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Author Topic: Suspension: Torsion Bars  (Read 23419 times)

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Reggie

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Suspension: Torsion Bars
« on: February 17, 2008, 16:37:17 »

F/J/M Torsion Bars

Background

All F/J/M Body Chrysler products share the transverse (crosswise) torsion bar setup attached to a fully isolated crossmember (K-frame). The transverse torsion bar design first appeared in the F-body (Aspen and Volare) platform in mid-1976.  It was a significant departure from the traditional longitudinal torsion bar design that Chrysler had used since 1957.  The transverse design is notable for three reasons:

  • Transverse torsion bars are "L" shaped. The older style longitudinal torsion bars are straight.
  • Transverse torsion bars are fully attached to the k-frame. The older style longitudinal torsion bars attach to the lower control arms and to the rear crossmember, but they do not attach to the K-frame at all.
  • In addition to serving as springs, transverse torsion bars also serve double duty as strut rods to stabilize the lower control arms. The older style longitudinal torsion bars only serve as springs.  There are separate strut rods to stabilize for the lower control arms.

Each torsion bar is anchored in the front of the K-frame opposite the the affected wheel.  From the anchor point, the torsion bar runs parallel across the K-frame through a "pivot cushion bushing" (attached to the k-frame), then turns and extends towards tha rear of the car to attach to the lower control arm.  The end of the torsion bar has an isolated bushing which bolts to the lower control arm, and also to the front sway bar.  Torsion bars are are marked with the letters "L" for left side or "R" for right side.  They are not interchangeable between sides.

Vehicle Height Adjustment

The height of the front suspension (also called "front suspension height" or "ride height", is controlled by turning the torsion bar anchor adjusting bolts located in the K-frame. It is important to note that the passenger side (right) bolt adjusts the driver side (left) torsion bar and the driver side (left) bolt adjusts the passenger side (right) torsion bar. Any time the suspension height is changed, it will also affect both the camber and caster, and thus the front end should be re-aligned. Factory ride height should be set to 12.5", plus or minus .25".  For reference:

  • Caster is defined as the number of degrees of forward or backward tilt of the spindle support arm at the top.  Forward tilt from true vertical is negative caster and backward tilt from true vertical is positive caster.
  • Camber is defined as the number of degrees the top of the wheel it tilted inward or outward from true vertical. Inward tilt is negative camber and outward tilt is positive camber.

GENERAL WARNING ABOUT TORSION BAR REPLACEMENT:

  • Torsion bars are under extreme pressure. You should remove torsion bars ONLY according to the procedure listed below. YOU RISK SERIOUS INJURY OR DEATH by removing torsion bars in any manner other than the procedure listed below.
  • Torsion bars are NOT interchangeable between sides, so do not mix them up when removing them. As mentioned, they are marked with the letter "L" and "R" for the correct side.
  • PROTECT TORSION BARS FROM DAMAGE WHEN WORKING ON THEM.  Be careful not to nick or scratch torsion bars when removing the rubber pivot cushion bushings.  Any nicks or scratches on a torsion bar can lead to complete failure, which can result in possible loss of vehicle control at speed. DO NOT clamp torsion bars directly in a vise.  Use brass or aluminum plates against the torsion bars to protect them from the jaws of the vise. DO NOT hammer, heat or use vise grips on torsion bars.
  • Inspect torsion bars for corrosion. Seriously corroded torsion bars should be replaced with a better pair from a salvage yard.
  • The bolts that secure the torsion bar end bushings to the lower control arms may be SPLINED just like wheel studs. DO NOT attempt to turn them, or you could ruin your lower control arm. Take the nuts off from the bottom and then pop the bolts up and out from the top.

Torsion Bar Removal

  • Block the rear wheels and place the front of the car on jackstands so that the front suspension is hanging with the wheels off the ground.
  • Turn the torsion bar anchor adjustment bolts counter-clockwise (to the left) to remove them. This will take the tension off the torsion bars.
  • With a floor jack, raise the lower control arm so that there is a 2 7/8 inch space between the k-frame ledge and the torsion bar end bushing flange. This height is called "design height", and is set by the factory to equal the height of the car sitting on the wheels with three passengers aboard. It is important to maintain this position in order to align the sway bar and lower control arm attaching points to allow disassembly and reassembly of the components.
  • Remove the sway bar to control arm attachment bolts and retainers.
  • Remove the two bolts that attach each torsion bar pivot cushion bushing to the k-frame.
  • Remove each torsion bar and anchor assembly from the k-frame.
  • Remove each torsion bar from the anchor assembly.

Torsion Bar Pivot Bushing Replacement

  • Use a bench vise to hold the torsion bars while installing the new bushings. IMPORTANT: Be sure and use brass or aluminum plates to protect the torsion bars from getting chewed up by the vise jaws.
  • Each pivot cushion bushing has a backing plate with four welds holding it on. With the torsion bar removed, drill out the four welds on the backing plate of the pivot bushing to remove the plate.
  • Cut the old bushing away with a knife. As mentioned in the general warning, take care not to
    nick the torsion bars while removing the pivot cushions.
  • Make up a solution of 1 part dish soap to 8 parts water, which will be used to help slip the new bushings on.
  • Soap up the torsion bar with the solution, dunk the bushing in the solution and let the fun begin. Push a new bushing onto the torsion bar over the hex end of the bar.
  • DO NOT USE OIL OR GREASE ON RUBBER BUSHINGS.  Oil or grease will attack rubber bushings and cause them to fail.
  • It may help to immerse bushings in a pan of very hot water first to make them more  pliable. Leave them in until they feel warm to the touch. DO NOT boil them, as this may cause the rubber bushings to deteriorate.

Replacement Torsion Bar Parts

Chrysler used to offer a service replacement torsion bar assembly which included:

  • The torsion bar
  • The "Pivot Cushion Bushing"
  • The "Bushing to Lower Control Arm"

The service replacement torsion bar assembly is no longer available from Chrysler. However, the following replacement parts are still available:

  • Pivot Cushion Bushing (rubber) - Mopar still sells these as Mopar 4186828. One package per torsion bar includes: Rubber Bushing, Two Piece Clamp assembly, Hardware (4 bolts), Frame Friction Plate, Bushing Clamps, and Instructions.  The price ranged from about $30 to $45 US each back in April 2006.
  • Pivot Cushion Bushing (polyurethane) - Sold by Firm Feel.  These bushings are much stiffer than the rubber ones, and they would probably be impossible to slip over the hex end of the torsion bar if they were solid pieces. For that reason, they have a slit on one side to allow easier installation. They are said to be much easier to install than the rubber pieces. They also have zerks so they can be greased.
  • Torsion Bar Bushing (Torsion bar to control arm) - Moog K7289 (old Mopar 4186805). This is the bushing or "end mount" that attaches the non-hex end of the torsion bar to the lower control arm. These should only be replaced if necessary. The part is sold by many parts houses, with the average price being about $80 each as of 02/15/08.

Other Front End Replacement Parts

Note: Mopar part numbers are provided for reference. Some are still available from  aftermarket suppliers.

  • Sway Bar Frame Bushing Kit (A38/AHB with 1 1/8" Bar) Moog K7108. Note: Cop car
  • Sway Bar Frame Bushing Kit (Except 1 1/8" Bar) Moog K7092 Note: Non-Cop car
  • Front Lower Arm Sway Bar End Link Kit (1 needed for each side) Moog K7087
  • Upper control arm bushings - Moog K7084
  • Lower control arm bushings - Moog K7097
  • Front Upper Control Arm Bumper - MOOG K7293
  • Sway bar bushing kit 15/16" 1976-1980 F & M-bodies Mopar P4876207 - available in  polyurethane from Southeast Performance
  • Sway bar bushing kit 1" 1976-1980 F & M-bodies Mopar P4876208 - available in polyurethane
    from Southeast Performance
  • Sway bar bushing kit 1 1/16" 1976-1980 F & M-bodies Mopar P4876209 - available in
    polyurethane from Southeast Performance
  • Sway bar bushing kit 1 1/8" 1976-1980 F & M-bodies Mopar P4876210 - available in
    polyurethane from Southeast Performance
  • Torsion Bar Dust Boot or Seal 1980-1988 M-bodies Mopar P2269250 - This part is no longer available,  However, Mopar P3402575 (Torsion Bar Seals '73-up) is still available as a possible substitute which might require modifications.

Front Suspension Tightening Reference Chart

Note: All torque values are in Foot-Pounds unless otherwise indicated in bold.

Adjusting Bolt Nut (Upper Control Arm - Pivot Shaft Bolt Nut)150
Ball Joint to Upper Control Arm (Upper)125
Ball Joint Stud Nut (Upper)100
Ball Joint Stud Nut (Lower)100
Rebound and Jounce Bumpers (All)200 in/lbs
Pivot Shaft (Lower Arm - Lower Control Arm Pivot Bolt Nut)75
Steering Knuckle Bolts/Nuts (Lower)160
Sway Bar Link Retainer Nut100 in/lbs
Sway Bar Strap Nut 30
Idler Arm Bolt Nut70
Tie Rod Ends (All)40
Tie Rod Sleeve Clamps150 in/lbs
Torsion Bar Bushing to Lower Control Arm Bolt/Nut70
Torsion Bar Pivot Cushion Retainer Nut-Bolt85
Shock Absorber (Upper)25
Shock Absorber (Lower)35
Sway Bar Cushion Bolt65
Upper Control Arm Pivot Bushing Nut110

Photos

  • Diagram of torsion bar assembly (Courtesy of Chrysler Corporation)
  • Diagram of torsion bars shown from underside (Courtesy of Chrysler Corporation)
  • Diagram of torsion bar anchor adjusting bolt (Courtesy of Chrysler Corporation)
  • Diagram of torsion bar anchor and swivel installation (Courtesy of Chrysler Corporation)

Vendors to Check With


Sources

« Last Edit: February 19, 2008, 21:59:02 by Reggie »
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"There is only one success - to be able to spend your life in your own way." - Christopher Morley 1890-1957, American author and editor

Library format and content © 2007- 2012 Reginald A. Royster, Sr., unless otherwise authored or noted.

Reggie

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Suspension: Torsion Bars - Page 2
« Reply #1 on: February 17, 2008, 17:27:21 »

F/J/M Torsion Bars - Page 2

Additional Photos

All photos on this page are courtesy of of Farley's member Woodvark unless otherwise noted.

  • Diagram of torsion bar and sway bar attachment point on lower control arm (Courtesy of Chrysler Corporation)
  • Old bushing:
    • Top: Torsion bar showing where it rubbed the K-frame as a result of the failed pivot cushion bushing.
    • Bottom:Deteriorated bushing after removing the backing plate. To remove the backing plate, you must either drill out the four welds holding it, or the shell must be cut of with a band saw.  Then the rubber bushing can be cut off with a knife.
  • New bushing installed. The new bushings must be pushed onto the torsion bar over the hex end of the bar.
  • Done. New pivot cushion bushings and sway bar bushings installed on car. The entire process took about four hours.
« Last Edit: February 20, 2008, 18:40:28 by Reggie »
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"There is only one success - to be able to spend your life in your own way." - Christopher Morley 1890-1957, American author and editor

Library format and content © 2007- 2012 Reginald A. Royster, Sr., unless otherwise authored or noted.
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