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Author Topic: Suspension: Solid K-Frame Isolators  (Read 20313 times)

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Suspension: Solid K-Frame Isolators
« on: January 25, 2008, 11:51:50 »

Improving Handling With Solid K-Frame Isolators

Below is information on improving your handling by eliminating the isolated front subframe (k-member) used in all M-bodies.


The isolated subframe design began around 1973 in B-bodies to provide a more cushioned ride by reducing roadway shock.  With the new design, the unibody chassis of the car no longer bolted directly to the subframe.  The subframe was now fully isolated from the chassis by the use of rubber "biscuits" or isolators with through bolts. The design was later carried over to F-bodies (Aspens and Volares) and then to M-bodies in 1977. 

The isolated design works flawlessly to provide passenger comfort.  However, the trade-off is less precise handling due to the tendency of the body and the K-member to want to move independently during hard cornering.  This was not a problem with civilian family cars, but it became an issue with high performance and police applications.  It also became more noticeable with civilian cars as the rubber isolators aged and began to deteriorate. To address the problem, Chrysler offered replacement isolators made from solid cast iron.  These isolators created solid attachment points between the chassis and subframe, making the two components act like one piece.  The result was vastly improved handling with less body roll.   Unfortunately, the solid cast iron isolators are no longer offered by Chrysler.

Replacement Isolators

Unless the factory rubber isolators have deteriorated, they are probably fine for normal driving.  However, if you plan on doing any performance upgrades, using any of the available aftermarket isolators is a very good idea to improve handling.  Below are upgrade options for subframe isolators.

  • Polyurethane: Polyurethane isolators are a great alternative to the solid isolators.  Although not rock hard like solid isolators, polyurethane isolators are typically very hard, with a Durometer (hardness) rating of close to 90 or better. Just Suspension used to carry them (see photo below), but they no longer appear on their website.   Fortunately, Springs n' Things (Espo) still sells them (listed as Body Mounts).
  • Aluminum: Aluminum isolators work as well as the cast iron isolators, and they are much lighter. Aluminum isolators are available in either billet or cast.  It is a good idea to have any aluminum isolators powdercoated to discourage galvanic corrosion. Billet aluminum is far stronger than cast, and it is probably more corrosion resistant.
    • Billet Aluminum - Farley's member CudaZappa sells high quality isolators machined from solid 6061-T6 billet aluminum.  These are always available as single orders, or through group guys.
    • Cast Aluminum - Firm Feel sells cast aluminum isolators.


  • Photo of cast iron isolators and a diagram showing the installation points on a isolated-style k-member. (Courtesy of Richard Ehrenberg, SAE)
  • Aftermarket polyurethane isolators. (Courtesy of Just Suspension, but apparently no longer available.)
  • Aftermarket billet aluminum isolators. (Courtesy of Farley's member CudaZappa)
  • Aftermarket cast aluminum isolators. (Courtesy of Firm Feel, Inc.)

« Last Edit: October 16, 2010, 22:51:35 by Reggie »
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