Pinion Angle Questions

[olddog]

Part of what beat the bearings up in my 9" was a terrible pinion angle.

I now have it set on 4 jack stands with the frame level. I have the rear end set to give the frame 5" clearance from the floor. I will set the front to give a 5" clearance from the frame to the floor (it's within a 1/4" of that now). This gives the oil pan about 3-1/4" off the floor.

The transmission is running down hill to the rear by 1 deg.

With the pinion yoke setting 1 deg down hill to the rear by 1 deg, this puts it parallel to the transmission. The drive shaft is running down hill from transmission to pinion 13.2 deg. This gives a 14.2 deg angle on the yokes!

I don't like the idea of running the oil pan any lower to the ground.

Note: With pinion set at zero not the (1 deg mentioned above) the pinion is 3" lower than the transmission. The drive shaft is 10-15/16" long from center of U-joint to center of U-joint.

Advise please.

[bobcowan]

The 14* angle of the drive shaft doesn't really matter, as long as the U-joints can handle it. What really matters is the pinion angle compared to the drive line angle.

[Paul F]

Correct. You need to adjust the pinion angle to exactly match the transmission. If you don't have adjustable upper or lower links, then get some. I'm assuming you have the canted 4 bar setup, like this:

Chris Alston's Chassisworks, Inc.; Chris Alston's Chassisworks, Inc. - Canted 4-Bar Rear System

edit - you can also get lower links that adjust both pinion angle and ride height.

[392cobra]

Ideally, the angles between the transmission output shaft and driveshaft, and between the driveshaft and the pinion will be equal and opposite.

[COBRANIP]

My understanding is that (with pinion yoke and transmission yoke parallel) it is preferable not to exceed about a 7 degree drive shaft angle.....for what it's worth.

Good luck.

[RICK LAKE]

Olddog Sears sell a digital meter for angles that works great.
I am going under the thought that the frame is straight. Is the motor off set in the frame?? Era and some others are from even to 1" off to the right.
The right/left on the output of the trans needs to be parallel. This cancels out the drive shaft having a vibration at certain rpm range.
Has far as the trans and read end you want a -1 degree on the rearend yoke and about a +1 on the trans output. If you can get it this close.
I always runs the rearend in the negative readings because of rotation when the car is accelleration. It want to twist up.
Start with the motor and see what the angle is on the top of the carb if it's flat, then work back from there. You may get a 2-4 degree angle There are shims and shorter trans mounts that you may need to use to get this where you cancel out the angles. As low as you are within 2-3 degrees, normal driving will be OK. IF you are going racing, this a different story Rick L.

[olddog]

I realized I made a mistake after going to bed. I should have subtracted the 1 deg from the angle on the shaft & I added it. Also I wrote the wrong number for the drive shaft angle.

The drive shaft is 12.2 deg from level subtracting 1 deg gives a 11.1 deg angle on the yokes.

The transmission and rear end appear to be centered it the frame, I will measure it. I cannot get back to it until Thursday evening.

Rick I have a digital inclinometer.

[bobcowan]

Pinion angle is measured against the drive line angle, not the horizon. This is an important concept, and the key to getting it right. For every little bit you're off, you lose a little bit of power.

I would not recommend measuring the drive line angle at the carb or intake. Too much chance for error. The easiest place is the front of the harmonic balancer. On a quality balancer, that should be a flat surface, parallel to the crank shaft.

Place a digital level across the front of the balancer. Then place it across the front of the pinion input flange. Those two angles should be about the same; depending on the type of rear suspension you have. For IRS, you want them exactly the same. For a stock rubber suspension, you'de want about 3-4* of down angle.

You also want to check the pinion angle in the lateral plane as well. This is a lot more difficult to do, especially with IRS. The easiest way is to make both the drive line and the diff are straight in the frame. If they are both perfectly straight in the frame, they will be aligned to each other. But if the axle is 2* to the left, and the driveline is 2* to the right, that's 4* of pinion angle. You won't hurt anything, but you'll lose power and efficiency. If the axle is off by 2-4*, the car will crab down the road.

A quality U joint can handle about 14-15* of misalignment. Any more than that and you start to get small vibrations. Not dangerous but can be annoying. for big angles, you need to use a CV type joint.

[RICK LAKE]

bobcowan Bob I started with the frame to get it zeroed on the working space first. Then start from the front and find out if the motor is level or at an angle, this is both front to back and right to left. My motor sits 1" off to the right to start. Some guys have rubber motor mounts which also will effect angle of degree. After you have these degrees you can then work your way to the back of the car. It's like building a house, if the foundation is off the house if going to lean. My single plane manifold is not on a wedge setup like the 2-4 barrel ones. Old dog didn't say what manifold or carb he had on the motor to start. For a Jag rearend with a cradle assembly like ERA, I run around -1 degree down. the rearend is still going to twist on accelleration. IF you are running a solid mount rearend, I would match the degree of the yoke from the trans and shim it to "0". Having to right springs,shocks, and alignment also all help in getting power to the ground without wheel hop and other problems. Rick L.

[bobcowan]

That's a good way to start. You have to have a flat and square surface and structure to start with. Then square everything to the squared surface.

I would not recommend use the carb or intake to measure the drive line. With each connection and with each component, you have the potential for a small margin for error. Eventually, all these small errors will add up to something significant. Basic scientific principle.

Ideally, you would want to measure the drive line angle at the transmission tail shaft. But I don't know of an easy and truly accurate way to do that.

How much down angle (compared to the drive line angle) you run depends on the type of rear diff you have. I have a solid mounted IRS, so I run 0*. A stock rubber 3 link rear has enough flex that you might need as much as 4-5* of down angle. It all depends on the application; including facters like vehicle use, tires, power level, etc. If you do a google search, there's some charts and opinions available to get you in the ball park.

Pinion angle itself doesn't really cause wheel hop. But if the rear is loose enough to cause oscillation of the pinion, that will probably cause wheel hop regardless of the static pinion angle.

[olddog]

I just got home in time to go to bed. Like I said I cannot get to it until tomorrow evening. It bugged me all day. Some numbers I measured before disassembly just were not jiving with what I got last night. I just did a quick check, and I think I do not have the rear axle in the correct spot for the ride height. I'm hopeful I will have better numbers when I get it right. I had a sinus head ache and took some meds last night. I think I made a lot of mistakes.

Yes trying to get a measure on the transmission flange is an exercise in futility. I could not get the same reading twice to save my a$$. It is 1 deg +/- 0.2. Thanks for the tip on the damper. Although I think the belt pulleys may get in my way.

It has a 5.0 block (347) with Edelbrock Vic Junior intake converted to EFI (MASS Flow Brand). I did measure the top of the throttle body (carb look alike). It is a nice precision piece. It was around 1* also, but it's been a while, so I don't remember the exact number. I can check it again.

[olddog]

Darn thing double posted

[olddog]

To answer some questions:
The transmission is setting ~ 1/2" shifted to the right. That is 12" from driver side frame and 11-1/16" from passenger side frame.

The pinion is setting ~ 3/32" shifted to the right. It's 11-9/16" from driver side frame and 11-3/8" from passenger side frame.

Right now I have the upper links off, the bottom links on blocks, and the pinion setting on a bottle jack, to adjust pinion angle. Oh yea the springs are off too. It is a triangulated 4 link, with the top links angling out to hold it centered. I would guess the pinion was intended to be centered and it may well be when the upper links are on.

Drive shaft is 11" so the off set gives a 2-3* side ways angle.

I couldn't get a good reading off the harmonic damper with the pulleys on. The pulleys are not machined perfect. I get anywhere from 0.8* to 1.2*. I tried the bell housing, oil pan, and others with no better results. The throttle body top gives a solid repeatable 1.1*. Everything else it near 1*, so I'm willing to call it 1*. Close enough.

I blocked it to equal a ride height of 5-5/8" frame above floor. The lower links start to angle and pulls the assembly forward. Then there is no free play left in the transmission yoke splines. The angle on the U-joints is much more reasonable here, but since I couldn't pull the drive shaft out to get a reading in the pinion yoke. I quit. Crawling in and out from under the car. Then jacking and blocking is a royal pain.

Ok, this is going to be much more involved than I thought. I am building adjustable upper links this week end at a friends shop. I will work some more on it then. It's looking like a may have to have adjustable lower links too.