Symptoms
Dark or burnt-smelling fluid, slipping, no overdrive, hard or erratic shifts, a missing 1–2 shift or third gear, or white exhaust smoke from ATF being drawn through a ruptured modulator.
The fix, step by step
- Drop the pan, change the filter, clean the pan and refill with Mercon-type ATF (The Ranger Station recommends Mercon V as the modern replacement; total capacity is about 9.5 quarts).
- Pull the vacuum hose from the modulator: fluid in the hose means the diaphragm has failed, and you can confirm it with a vacuum gauge before fitting a new one.
- Heat is the main enemy of the A4LD, so fit an auxiliary cooler in the return line to supplement the radiator cooler.
- On 1988-on dual-solenoid units, test the 3-pin connector if overdrive or lock-up is missing.
Tools & part numbers
- Drain pan
- sockets
- gasket scraper
- hand vacuum pump or gauge
- funnel.
Where to buy the parts
A4LD filter, 1988 Bronco IIRockAuto ↗Amazon ↗
A4LD pan gasket, 1988 Bronco IIRockAuto ↗Amazon ↗
A4LD vacuum modulator, 1988 Bronco IIRockAuto ↗Amazon ↗
Auxiliary transmission cooler, 1988 Bronco IIRockAuto ↗Amazon ↗
Hunting a used or discontinued part? Search eBay Motors for Ford Bronco II parts →
Rated for a competent home mechanic with a decent tool kit. Confirm torque figures, fluids and procedures against the factory service manual for your VIN, support the truck on stands rather than a jack, and work at your own risk (disclaimer). Some parts links are affiliate links, which pay us a small commission at no cost to you.