Alignment Checking
Use a measuring tram gage as an accurate method of determining the alignment of the underbody. The tram gage set required to perform the recommended measuring checks must include a vertical pointer capable of reaching 457 mm (18 in).
The following 2 types of measurement may be made using a tram gage
- Direct point to point measurements
- Measurements calculated on a horizontal plane (datum line) parallel to the underbody
Dimensions that are measured to gage holes are measured to the center of the holes and flush to the adjacent metal surface unless otherwise specified. It is recommended that the diagonal dimensions be cross body checked on both sides in order to verify the dimensional accuracy of the vehicle underbody. Set vertical pointers equally as needed per your application.
Checking Frame Alignment
The main components of the frame are the side rails and the crossmembers. The rails carry the load. The crossmembers stabilize the rails.
The 5 types of frame misalignment are the following
- Sag
- Buckle
- Diamond
- Sidesway
- Twist
A misaligned frame rail may move in the following directions from where the frame rail should be
- Forward
- Up
- Down
- To the side
The easiest way to inspect the frame alignment is with gauges that are made for this purpose. Detailed instructions are normally supplied with the gauges at the time of purchase. There are no instructions for gauge use in the manual.
Whether you inspect the alignment with or without gauges, park the vehicle on a level section of floor.
Certain conditions call for preliminary inspections before inspecting the frame. Suspension or axle problems may make it appear that the vehicle frame is out of alignment. If an axle has shifted, diamond or sidesway may appear to exist when neither do exist. A weak spring may make the vehicle appear to have a twisted frame.
A visual inspection of the top and the bottom flanges of each rail may reveal the specific area where the sag or the buckle exist. In the case of a sag, wrinkles may appear on the top of the upper flange. The wrinkles are definite evidence of sag. Wrinkles on the bottom of the lower flange are definite evidence of buckle.