Pinion Angle Measurement

[‘Ol Flossie]

Any chance I could get affirmation as to whether I’m properly attempting to measure the pinion angle? I’ve flipped the axle with a Western Chassis flip kit. The first image is from the rear with the driveshaft out. The second image is at the transmission tail shaft with the driveshaft out. I currently have the axle on jack stands, if it matters.

[‘Ol Flossie]

Based on this measurement, my though was that I need to shim the rear end 4 degrees in the upward direction, installing the shims from the front of the axle with the wide end of the shim pointing towards the front of the truck.

[mongocanfly]

I'm only seeing 1 pic...of the diff... and it's at 0deg it looks like..
You need the weight of the truck on the suspension..sounds like you do...
The rear diff needs to number match the trans angle,,,, but opposite

[SkinnyG]

Try it. See if it works.

Matching the angles between the trans and the pinion did NOT work on my '77, it was nasty vibration, especially under acceleration.

I tried shimming the pinion every which way but Sunday, and also raised the transmission 1-1/8" up (it -almost- contacts the floor now), and currently have the pinion angle such that the "operating angles" of each u-joint are the same.

While it's nice to have the angles match, you also want the operating angles between 1-3°, and within 1/2° of each other, and you want the driveshaft to angle down to the pinion, not up to the pinion.

Beyond that, it's black magic and voodoo.

[‘Ol Flossie]

Originally Posted by SkinnyG

Try it. See if it works.

Matching the angles between the trans and the pinion did NOT work on my '77, it was nasty vibration, especially under acceleration.

I tried shimming the pinion every which way but Sunday, and also raised the transmission 1-1/8" up (it -almost- contacts the floor now), and currently have the pinion angle such that the "operating angles" of each u-joint are the same.

While it's nice to have the angles match, you also want the operating angles between 1-3°, and within 1/2° of each other, and you want the driveshaft to angle down to the pinion, not up to the pinion.

Beyond that, it's black magic and voodoo.

After reading more of the Western Chassis documentation, you’re exactly right. With the axle flipped and essentially moving straight up, if an angle adjustment of the pinion is warranted, it should be in the downward direction. Thanks.

[mongocanfly]

Ok now I see both pics...some have had luck setup just like it is...on the theory that the diff nose will rise under acceleration...like skinny said..sometimes the numbers perfect setup just dont work..

[kipps]

There's also the theory that it matters how the truck will be used. If it's exclusively seeing the drag strip, you'd want to account for axle wrap when setting the angle. In other words, you'd want the angles correct under hard acceleration, but they'd be out of spec when cruising. The exact opposite would be true of most highway trucks.

For what it's worth, I plan to bolt my complete setup together, without welding the perches to the axle. I'll measure the downward angle of the engine/trans/t-case combo, and angle the pinion upwards to match that angle. Once I'm satisfied with the way it sits, I'll torque down the u-bolts, and weld the perches solid.

I should go measure a couple of OEM correct trucks first I reckon, and see how close they match the angles.

[‘Ol Flossie]

Originally Posted by kipps

There's also the theory that it matters how the truck will be used. If it's exclusively seeing the drag strip, you'd want to account for axle wrap when setting the angle. In other words, you'd want the angles correct under hard acceleration, but they'd be out of spec when cruising. The exact opposite would be true of most highway trucks.

For what it's worth, I plan to bolt my complete setup together, without welding the perches to the axle. I'll measure the downward angle of the engine/trans/t-case combo, and angle the pinion upwards to match that angle. Once I'm satisfied with the way it sits, I'll torque down the u-bolts, and weld the perches solid.

I should go measure a couple of OEM correct trucks first I reckon, and see how close they match the angles.

Truck won’t be seeing the track. Street truck only. Please keep me updated on your flip and the OEM measurements.

[kipps]

Originally Posted by ‘Ol Flossie

Truck won’t be seeing the track. Street truck only. Please keep me updated on your flip and the OEM measurements.

I'm actually not doing a flip. I'm using a newer axle, and need to move the perches to align with the squarebody spring spacing. It's the truck in my signature.

[‘Ol Flossie]

I should have the shims on Wednesday. I’ll post the results. Shims in front of the axle to get an upward angle, right?

[mongocanfly]

If you want the pinion nose up,then the thick part of the wedge will be in the front

[‘Ol Flossie]

Originally Posted by mongocanfly

If you want the pinion nose up,then the thick part of the wedge will be in the front

Thanks for the input Mongo. There’s a great deal of knowledge on this site.

[bigblock73]

I have done several flip kit installs, including Western Chassis. I have never worried about the pinion angle, never added any shims, never had any vibrations. The rear is simply going straight up, the axle angle should not be changing in relation to the engine/trans angle.