Armstrong Shock Absorber Manual

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Armstrong Lever Arm Dampers - adjustment

Armstrong lever arm dampers were fitted I believe up to the 1990's (I am sure somebody has the exact date - people are like that!). There is a lever attached to the axle with a short rubber bushed link. This lever operates a pair of pistons with a 'seesaw' in a pair of bores in the body. These pistons pump oil through two adjustable valves, one for bump damping and one for rebound damping. The pistons are usually sealed with polymer piston rings. There is a 10:1 lever ratio, so if the axle is moving 1 inch over surface irregularities then the damper pistons are moving only 1/10th inch, hence the bores wear in this small region. As the bores wear the hydraulic oil squeezes past the piston rings rather than being controlled by the valving in the units, thus loss of damping.

Besides the internal wear, these units can leak through the seals where the shaft comes out. These seals can not be replaced without removing the lever from the shaft, this is a job for experts with the correct tools and new parts. Best, unless desparate, to compensate for the wear and manage the oil loss - tough!

The units are easy to top up in situ, there is a filler plug near the top. Use SAE20 hydraulic oil (Motorcycle fork oil - easy to obtain) in an old fashioned trigger type oil can and squirt it in the filler hole. I tend to fill to brim, knowing some will escape as things get warm, but the lost oil lubricates the leaf springs!

First flush the units through: Remove the top plate of the damper unit, carefully keep the gasket. Flush out with white spirit or parafin, not petrol. Pump until it runs clear.

As these units run as std on SAE20 hydraulic oil, the first attempt at compensating for wear is to go up a grade in oil viscosity, as these units are sensitive to viscosity. (NB Many modern damper units are more sensitive to density so changing grade of oil has minimal effect). SAE 30 motorcycle fork oil is easy to obtain. DO NOT USE anything thicker, the risk is that you will damage the unit, either twisting off the lever or destroying the piston seals. No need anyway, as you can adjust the units!

These units can easily be adjusted for both bump and rebound damping independently. Bump damping is always around 1/3 rd the stiffness of rebound damping. Bump damping affects how much you feel through the seat going up over bumps and how hard the diff hits the parcel shelf. Rebound damping really controls the oscillations after a bump. The amount of rebound damping is quite subjective, whether it damps the first oscillation or the second or the third. Lift up and push down on the rack vigorously then release, to test yours!

The units are bolted to plates that are bolted to the chassis. To get the units off to adjust them means unbolting the plates from the chassis or drilling holes in the plywood inner wings to access the bolts. OR replace the nuts and bolts with studs from the plates as below:

Photo below from Morgan Club de France http://www.morganclubdefrance.com/Technique/Restauration_JC/Restauration_JC.htm

Below, is a trial fitment of a plate with studs, before things were cleaned up I hasten to add!!!!!!!!!!!!!!!!!

Adjusting the units: There is a large hex head 'nut' at the bottom of the units, this can be unscrewed to remove the damper assembly, take care of the 'O' ring. As below:

The damper assembly looks as below when assembled:

The little washers between the large diameter coil spring and the valve body set the preload on the BUMP damper valve. So add more washers to get more BUMP damping, try one or two washers at a time, you can easily find washers of similar id and od, if not file some.

The little nut that compresses the smaller inner coil spring controls the REBOUND damping. This nut is soldered on its thread to stop it moving, easy to unsolder and resolder. Screw this nut in increases the REBOUND damping. Try one turn at a time, it is quite sensitive.

Do both together, clamp them together in a vice, then by hand pressure on the end of the levers you can compare their resistances to get them both similar.

Refit to car and test. Hours of fun there then!

Rebound valve adjustment starting point ~ compress back of the car and release, eg kneel on bumper and get off; the suspension should return the car to static ride height and no more. It should not bounce beyond static ride height.

Bump damping adjustment ~ although it is ideal to set this low to get minimum vertical upward acceleration that you feel through your seat/spine, owing to the limited bump travel it is more usual to set the bump damping to minimise the impacts of the top of the differencial on the parcel shelf. If this is not a problem then set bump damping as low as you can to prevent bouncing after a series of bumps or wallowing after quick steering inputs.

I hope that this helps those who wish to or need to keep originality run theirs' for a little longer. PJB

Armstrong Lever Shock Absorbers Rebuild
Armstrong Shock Absorber Manual Parts
Shock Absorber Rebuilding
Lever Arm Shock Absorber

Armstrong lever arm dampers were fitted I believe up to the 1990's (I am sure somebody has the exact date - people are like that!). There is a lever attached to the axle with a short rubber bushed link. This lever operates a pair of pistons with a 'seesaw' in a pair of bores in the body. 3.1 Shock-Absorbing Lanyards / Personal Shock Absorbers 3.1.1 Single-Leg Shock-Absorbing Lanyards For fall protection applications, connect the shock-absorber end of the lanyard to the back D-ring on the full-body harness using the locking snap hook (see Fig. (For tubular lanyards with a built-in shock absorber. MONROE™ Shock Absorber Tester 2. User Manual USB 3. Calibration Certificate 4. Power Adaptor 5. Shock Absorber Tester Data logger software USB 6. Data Download USB Cable Optional Accessories: Bluetooth printer (MSTP001) Speed humps Polyethylene (MSTB001) or Rubber (MSTB002) MONROE Shock Absorber Tester determines the vertical suspension.

Function of shock absorber:

The shock absorber is a part of suspension system used as springing device to compromise between flexibility and stiffness. It absorbs the energy of shock converted into the vertical movement of the axle by providing damping and dissipating the same into heat.

Purpose of shock absorber:

(i) To control the vibrations on springs.
(ii) To provide a comfortable ride.
(iii) To act flexible and to be rigid enough.
(iv) To resist the unnecessary motion of the spring.

Construction of Shock Absorber :

The upper eye of the telescopic shock absorber is attached to the axle and the lower eye is attached to the chassis frame as shown in Figure 4.55. A two-way valve V1 is connected to a rod. Another one two-way valve V2 is connected to the lower end of the cylinder. The fluid occupies in the space between above and below the valve VI and also the annular space between the cylinder and tube. A gland is provided on the head. Fluid scrapped out by the rod is brought down into the annular space through the inclined passage.

Working of Shock Absorber :

When the vehicle comes across a bump, the lower eye will move up. So, the fluid follows from the lower side of the valve V1 to the upper side. Due to less volume of the space above valve V1 than the volume of the rod, the pressure is exerted on valve V2 Thus, the damping force is produced by this pressure of the fluid. The fluid will flow from the upper side of the valve V1 to the lower side when the lower eye moves down and from the lower side of the valve V2 to its upper side.
When a car absorbs shocks from the road surface, the suspension springs will compress and expand because the spring has the characteristic of continuing to oscillate for a long time of oscillation to stop. So, a riding comfort will be poor even the damp oscillation is supplied. Shock absorbers provide better road-holding characteristics and improved steering stability to tires.

The stronger is the damping force, the more will be the oscillations of the body. But, the shock from the damping effect becomes greater than the strength of the stronger damping force. The damping force varies with the speed of the piston.

Types of shock absorbers:

Armstrong Lever Shock Absorbers Rebuild

1. Mechanical shock absorber (friction type)
2. Hydraulic shock absorber.

Again the hydraulic shock absorbers are further divided into various types.
1. Van type
2. Piston type
a. Single-acting
b. Double acting
3. Telescopic type.

Twin-Tube or Dual Tube Shock Absorber

It is the type of shock absorber in which 2 hollow tubes named primary tube and secondary tube or shell are used which are merged together in telescope type fashion i.e. primary tube inside secondary tube or shell.

The primary tube contains the moving piston, compression valve along with other assembly components and is filled with high viscosity index oil.
The secondary tube or shell contains the primary tube along with low-pressure gas (mostly nitrogen gas).
This whole assembly of twin-tube is surrounded by a coil spring that provides the stiffness and also helps this assembly to regain its initial position after actuation.

Mono-Tube Shock Absorber

It is the type of shock absorber in which instead of a double tube, a single tube is used inside which the moving piston is placed.

High viscosity index oil along with the low-pressure gas (nitrogen in most cases) is filled inside a single tube in a particular proportion.
The oil and gas-filled inside this single tube is separated by a floating piston that is placed airtight inside the tube.
This whole assembly is surrounded by a coil spring same as a twin-tube shock absorber

Advantages of Mono-shock suspension system

1. Mono-shock suspension system improves handling of the motorcycle while going over potholes or bad roads as all the force is focused at one point.
2. Due to position of mono-shock suspension is placed ahead of the rear axle at the center of the motorcycle, the movement of the swing arm is not directly transferred to the suspension, this allows a more stability
3. motorcycle performance is more constant than using double shock.
4. More stylish suspension system.

Gas-filled mono-tube shocks

To prevent foaming and bubbles in the oil, which degrades shock-absorber performance, a gas-filled mono-tube shock has a chamber of high-pressure nitrogen above the oil chamber. This high-pressure gas makes it difficult for bubbles to form in the oil, even when the shock absorber moves in and out very quickly, as it might while traveling rapidly on a very rough or washboard road.

Gas-filled shocks are expensive since they require strict manufacturing tolerances, but they are very resistant to fade and consequently are popular in off-road racing and rallying. Gas-filled shocks, by the way, are not the same as “air shocks,” which use an air chamber separate from the shock oil. An air shock is actually an air spring that raises or lowers the vehicle when air is added or removed through a valve.

Advantages of Gas-filled shock absorber

Advantages of gas-filled shock absorber used at the rear end

1. The full diameter of the tube can be used as a working chamber and thereby a larger volume of oil becomes available for damping.
2. The larger volume of oil made available in any one stroke because of the adjustments between gas and oil volumes provides a better facility for the damping force.
3. The tolerance to heat in the gas-filled shock absorber is greater.
4. Gas-filled shock absorber gives longer life to tires and other related components in the suspension such as springs, brushes, etc.
5. A gas-filled shock absorber is designed to reduce the foaming of the oil.
6. Provide stability while graduating turns.

Difference between the telescopic shock absorber and gas-filled shock absorber.