GM ZW7 Suspension Issues Explained(+3 Troubleshooting Tips)

In this brief article, we are going to discuss the issues that occur in the General Motors RPO code ZW7 Premium Smooth Ride Air Suspension, what the causes are, and Troubleshooting Tips.

Top 4 Rear Suspension problems in GM ZW7

  • Car Side-to-Side Lean
  • Poor Ride Quality
  • Noisy Rear end
  • Leaky Shock

What is the GM ZW7 Premium Smooth Ride Suspension?

The Premium Smooth Ride, also known as RPO (Regular Production Option) Code ZW7, is GM’s trademark name for their own unique automatic pneumatic load-leveling Rear suspension. 

The Premium Smooth Ride suspension uses a conventional Coil Spring suspension in the front axle, while the rear axle uses a self-contained, self-leveling Nivomat shock. In RPO code ZW7 equipped trucks, the rear suspension comes with a softer coil spring because the Nivomat self-leveling system contains an air spring that shares load with the coil spring in parallel,

Many GM SUV’s were offered with an optional ZW7 suspension package on the Chevrolet Suburban, Tahoe, Avalanche, Yukon,  Cadillac Escalade.

How does a Nivomat Shock Work?

The main feature of a Nivomat Shock is its Self-Leveling Capability without the help of any external pressure. Apart from this, it operates the same way as a conventional shock does. What gives the shock its leveling capability is a pump mechanism and oil reservoir that can increase the accumulator pressure, which increases the shocks lifting capability.

Through this lifting capability, the Nivomat Shock maintains the axle ride Height at all loading conditions. The big advantage to the Nivomat shock absorber is that it requires absolutely no plumbing, Air compressor or Height sensing mechanism to help in leveling the vehicle.  The normal stroke of the shock over a regular road profile provides enough pumping action to cause leveling of the vehicle.

General Troubleshooting of Nivomat Shocks

To Test the general health of a Nivomat shock, you need to measure the rear ride height and also drive some distance with a load.

  • First do the measurement without any payload. You can do this with a simple ruler or tape measure. Park the car on a smooth flat and level surface. Now measure the distance from the center of the wheel to the top of the wheel well and record this value.
  • Place a load inside the car at the rear of at least 200 lbs. Position it such that it is as close to the Rear axle as possible.
  • Now do the Ride Height measurement with Payload the same way you did earlier without load. Write down the measurement.
  • Drive around in the loaded vehicle for at least two to three kilometers
  • Park the car on the same flat surface as before, and measure the ride height.
  • The last measured ride height in the loaded condition should match the first measured ride height in the unloaded condition. 
  • If these two values do not match then chances are that the rear Nivomat Shocks have failed internally.

Noticeable vehicle Side-to-Side Lean

  • If one of the Rear Nivomat Shock units has failed, then the rear suspension ride height will be noticeably reduced on that failed-shock side. 
  • Measure the  ride height difference from side-to-side on the rear axle. If you find that it’s greater than 1.5 inch, you must  inspect the Nivomats for either leaks or wear-out.

Troubleshooting Poor Ride Quality

  • A Nivomat is basically a conventional normal hydraulic Damper. 
  • Hence, it is susceptible to wear at the valves, seals and internal surfaces very similar to a conventional shock or strut. 
  • In normal driving, if a vehicle feels that it has reduced Road-hold or if it feels like the car is floating, it could easily be because of the Rear shock absorbers.

Troubleshooting a Noisy Rear End 

In normal driving conditions, a failed rear shock can make ‘knocking’ or ‘bumping’ noises if the internal load-leveling components are not functioning.

Shock Absorber Leakage

Nivomats will leak at the shaft seal and at the top of the body. Oil stains would be clearly visible if this happened.

Conclusion

In this brief article we have discussed the issues that occur in the General Motors RPO code ZW7 Premium Smooth Ride Air Suspension, what the causes are, and Troubleshooting Tips.

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