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1985 C4 Headlight Conversion

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Old 09-12-2017, 06:00 AM   #1
pdx_schmoogle
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Default 1985 C4 Headlight Conversion

Hi all,

I did a little searching and haven't found any posts like this, but maybe somebody has tried it before.

I have an 85' Vette with the old style headlight motors, and the driver side motor is an aftermarket motor replacement. Not sure when this was done, but this is how I bought it from the PO. Passenger side motor worked fine, but driver side refused to open. Problem is that the aftermarket motor wasn't made with a thermostat overload switch like the GM motors, so if the limit switch fails to disengage the motor just cooks like crazy until the plastic mounting plate melts, which allows the contacts to move out of spec and the motor doesn't work. So I tried bending the contacts back, but it only worked a few times before it overheated and melted again.

So I bought a control module for the newer style motors and soldered the green and white wires directly to the motor brushes, so the internal limit switch is bypassed and the module can be in full control. This worked great for a few tries, but now it jams the gears up at the end of the travel. When the motors try to reverse they are jammed so badly that they trip the module and shut off before even budging. I can't even get the motors to free themselves with a power supply. The only way to free them is to remove the assembly from the hood and relieve the pressure, then re-mount and try again.

My theory is that these straight cut gears for the 84-85 motors are not meant to be jammed so hard, thus the newer helical gears were designed that way in order to handle the extra force. So if I can reduce the force at which the motors are being jammed into the bump stops perhaps I can prevent them from jamming? Is there a way to adjust the current threshold on the headlight control module? I'm really trying to avoid spending $500 on the new style motors... Just seems so expensive for some shoddy motors, and that money could be used for much better things.

Thanks!
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Old 09-13-2017, 09:52 AM   #2
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pdx, The older style motors seem to turn faster when used like this with a newer limit module. My car was half converted when I got it with a module added and a new style motor on the passenger side but the driver side was not. I also modified the old motor to bypass the internal limit switches as you did. My old motor spins the light quicker than the new style motor but it has not jammed up so far. If yours is jamming the gears could you slow it down with a resistor but have it still move?
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Old 09-13-2017, 04:14 PM   #3
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My 1985's passenger side headlight has not needed any repair, I put a new gear in the drivers headlight, works great.
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Old 09-13-2017, 09:51 PM   #4
Hot Rod Roy
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Why not fix it right?

As you may have figured out, the motor armature in the early headlight motor needs to slide up and down to actuate the limit switches. This sliding action takes place when the headlight door hits its stops, and the worm gear "climbs up" the larger gear, compressing the spring on the motor shaft, which opens the limit switch. Proper lubrication of the motor shaft is very important. If they're working right, they won't overheat!

The "pellets/bushings" in the late model headlight motors are there for a reason! The early headlight motors don't have these pellets. When you use the late model control module with the early motors, that will cause the early headlights to jamb against the stops with much more force, since there's nothing to "slip" in the gear train!

I cleaned and lubed the headlight motors in my '84 about 13 years ago, but have never replaced any parts, and they work fine. Probably about time to give them another lube job!

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Old 09-18-2017, 09:09 AM   #5
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Quote:
Originally Posted by Hot Rod Roy View Post
Why not fix it right?

As you may have figured out, the motor armature in the early headlight motor needs to slide up and down to actuate the limit switches. This sliding action takes place when the headlight door hits its stops, and the worm gear "climbs up" the larger gear, compressing the spring on the motor shaft, which opens the limit switch. Proper lubrication of the motor shaft is very important. If they're working right, they won't overheat!

The "pellets/bushings" in the late model headlight motors are there for a reason! The early headlight motors don't have these pellets. When you use the late model control module with the early motors, that will cause the early headlights to jamb against the stops with much more force, since there's nothing to "slip" in the gear train!

I cleaned and lubed the headlight motors in my '84 about 13 years ago, but have never replaced any parts, and they work fine. Probably about time to give them another lube job!

I've never given much thought to the headlight motors on my '84.

What exactly needs to be lubed? Thanks.
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Old 09-19-2017, 03:12 PM   #6
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Quote:
Originally Posted by divotdug View Post
I've never given much thought to the headlight motors on my '84.

What exactly needs to be lubed? Thanks.
Quote:
Originally Posted by Hot Rod Roy View Post
The motor armature in the early headlight motor needs to slide up and down to actuate the limit switches. This sliding action takes place when the headlight door hits its stops, and the worm gear "climbs up" the larger gear, compressing the spring on the motor shaft, which opens the limit switch. Proper lubrication of the motor shaft is very important.
You'll want to use a light weight white grease, like Lubriplate or CRC Sta-Lube on the motor shaft bearings and the gears. Don't use chassis lube! Be sure to clean the contacts in the limit switches, too!

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