or less.

you can move your tranny up or down and you can do the same with your pinion yoke. currently, my setup is requiring a 2.5" spacer (read new crossmember) to get my angles correct at my ride height.


Tim

[dhutton]

Is it valid to measure the pinion angle on a bare chassis? Doesn't the suspension need to be fully loaded and at ride height before worrying about this?

Don

[rallye455]

I dont have the motor or trans mounted...just was mocking up the rear and noticed it was leaning up..put an angle finder on it and it was 87.7 degrees..frame is level..stock control arms...I was just wondering if that seemed normal or was the Moser housing off....I'm not looking to set pinion angle now, just worried that the rear may be off..I figured it would be pointing down, not up.

[ironworks]

The links are so short that when you put the weigh on the car on the frame it will compress the suspension and probabley get you into range. The pinion angle only matters in relation to the angle of the engine. Until you have the car setting on all it's own weigh, there is no reason to even take a guess.

Good luck

[crazycarl]

Whatever you do, do NOT take the driveshaft angle into account when setting your pinion angle. The driveshaft doesn't care what angle it's at. Think about a lifted 4x4. If driveshaft angle mattered, then all of their engines would be pulling wheelies under the hood and starving for oil. Measuring the driveshaft will only give you u-joint/driveline angle. Arguably, driveline angle should be minimized to reduce power loss, but not at the cost of vibration caused from the u-joints being out of parallel.

Pinion angle is the the difference between a straight line drawn through the crank and a straight line through the pinion on the third member. Theoretically, if you crank is pointing down 2 degrees from level with the ground, or -2 degrees, the pinion will probably be pointing up about 2 degrees, or +2 degrees. That would mean that when they are static, the two angles are parallel.

If your housing face is measuring out at 87.7 degrees from plumb, straight up and down, then you have 2.3 degrees of up angle on the housing (+2.3). If you were to set the pinion shaft at 0 degrees/level with the ground, that would put your housing face at 90 degrees with the ground. Under load/power/acceleration the pinion will rotate up and your angles will once again be parallel.

So, assuming those are the angles that your car has, and should have, then Moser definately built your housing correct.

If you go to page 5 of the instruction sheet I grabbed off of AirRide's site, you can see a diagram. This just happened to be the first one that I found with the diagram.
http://www.ridetech.com/instructions/docs/ABAR20400.pdf

[darren@ridetech]

Gotta be careful with A-bodies, floor pan clearance can be a problem if you aim the pinion up.

[crazycarl]

Originally Posted by darren@ridetech

Gotta be careful with A-bodies, floor pan clearance can be a problem if you aim the pinion up.

If the pinion is set to -2 degrees from paraellel the pinion itself won't point up until it's under load at which time it would be 2 degrees up. In my example at least. I'm pretty sure the stock crank angle is -2 to the rear. Of course, the amount of angle needed depends to a certain extent how much power you're pushing.

Not arguing, just making sure I'm not confusing people.

[The WidowMaker]

carl, some good points, except the driveshaft must be taken into account in the overall scheme and out of spec #'s WILL cause excessively worn u joints, and could lead to annoying vibrations. the working angle must be as close to 1* as possible, and the difference cannot exceed .5* btwn them. i didnt make this up, spicer (the largest mfg) did. if you just set them the same, you could be looking at some out of spec working angles, especially if the car is lowered a lot. i had to raise the back of my tranny 2" to get my numbers within spec. raising the tranny decreased its angle and therfore required a change in the pinion angle.


when was the last time one of those large 4x4's was doing 80+ on the freeway. when was the last time one of those large 4x4's ran tires that didnt make the truck shake to begin with. my point is, a car set up to run fast and quiet is much different than a truck whose tires alone are louder than the stereo, and thats my stereo when im driving next to them.

the pinion must match the trans, but they can also be equal and opposite. if your pinion is higher than the trans, you can actually point the rear of the trans down, and also point the pinion down ( like this \____/ ). again as long as the working angles are within .5* of each other (pinion can be .5* different to account for axle wrap), and as close to 1* as possible without being under, everything is optimal.

also, dont worry about the car being at parallel. the drivetrain doesnt care about that. put it at ride height and start measuring.