dtomar

Last night I noticed the left headlight motor runs about 5 seconds longer than the right headlight motor AFTER the headlight stops moving. The motor continues to run and makes a clicking sound while the actuator arm tries to move, but it can't since the headlight door is in its fully shut position. The left motor also does this when I go from "Parking Lights" to "OFF", even if the headlight doors were never opened. The right side does not do this. My concern is for the plastic gear inside the headlight motor itself. Both headlights do open and close however.
Is there some kind of adjustment or limit switch that could be the problem? Any thoughts would be appreciated. Thanks.

Dave

zr1fred

Your gears are probably all right, there are three "sacrificial" pellets in each motor that disintegrate. When you open up the motor, all you'll find is small pieces of nylon. the pellets are available in alot of places, (they are the same ones used in Ford window motors,etc).

dtomar

Thanks but any recommendations as to why the motor runs longer than it should?

zr1fred

The bushings (pellets) connect the hub to the gear. When they go, there is no or little "traction" between the hub and the gear. the gear forces the motor to rise against a set of contacts when the headlamp assembly hits the open or closed stops, shutting off the motor. No traction, no breaking of the contacts. In the older (pre-88 motors) when these contacts didn't make/break, it would break the gears and with the relays they used, the motors would run forever. When they went with the newer design, they use a solid state module that automatically times out after 5 or 6 seconds.

dtomar

ZR1Fred, any recommendations?

zr1fred

You need to get the pellets, sometimes called a headlight motor rebuild kit ($2 -$15 depending on what they call it, consisting of the three pellets). The motors rebuild fairly easy if you're mechanically inclined. Otherwise you can get rebuilt motors/exchange or have a shop do it. Check for previous threads, these come up about once a month (real common problem), someone had one in the past couple of days.. If you do it yourself, do both, one at a time so you get the parts together correctly. It should take about 1-1/2 hours to do them both, one side is easier than the other. You need to remove the complete headlamp asm. from the hood (really easy).

GREGGPENN

Contacts do not control headlight travel. Actually, there is a change in resistance in the circuit when the headlight hits it's stop. (The stop is a screw you adjust in/out). When the motor resistance goes up, the circuit is interupted. Even if your headlight rotates closed, it won't develop the resistance necessary to stop the circuit. That's because the "sacrificial bearings" allow the motor to continue to rotate.

You will need a 1/4" drive set with long extensions, some hex keys, and some patience.

There is a how-to article on Corvette Fever dot com. It includes nice pictures to step you thru it. That's what I used.

dtomar

Gregg,
Do you also believe it's those sacrificial pellets?

VetNutJim

Hmmmm let me get in on this 'Headlight Theory' discussion.

1) There are NO 'limit' switches on the 91 & up headlight control circuit.
2) There is no change in motor resistance on the 91 & Up (or down) headlight circuit.
3) This is how it works.......................

The "Headlight Control Module",mounted on the left front wheelhouse controls the headlight motors.
It does the polarity switching to run the motors either CW or CCW.

CW = Clockwise
CCW = Counter Clockwise

Inside the module there is a "Current Sense" circuit.
This circuit 'senses' the current the headlight motor consumes as it's running, in either direction CCW or CW.

When the headlight maechanical assembly reaches either end of it's normal travel, the motor is still running. When the motor has resistance due to the assembly 'hitting the mechanical stops' the motor current starts to increase.
When the current rises to the level predetermined by the 'Current Sense' circuitry, the 'Headlight Control Module" turns the motor off.

Simple, no pesky switches, no burned up motors, no fire hazzard.
Almost perfect, huh?

There's one more problem that needs to be solved.
What happens if the gear assembly is broken ot for whatever reason the motor becomes disconnected from the gear train?
The motor would run and run and run and run..well you get the idea.
The engineers anticipated this and added....tada....
A "Run Length Limiter" circuit for the headlight motor drive circuitry.
So instead of running until the motors were worn out OR the battery died, whichever comes first.....Now the motor will run for a predetermined time then stop.

So what makes the motors run for an excessive time??
Welll.... the engineers also thought about what would happen if the headlight assembly binded up. A direct drive gear train 'could' damage the drive gears so they put in a 'clutch' mechanism.
If the 'clutch' gets weak, the motors will never consume enough current to reach the 'cut off point' of the "Current Limiter" circuit.
That's why they run for a long time when they get 'old'.
The motor will keep running until the "Run Length Limiter" cuts off the power.

One more caveat..... What would happen to the 'good' motor/mechanical assembly if one side experienced any type failure???
Again, the engineers anticipated this and....
The "Headlight Control Module" is a "STEREO" controller.
That's right, it's a TWO CHANNEL controller with seperate circuitry for each headlight/motor assembly.
So if one side doesn't work right the other side can go right on working. You REALLY wouldn't want to end up with NO headlights one dark and stormy night, would you?

So, there was a LOT of thought that went into our headlight control circuit. This is one thing the engineers got exceptionally correct.

And that is pretty much how it works.
Straight from the 'Think Tank' of VetNutJim.

dtomar

VetNutJim,

Thanks for the detailed circuit operation. Based on my symptoms, what do you think my problem is?

VetNutJim

GladI could contribute soemthing here. These guys have sure taught me a lot.

It's the 'clutch' in the geardrive.
A couple of the guys hit it right on the head except the description of how it works.

It'll cost ya bout 10 bux to fix it with thelittle bushing thingys..

Jump over there to that Corvette Fever article as mentioned above and it should give you a step by step.

Everybody does this themselves.
It will be a little 'quality time' you'll get to spend with your Vette.

VetteUSA

, there are 3 bushings that have turned to dust. Buy yourself some new bushings, replace them, and the headlight problem will be healed. I replaced the bushings on each of my headlights some time ago. Very common problem, just do a search and you should find a detailed write up with pictures.

runner140*

David, you need to purchase three headlight bushings.... get them on eBay. When you receive them, go to this web site. It is a step by step with pictures. http://www.corvettemagazine.com/2002...hts/light1.asp

Just did mine recently.

onedef92

Also, check the C4 Tech Tips Section on this Forum for the excellent how-to repair articles written by Jeff Loftis (Jackyl) and others.

BTW, it's your Delrin bushings. They've turned into doo-doo, just like they're designed to do.

dtomar

Thanks for all your help guys! I'll let you know how it goes.

Dave

GREGGPENN

Yes. I am sure it's your headlight bushings (sacrificial pellets).

VetNutJim described how the circuit works with better technical correctness & detail, but that's what I meant. Thanks!

We are in agreement.

gp

JnC96CE

I dont post too much,
check my past post for some info (maybe a few months ago)

born2race

1991 - L98 - The hood on this car was replace and I think this hood is off of a 88-90. Wondering if that may help. Anyway here's a freaki one. I also thought the the bushings needed replacement on my headlight motors so when my drivers side lites wouldn't pop up and before i decided to dismanlte the motor from the housing I decided to just plug that lite into the right side the one that was working. Holly cow the lite popped up indicating that the gear was good in that head lite. Reading the FSM I checked the fuse block behind the battery thinking maybe a fusible link. So i decided to remove all the links from the block and noticed some connects were dirty cleaned them all up with some sand paper. Put the links back on the fuse block now neither on pops up. The motors don't even spin. Any one have any clues. Very much appriciated... Happy Corvetting All.

91 corvette

Just replaced the bushing and gear on mine last week,passenger side.

Yorcci

I had the exactly same problem with my '91.





Repaired:



Here are the instructions http://www.corvettemagazine.com/body...1988-1996.html