Complete replacement of all engine mounts (left, right, and rear) on the 1970 AMC Rebel Machine 390ci V8 to restore proper engine stability and reduce vibration.

Warnings

Tools required

Parts

• Left engine mount assembly × 1 — AMC 390 V8 left side mount
• Right engine mount assembly × 1 — AMC 390 V8 right side mount
• Rear engine mount (transmission mount) × 1 — AMC 390 rear mount

Preparation

1. Park vehicle on level surface and engage parking brake
2. Disconnect negative battery cable
3. Allow engine to cool completely if recently operated
4. Raise front of vehicle and support securely on jack stands under frame rails
5. Apply penetrating oil to all visible mount bolts and allow to soak
6. Remove engine oil dipstick to prevent bending during engine lift

Procedure

1. 1

   Install engine support
   Position engine support bar across inner fenders or attach chain hoist to engine lift points. Use the front carburetor mounting studs or intake manifold bolts as lift points. Take up slack to barely support engine weight but do not lift yet.
2. 2

   Remove right engine mount through-bolt
   Locate the right side engine mount (passenger side). Remove the through-bolt that passes horizontally through the mount and engine bracket. This is typically a 5/8" bolt. Support the bolt as you remove the nut to prevent it from falling.
3. 3

   Remove left engine mount through-bolt
   Locate the left side engine mount (driver side). Remove the through-bolt that passes horizontally through the mount and engine bracket. This is typically a 5/8" bolt. Keep left and right hardware separated if fasteners differ.
4. 4

   Support transmission and locate rear mount
   Position floor jack with wood block under transmission oil pan. Raise jack to just contact transmission without lifting. Locate rear transmission mount crossmember and mounting bolts.
5. 5

   Raise engine slightly
   Using engine support bar or hoist, raise engine approximately 1-2 inches. This relieves weight from mounts and allows clearance for removal. Watch for interference with firewall, hood, and accessories. Raise transmission jack proportionally to maintain alignment.
   ⚠Monitor fan clearance to radiator and all hose/wire connections. Do not exceed 2 inches of lift.
6. 6

   Remove right engine mount frame bolts
   Remove the bolts securing the right engine mount to the frame bracket. Typically 2-3 bolts using 9/16" or 5/8" socket. Remove mount assembly from vehicle. Inspect frame bracket for cracks or damage.
7. 7

   Remove left engine mount frame bolts
   Remove the bolts securing the left engine mount to the frame bracket. Typically 2-3 bolts using 9/16" or 5/8" socket. Remove mount assembly from vehicle. Inspect frame bracket for cracks or damage.
8. 8

   Remove rear transmission mount
   Remove the bolts securing the rear transmission mount to the crossmember (typically 2 bolts). Then remove the bolts or nuts securing the crossmember to the frame (typically 2-4 fasteners). Lower crossmember and remove rear mount from transmission extension housing.
9. 9

   Clean and inspect mounting surfaces
   Wire brush all mounting surfaces on frame brackets and engine brackets. Remove rust, old rubber debris, and corrosion. Inspect engine mounting brackets on block for cracks or looseness. Check frame brackets for damage or fatigue cracks.
10. 10

    Install new right engine mount
    Position new right side mount on frame bracket and install frame mounting bolts finger-tight. Ensure mount orientation matches original with rubber isolator properly positioned. Do not fully tighten yet.
11. 11

    Install new left engine mount
    Position new left side mount on frame bracket and install frame mounting bolts finger-tight. Ensure mount orientation matches original with rubber isolator properly positioned. Do not fully tighten yet.
12. 12

    Install new rear transmission mount
    Install new rear mount to transmission extension housing. Position crossmember and install crossmember-to-frame bolts finger-tight. Install transmission mount-to-crossmember bolts finger-tight.
13. 13

    Lower engine into mounts
    Slowly lower engine using support bar or hoist while guiding engine brackets into mount through-bolt holes. May need to use pry bar to align holes. Lower transmission jack proportionally. Ensure all mounts align properly before proceeding.
14. 14

    Install mount through-bolts and tighten all fasteners
    Install right and left engine mount through-bolts with washers and nuts. Tighten through-bolts to 45-50 ft-lbs. Tighten mount-to-frame bolts to 30-35 ft-lbs. Tighten rear transmission mount bolts to 35-40 ft-lbs and crossmember bolts to 30-35 ft-lbs. Follow a pattern to ensure even loading.
15. 15

    Remove supports and verify installation
    Remove engine support bar or hoist. Remove transmission jack. Reinstall oil dipstick. Rock engine gently by hand to verify mounts are secure and engine returns to center. Check for adequate clearance around all accessories, hoses, and wiring.

Reassembly

1. Reconnect negative battery cable
2. Lower vehicle from jack stands
3. Start engine and check for unusual vibration or movement
4. Verify engine sits level and centered in engine bay

Verification

• Engine should idle smoothly with minimal vibration transmitted to chassis
• No visible engine movement during acceleration or deceleration
• All mount bolts are tight with no visible gaps between mount and brackets
• Engine accessories, hoses, and wiring have proper clearance with no contact points
• Test drive vehicle and verify no excessive vibration or clunking during acceleration

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