I think you have been using a methodic and systematic process for
finding the culprit to your vibration. I have found 90% of vibrations
easily traced back to tires out of balance, bent wheels, bad tires, or
bent wheels that have finally effected tire wear to the point that a
vibration is experienced. The last 10% is much harder to find. You
have to start removing possible offenders from the equation one by one.
You took off the wheels and the problem has still persisted. You
removed the drums and it still persisted. You indexed the driveshaft
and it still persists.
-You need to examine interior components of the differential for
causes. The rear axles could be bent and even though the wheels dont
wobble back and forth, they may be hopping up and down. Problems with
internal bearings could also cause this.
-You are right in thinking that you may need to get the driveshaft
balance checked. I also rememeber someome who like to 4-wheel, and they
planted the truck in water up to the frame once, and then had a huge
vibration afterwards. Turned out that the driveshaft had taken on
water, and the truck never got parked with the point of entry for the
water turned down to let it drain out. If your driveshaft is hollow,
shake the bugger once if you 4x4. It could have thrown a weight that
you didnt realize too.
-Did you check all the suspension mounts?
-What about possible transmission problems? Can you run the engine with
the vehicle off the ground and the driveshaft out to see if you have a
vibration then? You'd have to find a way to keep trans fluid in the
tailstock where the driveshaft would go. Another good trick is to drive
down the road and get the truck to vibrate, then change gears and see
what happens with engine/trans rpm changes, and then throw the trans
into neutral to see what it does.
-A last thing: I have seen quite a few instances where a change in
tires, air pressure in tires, or shocks/struts will cause a person to
think there is a vibration due to being able to feel every little bump
in the road. If you went to extremely high pressure shocks, this could
magnify every pebble you run over, and the oscillations after you hit
the little bump may not go away in a nanosecond. Load the bed down with
500-1000 pounds and see what happens to the vibration. Then, take the
beached whale home and tell her you just want to be friends! If you
have installed oversized tires, you should be dropping the air pressure
in the tires to keep them from wearing prematurely in the center, as
well as maintaining a quality ride. A good tire shop will have a
load/inflation table that you can look at. Find the stock tires size
and air pressure, and the weight corresponding to it in the table, then
go to your present tire size and find what air pressure will support the
same weight as your old tire with the factory air pressure. You will
normally drop pressures when going to a larger tire. Dont be afraid,
pressures in the 20's will not peel the tire off the rim. 2 examples:
My wife's last Geo Tracker had P205/75R15's with a recommended pressure
from the factory of 23 psi. I also swapped out a buddy's Jeep Wrangler
factory tires (P215//75R15's) and an air pressure reading of over 30 psi
for a set of 30x9.5R15's. His air pressure was dropped to 25 psi, and
the tires rode great and lasted over 100,000 miles.
Hope some of this helps.
Patrick
This archive was generated by hypermail 2b29 : Fri Feb 06 2004 - 11:47:04 EST