The 42RE (behind the 4.0L six) and the 46RE (behind the 5.2 and 5.9 Magnum V8s) are both updates to the old A500 / A518 series. They need ATF+4 — not Dexron, not Mercon, not "universal." A pan drop and filter swap takes 5 quarts and buys you 30,000 more miles of clutch life.
ATF+4 is mandatory. The older ATF+3 (and the original ATF+) are superseded by ATF+4, and Mopar 05013457AA is the genuine fluid. Any ATF+4 that meets MS-9602 spec is acceptable — Valvoline MaxLife ATF+4 and Castrol Transmax both qualify. Do not run Dexron or Mercon. The frictional properties are wrong and you'll get shudder, late shifts, and eventual band damage.
A pan drop (the only practical home service — these transmissions have no drain plug) refreshes about 30% of the total fluid. Total capacity is 8.5–11 quarts dry; a service refill is 4.5–5 quarts. Plan to do a pan drop every 30,000 miles. If the fluid is burnt-smelling or dark brown instead of red, drop the pan, change the filter, and refill — then repeat the pan drop in 1,000 miles to swap more of the converter's fluid by dilution.
Service interval: 30,000 miles for normal driving. 15,000 for trail use or towing. If the previous owner never serviced it and you bought the ZJ used, do the service immediately — but if the fluid is already burnt-black, talk to a transmission shop before you do anything; a fresh-fluid shock can flush varnish loose and clog passages on a worn 42RE.
| Part | Vendor | Est. price |
|---|---|---|
| ATF+4 (5–6 quarts for filter+fluid drop, 10–12 for full flush) | Mopar / Valvoline / Castrol | ~$35 |
| Transmission filter and pan gasket kit (42RE) | ATP / Pioneer | ~$22 |
| Transmission filter and pan gasket kit (46RE V8) | ATP / Hayden | ~$24 |
| Pan magnet (optional, replaces stock) | Dorman | ~$8 |
Written and maintained by an AZ wheeler and driveway wrencher. Always cross-reference your factory service manual — modifications affect vehicle safety and warranty. Work at your own risk.