CAROLINAS AUSTIN-HEALEY CLUB
Reprinted from "HEALEY HERALD", newsletter of Original Austin – Healey Club of America in 1961
By Joe Petrovec
A car’s ride and handling are no better than its shocks; here is how to perform some shock therapy.
Unlike most telescopic-type shocks which are not adjustable, the Armstrong, a lever acting double action shock absorber with two parallel cylinders, which is standard equipment on the Austin Healey 100-4, 100-6, 3000 and Sprite, is adjustable and can be overhauled and serviced. What is more, the job is not too difficult and you can, with care do it yourself.
Shock absorbers are primarily an assist to a cars suspension system. The British name for them, "Hydraulic dampers" is more accurately descriptive. The springs take up road shocks and the shock absorbers merely dampen the oscillating motions of the springs.
An inoperative shock, or one requiring fluid, fails to control the body movements of the car properly. This failure results in a continuous up and down motion, or short jerky movements of the wheels which cause them to bounce over small bumps, spinning in the air and scuffing off rubber when they regain contact. The resulting loss of traction also effects fuel economy. Good steering, too, is more or less dependent upon the proper shock performance. When a shock fails to damp a jar the front wheel receives upon hitting a sharp bump, it permits this jar to be transmitted to the steerng wheel, which results in steering-wheel whip, wheel shimmy, wheel chatter or fight.
If your car has steering, cornering, or ride problems and a check shows that the tires, springs, and steering systems to be in proper working order, the cause of the trouble is likely to be defective shock absorbers.
Bouncing each corner of the car up and down can quickly check the shock absorber. If the car continues to bounce after the weight exerted to bounce it is released, the shocks are in need of service or repair. A more positive check can be made by disconnecting the shock arm from the car’s chassis and moving it through its fullest travel (i.e. complete
Stroke up and down). A lack of resistance may indicate a lack of fluid or air in the cylinders, dirt holding a valve open, or a broken cam or other internal parts. Too much resistance or binding at any point in the stroke can be broken internal parts, clogged valves, or frozen pistons. A moderately free movement of the arm should be felt in a properly functioning shock absorber.
The fluid level should be checked approximately twice a year or every 3,000 to 4,000 miles. If the fluid level is allowed to become low, air pockets may form in the working chambers and impair the action. Fluid leakage can be spotted by the presence of excessive fluid around the outside of the shock body. To pinpoint the leak, clean off the outside of the unit thoroughly, fill it to the proper level with the recommended fluid, drive over a bumpy road for a short distance, and then inspect the unit. Leaks around the seals on the arm shaft indicate that the unit needs a major overhaul. If, however, a leak is noticed around the cover or its gasket, valve plug, or filler cap (which is usually caused by the initial expansion of the fluid) it can be repaired by tightening the cover retaining screws, valve plug, filler cap, or a replacement of their gaskets. Check the body housing to see that it is not broken or cracked. To insure that the leakage has been checked, repeat the road test and recheck the unit.
If it has been determined that the shock is definitely the cause of a rattle or noise, and not a loose brake rod, loose tools in the trunk, noise from the spring shackles or mounts, or even loose body metal the cause is likely a loose or worn rubber bushing in the arm assembly, shock parts striking or rubbing against the frame of the car, loose shock mounting bolts, shock arm not tightly fixed onto its shaft, or broken internal parts of the unit.
There is no practical way the shock can be serviced on the car, so we must dismount it. To remove the front shock, jack up the car under the coil spring, remove the wheel, and remove the bolt connecting the shock arm to the wheel and hub assembly. Swing out the hub assembly until it clears the shock arm and support the hub assembly on a suitable stand to prevent straining the brake line. Then unscrew the four bolts securing the shock to the chassis, and the shock is free. To remove the rear shocks, jack up the car under the rear axle or spring, remove the wheel, remove the bolt, which connects the shock arm to the bracket on the rear spring assembly. Remove the two bolts securing the shock to the chassis and withdraw the shock.
In most cases there are few differences in the Armstrong Shocks from car to car – position of the arm assembly, same have only one arm and others two, position of the filler plug varies, slight differences in the construction in the shock body to facilitate easy mounting on that particular car etc. — but with these little differences the shocks are the same internally, and are serviced in the same manner.
The arms should nor be removed from their placement on the shaft at any time. They have been factory assembled on the shaft in the right relation to the cam so that there is lull equal range of movement on either side of the stroke. The first step in servicing should be to clean away all the accumulated dirt and grime from the shock body. It is best to secure the shock in a vise to simplify the operations.
Now to the shock for service. Remove the valve plug and its assembly, pressure in the cylinder will force the fluid through the piston valves and out the valve port. Remove the retaining screws holding the piston-link and Cam Cover in place. Caution; never pry this cover off- tap it lightly around the sides of the cover to break the seal. Drain any remaining fluid out of the piston cylinders by working the arm to its fullest travel a few times. With the cover off, we can see into the piston link and cam chamber, If any badly worn or broken parts are detected or when the arm is moved to is fullest travel each way, any binding and/or resistance is felt, the unit should be replaced or overhauled.
The unit is now ready for a thorough internal cleaning. Replace the valve assembly and plug and set the shock in the vise so that the piston link chamber is in an upright position and the arm is free to move. Fill the chamber with kerosene or paraffin (never gasoline or lacquer thinners) and work the arm to its fullest travel each way about half a dozen times to force the solution to work its way into all the cylinders. Remove the valve plug and assembly, and completely drain the shock. Repeat the process a few times to insure that the pistons and cylinders are thoroughly cleaned. It is important to make sure that all the cleaning solution has been drained out before the shock is filled with fluid.
The valve assembly controls the pressure to each cylinder as the shock functions, It consists of: valve plug and seat, valve assembly, "B" washers, and spring, with slight, careful adjustments, the pressure settings can be altered to stiffen or soften the damping action.
The following valve adjustments can be applied to all rear shocks and to front shocks where the arm is positioned towards the piston link cover: To increase the "bump stroke" pressure you can add up to 1 or 1-1/2 complete turn, with safety, to the soldered adjusting nut on the valve assembly, and resolder. To soften, turn off up to 1 to 1-1/2 turns. To increase the "rebound stroke" pressure you can add up to three additional "B" washers with safety. If "B" washers are not available, a spacer micrometrically equal to the existing "B" washers can be used. Each unit contains two or three "B" washers as standard. To soften, remove up to three "B" washers, with safety.
On the front shocks where the arm is positioned toward the valve plug (i.e. on the Austin Healey), the aforementioned valve adjustments for stroke pressures are reversed. To increase or decrease the rebound stroke pressure, you add or subtract the turns on the valve assembly-adjusting nut.
Normally, it is advisable that you adjust both the pump stroke and the rebound stroke pressures proportionally, and equally on each companion shock absorber. Unless you arc interested in the stiffest ride possible with your present shocks, take the valve adjustments in stages until the desired damping action is reached. Do not make any valve pressure changes unless you are determined to increase or decrease the damping action of the shocks, or before you have checked to see whether your springs and swing shackles are properly lubricated and work freely. As stated before, the shocks are only an assist to the suspension system, and if the springs or suspension are at fault, no matter how much you adjust the pressures you will nor correct the trouble.
When cleaning the valve plug and seat, valve assembly, and its port, never use a wire to clean out the passage. Clean with kerosene or paraffin and a soft lintless cloth, and blow clear with compressed air.
After making all valve adjustments, if necessary, and after the valve assembly and plug are cleaned replace the valve assembly into its seat in the valve plug. With a slight twisting action and pressure with your fingers, the valve assembly is seated in the plug. Replace the "B" washers and spring. Replace the valve plug and its assembly into the valve port in an upright position. Tighten securely.
Again place the shock in a vise so that the piston link and cam chamber is facing up and the arm is free to move. Fill chamber with the recommended fluid; if not available, use SAE 30 non-detergent oil. Fill the chamber to the top and work the arm through its fullest travel each way a few times. This is important because working the arm forces the fluid into all the cylinders and expels all the air. Refill the shock, replace the cover gasket cover, and retaining screws, and tighten securely.
After the cover is secured in place, right the shock and remove the filler plug to check the fluid level. The level should be approximately 5/8 inch from the top. This leaves space for the initial expansion of the fluid. When handling the shocks off the car, it is important to keep them in an upright position as much as possible; otherwise air can enter the cylinders