Symptoms
Oil weeping from the case or the joint with the transmission's intermediate housing, gear whine, jumping out of range, or a stiff shift.
The fix, step by step
- Work out which case you have before ordering.
- Wild Horses notes that 1966–72 cases use a T-handle with a 2.46:1 low range and 1973–77 cases a J-shift with 2.34:1, and the front output, bearings, shift rails and detents differ.
- Drain the case, disconnect both driveshafts, the speedometer cable and the shift linkage, and unbolt the case from the intermediate housing.
- Replace the bearings, seals and gaskets; a deluxe kit adds a new cluster shaft, thrust washers and shims.
- Fit a new intermediate seal and gasket, reinstall, and fill to the plug.
- ClassicBroncos regulars say Ford specified 50-weight motor oil for the Dana 20, and some warn that GL-5 additives can harm its brass and bronze parts.
Tools & part numbers
- Drain pan
- snap-ring pliers
- bearing puller and press
- seal drivers
- torque wrench
Where to buy the parts
Dana 20 master bearing and seal kit, 1966–72 (T-handle)Bronco Graveyard ↗Amazon ↗
Dana 20 master bearing and seal kit, 1973–77 (J-shift)Bronco Graveyard ↗Amazon ↗
Dana 20 intermediate oil sealBronco Graveyard ↗Amazon ↗
Intermediate housing to Dana 20 gasket, 1966–77Bronco Graveyard ↗Amazon ↗
Hunting a used or discontinued part? Search eBay Motors for Ford Bronco (1966–1977) 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.