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Ball-screw actuator slides: clutch, stops, diagnosis

On Lippert's actuator through-frame, a ball screw pushes the room, an automatic clutch lets the motor stop at the end of travel, and the stop can and nuts on the actuator shaft decide where in and out are. Most no-move calls are power and ground; most mid-travel stalls are something holding the room.

The short version

How the actuator system is built

Lippert calls the motor and ball-screw actuator the power unit, and it's one assembly. It mounts in the frame alongside the slide tubes, and the threaded end of the actuator shaft fastens to the front drive bracket on the room. The motor turns the ball screw one way to push the room out and the other way to pull it in.

The tubes carry gear racks that run through gear packs, and a cross shaft ties the packs together. Lippert calls this the guide system. Its rev B service manual also describes an active tube (driven by the actuator) and a passive tube with a synchronizing bracket. Either way, the gears keep the room square; they don't push it.

Lippert lists 18:1 and 28:1 Venture motors, an 18:1 Tuson, and a 58:1 Venture on a 43 in actuator. The system is negative ground: the chassis frame plus an independent ground wire back to the battery.

The clutch and the end of travel

The actuator has an automatic clutching system so the motor can drive the room into its stops without stalling hard. Lippert's rev B manual adds that if you keep holding the switch after the room reaches its limit, the control sees the stop and shuts the motor off after a few seconds.

So a short clatter at full in or full out is the system finishing its stroke. The same clatter halfway through travel is the room being held. Lippert's chart splits a mid-travel stall into three causes, in this order:

Stop can, nuts and seal compression

The actuator shaft carries a stop can and three nuts. The can and its 3/4 in jam nut (Jam Nut-1, on the outside of the can) set where the room stops coming in, which is your outside seal compression. The two 1 in nuts (Jam Nut-2 and the nylock) set where it stops going out, which is your inside seal compression.

Lippert's inspection standard is outside seals compressed when retracted, inside seals compressed when extended, and both sides moving smoothly and in sync. If one side seals and the other doesn't, that's synchronization, not the stop can.

Loose nuts on that shaft also cause the classic motor-runs-room-doesn't call. Lippert's first check for that symptom is whether the actuator is still attached to the front drive bracket and whether the jam and nylock nuts are tight.

Electrical diagnosis

On Lippert's wiring diagram, power goes from the battery through a 30 A auto-reset breaker, which Lippert specifies within 18 in of the battery and leaves for the coach builder to supply, then to the wall switch and out to the motor on 10 AWG minimum wire. The switch reverses polarity to reverse the motor, so if the room runs opposite the switch plate, swap the motor wires at the back of the switch.

Lippert lists the 18:1 Venture actuator motor at 30 A. Slow travel comes from a low battery, a poor ground or very low temperatures. An auto-reset breaker that trips on high draw resets itself once it cools, so a room that quits and then works again a minute later deserves a clamp meter and a look for a bind.

  1. Confirm a full 12 V DC charge, or plug in with the batteries installed.
  2. Meter the switch terminals with the switch held. 12 V present: go to step 3. Not present: go to step 4.
  3. Check the incoming leads at the motor. 12 V there and no movement: replace the motor, it isn't field serviceable. No 12 V: repair the wiring between switch and motor.
  4. Check the battery-to-switch connections and the 30 A auto-reset breaker, repair, and start again at step 2.
  5. While you're under there, check the motor leads where they run under the chassis. Lippert calls out road-debris damage and corrosion at the terminals.

Motor runs, room doesn't move

Lippert gives two causes: the actuator has come loose from the front drive bracket, or the motor or gear housing is bad. Check the shaft nuts and bracket first because it costs nothing. If the bracket is tight and the shaft isn't moving, the motor or its gearing has failed, and Lippert's fix is a new motor.

Replacing the actuator, the manual has you disconnect the manual crank shaft and the motor wires, then record measurements A and B (Fig. B) before you pull the three jam nuts and the stop can off the shaft. Those numbers are your record of where the stops were. Note the mounting bolt locations, remove them, and slide the actuator out of the frame.

Buy to the label. Owners report bargain motor-gearbox units with plastic gears and no clutch that crunch at the end of travel and fail within a few cycles.

On the job

  1. Charge the battery or plug in, and check the frame ground and battery ground for corrosion.
  2. Hold the switch. Nothing at all: 12 V at the switch, then at the motor leads, then the 30 A auto-reset breaker near the battery.
  3. Motor runs, room doesn't: actuator shaft nuts and the front drive bracket, then the motor and gear housing.
  4. Stalls mid-travel: clear ice, mud or debris from the tubes and check adjustment, then disconnect the battery and crank a short distance before retrying.
  5. Slow: voltage at the motor while it runs, the ground, and the outside temperature.
  6. Seal not compressing: stop can for the in position, 1 in nuts for the out position.
  7. Write down the power unit serial number and date code before you call Lippert.

Numbers

Shop tip

If the room runs opposite the switch plate after a motor swap, don't go cutting and re-pinning the motor plug. Lippert's fix is to swap the two motor wires on the back of the switch.

Where this comes from

Try it on a service call

Put the lesson to work on a hands-on troubleshooting case.

Keep going on slides and leveling

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Codes and specs

On the job