Determining Frame Centerline
- Move the vehicle to a level, well-illuminated section of the floor.
- Draw a diagram of the
frame on the floor beneath the vehicle:
| 2.1. | Use a plumb bob in order to transfer the corners of the frame
(points 1, 2, 11 and 12) from the inside of the
web to the floor. |
| 2.3. | Use a plumb bob in order to transfer the remaining points of the
frame from the outside of the web to the floor. |
Use points from the same place on both the right and the left frame
rail.
- Move the vehicle away from the points on the floor.
- Measure the distance between point 1 and point 2
(front corners).
| • | The distance between the points should be 704.85 mm (27.75 in)
for the standard front axle. |
| • | The distance between points should be 847.25 mm (33.75 in)
if equipped with an I-beam front axle (RPO FK4/FK5). |
| • | For the motorhome chassis, the distance should be 606.8 mm
(23.89 in). |
- Measure the distance between point 11 and point 12
(rear corners).
The distance should be 847.25 mm (33.75 in).
- If both of the measurements in Steps 4 and 5 are
not correct, refer to Step 2 in Horizontal Check.
- Mark the centerline through the intersection of the 2 sets
of diagonals that have equal measurements.
- Make a mark on the floor exactly halfway between point 1
and point 2 (front corners).
- Make a similar mark on the floor exactly halfway between point 11
and point 12 (rear corners).
- Use a chalk line in order to mark a line through the points. This
is the centerline of the frame.
Horizontal Check
- Measure the distance from the frame rail to the centerline at
points 3-10.
Each pair of corresponding points should be an equal distance from the
centerline within 3 mm (1/8 in).
| • | Points 3 and 4 should measure equally from the centerline. |
| • | Points 5 and 6 should measure equally from the centerline. |
| • | Points 7 and 8 should measure equally from the centerline. |
| • | Points 9 and 10 should measure equally from the
centerline. |
- Measure diagonally from each front corner to the middle of the
frame (point 1 to point 6, and point 2 to point 5).
- Mark the floor where the diagonals cross the centerline.
The diagonals should measure the same distance within 5 mm (3/16 in),
and should cross at the centerline. If the frame is within specifications,
the frame within these points is properly aligned.
- Repeat Step 2 on other pairs of diagonals until the entire
frame has been checked:
- Refer to
Frame Repair
in order to repair any damage that you find.
