Re: Rear suspension problems

From: Tubamirbls@aol.com
Date: Wed Aug 21 2002 - 14:04:15 EDT


Hi Adam
     Truck rear suspension is basically very simple. In concept it is a
carryover into motor vehicles from horse-drawn wagons, buggies and stage
coaches with not a lot of refinements in 100+yrs.
     Your rear axle assembly is supported by a multiple leaf spring parallel
to the driveshaft at each rear wheel. The springs are mouted to the truck
frame by a shackle at each end, a single forward and a double aft. A pair of
shock absorbers are mounted vertically next to each spring to dampen rebound
from upward movement of the axle as you drive over irregular pavement
surfaces. On many Dakota models after 1997, a stabilizer bar is attached to
the axle housing and suspended from the truck frame to work as a torsion bar
to resist body lean when cornering. Since movement is necessary for each of
these components, they are all mounted on some kind of rubber bushing to
allow for that. That's it.
     When you drive onto a speed bump, both springs contract, both shocks
contract and the stabilizer bar simply moves in free travel upward. If any
of these components have worn and/or defective parts they may be transmitting
to the chassis the "sound" you're hearing. The extreme aft end of your
exhaust system is routed over the rear axle housing. If that tailpipe
assembly is incorrectly positioned it can contact the axle when substantial
upward movement is caused by a tall speed bump and you would hear such
contact.
      So where does one look for the annoying sound you're hearing (again
assuming it's not coming from cargo in the bed, a loose tailgate or toneau
cover, loose rear bumper or trailer hitch, loose fastenings of the cargo bed
to the truck frame, loose spare tire, an incorrectly hung tailpipe or some
part of your fuel tank and its plumbing). If your truck is still under the
36k warranty it is not likely any of these are the cause however there is a
possible exception to anything these days.
     I'd concentrate on the rear suspension components. If everything
appears normal for them, you can disconnect the shocks, one at a time, drive
over the test bump and see if you noise disappears from either of them, same
for the left & right connections for your rear stabilizer bar, if so
equipped. If neither has any impact, then look for a defective shackle
bushing, loose fasteners on the shackles and carefully inspect both springs
and each leaf in same for a crack.
     If none of these lead to the cause, then stay out of parking lots with
speed bumps.

Paul Sahlin



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