One of the more unique features of 1965-1998 Rolls-Royce motorcars is the hydraulic system. The hydraulic system powers the brakes and the rear suspension’s height control. These systems are legendary for their complexity and potential for bank-breaking repair costs. In this essay I'll show you how to check yours out so you can get a sense of what's happening before disaster strikes.
The early version of this system (1965-80) is filled with a derivative of conventional brake fluid (RR363). Newer cars (until the advent of the Silver Seraph series) used Castrol hydraulic system mineral oil, or HSMO. The two fluids are not compatible. Use of the wrong fluid in a car will cause severe system damage. All reservoirs are clearly labeled RR363 or HSMO.
The system contains two hydraulic circuits that operate in parallel for the brakes. One of the systems also powers the rear height control. Hydraulic fluid is stored in reservoirs on the left fender well. Lines carry the fluid to the hydraulic pumps, which are located in the center top of the engine; under the carburetors or the fuel injection. High-pressure pipes carry the hydraulic fluid to the accumulators under the motor. From there excess fluid is returned to the reservoirs. Braided lines carry the high-pressure fluid to the distribution valve assembly located under the driver seat.
A network of steel pipes carries hydraulic fluid to the calipers at each wheel and to the rear suspension and height control. The rear suspension contains height control valves, shocks, and gas springs that sit above the shocks in the trunk area.
All the pumps, valves, and moving parts are subject to failure. Calipers rust or leak. Gas springs and accumulators lose their gas charge. Metal lines rust and rubber hoses deteriorate invisibly. A system this complex can only be fully tested by trained people using special tools in a workshop. However, it’s possible to do a pretty good “quick check” without tools, using the following procedure:
Begin with the vehicle sitting, engine cold. Get in the car and pump the brake pedal 10-15 times. Open the hood and check the level in the hydraulic reservoirs. If the level is low, look for leaks (as evidenced wet spots) Turn the key on but do not start the engine yet. You should see two lights, Brake 1 and Brake 2. Depending on the year of the car these may be in an electronic unit, in a group of lamps, or by themselves in the middle of the dash.
If you do not see the lamps, or if only one is lit, give the brakes 10-20 more pumps. If the light does not come on you can assume that warning circuit is broken. Start the car. Watch how long it takes for the lights to go out. If it takes more than 20 seconds the hydraulic pumps are probably weak.
Run the car 2 more minutes, shut it off, and turn the key back on. Begin pumping the brake and note how many pumps before the Brake 1 and 2 lamps illuminate. Less than 20 pumps indicates the car has weak accumulators.
Start the car again and wait for the lights to go out. Go to the back of the vehicle and bounce each corner. If the car is soft and pushes down a few inches with your weight that’s normal. If it’s rock-hard that is a sign of failed gas springs in the rear suspension.
Sit down on the rear bumper (even better, have two people sit on the bumper) and wait 30 seconds. You should feel the car lift to the original (and visibly correct) ride height. If it does not lift that’s a sign of problems in the height control.
Take the car onto the road. Try braking slowly and quickly. Pay attention to any pulling or diving that may indicate caliper problems or air in the lines. Look for any pulsation or shudder that may indicate warped or damaged rotors. Let the car come to a stop on a gentle slope and release the brake. Make sure the vehicle begins rolling smoothly and the brakes do not drag.
Shut the car off and put it in neutral. Press and release the brakes a few times.
Finally, put the vehicle on a lift and make sure all four wheels spin freely. If any wheels drag that may be a sign of caliper trouble. Next check all the components for leakage. Look at the reservoirs (top left fender well), the pumps (top of the engine), the main valves and accumulators (under side of the engine), the distribution valves (under driver seat), the brake lines and calipers, and the rear suspension components.
Look at the fluid and make sure it looks smooth and uncontaminated. RR363 (used 1965-1980) should be almost clear; HSMO (used 1980-1998) is dark green. There should not be any foam, sediment, or sludge visible. Color should be consistent.
Look at the rubber hoses to see if they are original. If your car is more than 10-15 years old I suggest you replace all rubber hoses as they can swell inside, creating invisible failures. A swollen hose may cause brakes to drag and overheat. Old hoses are also prone to bursting.
Look at the rubber hoses to see if they are original. If your car is more than 10-15 years old I suggest you replace all rubber hoses as they can swell inside, creating invisible failures. A swollen hose may cause brakes to drag and overheat. Old hoses are also prone to bursting.
If your car passes all these tests you can give yourself and the vehicle a pat on the back. If you see potential failures, I suggest you find a specialist and get a more thorough evaluation.
John E Robison
JE Robison Service
RROC Tech Consultant