I recently noted a mild drivetrain vibration that progressively got worse. First thing checked was U joints to find they had worn, having play. They are new so why did they wear? Anyway, new joints and vibration improved, but still there. So thinking the pinion angle is out, I changed it by extending the adjustable upper arms on the rear end which made a great improvement....almost gone. Since this angle should not be in perfect line with the drive shaft, the question is; should the diff pinion be pointing upward or down? It is currently downward at about 5-6 degrees and every vehicle I look under is pointing upward. Thoughts?
Ideally, the angles between the transmission output shaft and driveshaft, and between the driveshaft and the pinion will be equal and opposite.
How well the rear suspension controls the position of the rearend is the most critical issue that determines how much pinion angle will be needed. Some types of rear suspensions offer more control than others and require different angles. According to Bickel, a ladder-bar suspension normally requires ½ degree of pinion angle, a four-link requires 1-2½ degrees, and a leaf-spring suspension requires up to 6 to 7 degrees. In all examples, were talking about negative pinion angle, i.e., the pinion is nose-down in relation to the driveshaft.
Ray Currie of Currie Enterprises, which specializes in rearends and rear suspension systems for race, street, and off-road applications, agrees that pinion angle is a pretty simple (theres that word again) concept. He explains that a universal joint is designed to handle between 1 and 3 degrees of pinion angle. This is a safe operating range for the U-joint. If the U-joint is forced beyond its normal range, it can hyperextend and lead to catastrophic failure. Currie always strives for 2 degrees of pinion angle on a street car regardless of the type of rear suspension being used.
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1967 Parisienne 2+2 1967 Grande Parisienne
1967 Laurentian 1967 Strato Chief
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Thanks for the helpful input. I suspected that I could further reduce the current tilt a bit more and expect it will be a trial and error untill it 'feels' right, but aiming for 1-2 degrees. Especially since I have upgraded the rear to a 4 link, adjustable system. My 65 shop manual doesn't state an exact angle but rather has a scale showing that increased ride height requires less pinion angle and opposite for the trans end. Interesting about the leaf spring rears at 7 degrees, as all the vehicles I checked were leaf set ups (pick ups) and the diff is definitely upward.
Remember it is the difference between the drive shaft angle and the pinion angle.
Tacken from Wolf racing site;
Using a gravity angle gauge (Available at hardware stores) to measure the angle between the driveshaft and the ground & the pinion flange and the ground.
Hold the gauge on the bottom of the driveshaft. Align the gauge front-to-back under the car in line with the driveshaft and read the number from the gauge (Note if angle is up{+} or down{-}). Write down this number.
Next, hold the side of the gauge against the front of the pinion flange (beside the driveshaft). Write down this number (Note if angle is up{+} or down{-}).
Subtract the first number from the second number. This is your pinion angle
Examine the diagram at the bottom to determine if the pinion angle is nose up or nose down.
Thanks for the diagram. Because of all the mods and upgrades done, I will likely need to make adjustments at the tail shaft as well to match the pinion. This won't be an issue once I conjure up a way to level the car. . . .at the same time get underneath to do it. ...plans are in the works
Thoughts?