ZR-1 Maintenance Tips

General Maintenance

by Jim VanDorn


The most common call we receive by far is from a confused ZR1 owner. After years of reading everything from which thermostat to use, to what type of spark plug is best, the average owner is totally and completely confused...and for good reason. There are many varied opinions of what is best for our cars but that may depend greatly on how you use your ZR1.


After seven years plus, many ZR1's are finally accruing some mileage. We have had the opportunity to closely inspect many engines with a variety of types of use from normal street driving to severe "weekend" use (track time). Compiling this information we can now offer the ZR1 owner some observations. One rule we've adopted after hearing so many owners say the same thing is the "DIMWIT" or "Darn, if I didn't Mess With IT" rule. In other words, if you didn't have a problem, then what are your intentions in the first place? To date, the only company known to have a fleet of engineering ZR1's to test with was GM and it's affiliates.


Therefore, we must ask ourselves if their suggested procedures and parts recommendations should have a considerable amount of merit. Obviously they do, but on the other hand, there are no doubt areas for improvement. Although we will begin our segment discussing the routine and normal maintenance of the ZR1, there are many areas where an upgrade will be suggested.


Please understand that these are personal opinions and experiences and are not intended to conflict with service procedures outlined in the appropriate service manual.

As with many other systems on the ZR1, constant improvements were made each year to enhance handling performance. With the exception of the '95 model year, the ZR1's shock valving and calibration was changed every model year. In 1992, the factory Bilstein shock absorber was changed dramatically from a single piston design to a "dual digressive" or two piston per rod design. Simply explained, the new valving assembly controls oil flow through the bypass orifice passage and this generated characteristic again becomes digressive. This re-designed provided a wide range of new low speed controllability.

The '90-'91 model shocks have an internal rod travel of 160 degrees, controlled by the control module located behind the driver's seat in the rear compartment (by the ABS controller). The '92 and up models have only a 80 degree rod travel. Therefore, it is essential that an earlier style controller NOT be used on a later style system or the result will be 4 stripped actuators.
Bilstein Gas Pressure Shock Absorbers, due to their extremely high internal pressures, must use a seal which is extremely tight. To prevent deterioration from the friction between the piston rod and seal, a self lubricating seal is used. By design, a small amount of the shock absorber oil is allowed to pass by the seal onto the piston rod, thus creating a constant film of oil on the rod. In fact, approximately 10% of the total oil capacity of the shock is intended for this purpose.

After an extended period of time, this oil will create a blackish film on the shock body. The appearance of this oil is normal and should not be taken to indicate a defective Bilstein shock. This gradual oil loss will not affect the performance of the shock except after a long service life (50,000-75,000 miles) depending on driving conditions.

When the shock's performance is questionable, your Bilstein distributor can have the Bilstein units completely rebuilt and rebuilt units carry a lifetime warranty from Bilstein. In addition, we also upgrade older shocks to the newer dual digressive design and install programmable controllers in which replaceable proms are used for various driving conditions. This allows an owner to have both the comfort of a daily driver and the ability to easily convert to a much more aggressive ride for performance usage.
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