How to adjust the 4 headlights on a 1984 GMC k1500

[72timemachine]

I have read many articles here and on the web about aiming headlights. Typically they tell you to back up 25' feet on level ground, so on and so on. The problem is, this person's k1500 is lifted, to a comfortable height, nothing crazy high. A person of average height standing on a milk crate can work comfortably on the engine. I tell you this just to give you an idea of how high the truck is lifted.

So, if anyone knows how to properly adjust all 4 headlights, I would appreciate your help. I have reconditioned all the headlight buckets, greased the 3 contact points for ease of adjustment and replaced all 8 of the aiming screws.

Thank you for any help.

[andyh1956]

1-You get out on a lonely dark straight road (At Night) & have your wife 1/4 mile away facing you. Have something you can cover a light on each side with so you can adjust highs / lows independently.
2-You adjust the lights to suit you & wife tells you when they are too high or bright using your phones.
3-You & wife reach happy compromise with headlights.
4- Go home you watch ball game & drink beer wife installs new clutch in your pickup so you can drive to work Monday morning.

[hatzie]

You need the following to do this.
1" wide tape.
1/4" wide tape.
Tape measure.
Two Buckets.
Sand to fill the buckets.
Two landscaping stakes standing straight up in the buckets.
Sharpie.
Obviously you also need the correct screwdriver to run the adjuster screws.

LH is from the perspective of someone in the Drivers' seat. The Driver side is the LH side Passenger side is RH side of a vehicle setup for North American roads.

Find a door or wall as tall as the roof of the truck that has a flat level area at least 35' straight back so your rear tires are still level with the front tires when the front bumper is 25' back from your aiming surface.

Since these allow you to adjust Horizontally (L & R) as well as Vertically (up and down) you have a bit of a chore.

Put 1/4" wide tape across the centre of all four bulbs horizontally and vertically. This will project a dark cross on the aiming surface at the centre of the bulbs when the light shines around it.

Measure from the ground to the horizontal centreline of the bulbs and write it down.
Measure from the centreline of the truck to the vertical centres of all four bulbs and write those measurements down.

Place 1" tape horizontally on the wall/door with the bottom edge at the horizontal centreline of the bulbs.
Place centre of a line of 1/4" tape horizontally @ 1.5" down from the first tape line. This is your LO beam vertical centre line. That should be roughly a 6° downtilt.

Drive the truck up close to the target at 90° to the target and mark the center of the truck on both chunks of tape with a vertical peice of 1/4" tape.

Measure 25' from the target on both sides of the truck and put the stakes in the buckets there. Now you can easily see the back-to-here line inside the cab. Back the truck STAIGHT BACK to line up the stakes with the front bumper corners.

Measure and Mark the vertical centres of the RH bulbs on the target from the marked centre of the truck with 1/4" wide tape.

Subtract 1" from the measured LH actual bulb centres then Measure and Mark this on the target as your vertical aim line. This aims the LH beams 1" toward the centre of the hood from the actual measured vertical centres of the bulbs.

These are your LO Beam Horizontal aimpoints.

Turn your LO beams on and adjust both bulbs so the projected cross covers the aimpoints you marked on the target.

Set your HI beams on and measure from the marked LO vertical centre tape line to the HI aimpoint being projected from the HI/LO bulbs.
This is the HI Beam offset.
Measure and mark that offset with a second vertical tape line on the target for the HI beam only bulbs then aim the HI-beam-only bulbs L-R on those lines.

Adjust the up-down screw on the HI only bulb so the projected horizontal line matches the line being projected from the already adjusted HI/LO bulb... It's worth noting that some people like to set the HI-Only vertical aim slightly higher rather than even with the HI/LO bulb aimpoint. I figure this is personal preference.

This should be as close as you can get to proper aiming standards It'll keep you from blinding other drivers while allowing you to see at night.

A good set of Sylvania XtraVision bulbs will light things up quite well without blinding other people.

[72timemachine]

Thank you both for the information, I do appreciate it.

[Loco83]

https://www.youtube.com/watch?v=GWvSWBlAwnI