Pop up headlight motor problem.

[Mark42]

I have a 1998 Pontiac Firebird with power pop up headlights. The design uses a control module to reverse the 12v dc motor to make the headlights go up or down.

There is an inherent problem with the design where a plastic gear in the motor assembly gets stripped out by the driving worm gear over time. Part of the flaw is that the motor is not turned off (either opening or closing) until a solid state control module detects the load created when the headlight housings reach their full open or closed position. This means that the motor is running right up to the point that the headlight housings hit their stops. I believe the shock load is putting undo stress on the plastic gear, making it wear.

To "lessen the blow" to the plastic gear, I was wondering if a resistor can be put across the motor poles to make it run slower. Not sure if the solid state module will read the load properly if this is done.

Thats what I'm asking you electronics wizards on the forum. How to reduce the impact on the motor gear to extend its life.

Here is a wire diagram of the motor control box (linked from Firebird Nation):

This link will take you to a forum where the above images can be viewed much larger for ease of reading:

http://www.firebirdnation.com/forums/index.php?showtopic=10304&st=0&p=91475&#entry91475

And a pic of the motor with gear box open just for reference:

 

[10thHawk]

Re: Pop up headlight motor problem.

Not sure if this may help you also, but I have heard of replacements for those gears made out of aluminum . Might be a simpler fix for you. I have an 01 firehawk, though i havent had any issues with the headlights.

 

[Mark42]

Re: Pop up headlight motor problem.

Not sure if this may help you also, but I have heard of replacements for those gears made out of aluminum . Might be a simpler fix for you. I have an 01 firehawk, though i havent had any issues with the headlights.

Yeah, I found the site that sells the aluminum gear (used to be brass). I'm trying to extend the life of the plastic gear as long as possible before having to pull the housing apart and change the gear.

I was thinking that a resistor would slow down the motor, the headlights will open slower, and the shock load would not be as great when the headlamp housing hits the stop.

 

[Les Robb]

Re: Pop up headlight motor problem.

Well good luck, but even running at a slower speed if the dc motor is driving against a plastic gear something will eventually give. I guess you can't install limit switches to shut it down at top high and low? I'm amazed seeing the results of a limit switch failing on the finisher trays of our copiers. They will lower till they can't go any further and then the main plastic drive gears go. (A heck of a lot of damage). Think the tougher aluminum gear would be the way to go.

 

[Mark42]

Re: Pop up headlight motor problem.

Well good luck, but even running at a slower speed if the dc motor is driving against a plastic gear something will eventually give. I guess you can't install limit switches to shut it down at top high and low? I'm amazed seeing the results of a limit switch failing on the finisher trays of our copiers. They will lower till they can't go any further and then the main plastic drive gears go. (A heck of a lot of damage). Think the tougher aluminum gear would be the way to go.

I expected to find limit switches. But I guess technology that can sense the load draw on the motor to turn it off is cheaper and works. The draw back to cheaper to build is expensive to maintain.

Will adding a resister to slow the motor down still let the circuit detect motor load when it hits the end of travel?

 

[chuckz]

Re: Pop up headlight motor problem.

Short answer No. A series resistor will slow down the motor but it will also confuse the sense circuit. The sensed voltage will always be lower with the series resistor. The sensing resistor to ground in the coast mode would have to be changed to correct for the "new" voltage.

Besides, it would have to be a very high wattage resistor. For instance, 5 amps at 12 volts is 60 watts.

 

[MrBigStuff]

Re: Pop up headlight motor problem.

The resistor won't work for the reasons you already mentioned.

I believe the plastic gear was originally intended as a sacrificial weak link to protect the motor from permanent damage. Replacing a cheap plastic gear is much better than an entire motor assembly. I have a number of Corvettes and owned quite a few over the years. I have replaced a few of the plastic gears over the years but never had to replace a motor. One of them got jammed when the trim came loose and it never hit the current limit to shut off and the motor eventually stripped the gear. If you price out gears versus entire motor assemblies, you might be willing to live with the plastic gears...

 

[Mark42]

Re: Pop up headlight motor problem.

The resistor won't work for the reasons you already mentioned.

I believe the plastic gear was originally intended as a sacrificial weak link to protect the motor from permanent damage. Replacing a cheap plastic gear is much better than an entire motor assembly. I have a number of Corvettes and owned quite a few over the years. I have replaced a few of the plastic gears over the years but never had to replace a motor. One of them got jammed when the trim came loose and it never hit the current limit to shut off and the motor eventually stripped the gear. If you price out gears versus entire motor assemblies, you might be willing to live with the plastic gears...

The gear is not a service item. The plastic housing has to be broken apart to get the gear out. After installing a new aftermarket gear, the housing is epoxied back together.

I noticed that there are a number of suppliers of rebuilt motors. I suspect they are using the brass or aluminum gear because I can't find a plastic replacement.

 

[MrBigStuff]

Re: Pop up headlight motor problem.

The gear is not a service item. The plastic housing has to be broken apart to get the gear out. After installing a new aftermarket gear, the housing is epoxied back together..

I don't know how you made the leap from sacrificial part to expected maintenance item.

I can't speak to the availability of your particular gear but I have replaced mine with the OEM plastic gears when necessary. The idea that aftermarket companies might offer a replacement that defeats some originally intended purpose in a misguided attempt to address consumer complaints is not without precedent.

 

[Mark42]

Re: Pop up headlight motor problem.

I don't know how you made the leap from sacrificial part to expected maintenance item.

No leap at all. Sacrificial parts are almost always serviceable parts (ie roll pin, shear pins, break pads, etc). The whole point of a sacrificial part to to preserve another more expensive part for continued use. In this case, once the gear is worn, the entire unit is garbage. So the gear is not a sacrificial part.

I can't speak to the availability of your particular gear but I have replaced mine with the OEM plastic gears when necessary. The idea that aftermarket companies might offer a replacement that defeats some originally intended purpose in a misguided attempt to address consumer complaints is not without precedent.

There are no OEM gears for that year motor. The entire motor and gearbox are one service item. The aftermarket gears solve the problem, and the units perform without error aftwards. I wouldn't call that misguided. I call that a good fix to a bad design.

Thank you for your thoughts on the topic.

 

[MrBigStuff]

Re: Pop up headlight motor problem.

It seems you are contradicting yourself. On the one hand you say the gear is not a sacrificial part and once the gear fails the whole assembly is junk.

In this case, once the gear is worn, the entire unit is garbage. So the gear is not a sacrificial part.

On the other hand, you say the aftermarket makes a replacement gear that is superior to the OEM gear.

The plastic housing has to be broken apart to get the gear out. After installing a new aftermarket gear, the housing is epoxied back together.

The aftermarket gears solve the problem, and the units perform without error aftwards.

Which is it?

A sacrificial part does not mean it has to have a door to access it. You were able to open the housing and replace the gear. It's not an EXPECTED failure part but it is serviceable if it fails. The fact you were able to open the housing and replace the gear proves that. Nobody said it was going to be as simple as removing a screw.

 

[Mark42]

Re: Pop up headlight motor problem.

Sorry, I am no longer able to help you with your comprehension issue.

 

[dolluper]

Re: Pop up headlight motor problem.

Mark try Dorman part # 42400 for your gear ....@ rock auto 11.26 each replaces many other part numbers works on your vehicle as well as others ...I know of a guy who makes what you were talking about saw when researching Vet lights + motors
Here's a very good read on fixes plus they have metal gear replacements check the whole page...video's also
http://www.bfranker.badz28.com/headlightfix/index.htm#FreeGuide
Still checking on the limiter

 

[MrBigStuff]

Re: Pop up headlight motor problem.

Sorry, I am no longer able to help you with your comprehension issue.

I find it very amusing that when you're caught in an obvious inconsistency in your argument, you resort to impugning my comprehension skills. Based on your statements in this thread, you would be the last person I would look to for help in that regard...

 

[Mark42]

Re: Pop up headlight motor problem.

Besides preserving the door motor gear, I also wanted to make the headlight doors stay open and the lights off. Here is the latest with this project:

I went ahead and made the modifications to the system to keep the headlight doors open. The project took about 3 hours, about 1 hour spent installing and 2 hours analyzing the car to decide the best way to route wires, where to put the switch, etc.

This is how it went:

Went to Radio Shack for supplies. Found a 12 rocker switch with a very low profile, and it just happens to have a nice LED. Also picked up a DPDT 12v relay that R/S has carried for years. The rest of the supplies I had on hand (connectors, wire, etc)

1) After sitting in the car a while, I decided to put the switch in a hidden location, rather than out in the open. Its not going to be used often, and I like to keep the car looking as original as possible. I decided to put a small rocker switch with red LED in the center console storage box. Drilled a 3/4" hole just above the coin holder and mounted the switch.

2) The switch takes three wire connections. A feed, the load (a relay under the hood) and a ground (for the LED in the switch). The wires were threaded through the console up to the cigarette lighter where the cigarette lighter feed was tapped into to feed the switch. The thin orange wire is the factory cigarette lighter feed, the thicker orange wire (yep, marine grade wire) is the new feed to the switch. The ground connected to the metal framework of the console using a spade end under a screw. Please excuse the fuzzy photo, I didn't realize the camera did not focus until I unloaded the pics.

3) Ran the switched load wire through the firewall near the main wire loom on the drivers side. Put the wire in a loom to protect it and give it an OEM look.

4) The wire from the console switch connects to a double pole double throw 12v relay. The headlight door control module (DCM) is located on the drivers side of the car next to the radiator. The light yellow wire is powered on with the headlights, the brown wire is powered on with the parking lights. (these are wires connected to the DCM on the left side in the photo) The yellow and brown wires are cut and connected to the relay so that in its normally closed position the original circuit is maintained. When 12v is applied by turning on the switch in the console, the relay opens the yellow and brown circuit, and applies power to the yellow wire only connected to the DCM, but isolates the DCM from the headlight switch on the dash. This causes the headlight doors to open as if the headlights were turned on, even though the headlights are off. When the console switch is turned off, the relay switches back to its normally closed setting, and the headlight doors work normally with the headlight switch. In the photo, the bright yellow wires with the pink crip to the orange wire is the feed from the dash switch.

The relay is held in place with wire ties around the DCM.

Here is a view of the switch in the "ON" position.

Continued next post.......

 

[Mark42]

Re: Pop up headlight motor problem.

And the result of turning the switch on:

If you want to see bigger/higher res photos, I have this documented on Shareaproject.com

Next weekend I will put the finishing touches on the project. Will seal the ends of all crimps with BoatLife sealer, and put a piece of double sided sticky 1/4" foam between the relay and the DCM to keep if from moving around under vibration.

Left the headlight doors up all night, and in the morning, they were still up and here was no fire

One thing that surprised me was when 12v were applied to BOTH the parking and headlight feeds into the DCM, the headlight doors would go up, but when turned off, they would not go down! A quick check of the wire with my multimeter showed that the parking light feed was back feeding 12V into the relay, keeping the solenoid engaged. The solution was to remove power from the parking side, and only power the headlight circuit in the DCM when the switch is on. The reason I powered on both the parking and headlight feeds into the DCM was because of the way the headlight switch on the dash works: put on the parking lights and the doors do not open, switch to headlights and the doors open, switch back to parking and THE HEADLIGHTS STAY OPEN. Only when both parking and headlights are turned off by the factory dash switch will the doors close after being opened. I tried to emulate that behavior, but it turns out the circuit in the DCM only needs the headlight feed to determine if the headlight doors should be open or close.

Cool, no?

Quick, cheap, and will save me a ton of aggravation because I won't be standing in a parking lot with the car covered in snow and sleet trying to chip away at a layer of ice to get the doors open.

PS. most of the time when bad weather is forecast, I work from my home office and the cars never leave the garage. Its just those few times when I get stuck in a storm that is a problem.

Hope this helps any members with Firebirds living in the north. l

 

[rather_be_boatin]

Re: Pop up headlight motor problem.

I have a 96 FB coupe and I just ponied up the $325 for the new assemblies from AC Delco, no prob since. Sounds like a lot more time weighted trouble & aggravation to go toggle switch route.

 

[Mark42]

Re: Pop up headlight motor problem.

I have a 96 FB coupe and I just ponied up the $325 for the new assemblies from AC Delco, no prob since. Sounds like a lot more time weighted trouble & aggravation to go toggle switch route.

I do believe you missed the whole point of the switch:

Quick, cheap, and will save me a ton of aggravation because I won't be standing in a parking lot with the car covered in snow and sleet trying to chip away at a layer of ice to get the doors open.

What exactly is "time weighted trouble"?

And where did you get "aggravation" from?