Frame and Underbody: Adjustments GMC Sierra 1500 HD

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

1. Sag
2. Buckle
3. Diamond
4. Sidesway
5. Twist

A misaligned frame rail may move in the following directions from where the frame rail should be

1. Forward
2. Up
3. Down
4. 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 does 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.

Scheme 4

Scheme 5

Scheme 6

1. Raise the vehicle. Refer to LIFTING AND JACKING THE VEHICLE in General Information.
2. Support the transmission with a transmission jack.
3. Remove the nut retaining the transmission mount to the transmission support.
4. Raise the rear of the transmission.
5. Remove the bolts and the nuts retaining the transmission support to the frame. (15 series)
6. Remove the bolts and the nuts retaining the transmission support to the frame. (25/35 series)
7. Remove the transmission support from the frame.

Scheme 7

Scheme 8

Scheme 9

1. Install the transmission support to the frame. (15 series)
2. Install the transmission support to the frame. (25/35 series) NOTE: Refer to «FASTENER NOTICE»(ref-175132-S17785009232005041500000) in Cautions and Notices.
3. Install the bolts and the nuts in order to retain the transmission support to the frame. Tighten Tighten the nuts to 95 N.m (70 lb ft).
4. Lower the rear of the transmission.
5. Install the transmission mount to the transmission support.
6. Install the nuts in order to retain the transmission mount to the transmission support. Tighten Tighten the nuts to 40 N.m (30 lb ft).
7. Remove the transmission jack.
8. Lower the vehicle.