Transmission Cooler Lines

Remove and replace transmission cooler lines between the automatic transmission and front-mounted cooler, including routing inspection and fitting torque verification.

Warnings

Tools required

Parts

• Transmission cooler line set (supply and return) × 1 — Use OEM specification or equivalent aftermarket
• Transmission cooler line fitting O-rings (if equipped) × 4 — Verify fitting type on vehicle
• Nylon cable ties or line clips × 4 — For securing lines to chassis

Fluids

• Mopar MS-9224 or 75W-90 GL-4 — 2 qt

Preparation

1. Park vehicle on level surface and engage parking brake. Place wheel chocks behind rear wheels.
2. Allow transmission to cool completely if vehicle was recently operated (minimum 1 hour cool-down).
3. Raise front of vehicle with floor jack and support securely on jack stands at manufacturer-specified lift points on frame rails.
4. Verify adequate working clearance beneath vehicle (minimum 24 inches recommended).
5. Place drain pan beneath transmission cooler line connections at transmission case.
6. Photograph cooler line routing and clip locations for installation reference.

Procedure

1. 1

   Access transmission cooler line connections
   Locate the transmission cooler lines at the right side of the transmission case. The lines connect to the transmission via threaded flare fittings. Identify the supply line (from transmission to cooler) and return line (from cooler to transmission). Clean debris and dirt from fitting areas using wire brush and shop towels.
2. 2

   Disconnect lines at transmission
   Position drain pan directly beneath fittings. Using appropriate flare nut wrench, loosen the transmission-side cooler line fittings by turning counterclockwise. Hold the transmission fitting boss with backup wrench to prevent case damage. Expect approximately 1 pint of fluid to drain from each line. Allow lines to drain completely before proceeding.
3. 3

   Trace and release line routing
   Follow both cooler lines forward from transmission to radiator-mounted or frame-mounted cooler. Document all mounting clips, cable ties, and routing points. Release lines from chassis clips by squeezing clip tabs or cutting cable ties. Note any areas where lines pass through frame brackets or near exhaust components.
4. 4

   Disconnect lines at cooler
   Locate cooler line connections at the transmission cooler (typically mounted in front of radiator or integrated into radiator tank). Position drain pan beneath cooler fittings. Use flare nut wrench to loosen fittings at cooler, turning counterclockwise. If cooler has compression fittings rather than flare fittings, use appropriate line wrench. Allow remaining fluid to drain.
5. 5

   Remove cooler lines from vehicle
   Carefully extract cooler lines from routing path, working from transmission forward to cooler. Avoid kinking or bending lines excessively during removal. Inspect removed lines for damage, corrosion, rubbing wear, and connection integrity. Check for internal restrictions by attempting to blow compressed air through lines (if available).
6. 6

   Inspect fittings and mating surfaces
   Examine transmission case fitting threads for damage, cross-threading, or debris. Inspect cooler inlet/outlet fittings similarly. If fittings use O-rings or compression seals, verify seal condition and replace if damaged, flattened, or hardened. Clean all fitting threads with wire brush and wipe with clean shop towel.
7. 7

   Prepare new cooler lines
   Unpack new cooler line set and verify correct length and fitting configuration. Compare new lines to old lines for routing compatibility. If lines have protective caps on fittings, remove caps and inspect threads for shipping damage. Apply light coating of clean ATF to fitting threads and O-rings (if equipped) to aid installation.
8. 8

   Route and install new lines
   Begin installation at transmission end. Thread new supply line into transmission fitting by hand, ensuring straight thread engagement for minimum 3 full turns before encountering resistance. Repeat for return line. Route lines forward along documented path, ensuring adequate clearance from exhaust components, steering linkage, and suspension components. Maintain minimum 2-inch clearance from exhaust manifolds and pipes.
9. 9

   Connect lines at cooler
   Connect forward ends of cooler lines to transmission cooler fittings. Hand-thread fittings until snug, verifying straight thread engagement. Ensure correct line orientation (supply to inlet, return to outlet). If cooler has directional flow markings, verify proper connection.
10. 10

    Torque all fittings
    Using flare nut wrench with backup wrench on transmission case bosses, tighten transmission-side fittings to the torque specified by the aftermarket automatic transmission manufacturer (verify against their documentation). Move to cooler end and tighten cooler fittings to the specification provided by the cooler manufacturer; verify against their documentation before applying torque. Do not overtighten; flare fittings seal on cone contact, not thread torque.
11. 11

    Secure line routing
    Install new cable ties or reuse chassis clips to secure cooler lines at documented mounting points. Ensure lines do not contact sharp edges, exhaust components, or moving suspension parts. Verify lines have no tension or pulling at fittings; routing should allow natural line curvature without stress.
12. 12

    Fill transmission with fluid
    Lower vehicle to ground. Locate transmission fill plug (typically on side of transmission case). Remove fill plug and insert funnel. If the vehicle has an automatic transmission (aftermarket conversion), add the appropriate ATF specified by the transmission/converter manufacturer to replace fluid lost during line replacement. Note: The factory 1992 Viper T-56 manual transmission uses fluid per Mopar specification and has no cooler lines; do not perform this procedure on a factory manual transmission. Note: If this is an automatic transmission conversion, use appropriate ATF per converter manufacturer specification.
13. 13

    Initial leak check
    With vehicle still on ground, start engine and allow to idle. Observe transmission cooler line fittings at both transmission and cooler for leaks. Check along entire line routing for drips or seepage. If leaks observed, shut off engine immediately and re-torque affected fitting. Do not operate vehicle with active transmission fluid leak.
14. 14

    Road test and final inspection
    Drive vehicle for 10-15 minutes, including varied speeds and gear changes (if automatic). Return to shop and raise vehicle on jack stands. Perform final inspection of all cooler line fittings and routing points for leaks or seepage. Wipe all fittings clean and observe for 2-3 minutes for fresh fluid appearance. Check transmission fluid level per manufacturer procedure and top off if needed.

Reassembly

1. Installation is reverse of removal with attention to proper line routing and fitting torque.
2. Ensure all chassis clips and cable ties are reinstalled to prevent line vibration and chafing.
3. Verify transmission fluid level after test drive and top off as necessary.

Verification

• Start engine and verify no transmission fluid leaks at any cooler line connection point.
• Drive vehicle and verify normal transmission operation with no slipping, harsh shifts, or unusual noises.
• Check transmission fluid level is within proper range on dipstick (if equipped) or at fill plug level.
• Verify cooler lines have adequate clearance from all moving and hot components.
• Re-inspect all connection points after 50-100 miles of driving for delayed leak development.

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