Spring Shock Insulator, Installation
M-652-004
(May 2007)

Valid for
All models built with SS-SW suspensions

Case description
To announce availability of special insulators designed to facilitate adjustment of unequal bogie wheelbase.

Repair
Install the special shock insulator if bogie right and left side wheelbases cannot be brought within the specified
variation by means of normal maintenance and repair procedures. It is not meant as a cure-all for worn parts or poor
maintenance practices.
The service insulators have the locating pin located 0.125 in. (3.175 mm) off center as shown in figure below. This
feature makes it possible to lengthen or shorten the bogie wheelbase, depending on which way the offset is located.
The insulators are marked to show long and short side.
Special Service Shock Insulator

Parts
Two versions of the insulators are available, standard-duty insulators made of rubber and heavy-duty insulators made
of urethane. Part numbers are shown in following chart.
Standard
Upper/Lower Shock

Standard Upper/Offset
Lower Shock Insulator
Configurations

Insulator
Configurations
Axle
Housing
Model

Rubber

Urethane

Rubber

Urethane

S34,
S38,
S40,
S440,
S501,
S52

10QK365A,
upper

NA

10QK365A,
upper

NA

10QK36B,
lower

10QK388,
lower

10QK48,
lower

10QK48P2,
lower

S441,
S462,
S522

10QK370,
upper

NA

10QK370,
upper

NA

10QK36B,
lower

10QK388,
lower

10QK48,
lower

10QK48P2,
lower

10QK32B,
upper

NA

10QK32B,
upper

NA

10QK372,
lower

10QK389,
lower

NA

10QK49P2,
lower

S582,
S652

Note: The standard rubber upper insulators can be used with any of the available lower insulators (standard rubber or
urethane, and offset rubber or urethane) as applicable to the axle housing model.
Note: On chassis equipped with a transverse torque rod, it may be necessary to disconnect the torque rod from the
frame in order to obtain an accurate thrust measurement on the axle.

Procedure
An example showing how to use the special shock insulators is given below. This example covers just one situation
and is offered as a guide only. Other conditions will require a different solution. Detailed information concerning
tandem wheelbase adjustment with offset insulators is given in the Frame, Axle and Suspension Service and Total
Vehicle Alignment Manual, 14–103.
1. Determine wheelbase variation by subtracting shortest side from longest side (Dim. C minus Dim. A). In this
case, the difference is 0.625 inch (15.875 mm).
2. The maximum allowable variation is 0.250 inch (6.4 mm); therefore, an adjustment is required to equalize the
wheelbase. Because the right side exceeds the nominal wheelbase dimension (50″), it should be shortened.
3. Any change in axle location at the insulators (Dim. E and F) will cause a change at the axle ends (Dim. A, B,
and C, D) of approximately twice as much. In this case 0.250 inch (6.350 mm) difference in Dimensions (E) (F)
results in a 0.50 inch (12.7 mm) difference in (A, B) and (C, D).
By installing two offset insulators with short side away from bogie centerline as shown in Figure 2, the right side
at the insulators (Dim. F) will be shortened 0.250 inch (6.350 mm) i.e. 0.125 inch (3.175 mm) per insulator. The
right side wheelbase will now be 50.250 inch (1276 mm) for Dimension (D) and the left side wheelbase will now
be 50.125 inches (1273 mm) for dimension (B); the difference is 0.125 inch (3.175 mm).
Before making final dimensional check, move chassis back and forth several times to normalize suspension
components.
Example for Correcting Unequal Wheelbase with Offset Insulator

1. Standard insulator used front and rear.

5. Bogie wheelbase with offset (2)
insulators.

2. Offset insulator (enlarged) installed with
“long side” toward rear.

6. Centerline of rear-rear axle.

3. Centerline of front-rear axle.

7. Offset insulator (enlarged) installed with
“long side” toward front.

4. Bogie wheelbase with standard
insulators.

Issued by
Technical Service