Chrysler / Mopar Solutions

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Sub-Frame IRS Challenger Charger Magnum 300C LX

Man y LX owners report a mystery noise in their rear suspension. Some call it a clunk and others a bang or knock. As part of a Pedders 28 Point Inspection we check the "tracks" of the four rear sub-frame bushes that hold the IRS in the chassis. On a lift with a shop light points of contact and wear indicate sub-frame bush wear and failure. NVH voiding is the primary suspect. The voids allow the entire sub-frame assembly to move under load at hard launch or at speed over road imperfections.

The OE bushes allow the sub-frame to make contact with the monocoque (uni-body) when driven aggressively or over all but the smoothest of roads. These pictures and video take the mystery out of the mystery noise. The OEM sub-frame connector bushes on the LX are tuned for the ordinary driver and driving conditions. They suit a range of engine applications from the base 3.5 to the maxed out SRT 8 editions. Noise is an obvious consequence. Less obvious is Rear End Step-Out. Rear end step-out occurs when the rear wheels begin to steer the car from the rear. In transition from left to right and back to left the rear sub-frame literally cannot keep up. When the front wheel are turned left and right the rear wheels follow in the first motion. in the second they lag behind and by the third they are far behind -- rear end step-out. The same motion occurs as you turn and encounter a bump or transition in the pavement. The sub-frame becomes unsettled and the driver encounter rear end step-out. This is a direct result of the highly compliant rear sub-frame connector bushes.

Bush squirm under load created these track. You can see where the metal to metal contact has occurred. How does this occur? One video is worth a thousand words.

You now know why Pedders designed our EP1172 sub-frame connector bushes for the LX with a surface area of 26,580 mm compared to the OE size of 4,284 mm. Pedders sub-frame connectors have 640% more control surface to prevent rear end step-out, mystery noises and virtually eliminate sub-frame connector bush failure. Pedders warranty does not have a 'speed contest' exclusion. We know what you did last Friday night -- we do it too.

The OEM sub-frame connector bushes for the LX function are designed for an average driver and average driving conditions. This picture illustrates the failed OE bush with less than 20,000 miles of spirited driving on OE tires and wheels. If the car had been shod with 20 inch wheels and an aggressive tire like an REO1O, Michelin Pilot Sport 2 or Nitto NT01 the bushes would be worse. This is not

The SRT 8 bush on the lower left is delaminated from the ferule and torn. This is not a bad suspension design. Chrysler’s warranty, as do virtually every company’s warranty, excludes vehicles used in speed contest on the street or track. Most HEMI LX owners will be ‘guilty’ of using their RWHP to have some fun – or they would be driving a four cylinder econo-box. The owners of these vehicles are guilty as charged. They DRIVE their LX HARD.

The LX is not the only vehicle on the road where this can be found. The all new billion dollar ZETA Global Rear Wheel Drive platform from GM has rear end step out. Replacing the OEM sub-frame bushes with Pedders EP1172 Sub-Frame Bushes resolves this issue. Our urethane bushes are voided to maintain a high level of OE quiet in the cabin while eliminating any possible contact between the sub-frame and the monocoque.

With the rear sub-frame more controlled rear end-step out is controlled. Every-Day drivers will notice the difference in driving feel. The car will be more precise and controlled. In the event an evasive maneuver must be made you will have be confident in the response of the vehicle. If you define an evasive maneuver as the drag strip green light you will find more power available at launch as your RWHP is not lost in sub-frame squirm.

OEM components are limited by many constraints from cost to NVH tuning for ultimate quiet at the expense of control. Pedders does not have tocompromise our components for the LX. We design our parts as we feel the OEM would is they did not require approval by committee. Pedders manufacturespremium bushes for the most demanding driver and driving conditions to deliver both close to OE NVHand track like performance.

Chances are you didn’t buy your LX to drive 55 MPH and live life in the slow lane. The exhaust you added, the tune you paid for, the cam and all your other mods promised higher horse power and place higher loads on your suspension. The added power, your driving style or both will create premature OE bush failure. Pedders LX bushes are designed for the MOPAR enthusiast. Our warranty does not exclude use in speed contests. We are enthusiasts who design suspension systems for enthusiasts – yeah we know what you did last night. A Pedderised LX will ride this close to OE, will be far more stable under load and were designed to last for they way you drive.

The OE sub-frame connector bushes on the LX are tuned for the ordinary driver driving on ordinary roads in ordinary conditions. City roads in New York, Philly, Chicago and LA are not ordinary. They are rough. Rurtal roads are not ordinary either. Actually, very few of us are ordinary drivers driving in ordinary conditions. The OEM sub-frame bushes suit all engine applications from the base 3.5 to the maxed out SRT editions and drivers. That is a compromise that is required in a production automobile. Pedders is not limited by that standard. We make premium bushes for the most demanding driver to deliver both OE like noise, vibration and harmonics (NVH) and track prepared performance. The OE bushes allow the sub-frame to make contact with the monocoque (uni-body) when driven aggressively.

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