knew i was a little dumb but not that dumb?

[stretch67]

been having driveline vibe trouble. 208 slip yoke tcase. 7" spring lift, 4 degree shims, shakes the rearview!i noticed awhile back i had a measurement difference at the rear tire to wheelwells, front to tire different left to right. so i tried to adjust by lossening the u-bolts and shifting the axle on the springs but no difference. so i figured vibe was driveline related. yesterday my buddy was following behind my truck and noticed it dog-tracking! i am using 2nd gen 6" lift springs on the rear. question is the spring eye to center pin measures different on the 4" springs i took off,26" vs 27". i have yet to measure the ones on my truck but are the springs different front to back and has this been my problem all along? i thought i had measured rear springs before and they were same front to back? /forums/images/graemlins/dunno.gif

 

[GMCLegacy]

the lift springs may not be symetric like the stock springs.

 

[Blue85]

Aftermarket springs put the center pin in different locations. If you switch brands your axle could move 1-1.5" forward or back. Sometimes this is required because with more arch, you need a longer spring, the location of the center hole will be a different distance from the spring eye.

If things are not the same left to right, then that is a problem.

Are you sure it is dog-tracking. The different front and rear track-widths on Chevy trucks is often mistaken for dog-tracking, especially on lifted vehicles. I would take a tape measure to everything, including diagonal measurements.

Even if you are crooked, this may not be the source of your driveline vibs. At your lift height, you must be running over 15 degrees in the U-joints. You may have to upgrade to a C/V shaft. First things, first, though. Make sure the upper and lower U-joint angles are the same. Even if they are only different by 2-3 degrees, the whole vehicle can shake.

 

[stretch67]

so even different brands vary center pin placement. i think i measured the stock springs when i got equal measurements! when i received my 6" springs the center bolts were loose enough for the overload and tapered shim to have rotated 180 degrees. so one spring could be backwards that sucks! i plan on upgrading to a cv rear shaft just can't decide if i should cut my losses and go with a doubler case or atlas before i spend$$$$$ on new shafts /forums/images/graemlins/doah.gif

 

[hawkeye649]

IIRC chevy says that shafts that spin at 3,200RPM or less during normal "work" can have a angle difference as much as 2*, and that anything that runs over 3,200RPM needs to be either 1* or 1.5* (kint remember)