Drivetrain alignment and vibration

[npdunn]

Hi there!

Need some help on the following:

I have a SWB 67, 2 wheel drive, 454 w/ 400 tranny.

Issue(s): the driveshaft is not centered through the crossmember (where the trailing arms are attached). I am just curious if it's supposed to be?? There is at least 1/4" difference when comparing each side.

My reason for concern is that I am getting an oscillating vibration starting at 50 mph and it stays no matter how fast you go. I have ruled out the following causes: driveshaft, u-joints, entire rear-end, tires/rims, tranny, flywheel, pinion angles.

My thought is: if the drive shaft should be centered through the crossmember, than the engine is sitting crooked- throwing off everything behind it. Which would also add another angle into the drive-train.

I am possibly stating the obvious, but I would like to get other's opinions.

Thank you for your help! I appreciate it.

[npdunn]

Originally Posted by npdunn

Hi there!

Need some help on the following:

I have a SWB 67, 2 wheel drive, 454 w/ 400 tranny.

Issue(s): the driveshaft is not centered through the crossmember (where the trailing arms are attached). I am just curious if it's supposed to be?? There is at least 1/4" difference when comparing each side.

My reason for concern is that I am getting an oscillating vibration starting at 50 mph and it stays no matter how fast you go. I have ruled out the following causes: driveshaft, u-joints, entire rear-end, tires/rims, tranny, flywheel, pinion angles.

My thought is: if the drive shaft should be centered through the crossmember, than the engine is sitting crooked- throwing off everything behind it. Which would also add another angle into the drive-train.

I am possibly stating the obvious, but I would like to get other's opinions.

Thank you for your help! I appreciate it.

Meant to say:

My thought is: if the drive shaft is not centered through the crossmember, than the engine is sitting crooked- throwing off everything behind it. Which would also add another angle into the drive-train.

[brad_man_72]

How did you rule out driveshaft? Only way to know is to have it ballanced Or if the vibration is still there when the driveshaft has been removed.
Then you would know your vibration was in the engine/trans, torque converters can cause a vibration.

Don't worry about the driveshaft being centered, I'm pretty sure the pinion isn't centered in the axle. Either way your truck doesn't care.

[npdunn]

I have had the driveshaft checked 2x @ 2 different shops.

[fleetsidelarry]

if it's a one-piece driveshaft it won't be centered for the reason brad_man mentioned. looking down, your engine/tranny and pinion centerlines will be parallel and slightly offset. same goes when looking from the side. yes, you are correct, this means a compound angle on the u-joints. designed that way

[geezer#99]

Here's a good read and some vibration troubleshooting info.
http://www2.dana.com/pdf/J3311-1-DSSP.pdf

[cdowns]

99.9% of drivetrains that have come out are not centered from the factory and they run just fine with no vibration

[brad_man_72]

No matter what direction the driveshaft is pointing there is only one angle at each end. No compound angle. Just an angle and a direction.

[fleetsidelarry]

Originally Posted by brad_man_72

No matter what direction the driveshaft is pointing there is only one angle at each end. No compound angle. Just an angle and a direction.

when there are angles in both the horizontal and vertical planes, Spicer calls it a compound angle. see page 9 and 10 of Geezer's link.

[jjzepplin]

subbed to see where this goes

[Gumby]

none are centered,

#1 due to steering shaft room

#2 it makes the drive line last longer, everything is off a little in severla direction down the line to make the drive shaft u joint last a long long time, if al lwas 100% centered and level, the bearings would sit in one spot and wear out, instead of rolling around inside.

#3 the need for #2, makes making room for #1 easier and made GMs life easier.

[npdunn]

Thanks for everyone's input, back to the drawing board.