Brake Fluid Flush

Complete replacement of brake hydraulic fluid by bleeding all four wheels to remove old, contaminated fluid and moisture from the brake system.

Warnings

Tools required

Parts

• Bleeder screw dust caps (if damaged) × 4 — Use OEM specification

Fluids

• DOT 3 or DOT 4 brake fluid (use manufacturer recommended specification) — 1 qt

Preparation

1. Park vehicle on level surface and place transmission in Park (automatic) or gear (manual)
2. Apply parking brake firmly
3. Place wheel chocks behind rear wheels
4. Verify brake fluid type specification in owner's manual or on master cylinder reservoir cap (typically DOT 3 for 1970 AMC)
5. Raise front of vehicle and support securely on jack stands at frame rails
6. Remove all four wheels for access to bleeder valves
7. Inspect all brake lines, hoses, and cylinders for leaks or damage before proceeding
8. Clean area around master cylinder reservoir cap to prevent dirt contamination

Procedure

1. 1

   Extract old fluid from master cylinder reservoir
   Use turkey baster or fluid extraction pump to remove as much old brake fluid as possible from the master cylinder reservoir. Dispose of old fluid in sealed container according to local regulations. Wipe reservoir interior with clean lint-free cloth if accessible, being careful not to introduce debris.
2. 2

   Fill master cylinder with fresh fluid
   Fill master cylinder reservoir to MAX or FULL line with fresh brake fluid from an unopened container. Keep fresh fluid container sealed when not pouring to prevent moisture absorption. Keep a reserve supply ready as you will refill multiple times during bleeding.
3. 3

   Prepare bleeder valve at right rear wheel
   Locate bleeder valve on back of wheel cylinder or caliper at right rear wheel. Clean around bleeder valve with wire brush. Apply penetrating oil if valve appears corroded. Fit box-end wrench onto bleeder valve (typically 3/8"). Attach clear vinyl tubing over bleeder valve nipple with other end submerged in catch bottle containing 1-2 inches of fresh brake fluid.
4. 4

   Bleed right rear wheel
   Have assistant press brake pedal slowly to floor and hold. Open bleeder valve 1/4 to 1/2 turn while pedal is held down. Watch for fluid and air bubbles flowing through tubing. When flow stops, close bleeder valve BEFORE assistant releases pedal. Repeat process 5-8 times or until fluid runs clear with no air bubbles. Check master cylinder level after every 3-4 pumps and refill as needed to prevent running dry.
   ⚠️Assistant must NOT release brake pedal until bleeder valve is fully closed or air will be drawn back into system.
5. 5

   Bleed left rear wheel
   Move to left rear wheel and repeat bleeder valve preparation and bleeding process. Ensure master cylinder remains filled above MIN line throughout process. Continue bleeding until fluid is clear and free of air bubbles. This wheel typically requires fewer pumps if right rear was thoroughly bled.
6. 6

   Bleed right front wheel
   Move to right front wheel. Clean and prepare bleeder valve on wheel cylinder or caliper. Attach vinyl tubing and catch bottle. Repeat bleeding procedure with assistant operating brake pedal. Front wheels may produce more old fluid, so continue until fresh fluid color is consistent and no air bubbles present. Monitor master cylinder level constantly.
7. 7

   Bleed left front wheel
   Complete bleeding procedure at left front wheel, the final wheel in sequence. This wheel should require minimal pumping if previous wheels were properly bled. Continue until absolutely no air bubbles are visible and fluid color matches fresh fluid from container. Ensure bleeder valve is tightened securely when complete.
8. 8

   Final master cylinder fill and inspection
   Fill master cylinder reservoir to MAX line with fresh brake fluid. Wipe any spilled fluid from painted surfaces immediately. Install reservoir cap securely. Inspect all four bleeder valves to confirm they are tight and install dust caps if equipped. Check entire brake system for leaks, particularly at wheel cylinders, calipers, and along brake lines.
9. 9

   Reinstall wheels and lower vehicle
   Reinstall all four wheels and torque lug nuts in star pattern to factory specification (typically 75 ft-lbs for 1970 AMC). Lower vehicle from jack stands to ground. Remove wheel chocks.

Reassembly

1. Double-check that all bleeder valves are closed tight
2. Verify master cylinder reservoir is filled to proper level and cap is secure
3. Ensure all wheels are properly torqued
4. Clean up any spilled brake fluid from components and floor

Verification

• With engine off, pump brake pedal 5-6 times - pedal should become firm and maintain resistance
• With firm pedal established, hold moderate pressure for 30 seconds - pedal should not slowly sink to floor
• Start engine and verify brake pedal does not sink excessively (slight drop is normal with power brakes)
• Perform low-speed test in safe area: brake pedal should feel firm with immediate response and vehicle should stop straight without pulling
• Check master cylinder reservoir after test drive - level should remain stable with no signs of leaks
• If pedal feels soft, spongy, or sinks, DO NOT DRIVE - repeat bleeding procedure or seek professional service
• Recheck brake system after 50-100 miles for any leaks or changes in pedal feel

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