Model A Shock Absorber Care, Maintenance & Repairs

About This Guide

This vintage service booklet from Antique Auto Parts, Inc. covers the design, adjustment, disassembly, repair, and reassembly of original-style Model A hydraulic shock absorbers. The source combines explanatory text with a 20-figure repair sequence.

This online version reorganizes the booklet for easier workshop reference while retaining the original procedures, settings, terminology, and cautions. The original scanned booklet remains available from the PDF link above.

Basic Design

The booklet describes the Model A unit as a double-acting hydraulic shock absorber. A working chamber is filled with oil, and the rotating wing shaft operates within the shock body. Resistance is created as oil is forced from one compartment to another through controlled passages.

The resistance in the shock depends on how quickly oil can flow between the chambers. The source identifies the needle valve as the means of changing that flow and therefore changing shock resistance.

Needle-Valve Adjustment

The guide notes that needle-valve settings varied when the cars were new and that wear makes a single universal setting even less practical today. Its recommended approach is to adjust resistance according to the condition of the individual shock and the ride preferred by the owner.

For a softer ride, the needle valve is opened farther; for greater resistance, it is screwed farther in. The booklet emphasizes checking actual shock resistance rather than relying only on the number of turns of the valve.

Checking Shock Operation

1. Check the fluid level at the filler-plug opening. The source says the level should be approximately at the bottom of the opening and warns against excessive filling.
2. Disconnect the shock from the link assembly and move the shock arm through its operating range to feel the resistance.
3. Resistance should be reasonably consistent through the stroke. The booklet notes that unequal or insufficient resistance can indicate internal wear, leakage, or other service needs.
4. Once the shocks are operating properly, resistance can be adjusted to provide the ride preferred by the owner.

Disassembly

The booklet's illustrated sequence begins with the shock securely clamped or bolted to a bench and proceeds through removal of the reservoir, inner plate, impeller assembly, and needle valve.

1. Remove the filler plug, drain the fluid, and secure the shock absorber firmly.
2. Clean rust and debris from the lock-ring and shell threads. The source cautions against damaging or distorting the lower ring.
3. Relieve the lock-ring tension and remove the reservoir cover.
4. Remove the reservoir gasket and the retaining components beneath the reservoir.
5. Remove the inner plate. The source describes this as one of the more difficult parts of the operation and notes that heat may be useful when corrosion is severe.
6. Remove the needle valve from the main shaft. The packing nut beneath it must also be loosened and removed.

Inspection & Cleaning

The source calls for thoroughly cleaning all parts in a solvent bath and then evaluating the internal condition of the shock. It treats this inspection as the point at which the rebuilder decides whether the unit can remain adjustable or whether corrosion and pitting have made the parts unsuitable for normal service.

It also warns against automatically plugging internal holes before determining whether they need to be sealed. The booklet's repair procedure intentionally uses different passages for its two ride configurations.

Ride Configuration

The booklet describes two internal configurations using its original terminology:

“Pleasure Ride”

Insert the restrictor tube in both sets of holes and reassemble the unit.

“Firm Ride”

Insert the lead balls used for caulking into the four holes at the base of the impeller. Other holes are blocked by peening the small lead balls into place.

For the firm-ride procedure, the source also directs shortening the needle valve by approximately one inch and chamfering the end, then carefully preparing the sealing surface of the impeller shaft before fitting the new seal.

Vent Plugs & Replenishing Valve

The guide gives special attention to the two small vent plugs at the top of the inner plate. It calls for removing them, cleaning the vent holes and the groove in each plug, and reinstalling the plugs close to their original positions.

It then describes installing the replenishing or special check valve. The original procedure includes drilling and tapping the valve location and stresses that the installed valve must sit properly and not project through the bottom of the inner plate.

Reassembly & Filling

1. After the parts are thoroughly cleaned and dried, reassemble the wing-shaft and internal parts.
2. Install the new seal over the inner shaft, making sure the mating surfaces are clean and smooth.
3. Install the outer hub and tighten only until the large O-ring just begins to curl; the source warns against over-tightening.
4. Fill the reservoir approximately three-quarters full with shock fluid.
5. Operate the shock arm about 15-20 times and check the action of the unit.
6. If further adjustment is required, the booklet directs draining the fluid before reopening the unit and repositioning the inner plate.

Final Maintenance

The final illustration calls for regularly checking the shock fluid level and the mechanical connections around the shock absorbers. It also identifies the shock links as lubrication points.

The booklet closes by noting that original shocks may not all remain fully adjustable because of parts availability and internal condition, but that properly rebuilt units can still provide satisfactory performance.