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2002 Chevrolet TrailBlazer LTZ 4.2L
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Discussion Starter · #1 · (Edited)
Good morning,

I'm going to be aiming my headlights since I got a replacement set of housings. I noticed on the plastic trim cover over the radiator, near where the headlight adjustment screws are, there is a marking with a picture of the headlights and 1.25" molded into the plastic.

Everything I've seen has said that there should be a 2" drop from the center of the headlight lens compared to the actual bean hotspot output on the cross section on the wall. Does this mean on the Trailblazer that the drop should be 1.25" instead? Its a 2002 LTZ.

Any input would be ideal. Thank you.
 

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Premium Member
2004 chevy trailblazer_lt
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3,001 Posts
I'm of no help. I take it to a shop that has a rail mounted external light meter that measures the light pattern. To me it is worth the $40 - $50 to have it done right.
 
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Premium Member
2002 Chevrolet TrailBlazer LTZ 4.2L
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303 Posts
Discussion Starter · #3 ·
I wish the shops near me only charged $40 or $50 to do a light alignment. I think I'll do the 1.25" drop first, take it for a drive to see how it shines, and adjust up to the 2" drop if needed. I assumed the .75" difference was due to vehicle height.
 

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Premium Member
2002 Chevrolet TrailBlazer LTZ 4.2L
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303 Posts
Discussion Starter · #4 ·
I made an error. It's 1.25%, not 1.25". Still have no idea what that means.

Image pasted below for clarity.

Rectangle Bumper Wood Gas Auto part
 

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'05 Chevy TB EXT
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5,138 Posts
As a retired Brake/Lamp/Smog Inspector/Adjuster --- I have absolutely NO IDEA either.

I've never seen those numbers --- but they make sense - in a strange way.
 

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'05 Chevy TB EXT
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5,138 Posts
.... and it shows a Low Beam dip of 1.25% --- whatever THAT means.

A 1.25% dip from WHAT REFERENCE POINT?

INCHES I can unnerstand --- but percentages are a strange metric...............................<ahem>
 

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Premium Member
2002 Chevrolet TrailBlazer LTZ 4.2L
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303 Posts
Discussion Starter · #7 ·
.... and it shows a Low Beam dip of 1.25% --- whatever THAT means.

A 1.25% dip from WHAT REFERENCE POINT?

INCHES I can unnerstand --- but percentages are a strange metric...............................<ahem>
Maybe whatever 1.25% drop would be over 25 feet?
 

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'05 Chevy TB EXT
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5,138 Posts
I don't remember even when we used the shadowboxes to set headlights, there was never a percentile value to the setting. ''It was the "hot spot" was to be 4° to 5° to the right at 36 feet and 24 inches lower than the center of the bulb as measured in the vehicle from ground to the center of the bulb".

This setting had to be for all possible loads and road conditions. That never worked out because a pickup truck was always gonna drop the rear with a load .... and then the lights would be illegally adjusted --- ticket time.

The criteria form testing was the vehicle had to have 1/2 tank of fuel and 200 lbs in sand bags in the driver's seat.

I remember that the VWs barely made their minimum height to the center of the bulb by --- maybe 1/16th of an inch from the ground. That across-the-board spec was 24" and a VW with gas in the tank and a 200lb sandbag took the lights below that Federal minimum. That was STOCK --- nevermind if you dropped the front end!

So ... lessee ... if you have a vehicle with max-height bulbs (48 inches was IIRC) and at a certain distance (let's assume 40 feet) the hot spot had to be 1.25% of the 48 inch height which is ,,,, uhhhhmmmm .... I ain't going there --- I just ate and you're not supposed to perform any calculations for 1/2 hour after eating.


.
 

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2004 chevy trailblazer_lt
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3,001 Posts
So ... lessee ... if you have a vehicle with max-height bulbs (48 inches was IIRC) and at a certain distance (let's assume 40 feet) the hot spot had to be 1.25% of the 48 inch height which is ,,,, uhhhhmmmm .... I ain't going there --- I just ate and you're not supposed to perform any calculations for 1/2 hour after eating.
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I thought 1/2 hour was for swimming and swearing, and 12 hours was for calculating!
 

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2002 Chevrolet TrailBlazer LTZ 4.2L
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303 Posts
Discussion Starter · #10 ·
Unless it has something to do with the fog lights? At this point it's in "The bin of who knows".
 

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2004 chevy trailblazer_lt
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I vote for who knows!
 

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2002 Chevrolet TrailBlazer LTZ 4.2L
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Discussion Starter · #13 ·
Aimed them the other night using the parking lot and the side of the shed. I'm happy with the results and nighttime visibility has improved dramatically.
 
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