Jaguar Roof Hydraulic Relief Valve Kit for XK8/XKR through MY2006

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  This page has been set up to provide information and guidance for individuals who would like to purchase the Hydraulic Upgrade Kit for XK8/XKR vehicles Model Years 1996-2006. If you have questions about compatibility, compare your pump the one pictured below. Please note that this kit is designed to allow the roof system to operate fully without risking damage to the pump motor. Do not confuse this with cheap fixes that starve the motor by inserting resistors in the motor circuit. This causes the motor to run excessively slow, does not eliminate the dead head problem, and will ultimately damage the motor. The kit sold here allows the motor to run at its full design speed and only acts to reduce pressure at the critical point after the work has been done. The problem with the original system is caused by the pump being held on after all motion has stopped, resulting in dead head high pressure spikes and extreme stress on all the components. This kit eliminates those factors and as a result will increase the reliability of all components including the latch hoses and lift cylinders.

System diagram without kit installed

The President of LSI Controls (Walt Nuschke 00XKR Conv) is also the owner of a 2000 XKR and became interested in this problem through participation in various forums and his own difficulties with the roof system in his car. LSI Controls has tested the hydraulic system that operates the roof and configured a kit that will improve the reliability. This involved tearing apart a pump to discover how it works and installing a pressure sensor to measure the operational requirements of the system. From this it was discovered that the pump generates 30-40% more pressure than is necessary to operate the system. The upgrade kit is designed to regulate the pressure which will relieve stress on the components. Less stress equals longer life. Read on to learn more.

Jaguar Upgrade Kit

Download Installation Guide      

Background Information:

This upgrade kit is designed for the Jaguar XK8/XKR model years 1996-2005. The automatic convertible top in these model years is operated by a hydraulic system manufactured for Jaguar by the Power Packer company. Power Packer is the primary designer and manufacturer of convertible top systems that are also used by a long list of car manufacturers. This system has suffered from a variety of premature failures. The kit offered here is designed to overcome flaws in the design of the Power Packer roof system and improve reliability. The failures, in approximate order of severity, have been the latch hoses, where they fasten to the latch cylinder, the latch cylinder seals, the lift cylinder seals (located behind the rear jump seat on both sides), and sporadically hoses in random locations. The observed failures have been in majority related to high operating temperatures in the latch area. Hydraulic components are rated by maximum operating pressure and temperature. These two parameters interact such that a hose with higher temperature rating will have lower pressure rating at that temperature and visa versa. The operating temperature in the Jaguar is beyond our control (talk to the Sun about this) but this upgrade kit is able to reduce operating pressure by over 30% without affecting operation. This large pressure reduction therefore increases the safe operating temperature range of the system. The relative effect amounts to about 600 pounds of force that no longer must be contained by the hoses and seals. Model years up to about 2001 used Nylaflow hose manufactured by Parker. This hose was particularly unreliable. Later models have Polyflex hose (also manufactured by Parker) installed. Polyflex hose has performed better but still has an unacceptable failure rate in this system. Both of these hoses are custom for Power Packer and not commercially available. The name of the hose and product number (363) is clearly printed on the hose. Also printed on the hose is a date code in the form “1-Q-03″ which in this case is the first quarter of 2003. This date can be matched to the model year and other hoses in the system to diagnose what has been done to the hydraulic system in the past. The installation of hoses of different type and/or date code is an indication of prior replacement and subsequent years of service. The hose connection at the latch has the highest failure rate due to high temperatures from the sun in this area. Failures in this area are immediately recognized. The lift cylinders, located on both sides behind the rear seat, also fail but at a lower rate. These cylinders develop leaks in the shaft seals that gradually escalate. If the hydraulic fluid must be repeatedly topped off this is the likely cause. A leaking lift cylinder will leave a small spot of oil on the ground directly in front of the rear wheel. The graph below shows a comparison of hydraulic pressure as the roof is raised. A pressure sensor was installed in the hydraulic lines and the data recorded by a computer. Data for Stock and Resistor were taken from the same car. Relief Valve data was taken from another car fitted with our Upgrade Kit. Resistor data is shown because some have been erroneously led to believe that this is a cheap solution. The graph below clearly show that this is not true as the pressure is only reduced by 3.5% while the lift time in increased by 25%. In this comparison the Relief Valve reduces pressure by 42% although exact values will vary due to mechanical tolerances. The primary area of concern occurs at the end of travel in the area labeled “Dead Head After Latch Closure”. This is the point where the roof controller holds the pump on after all motion has ended which causes the pressure to spike. This pressure spike is what accelerates the degradation of the hoses and cylinder seals.

Pressure vs Time

You will note in the graphs above that the peak pressure with a series resistor is about 500psi higher (1578 vs. 947) than the peak pressure with the relief valve in our kit. One way to appreciate this would be to load a barbell with 500 pounds. The round end of the bar is about 1 square inch so the pressure exerted will be about 500psi. Pick the bar up (with the help of several friends), holding the bar vertical, and drop the end (to simulate the pressure pulse) on something you don’t care to see again. This will give a good approximation of the amount of force that is removed from the roof system by the kit offered here.

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All information provided is believed to be correct and it is given in good faith. Users of this information will use good judgment and comply with all the safety rules that apply to operating tools and equipment. cannot be held responsible if any of the information provided is not correct or does not work for you. Owner of the vehicle accepts responsibility with any and all applications they choose to use.

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