How to Rebuild a Serco Hold Down Unit - DDM Garage Doors Blog

Posted January 11th, 2023 at 4:42 pm by Philip Kendall

In this video, Dan explains how to take apart and then put back together a Serco dock leveler hold down unit.

Disassemble the Hold Down Unit

A Serco hold down unit in the dock leveler
Serco hold down unit in the dock leveler
Serco hold down unit that we used for demonstration purposes in the video.
Serco hold down unit used for demonstration purposes

To take apart and rebuild a Serco hold down unit, you will need 9/16″ and 3/4″ wrenches, as well as an adjustable wrench.


Dan securing the dock leveler in place
Securing the dock leveler in place
  1. Firstly, make sure the area you will be working in is secure.
  2. Raise the deck of the leveler, then secure it in place with two maintenance struts.
  3. Before disassembling the unit, support the rack with a C-clamp.
Supporting the rack with a c-clamp

Remove the Hold Down Unit

  1. Next, remove the release rod assembly.
    1. Remove the pin.
    2. Then, lift and separate the release rod.
Release rod assembly in a Serco dock leveler
Release rod assembly
  1. Remove the two 1/2″ lock nuts and bolts that attach the release gear assembly to the housing assembly, using 3/4″ wrenches.
1/2-inch lock nuts in the Serco hold-up unit
1/2″ lock nuts holding the Serco hold-up unit together
  1. Release the C-clamp.
  2. Remove all parts from the housing assembly and rack.
Separating the release gear assembly from the housing assembly
Serco release gear assembly within the housing assembly

Take Apart the Hold Down Unit

Separating the release gear assembly from the pinion, shaft, and guide assembly
Pinion, shaft, and guide assembly separated from the release gear assembly
  1. Separate the pinion, shaft, and guide assembly from the release gear assembly.
  2. Then, remove the end plate from the release gear assembly.
  3. Use the 9/16″ wrench and adjustable wrench to remove the 3/8″ lock nut on the release gear assembly.

Doing this will release the tension. As a result, the return spring and shaft retaining plate should fall out.

Shaft retaining plate and return spring, with the end plate already removed
Shaft Retaining Plate and Return Spring. The Pinion, Shaft, and Guide Assembly can be seen on the bottom left, next to the end plate.
  1. Remove the lock nut completely.
  2. Finally, separate the release lever assembly from the release gear assembly.
A fully disassembled Serco hold down unit
Release lever assembly, among the parts of a Serco hold down unit that has been completely disassembled

Now that the Serco hold down unit has been disassembled, you can reassemble it and replace the necessary parts.

Rebuilding the Serco Hold Down Unit

When rebuilding a Serco hold down unit, the parts must be reinstalled in a slightly different order than they were removed. Before you do so, be sure to grease the shaft on the pinion, shaft, and guide assembly, if it is not greased already.

Replacing the Hold Down Unit

  1. Reattach the release gear assembly and the pinion, shaft, and guide assembly.
  2. Then, replace both in the housing assembly.
  3. When you replace the assembly, make sure the rack is correctly positioned inside the guide assembly.
  4. C-clamp the rack in place.

Rebuilding the Hold Down Unit

  1. Slide the spring onto the shaft.
  2. Then, replace the shaft retaining plate.
Replacing the shaft retaining plate, where the two 1/2 inch hex bolts will slide through
Replacing the shaft retaining plate
  1. Replace the end plate.
  2. Reinsert both 1/2″ hex bolts with their washers.
  3. Secure with the 1/2″ lock nuts.
The location of the two 1/2 inch hex bolts in the housing assembly
Reinserting the 1/2″ hex bolts

To maintain the correct alignment, finger-tighten both lock nuts before tightening fully with the 3/4″ wrench. When using the wrench, alternate between each set of nuts.

Using two wrenches to tighten the 1/2 inch lock nuts
Tightening the 1/2″ lock nuts
  1. Slide the release lever into position.
  2. Insert the 3/8″ hex bolt, and secure with a 3/8″ lock nut. Then, using the 9/16″ wrench, tighten the 3/8″ nut and bolt.
Tightening the 3/8 inch hex bolt to secure the release lever in place
Tightening the 3/8″ hex bolt that secures the release lever in place

Tighten until the assembly is secure, while leaving it loose enough for unimpeded operation.

Finishing Up

Testing that the gears release properly after having been reinstalled
Making sure the gears release properly on a fully installed Serco hold down unit
  1. Test that the lever functions properly, and readjust the 3/8″ nut and bolt as needed.
  2. Then, make sure that the gears release properly.
  3. Remove the C-clamp.
  4. Lastly, reattach the release rod to the release lever, and secure with the pin.

We hope this helps you to repair or replace your Serco hold down unit. More information about dock levelers is located in our blog posts about snubber assemblies and hinge lubrication.

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