CURT C-636 SUBKIT Installation Guide for Ford Trucks

Product Overview

This document provides installation instructions for the CURT C-636 SUBKIT trailer hitch designed for 1980-1998 Ford trucks. It includes detailed steps, necessary measurements, parts identification, and maintenance recommendations.

Installation Steps

An overhead lifting device, such as chain falls, engine hoist, or cable come-a-long, can be used to lift the center section of the hitch in place. Lower a loop of rope or chain through the hole in the truck bed floor and attach it to the round hitch receiver tube in the center section. Use the lifting device to raise the center section until the round hitch receiver tube that protrudes from the center section fits in the hole in the truck bed floor. Maintaining upward pressure may facilitate fastening the cross-member to the center section, especially if the truck bed floor has been distorted downward from heavy use. If you use an overhead-lifting device, it should be disconnected before squaring the center section across the frame, installing the sideplates and torquing fasteners.

1. Lower and remove the spare tire and heat shield. The heat shield is located above the rear axle under the truck bed. It is attached with four sheet metal screws (7/32" hex head). Replace the front screw after removing the heat shield.
2. Mark the location for the hole in the truck bed. Measure from the tail gate end of the truck bed, by hooking a tape measure over the back of the truck box and marking the correct location. (NOTE: DO NOT MEASURE FROM EDGE OF TAILGATE) Next, mark the center between the wheel wells. This marks the center point for the drill hole. This hole location is critical for the correct installation of this hitch. Measure, mark, and saw carefully. This location will put the ball 4"-5" in front of the axle.
   • Short Bed Installation: 48 1/16"
   • Long Bed Installation: 48 1/16"

   Note on Plastic Bed Liners: If the truck has a plastic bed liner, you may drill through both, but it is more difficult to accurately locate the midpoint between the wheel wells, and to keep the bed liner from moving while cutting the hole. Make a 4" (3 5/8" for C-630/C-640) hole at this location using a 4" (or 3 5/8") hole saw, or by making a 4" (or 3 5/8") circle and cutting it out with a saber saw equipped with a metal cutting blade.

3. On power stroke diesels only, loosen the tail pipe hanger bracket in front of the rear axle. Place a ratchet strap around the highest part of the tail pipe and the rear axle. Pull the tail pipe down by tightening the ratchet strap to achieve sufficient clearance for hitch parts. After installing parts, insert a 1/4" shim in the tail pipe bracket and tighten. Cut the safety chain U-bolts, on the exhaust pipe side, off to an inside length of 3 1/4", and cut 1 1/2" off of the safety chain springs.
4. Install the rear cross arm (has the deepest notches at the ends) by sliding it between the bed and the frame on the passenger side in an inverted V position. In order to do this, the bed floor flange must be cut about 2" to the rear of the front most bed frame rail. (NOTE: the notches must face the front of the truck) After it rests on the frames, slide it towards the back of the truck. Rotate the arm so the notches are perpendicular to the truck bed. This process is made easier by loosening the bed bolts in the frame rails behind the axle and using a crescent wrench or channels locks on the slotted side of the cross arm to rotate it down on its long axis, placing the side without slots flush against the truck bed floor and the cut-outs span the truck frame.
5. Install the front cross arm by sliding it between the bed and the frame on the passenger side in an inverted V position. (NOTE: the notches must face the rear of the truck.) After it rests on the frame, slide it towards the front of the truck. Rotate the arm so the notches are perpendicular to the truck bed and the cut-outs span the truck frame.
6. Before raising the center section into position between the cross arms with the ball cylinder towards the back of truck, drop the back exhaust hanger. The round hitch receiver that protrudes from the top of the center section must fit through the hole in the truck bed. Using (8) 1/2" carriage bolts, attach the center section to the holes in both cross arms. Finger tight only with (8) 1/2" flange nuts. When re-attaching exhaust hanger, bend upward to adjust if tailpipes touch the center section.
7. Square the center section and cross arms across the frame. Place a 1 1/2" bolt with a washer through the back flange of the sideplate into the rear cross arm and Finger tight only with a 1/2" flange nut. Place a 1 1/2" bolt with a flat washer through the front flange of the sideplate into the front cross arm. Finger tight only with a 1/2" flange nut. (REPEAT FOR OTHER SIDE) (NOTE: locate and release the brake line and fuel line retaining clip from the frame rail on the driver side before attaching driver sideplate.) If bed bolts were loosened in step 4, re-tighten them now.
8. For Trucks without Overload Springs: Align the large 1" hole and the rear hole on each sideplate to the existing holes in the truck frame. Place a 1" bolt with a 1" washer through the inside of the frame. Place the tube spacer between the frame and sideplate and attach a 1" washer, 1" lock washer, and 1" nut on the outside of the sideplates and Finger tight only. On the rear of the sideplate, place a 1/2" x 1 1/2" bolt through the inside of the truck frame through the sideplate and attach with a 1/2" flange nut. Finger tight only.
9. For Trucks with Overload Springs: The sideplates can be modified to fit trucks with overload springs. To do this, cut 10" off the back of the sideplates (the narrow end of the sideplates). Install the 1" bolts as described in the above paragraph. Now drill a 1/2" hole through the frame rails at the slot nearest the front of the sideplate. Attach with a 1/2" x 1 1/2" bolt and washer from the inside of the frame and Finger tight only with a 1/2" flange nut.
10. With the sideplates installed on both sides, torque all 1" fasteners to 250 ft-lbs. and all 1/2" fasteners to 75 ft-lbs in the following order:
    1. Torque the center section to the front and rear cross arms.
    2. Torque the sideplate flanges to the front and rear cross arms.
    3. Torque the sideplates to the truck frame on both sides.
11. When installing the C-600 handle, it may be necessary to notch the bed floor flange on the driver side of the truck similarly to the notch placed on the passenger side in step 4. The placement of the notch will be determined by the handle placement. (REFER TO GOOSENECK HITCH INSTRUCTIONS FOR INSTALLATION AND OPERATING PROCEDURES)

Diagram Descriptions

Figure 1: Bed Floor Flange Measurement

This figure illustrates the measurement for cutting the truck bed floor flange on the passenger side wheel well. It shows the approximate cut line relative to the bed frame rail. Key dimensions provided are 1.5 inches and 1 1/4 inches, indicating the depth of the cut or flange.

Figure 2: Hitch Component Placement

This diagram shows the underside of a truck bed and frame, illustrating the placement of the hitch components. It labels the Front Cross Arm, Rear Cross Arm, Driver Sideplate, and Passenger Sideplate. It also indicates where the Tube Spacer installs between the sideplate and frame. The orientation of the truck is shown as Front of Truck and Rear of Truck.

Cab to Trailer Clearance Calculation

This section provides guidance on calculating the clearance between a truck's cab and a trailer to prevent interference. It outlines general trailer designs and provides formulas for calculating minimum clearance (Z). The formulas are:

• For standard trailers: Minimum Clearance (Z) = (Cab to Ball Center (X)) - (Trailer Width (Y))
• For trailers with overhang: Minimum Clearance (Z) = [(Cab to Ball Center (X)) - (Trailer Width (W))] / (Coupler Overhang (Y))

A positive Z value indicates no interference, while a negative Z value indicates potential interference between the trailer and the truck cab. The document includes example calculations and a template for users to perform their own calculations.

Parts List

Maintenance

(Required every 30 days or prior to use)

1. Keep hitch ball lubricated regularly. Use silicone spray or equivalent to prevent wear and rust.
2. Keep hitch assembly free of dirt and other foreign debris.
3. Check for proper torque on all nuts and bolts before each use. Also check for excessive wear.
4. Check for ball wear before each use. (Note: Do not tow trailer with worn or damaged parts.)

Refer to Gooseneck Hitch Instructions for installation and operating procedures.

Warranty Information

Curt Manufacturing Inc. warrants this product to be free of defects in material or workmanship at the time of retail purchase by the original purchaser. If the product is found to be defective, Curt Manufacturing Inc. may repair or replace the product, at their option, when the product is returned, prepaid, with proof of purchase. Alteration to, misuse of, or improper installation of this product voids the warranty. Curt Manufacturing Inc.'s liability is limited to repair or replacement of products found to be defective, and specifically excludes liability for incidental or consequential loss or damage.