Installation Of Demco Underbed Rail Kit On 2005 Dodge Ram With 8-Ft Bed

Updated 06/12/2017 | Published 06/08/2017

Question:

Hijacker 5th Wheel hitch 16,000 lbs. What are the measurements for the rear rail from back of box to wheel wells? I know I have to center the rails. Can I get the measurement for the front rail using the hitch? My rail assembly has 4 L brackets plus bolts also I have 2 U shaped brackets about 10 inches long with 2 holes one at each end. I think this is for the back rail closest to the cab. If you know of any good videos for installing this type hitch I would appreciate the reference to them. Most videos I have found are for a short box truck. Thank you.

asked by: Terry C

Expert Reply:

The installation of the Underbed Rail and Installation Kit # DM8551005 is measured from the back of the truck bed.

We do not have an installation video for the rail kit as you requested, but here are the instructions per the installation manual. I also attached the drawings referenced in the instructions you can check out. You can compare the brackets you said are on your truck to the measurements in the instructions.

NOTE: It may make the install easier if the truck’s rear end was lifted and blocked and/or remove
the rear wheels to have more access for drilling of the frame.
The four 2” holes that need to be drilled through the box are done by the following method:
1. Use the measurements shown in (drawing #1) to mark out the four holes that will be drilled
through the truck bed.
2. Start out by measuring (Dodge vehicles: 34 1/4” for 6 1/2’ box and 36 1/4” for 8’ box models &
Chevrolet/GMC vehicles: 31 3/4” 6 1/2’ box & 36 1/4” for 8’ box models) from the end of the
bottom of the truck bed (tailgate end) to a point on the left side of center of the bed and mark
it. Do the same on the right side of center of the bed and mark it. Draw a line across the bed
using these two marks as a reference.
3. Measure out and find the center of the truck bed and draw a line from the front to the rear of
the bed.
4. Measure out 14 13/16” to either side of the middle center line slightly ahead of the fender well
and slightly behind the fender well.
5. Draw a line between these two points. Do the same on the other side.
6. Measure out (towards the cab) 13 1/2” from the points where the line that goes across the bed
intersects with the two lines that are 14 13/16” off the center running the length of the bed.
Mark these two points.
7. There should now be four spots marked out for drilling. Double check that the rear to hole
marks are exactly as depicted in drawing #1 from the end of the bed and that the front holes
marks are exactly 13 1/2” forward of those marks.
DODGE: Dodge Ram 1500 (6 1/2’ & 8’ Boxes)
Dodge Ram 2500 Includes 4x2 & 4x4 models and MegaCab
Dodge Ram 3500 Includes 4x2 & 4x4 models and MegaCab
CHEVROLET/GMC: Silverado & Sierra 1500 (6 1/2’ & 8’ Box tube frame)

Page 3
Drawing #1
Drawing #2
8. Check the hole marks from side to side and make sure they are exactly 29 5/8” apart from each other.
9. Finally, check for square by measuring diagonally from opposite corners (drawing #2). The measurement should be the same both ways. It should measure 32 9/16”.
10.After all the hole marks have been double checked for proper placement, use a center punch and hammer to mark out the spots for drilling.
11.Drill the holes using a 2” hole saw. Deburr the holes using a small file and apply some touch up paint to match color (not supplied).