At a loss, Acceleration Shake

[clgodwin79]

Drive shaft or U joint maybe. But I would think that those would affect through all speeds and RPMs.

Can you lift and set it on jack stands and see if you can recreate the issue with the tires off of the ground? That would be a good way to half split if it’s in the driveline or drivetrain or something off balance that contacts the pavement.


1995 Z71 standard cab stepside
Swapping to 1996 Vortec OBD II

 

[CBenZ71]

Pinion angle is easy to check. get an angle finder and put it on the bottom pulley to see how far from vertical it is. The put the angle finder on the front of the rear end yoke where the driveshaft connects. The pinion should be pointing slightly down compared to the pulley. Under load the angles should be the same. Because of the torque reaction trying to counter rotate the axle the pinion angle needs to be 2-4 degrees downhill at rest with leaf springs.

Thank you for this, I will be working on it next. Just visually, the pinion is clearly pointing up towards the transfer case. It looks like I need to adjust that. With our trucks, do we need to use shims to adjust them?

 

[Frank Enstein]

Yes you would use shims. Try to get steel ones and they should be the same width as the springs.

Another option is to remove the axle perches and put new ones on at the correct angle.

If you have lift blocks there are some with an angle built in.

 

[Marko Garcia]

Does the shake go away immediately when u let off the throttle? If so, at least one of the u-joints is faulty.
Also, I didn’t see anywhere in ur texts whether or not the 3 u-joints are timed correctly, a common mistake that will cause a shake.

 

[clgodwin79]

Does the shake go away immediately when u let off the throttle? If so, at least one of the u-joints is faulty.
Also, I didn’t see anywhere in ur texts whether or not the 3 u-joints are timed correctly, a common mistake that will cause a shake.

I second his thoughts here on the driveshaft phasing.

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1995 Z71 standard cab stepside
Swapping to 1996 Vortec OBD II

 

[CBenZ71]

Does the shake go away immediately when u let off the throttle? If so, at least one of the u-joints is faulty.
Also, I didn’t see anywhere in ur texts whether or not the 3 u-joints are timed correctly, a common mistake that will cause a shake.

The reason I didn't think it was the U- Joints is because the shake existed with the stock joints, and also with the new ones. It's shaking slightly less because the center support bearing has new rubber, so it has decreased it some but still exists. I will have to test the letting off the throttle idea and see what happens. I cannot exactly remember if it stops when I let off.
What do you mean by timed correctly? Like a high-speed balance? There is a shop here that does high speed driveline balancing.

 

[clgodwin79]

The reason I didn't think it was the U- Joints is because the shake existed with the stock joints, and also with the new ones. It's shaking slightly less because the center support bearing has new rubber, so it has decreased it some but still exists. I will have to test the letting off the throttle idea and see what happens. I cannot exactly remember if it stops when I let off.
What do you mean by timed correctly? Like a high-speed balance? There is a shop here that does high speed driveline balancing.

Look at the link I sent


1995 Z71 standard cab stepside
Swapping to 1996 Vortec OBD II

 

[CBenZ71]

Okay,

What kind of lift in the back? Blocks or shackles? If its longer shackles your differential driveline angle changed

I thought it was blocks, but could it be both? I definitely have larger blocks, but these shackles don't look stock to me. Can anyone confirm if these are part of the lift or if they are stock?

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[CBenZ71]

Look at the link I sent


1995 Z71 standard cab stepside
Swapping to 1996 Vortec OBD II

I will check that tomorrow! Here's a picture from today, the pinion is pointed up. That's bad right?? Lol
I took it to a rear end shop and the owner took a quick look under and he said and eyeball look his guess is I'm +2° on the pinion and +2° on the TCase.

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[CBenZ71]

Off the line acceleration vibration, after a lift kit with blocks? Your problem is your pinion angle. Lower the nose of the axle, it's too high.

I think you have a point here. It looks like its clearly pointing up right? I'm assuming that's not good...

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