The YJ uses DOT 3 brake fluid. Flush every two years or 30,000 miles in the order furthest-from-master-cylinder first: passenger rear → driver rear → passenger front → driver front. The whole job takes about an hour with a helper.
Brake fluid is hygroscopic — it absorbs water from the atmosphere through the seals, master cylinder cap, and flex hoses. Water-saturated fluid boils at a lower temperature, which means pedal fade during long descents, and it corrodes the inside of every steel brake line, caliper bore, and wheel cylinder. The YJ's brake system is unsophisticated (no ABS, no proportioning valve drama) but every component is steel or cast iron, so neglected fluid eats the system from the inside out. Flush every two years and the master cylinder, calipers, and wheel cylinders will outlive the truck.
DOT 3 is the factory spec. DOT 4 is acceptable as an upgrade — it has a higher dry boiling point and the same chemistry, so it mixes cleanly with existing DOT 3. Do not use DOT 5 silicone fluid; it is not compatible with DOT 3/4 systems and will destroy the seals. Stick with DOT 3 from any major brand (Valvoline, Prestone, Wagner) and you're fine. Two 32-ounce bottles is enough for a full flush with margin.
The bleeding sequence on a YJ is the same as any non-ABS truck: **start at the wheel furthest from the master cylinder and work back**. That's passenger-side rear first, then driver-side rear, then passenger-side front, then driver-side front. The rear wheels use wheel cylinders with the bleeder on top; the fronts use caliper bleeders also on top. Every bleeder is 10mm. Crack each one before you raise the truck — frozen bleeders are common, and breaking one off means a wheel cylinder or caliper replacement.
The two-person method is: helper pumps the pedal three times slowly and holds; you open the bleeder, watch fluid jet out, close before the pedal hits the floor; helper releases. Repeat until clean fluid runs and no air bubbles come out. **Keep the master cylinder reservoir at least three-quarters full the entire time** — let it run dry and you'll pull air into the master, doubling the job. Suction the old fluid out of the reservoir with a turkey baster before you start to speed the flush.
| Part | Vendor | Est. price |
|---|---|---|
| Valvoline DOT 3 brake fluid, 32 oz | Valvoline | ~$8 |
| Prestone DOT 3 brake fluid, 32 oz | Prestone | ~$7 |
| Speed bleeder check-valve bleeders (set of 4) | Speed Bleeder | ~$28 |
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.