Frame and Underbody Chevrolet Cobalt I

Fastener Tightening Specifications

Fastener Tightening Specifications

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

1. Direct point to point measurements
2. 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

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 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.

Underbody Inspection

1. Raise and suitably support the vehicle. Refer to «Lifting and Jacking the Vehicle»(/chevrolet/cobalt/i-2004-2010/remont/hoistjack/#general-information__lifting-and-jacking-the-vehicle) in General Information.
2. Check for obvious deterioration on the floor pan.
3. Check for loose dirt and corrosion around the inside of the floor pan reinforcement member access holes. This is the first indication that corrosion may exist in hidden areas. Perform all repairs before the final cleaning and protective treatment is performed.
4. Using a chisel, ensure that the drain provisions in the floor pan reinforcement members are open. Open the drain holes in the body side panels using a punch and a drift.

Frame Replacement

Tools Required

1. J 24319-B Steering Linkage and Tie Rod Puller
2. J 43631 Ball Joint Remover. See «Special Tools»(/chevrolet/cobalt/i-2004-2010/remont/frames-subframes-crossmembers/#frame-and-underbody__special-tools) .

Removal Procedure

1. With the wheels in the straight ahead position, remove the key from the ignition switch.
2. Secure the cooling module to the upper body structure.
3. Raise and support the vehicle. Refer to «Lifting and Jacking the Vehicle»(/chevrolet/cobalt/i-2004-2010/remont/hoistjack/#general-information__lifting-and-jacking-the-vehicle) in General Information.
4. Remove the front wheels from the vehicle. Refer to «Tire and Wheel Removal and Installation»(/chevrolet/cobalt/i-2004-2010/remont/wheel-tire-system/#tires-and-wheels) in Tires and Wheels.
5. Remove the left and right splash shields. Refer to «Splash Shield Replacement - Engine»(/chevrolet/cobalt/i-2004-2010/remont/exterior-body-panels/#body-front-end__splash-shield-replacement-engine) .
6. Remove the front transaxle mount to cradle through bolt.
7. Remove the rear transaxle mount to frame bolts.
8. Remove both stabilizer link to stabilizer shaft nuts. Refer to «Stabilizer Shaft Link Replacement»(/chevrolet/cobalt/i-2004-2010/remont/suspension-front/#front-suspension-system) in Front Suspension.
9. Remove both tie rod to steering knuckle nuts.
10. Use the J 24319-B to separate the outer tie rods from the steering knuckles.
11. Remove the intermediate steering shaft to steering gear pinch bolt and discard.
12. Disconnect the intermediate steering shaft from the steering gear.
13. Remove both lower control arm ball stud to steering knuckle pinch bolts.
14. Lower the lower control arms in order to disengage the steering knuckle. If necessary, use the J 43631 . See «Special Tools»(/chevrolet/cobalt/i-2004-2010/remont/frames-subframes-crossmembers/#frame-and-underbody__special-tools) .
15. Mark the frame to body position with a paint pen or permanent marker.
16. Lower the vehicle to about 3 feet off the ground in order to place a hydraulic lift table under the frame.
17. Use two 2 x 4's between the lift table and the frame and lift the table to the frame.
18. Slowly remove the frame bolts using the following sequence: Remove the front frame bolts. Partially unscrew the rear frame bolts exposing 25.4 mm (1.5 in) of bolt shank.
19. Slowly lower the lift table to the floor.
20. Continue with the following steps when replacing the frame: Remove the steering gear from the frame. Refer to «Power Steering Gear Replacement»(/chevrolet/cobalt/i-2004-2010/remont/manual-power-steering/#power-steering-system) in Power Steering System. Remove the stabilizer bar from the frame. Refer to «Stabilizer Shaft Replacement»(/chevrolet/cobalt/i-2004-2010/remont/suspension-front/#front-suspension-system) in Front Suspension. Remove the lower control arms from the frame. Refer to «Lower Control Arm Replacement»(/chevrolet/cobalt/i-2004-2010/remont/suspension-front/#front-suspension-system) in Front Suspension. Remove the radiator brackets from the frame.

Installation Procedure

1. If replacing the frame, perform the following steps: Install the radiator brackets to the frame. Install the lower control arms to the frame. Refer to «Lower Control Arm Replacement»(/chevrolet/cobalt/i-2004-2010/remont/suspension-front/#front-suspension-system) in Front Suspension. Install the stabilizer bar to the frame. Refer to «Stabilizer Shaft Replacement»(/chevrolet/cobalt/i-2004-2010/remont/suspension-front/#front-suspension-system) in Front Suspension. Install the steering gear to the frame. Refer to «Power Steering Gear Replacement»(/chevrolet/cobalt/i-2004-2010/remont/manual-power-steering/#power-steering-system) in Power Steering System.
2. With the frame on the lift table, raise the frame to the vehicle.
3. Hand start all the frame bolts while aligning the frame to the paint marks.
4. Tighten the frame bolts. Tighten: Tighten the bolts to 100 N.m plus 180 degrees (74 lb ft) plus 180 degrees.
5. Lower and remove the hydraulic table.
6. Connect the lower control arm to the steering knuckle.
7. Install the ball joint pinch bolt and nut. Tighten: First Pass: Tighten the nut to 50 N.m (37 lb ft). Reverse nut 3/4 turn Second Pass: Tighten the nut to 50 N.m (37 lb ft) plus 30 degrees.
8. Hand start the front transaxle mount through bolt.
9. Loosen the rear transmission mount through bolt.
10. Tighten the rear transaxle mount to frame bolts. Tighten: Tighten the rear bolts to 50 N.m (37 lb ft).
11. Tighten the front and rear transaxle mount through bolts in the following order. Tighten: Tighten the rear bolt to 100 N.m (74 lb ft). Tighten the front bolt to 100 N.m (74 lb ft).
12. Install the outer tie rods to the steering knuckles.
13. Install the new outer tie rod to the knuckle nuts. Tighten: Tighten the nuts to 20 N.m (15 lb ft) plus 180 degrees.
14. Connect the stabilizer links to the stabilizer shaft. Refer to «Stabilizer Shaft Link Replacement»(/chevrolet/cobalt/i-2004-2010/remont/suspension-front/#front-suspension-system) in Front Suspension.
15. Connect the intermediate shaft to the steering gear.
16. Install a new intermediate shaft pinch bolt. Tighten: Tighten the bolt to 25 N.m (18 lb ft).
17. Install the left and right splash shields. Refer to «Splash Shield Replacement - Engine»(/chevrolet/cobalt/i-2004-2010/remont/exterior-body-panels/#body-front-end__splash-shield-replacement-engine) .
18. Install the front wheels. Refer to «Tire and Wheel Removal and Installation»(/chevrolet/cobalt/i-2004-2010/remont/wheel-tire-system/#tires-and-wheels) in Tires and Wheels.
19. Lower the vehicle.
20. Road test the vehicle in order to test for the following conditions: Steering leads or pulls-Refer to «Measuring Wheel Alignment»(/chevrolet/cobalt/i-2004-2010/remont/wheel-alignment/#wheel-alignment-system__measuring-wheel-alignment) in Wheel Alignment. Abnormal powertrain noise or vibration at idle-Refer to «Checking Frame Alignment»(/chevrolet/cobalt/i-2004-2010/remont/frames-subframes-crossmembers/#frame-and-underbody__checking-frame-alignment) in Frame and Underbody.

Scheme 1

A datum is an imaginary horizontal plane that runs below and parallel to the vehicle. Height dimensions are calculated at right angles from the datum to the given control or reference points on the underbody.

The company that develops height dimensions determines the location of the datum based on the equipment being used. Therefore, different datum lines are established for the same vehicle. You can add or subtract an equal amount from all height dimensions and create a new datum line for your usage.

Scheme 2

A centerline is an imaginary vertical plane that is perpendicular to the length of the datum plane through the center of the vehicle. The centerline is any line drawn through the center of the vehicle's datum. The symbol for centerline is CL.

Length

Centerline length measurements are 3-dimensional measurements. The 3 dimensions are the following

1. Length - The distance between 2 points when the height is parallel to the center plane.
2. Height - The measurement is parallel to the datum plane.
3. Width - The measurement is parallel to the center plane.

When reading dimension charts, horizontal width and length dimensions of the underbody are shown as viewed from the bottom of the underbody. Vertical dimensions use the datum plane as a base for all vertical (height) measurements.

Centerline measurements are used with universal measuring equipment.

Scheme 3

The vertical body zero line is an imaginary line drawn through the frame either at the forward or rearward torque box area of the frame.

Floor Pan Insulators Description

Floor pan insulators have been designed for the higher floor pan temperatures. Higher temperatures result from the use of the catalytic converter in the exhaust system. If you remove or disturb any insulators when servicing the vehicle in the field, reinstall the insulators in the original sequence and location. Use the material specified for that particular location on the floor pan if you replace an insulator.

1. Floor pan insulator (cerra blanket thermal) Consists of 10 mm (3/8 in) thick aluminum silica (type 1).
2. Floor pan insulator (amberlite) Consists of 10 mm (3/8 in) thick resinated fibers (type 2).
3. Floor pan insulator sheet (phenolic bonded fiberglass) 305 x 457 mm (12 x 18 in) cut to size (type 3)

Types 1 and 2 have the following characteristics

1. Rolled stock
2. Ordered by linear foot
3. Cut to fit

When servicing or replacing interior insulators, observe the following instructions

1. Install the insulators in the original position and sequence. Place the pieces close together in order to avoid gapping or overlapping.
2. Use the original part for the following reasons: In order to determine the amount of replacement material required As a template for cutting and fitting the new piece to the floor pan
3. When installing the insulator, do not enlarge the cutouts or holes. The cutouts or holes are used for the attachment of the interior components such as seats or seat belts.
4. Route the cross body harnesses for the following interior components over the floor pan insulators and into the original location: The power seats The lap belt warning light and alarm The rear speakers Clip the cross body harnesses into place.
5. Do not apply the spray-on deadeners and trim adhesive to the top of the floor pan at the area located directly over the catalytic converter or muffler(s).

The front suspension lower control arms are bolted to a suspension support. The front suspension support attaches to the underbody using four bolts. The engine bolts to the integral front side rails. Ensure that the suspension strut towers are dimensionally correct in relation to the remainder of the underbody. This will allow the vehicle to maintain correct caster and camber angles.

The individual underbody components contribute directly to the overall strength of the body. Ensure that you use the proper welding techniques. Properly seal and rustproof the underbody components under the following conditions

1. Whenever the body repair operations destroy or damage the original sealing
2. Whenever the body repair operations destroy or damage the rustproofing

When rustproofing critical underbody components, use a good quality type of air dry primer such as corrosion resistant chromate, or an equivalent material. Do not use combination type primer surfacers.

Special Tools

Special Tools Illustration Tool Number/Description J 43631 Ball Joint Remover SA91100C Tie Rod Separator

Scheme 4

Scheme 5

See also:
• Lifting and Jacking the Vehicle
• Tire and Wheel Removal and Installation
• Splash Shield Replacement - Engine
• Stabilizer Shaft Link Replacement
• Power Steering Gear Replacement
• Fastener Notice
• Measuring Wheel Alignment
• Special Tools
• Checking Frame Alignment