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Couplers How-To's

70LP Master Cylinder Replacement

70LP Master Cylinder Replacement

An easy to follow step by step process to replace this. Shows you exactly what needs to be done.... read more

Video Transcript

This video covers the installation and replacement of the master cylinder coupler assembly for the Tie-Down Engineering LP70 Low Profile Actuator. Bleeding the LP70 is also covered. The tools required for the removal and replacement of the coupler master cylinder assembly include a hand-greased gun, channel-locked pliers, three-eighth inch and three-quarters inch wrenches, a medium-sized flat blade screwdriver, Allen wrench set, c-clip pliers, and 242 medium hold Loctite.

The replacement instructions cover both the drum brake version and disc brake version of Tie-+-Down Engineering model LP70 Actuators. Disc brake and drum brake master cylinders must be used with the proper brakes. Using the drum brake actuator on these brakes will cause overheating. A disc brake actuator used with drum brakes will cause delayed braking.

Remember, safety first. Trailer must be on a level work surface with the wheels properly blocked front and rear to keep the trailer from moving. Shop rag should be used to catch any brake fluid from the actuator as the brake lines will be disconnected.

The coupler and master cylinder will be removed in one piece. Start by removing the c-clips on each side with a c-clip plier. The c-clips will not be reused. Your actuator may have nyloc nuts instead of c-clips. If so, remove these and save for the reassembly process.

Hold the pens from the housing. Remove the bushings from each side. Remove the plastic access cap. Remove the four Phillips screws that hold the master cylinder in place. Take hold of the coupler and pull the assembly out of the housing. Remove the brake line from the master cylinder with a three-eighth inch wrench. This is a good time to use shop rags for catching any brake fluid that may come from the brake lines or the master cylinder.

Your replacement coupler and master cylinder should have plastic ties holding the rollers in place. Do not remove these ties. The ties hold the rollers in place to make the assembly easier. The ties will break loose when the coupler is pushed in for the priming operation of the dampener.

Remove the protective plug from the solenoid. Attach the brake line to the master cylinder. Insert the coupler master cylinder assembly into the actuator housing. Replacement kits come with new slider bolts and nyloc nuts.

Place a recessed washer on one of the slider bolts. Place the bolt through the top hole in the housing and through the roller. Place a recessed washer on the bolt and loosely attach a nyloc nut to the bolt. Do not tighten at this time.

Repeat this for the lower hole with the bolt and nyloc nuts and recessed washers. Attach the master cylinder to the housing with the four stainless steel screws using Loctite on each screw. An Eight foot pound is recommended if you have a torque wrench.

At this time, the slider bolts can be tightened using the channel lock pliers and the three-quarter inch wrench. Do not over tighten the nyloc nuts. The bolts should be tightened only to a point where there is not any play in the bolt.

Using a hand-operated grease gun, pump grease into the two zinc-equipped bolts. Three pumps for each bolt is generally adequate. This lubricates the rollers ensuring smooth operation and a longer life for the actuator.

Remove the pillar cap from the master cylinder. Be careful to place the cap in a clean area where it will not pick up contaminants. Fill the reservoir with new DOT 3 brake fluid. Do not use any other brake fluid. The actuator and brakes are designed to use the DOT 3 formula. The use of other types can cause the seals to swell and deteriorate overtime. This will lead to brake failure.

Before the brakes are bled, the shock dampener must be primed with brake fluid. The LP70 uses a dampener for shock absorption. Push the coupler in as far as possible three times, each time pulling the coupler back to the most extended position. This will pull fluid from the master cylinder into the dampener.

If the coupler is hard to push, opening one of the bleeder valves on one of the brakes will make this easier. To bleed the LP70, use a power bleeder or you can manually bleed the actuator with a flat blade screw driver. A second person is required to open and close the bleeder valves on the brake calipers or wheel cylinders.

Insert the flat blade screw driver into the front, top hole of the actuator cover. Pump the master cylinder several times until pressure is felt. Release the bleeder valve on the brake cylinder or a caliper to allow the fluid and air to pass through. Close the bleeder valve and repeat the pumping action and releasing of the pressure at brake bleeder valves.

Repeat until the master cylinder is hard to pump signifying that any air has been removed from the brake lines. Fill the actuator with DOT 3 brake fluid. Reattach master cylinder cap and cover. Please note that the dampener can only be primed by pushing in the coupler. Bleeding the brakes does not prime the dampener.

Reattach the safety cable bracket to the underside of the actuator. After completing the assembly and bleeding of the brakes, recheck the actuator to make sure all bolts are properly tightened. Test the trailer braking system in a parking lot or road without traffic.

Inspect the braking system for leaks and proper working condition. The LP70 shock dampener is also an early warning system. Should the actuator make a loud, knocking noise, this could be an indication that the master cylinder is low on fluid indicating a leak or air in the brake lines.

If this occurs, check all fittings for leaks. Correct if necessary. Fill the master cylinder with DOT 3 brake fluid and re-prime the dampener and re-bleed the brake system.

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