Light Duty and Medium Duty Dump Kit Installation Overview

Light Duty and Medium Duty Dump Kit Installation Overview

This is an overview of a PIERCE Light Duty Dump Bed Kit installation. We are installing the Light Duty hydraulic dump kit on a Chevrolet cab and chassis. This is a 60 inch cab to axle.  It’s a very standard installation and the perfect truck for the Light Duty hydraulic dump bed kit. We had a bed specially built for this truck that’s going to be 10 feet long. Normally with a truck this length you would use a 9 foot bed, but due to extra space needed for the rear hinges in the dump hoist kit it’s going to be a foot longer.

NOTE: Do not install this kit if you do not have the expertise or equipment. It is better to find a licensed converter than put your equipment and self in danger. Modifications may be necessary on some trucks, makes, and models. We are happy to provide phone support, give us a call with any questions.

Part 1:

Hefty Hoist Measurements and Pre-Installation

Shorten Chassis

We have taken the taillights off of this chassis and looked at the rear of the truck. We have determined that we want to cut this chassis off just a little bit. We do like to shorten the chassis as much as possible because we want as much overhang as we can get on the bed. The more overhang past the hinges gives a counter lever affect and makes, in essence the dump kit stronger.

Rear Hinge Placement

We have determined that we are going to cut the frame up close to the rearmost cross member. There is space to slide the frame hinge in a slot between the outer frame and the cross member.

We are going to cut this frame at a 45 degree angle so that we have pin clearance above the cut, and yet we still have metal to weld or bolt to the frame hinge to the truck chassis frame. We don’t have a problem welding at the rear of a chassis frame, we do not weld anywhere forward of the rear frame hanger. This is in order to keep a crack from developing in the frame and possible weak spots from the welding process. The front of the frame hanger will be bolted to the chassis.

Scissor Placement

Now that we have determined the location of the rear hinge pins we can get an accurate measurement on where to place the scissor assembly on the front of the chassis. According to the directions we have a range of 5’ 8”inches to 6’ 6” from the rear hinge to the pin in the crossmember assembly in the lower frame rack.

We have determined due to clearance issues with the front fuel tank filler hose that we need to be behind that. We also had to decide how to fasten the L brackets that the scissor assembly will be connected to, to the frame. Those have to be bolted. On this particular installation there is an overload spring perch that is bolted to the frame. We can use the same bolt holes by transposing them onto our bracket, sandwiching them together, put in longer bolts, and bolt it into the frame using the existing spring perch.

This puts our scissor assembly bracket, or frame bracket right at 5’ 11.5” which is right at the rear of our parameters. This will give us a little bit more lift height, and a little bit less capacity. Everything is give and take when it comes to lift height vs. capacity. A Light Duty unit on a short cab and chassis such as this is going to give very satisfactory results.

Bed Height

One thing that must be considered in this application is the thickness of the fuel filler hose. This is a Chevrolet installation if it was a Ford or a Dodge the fuel filler hose enters the fuel tank through an opening in the frame and it does not have to be considered. You can lower the bed stringer as low as possible to get the bed height as low as possible. In this particular installation we could go as low as ¾ of an inch however it would not allow room for the hose to remain open for fuel to pass through with the bed in its lowered position. We have to determine that height it needs to be for fuel to pass through before we mount the rear frame hinge.

Measure to determine the space needed between the rear seal hinge and the frame to give you enough space for the fuel fill hose. In this application the space needed was 2 inches. It goes between the bed seal of the main runner on the chassis frame.

Cross Member Modifications

The cross member comes extra-long in the kit because we never know what frame the customer is going to be dealing with. This particular truck has a standard cabin chassis with a 34 inch frame width. In order to keep from welding on the truck frame as I mentioned earlier we added our L bracket to the spring perch. To attach the cross member to the L bracket we will cut the cross member at the appropriate length to allow us enough room to run a bead and weld the cross member to the L bracket. These actions leave the unit bolted to the truck frame through original bolt holes with no damage to the chassis and no compromise to its capacity.

Front Frame Hinges

If we use the stock location we are not going to have enough distance between the frame of the chassis and the seal. There are several different ways to take care of this problem. You can add a spacer underneath the cross member. You can add a spacer in between the seal support and the cross member. We like to have the scissor assembly in a fully retracted position whenever it’s in its full down position in order to gain the use of the full stroke of the scissor assembly. In this particular installation we have decided to make some modifications.

We have trimmed the seal support to fit inside the bed main runner.

Checking the Measurements

We know that our bed will be made with a 4 inch seal and a 3 inch cross member with the deck setting on that. It gives us 7 inches to work with from the deck of the bed to the top of the seal. In this installation we know we are going to raise it up 2 and a half inches above the chassis by adding a spacer at the rear hinges. That gives us an overall height of 9.5 to 10 inches. Take a straight edge and run across the top of our scissor assembly and we see as by measuring to the chassis frame we are going to be in the area of 9 inches overall height, so we have plenty of room to work with a one .5 to 1 inch clearance between the vent and the deck. This space can be changed by raising and lowering the bed, it can also be changed by raising and lowering the scissor assembly. You can make the bed lower by lowering the scissor assembly in between the frame rails. This particular assembly has a fuel tank in the way and this is the lowest position that the scissor assembly can be installed.

Part 2:

Light Duty Dump Hoist Kits Wiring Connections

The wiring kit includes:

  • Positive and negative battery cables that need to go directly to the battery post. You will notice one is red and one is black the red is for the positive cable.
  • Hydraulic hose, switch, wiring and hardware for mounting the pump.

Installing the Pump

The pump needs to be mounted in a safe location the kit does not come with a bracket so it will be up to you to fabricate a bracket. It can be mounted inside the frame, outside the frame. In the Pierce shop we have mounted the pump behind the back seat, underneath the seat, anywhere it looks like a safe location. If you live in a particularly harsh environment something out of the weather might be considered.

Once you mount the pump it’s time to start hooking up the plumbing. In this installation we are using Teflon paste; any suitable pipe sealant would work. It’s a 90 degree fitting so there is not enough room to make the full rotation to thread it into the unit. So the control valve solenoid coil, it’s a black plastic square bolted next to it can be removed. Remove the nut off the end of the stem, and just slide that black coil off of there. Don’t worry about anything coming apart.

When you tighten the 90 degree L, it has to be installed pointing in the correct direction so the hose doesn’t come into contact with any other hardware. The hydraulic hose can then be run to the scissor assembly cylinder which is located inside the scissor assembly. The hose should not be in contact with any muffler, tailpipe, drive shaft, or any moving parts.

When installing the black coil back onto the valve stem the nuts to be installed on top we will continue with the application of the wires.

It requires three wires to control this pump:

The YELLOW wire is connected to the coil which controls the down function

The GREEN wire to the small post on the black motor solenoid

The RED positive cable goes to the power supply post on the black motor solenoid, the post that’s open closest to the truck frame.

The BLACK wire connects to the ground post on the back of the motor.

We will not connect the brown wire in this installation to the pump. The customer requested that the dump kit only operate when the ignition key is turned on and the truck is running. This controls access to the lift that only allows persons with a key to operate the system as a safety feature.

Positive and negative battery cables that need to go directly to the battery post. You will notice one is red and one is black the red is for the positive cable.The positive needs to go to the 150 amp breaker then to the battery.

Installing the controls in the cab

Next we will install the controls inside the cab. We drilled a ½ inch hole to install the control switch. This is a momentary on/off switch for up and down, spring loaded back to the center position. To make the switch operate properly; the green wire attaches to the bottom screw on the back of the switch. The yellow wire would go to the top screw on the back of the switch. If you use the ground for the hot runner from the battery lead at the motor it would go to the center.

In this installation the brown wire will be rerouted to the fuse box of the vehicle to a position that only has power when the ignition switch is turned on.

The last step in the wiring process will be to run the negative and positive cables to supply power to the pump directly to the battery. We run the cables directly to the battery. Crimp the end onto the welding cable using crimper. In order to ensure proper ground we always ground our pump units directly to the battery. We use a number 4 welding for the positive and the negative and they are supplied with the kit. It’s very important to secure the battery cables at least every 12 to 15 inches. Driving down the road these cables get blown by wind and can be coated with mud and could wear through the insulation.

Part 3: 

Light Duty Dump Bed Kit Installation

Hinge Installation

In your kit you will notice there are two hinge pins you can use one large hinge pin it might add a little bit of strength. 

Tack Weld

Tack weld everything into position to make sure that you have the proper alignment, and the bed is on good and straight before we do final welding

Frame Bracket Installation

We are going to bolt the front cross member L brackets behind an existing overload spring bracket. They are pre-drilled to match existing holes.

Cross Member Modification

Bolt them on with grade 8 ½ inch bolts and self-locking nuts. Set the scissor assembly on the truck mark the cross member. We cut the cross member a little extra short to allow for ease of welding when we weld the cross member to the L brackets.  

Scissor Support Modification

We built a bracket for the scissor assembly to rest on when the bed is in the down position. Be aware that through the life of the product the scissor assembly will get lower and lower if you do not place something there to stop that lowering.

Front Frame Hinge Modifications

The 4 inch channel iron represents the main runner or the seal in the directions underneath the bed. We will slide those up inside the 4 inch channel iron once the bed is installed on the truck. Slide the seal supports out until they contact the channel iron and bolt it there with two ½ inch grade 8 bolts on each side.

Modification to the Guides

Modifying the bed guides for a lock down bracket that the customer requested to be installed on this truck. Next you will see we are fabricating a cross member to go on top of the frame to go in front of the scissor assembly. These guides will weld to the end of this cross member and be permanently attached to it. We will bolt this cross member down to the top frame flanks? Flanges? Right behind the cab of the truck. We are using existing holes that were already drilled in the truck frame, and in this particular case the heads of the bolts would interfere with the bed when it comes down, it would actually set on the bolts and we didn’t want it to do that. So, we countersunk the bolts down inside the cross member and we had to saw holes in order for our sockets to go down inside the cross member.

Under Bed Modifications

We will now move underneath the bed. There is a lot of work to be done on the bed before we install it on the truck. At this point we set the bed on the truck and do what we call a dry fit. Sit it down on the chassis as close as we can. See if any trimming needs to be done on the rear hinges to clear cross members or rear hitches that happen to be on the bed. In some cases they have to be trimmed quite a bit if you don’t have a ten foot bed for a 60 inch cab to axle or a 12 ft. bed for an 84 inch cab to axle you’re going to have some clearance problems. Don’t be afraid to trim the back of those hinges off. That is more than likely going to be the case when you install it.


Mark all the holes for drilling where the seal supports contact the seals. In this particular case we mark the hole for our front tie down bracket. Should you choose to put that on your truck it’s a lot easier to take care of all that before the bed is installed on the truck.

Drilling the Holes

We chose to pre-drill our holes so we didn’t have to work underneath the truck bed in the raised position. We reached inside the frame with a paint marker and marked the hole location and notice the pre-drills. We also marked interference location with the cross members of the bed.

Under Bed Cross Member Modification

We trimmed two cross members to allow room for the scissor assembly when the bed is in its full down position. Sometimes you can get by with cutting one cross member but most of the time it’s necessary to trim two.  

Final Assembly and Installation

If you have done all of your measurements correctly and marked all the holes correctly the bed should sit right down on all four corners. Make sure that it is contacting all 4 corners. Make sure both hinges at the back are up against the seal of the bed good and flat. Make sure your bed is in proper alignment front to rear. You don’t want it fastened on at an angle. This shouldn’t be possible at this point at the front because your guides are in place and your rear hinges are in place.

Welding and Bolting the Bed to the Frame

Once it’s welded at the back and bolted at the front everything should work properly raise it up for proper operation. Make sure you don’t fill that tank when the bed is in its up position. As mentioned before as the bed goes up the oil level in the tank goes down this is a single acting system. So anytime you fill the tank the bed must be in its lowered position.

To Remove the Bed for Service or Repair:

Unbolt the L brackets from the frame. Take the bolts out where the scissor assembly attaches to the bed seals. You can then remove the rear hinge pins so the bed can be lifted off the truck. 

Read More: Manuals, Specification Sheets