Transmission Oil Cooler

Replace or install the transmission oil cooler and connecting lines to prevent transmission fluid overheating in the 1970 AMC Rebel Machine with 390ci V8 and automatic transmission.

Warnings

Tools required

Parts

• Transmission oil cooler × 1 — Use OEM specification or equivalent
• Transmission cooler line kit × 1 — 3/8" steel or braided stainless to fit application
• Transmission cooler line fittings × 4 — Match existing thread pitch
• Transmission fluid (Type A) × 4 — Dexron compatible ATF

Fluids

• Automatic transmission fluid (Type A or Dexron) — 4 qt

Preparation

1. Park vehicle on level ground and apply parking brake firmly
2. Place wheel chocks behind rear wheels
3. Allow engine and transmission to cool completely if recently operated
4. Raise front of vehicle and support securely on jack stands at frame rails
5. Verify vehicle stability before working underneath
6. Place drain pan under transmission pan area to catch fluid spillage

Procedure

1. 1

   Locate and identify cooler configuration
   From underneath the vehicle, locate the transmission cooler lines running from the transmission to the radiator. The 1970 Rebel typically has lines exiting from the right side of the transmission, running forward along the frame rail to the lower right side tank of the radiator. Note the routing and any existing clamps or brackets for reinstallation reference.
2. 2

   Disconnect cooler lines at transmission
   Using a flare nut wrench, carefully loosen the transmission cooler line fittings at the transmission case. There are typically two lines - one supply and one return. Have the drain pan positioned directly below as fluid will drain when lines are disconnected. Once fittings are loose, unthread by hand and allow fluid to drain completely. Cap or plug the transmission ports temporarily with clean rags to prevent contamination.
3. 3

   Disconnect cooler lines at radiator or existing cooler
   Move to the front of the vehicle. If the cooler is integrated into the radiator, use a flare nut wrench to disconnect the lines at the radiator tank fittings. If an external cooler is present, disconnect lines at the cooler inlet and outlet. Again, expect additional fluid drainage and position drain pan accordingly. Allow lines to drain completely.
4. 4

   Remove existing cooler lines
   Remove any mounting clips, clamps, or brackets securing the cooler lines to the frame or body. Carefully remove the old cooler lines from the vehicle, noting the routing path for installation of new lines. Inspect the path for any sharp edges or areas where lines may have rubbed through.
5. 5

   Remove old transmission cooler (if external)
   If replacing an external cooler, remove the mounting bolts or brackets securing it to the vehicle. The cooler is typically mounted in front of the radiator or condenser. Remove the cooler assembly. If the cooler is integrated into the radiator and being replaced with an external unit, this step prepares the mounting location for the new cooler.
6. 6

   Install new transmission oil cooler
   Mount the new transmission oil cooler in the desired location, typically in front of the radiator for maximum airflow. Ensure mounting brackets are secure and the cooler does not contact the radiator, condenser, or fan blades. Orient the cooler so inlet and outlet ports are accessible and positioned to minimize line bending. Tighten all mounting hardware securely.
7. 7

   Route and install new cooler lines from transmission
   Beginning at the transmission, route the new cooler lines forward along the frame rail following the original path or an improved route that avoids heat sources and sharp edges. Use existing mounting clips or install new clips every 12-18 inches to prevent vibration and chafing. Ensure lines do not contact the exhaust system, steering components, or suspension parts through their full range of motion.
8. 8

   Connect lines to transmission fittings
   Thread the cooler line fittings into the transmission case ports by hand to ensure proper thread engagement. The lower port is typically the return line from the cooler. Once hand-tight, use a flare nut wrench to snug the fittings firmly. Do not overtighten as the transmission case is aluminum and threads can strip. Fittings should be snug with no gaps visible at the sealing surface.
9. 9

   Connect lines to cooler fittings
   Route the cooler lines to the new cooler inlet and outlet ports. Connect the line from the transmission lower port to the cooler outlet, and the line from the transmission upper port to the cooler inlet (verify correct flow direction per cooler manufacturer instructions). Hand-thread fittings first, then snug with a flare nut wrench. Ensure no twisting or stress on the lines.
10. 10

    Verify line routing and clearances
    Visually inspect the entire cooler line routing. Verify at least 1 inch clearance from exhaust components, and that lines do not contact sharp edges. Turn the steering wheel lock-to-lock and verify no interference with steering linkage. Check that all mounting clips are secure and lines are properly supported.
11. 11

    Refill transmission with fluid
    Lower the vehicle to the ground. With the engine off, add approximately 3-4 quarts of Type A or Dexron-compatible automatic transmission fluid through the transmission dipstick tube using a funnel. Do not overfill at this stage. Start the engine and allow it to idle in Park. Shift through all gear ranges, pausing 2-3 seconds in each position, then return to Park.
12. 12

    Check fluid level and inspect for leaks
    With the engine idling in Park and transmission at operating temperature, check the fluid level on the dipstick. Add fluid as necessary to bring level to the FULL mark. Raise the vehicle and inspect all cooler line connections for leaks. Check transmission case fittings, cooler connections, and any line joints. Tighten any weeping connections slightly. Lower vehicle.

Reassembly

1. Ensure all cooler line fittings are snug but not overtightened
2. Verify all mounting clips and brackets are installed and secure
3. Confirm transmission fluid level is correct with engine at operating temperature
4. Double-check that no lines contact exhaust, steering, or suspension components

Verification

• Start engine and allow to idle for 5 minutes, checking underneath for any fluid leaks at all connection points
• Take vehicle for a 10-15 minute test drive including highway speeds to bring transmission to full operating temperature
• After test drive, recheck fluid level with engine idling in Park on level ground and top off if necessary
• Perform final inspection underneath vehicle for any seepage or drips at cooler lines and fittings
• Monitor transmission temperature gauge (if equipped) during initial drives to verify cooler is functioning properly

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