driveline questions

[CameronT]

i am having driveline issues, i am lowered a ton in the front and 3 inches in the back so i am pretty raked.... 14 inch tires fronnt and 15 inch tires in the rear so it adds a half inch top to bottom difference, now! i am having massive shakes from the driveline, i did crash it into a curb and its all fixed now. but i was replacing the carrier bearing and i loosened the driveline to pull it and it shot to the floor board, at that time i was even 3 inches front and rear,

my question is could it be to long and un balanced? or do i just level the ride height and drive it or do i shorten it and have it fixed to wear it works?

 

all feed back is welcome even that guys that will point out my curb incident

[DanielC]

My opinion, the curb is not the problem.  The lowering is.

 

The carrier bearing should pretty much hold, or point the drive shaft at the transmission.  You might have something going on there.  If you have separated the two halves of the drive shaft, and you put them back together with the two halves not the same way as they were originally, that might be a problem.  The drive shaft is balanced as a single unit.

 

U-joints do not run at a constant speed if they are bent.  If you run a constant speed at the transmission, and the U-joint is bent, on a normal height truck, the drive shaft is speeding up and slowing down every half revolution, and if the angle at the differential is the same but opposite, the speeding up, and slowing down of the driveshaft is cancelled out.

 

Long story short.  Try to reduce the angle your U- joints bend.  After that, try to match the angles the U-joints bend.  You can adjust the differential angle with angled lowering blocks.

[datsunaholic]

Lowering the front has no effect on the driveshaft, but the rear does.  It effectively shortens the distance from the transmission to the differential flange, so you've bottomed out the driveshaft in the transmission.  Angled lowering block in back might solve it, if it's a little bit, bit you may need to have the driveshaft shortened slightly.  I've heard RAISING the carrier bearing can help too (effectively lengthens the distance), but if the driveshaft hits the floorboards when the carrier is unbolted you're really bound up.  Like an inch or more bound up.

[CameronT]

i currently have a inch and a half spacer, it helped aftert the snow cleared i noticed the vibration, about a month or 2 ago now, in portland, OR it started making vibrations than i went lower and it made it a little worse... i am going to go lower on the drivers side to even that height out, but the driveline will need to be assesed as i cant go over 50mph, so eliminates a lot of roads

[datzenmike]

Drive  shafts.... angle in, must equal angle out. As Daniel stated, a U joint cannot turn at the same speed when joined to two shafts at a bend. the bigger the bend the more it speeds up and slows down. To counteract this the second U joint is arranged 180 out so the acceleration on one is cancelled by deceleration on the other. Naturally if one bend is different than the other, it will vibrate.

 

Everyone likes a demonstration so imagine the left side connected to an engine and driven at a steady speed. Actually if you watch it IS turning at a steady speed. Now watch the right side. You'll see it speeds up and slows down as it turns.

 

 

Take a good look at your rear driveshaft. Does the front U joint bend look the same as the one to the differential? There are tools for measuring this. You can put wedge shaped shims under the axles to tilt it. On my lowered 710 I had to tilt the diff downward by placing a 1/8" shim to the rear of the spring perch. Lifting the back tilted the front down and angle balance was restored and the loud hum is gone. Well worth the trouble.

[TruenoGuy]

I had the same issue after I lowered mine.  Tried raising the carrier bearing mount, but it was still vibrating like crazy.  With 3" blocks in the rear it was low enough to convert to a one-piece driveshaft.  Had a local shop make me one for $170.