I've had a 2000 Firebird since I was 16 and I've been driving it daily. I'm very nostalgic for the car, and though it's showing a lot of wear I try my best to keep it in shape. But after almost 15 years the teeth of the headlight motor gear sheared off and the passenger light made a 'jackhammer' sound whenever the motor was engaged. It's a common problem, and there are a lot of solutions out there including buying a new gear or just replacing the headlight motor altogether.
The original gear in question was made by GM/Pontiac out of nylon. Very recently I finished designing and building my own custom 3D printer and I knew it could print Nylon filament. So this was the perfect opportunity!
In my personal experience, I believe having 3D printing technology at home can save a lot of money particularly if you're already skilled with CAD. And yes printing a new gear was accomplished for ~25% of the cost for a new gear. But I'm really doing this because it a more 'personal' solution than just buying something off-the-shelf and let's me put my touch on the car.
I built my own fused deposition printer for projects like this one but a stereolithographic printer like the Form 1+ would give me capabilities not possible with my FDM machine. For example, I'm very envious of the new castable resins available from Formlabs and that would have enabled me to make this gear out of brass or aluminum.
For future projects, I've always thought LCD keyboards like the the Optimus and Razer Switchblade were incredibly cool but way overpriced. I've thought about making my own using hall-effect sensors and a 15" salvaged laptop LCD. It would be exceptionally difficult and time consuming but a fun potential project. The Form 1+ would let me print the optically clear keys needed for such a build.
Step 1: Headlight Motor Removal
First thing is first, the headlight motor must come out.
In the interest of completeness I'm going to give a procedure for removing the gear. But I'm giving credit for these instructions to bfranker.
1. Open the hood and raise the headlights manually. You can do this by inserting a hex key into the manual adjustment knob right above the light. Turn counterclockwise the raise the light.
2. Remove the plastic bezel (3 screws). If you'd made it this far you're probably familiar with this already. The plastic bezel is usually removed for replacing the headlights when one burns out.
3. Remove the headlight arm (1 nut). Before starting, take a moment to investigate and understand how the headlight mechanism works. In engineering circles, we call this a 4 bar linkage. The nut holding the arm in place is a 10 mm size. Even after removing it the linkage will probably be difficult to remove. I recommend finding a "crowbar of mass persuasion" to help. But be careful. The linkage is the only thing holding the light up so it will fall unless you have something else to hold it up.
4. Dismount the headlight motor (3 bolts, 3 nuts). Again, these are 10 mm. You'll see two close to the front of the car and they're easy to remove. The one is the back is a bear. If you have a socket extension I think you can reach it that way but in my case I preferred to use two 10 mm wrenches.
5. Unplug the headlight wire harness. The headlight motor and low/high beam headlights are all tied into the same wire harness connector. So you'll have to unplug all of it but the headlight motor is finally free once you do.
Step 2: Motor Disassembly
The headlight motor was designed to be replaced as a whole unit rather than repaired. So there's no screws to loosen. Instead, the motor cover is epoxied into place and you'll have to pry it off to gain access. Fortunately this wasn't too difficult for me.
And as you can see from the pictures below, after 15 years of driving two teeth finally sheared off the gear inside. Almost nothing ever goes wrong with the rest of the motor. A whole motor can cost as much as $270. Printing a nylon gear costs $1-3 depending on how many copies you make.
Other than the nylon gear we're so interested in, we have a metal shaft through which the assembly motor outputs it's work and a rubber coupler transmits mechanical energy between the pieces. We'll keep these pieces and use them again.
It's important to note this gearing system is a worm drive. The screw which turns the gear is called the worm. When you turned the 'manual adjustment knob' to raise the light in the last step you were actually just spinning this worm.
Step 3: Gear Design!
I must confess I'm cheating a little here. My CAD package is Solid Edge and includes an 'Engineering Reference' toolbox. A 'Worm Gear Designer' is part of that package and calculates my gear geometry for me as long as I give it a few common parameters such as the number of teeth, center to center distance, and helix angle. Many other CAD packages including Autodesk Inventor include gearing calculators.
If you're truly interested in proper gear design (without cheating like I did), then you can find great resources online and in machine design textbooks. But the subject is much too deep to summarize on this page and I simply couldn't give it justice.
Once the automated geometry is generated, I modified it to mirror the nylon gear we pull out of the car. For this part, a pair of calipers was the only thing needed.
Step 4: Print It!
Now the exciting part.
I strongly recommend using Taulman 645 Nylon because it's formulated for mechanical strength. The last gear worked for 15 years. So don't use weak nylon, use a strong formulation.
I printed the gear at 240 C but use your best judgement. Every machine is different. Also cover your head bed with Garolite (G10 epoxy glass laminate). Or if like me you don't have any handy use wood instead. Nylon sticks very well to these materials and that's key to getting a good print.
Last, print a range of gears. We're going to have some shrinkage occur as the part cools. Even more, my tolerance with calipers probably leaves a little to be desired when comparing to the original gear. So I printed a total of 4 gears each scaled to 100%, 102%, 103%, and 104%.
I'm also including here a small nylon spacer. Print three of those as well. We'll use them later.
Step 5: Motor Re-Assembly
After pulling the newly made gears off the machine, clean them up and test fit them with the rest of the assembly. Look for complete (or close to) meshing of the teeth. Manually turn the adjustment knob and watch the gears turn. Make sure there's not too much friction.
Once you're happy with the fit, take your finger and spread some of the grease left inside the motor housing around your gear. This is done to reduce friction and improve the gear lifespan. Fingers crossed for another 15 years!
Since the motor plate was epoxied in place, mix up some new epoxy and re-secure it the same way. We'll further address this in the next step.
Step 6: Motor Re-Installation
Yes, installation is just the reverse of removal. But there's one key difference.
The motor plate which holds everything in place is just epoxied in right now. If that plate broke loose while you're driving...well it'd be bad.
So let's give ourselves a little mechanical piece of mind. Use the nylon spacers printed earlier to make sure the motor place stays put.
- Re tighten your bolts.
- Plug your wire harness and electrical connection back in.
- Remount the four bar linkage from before but be careful to verify the linkage is oriented correctly.
Step 7: Testing and Conclusion
Results are mixed but overall positive.
As you can see from the video, no more jackhammer noise! But there's a little extra friction which is causing the gear to turn slowly. Even so, I'm counting this as a win. And I believe the friction will correct itself as the mechanism wears over time. In retrospect, the gear I used was scaled to 104% and it probably would have been perfect if I'd used 103% instead. But I'm proud of this fix.
It's also worth noting, corvettes used a similar mechanism with nylon gears. I'd think it'd be really cool to see this done in a 90s era corvette.
I completed this work on November 14, 2014. I hope this instructable is useful to other TransAm/Firebird owners and I'm committed to updating this page the day the gear wears out. (Who knows how long it will last?)
Update 12-22-14: One month later and it still works! Lights are typically cycled once per day at minimum.
Update 1-5-15: Looks like trouble! The grinding noise is back and the light no longer lifts on it's own. Hopefully I'll get to fix it soon but I have some other home restoration projects that have to take priority.