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Failure of 3057 automotive tail lamp

Hello all!

A couple of months ago I helped a friend change one of the stop/tail
lamps on his '98 Chevy Malibu. It was a 3057 lamp - the "wedge base"
type where the base is rather flat, instead of the more traditional
round brass base. Anyway, I got it out of the socket pretty easily,
and noticed that the bulb didn't have any black or silver spots on it.
I held it up to the daylight and saw that the filaments looked OK -
tapping the bulb didn't result in loose filament ends flopping around.
Finally, I looked at the base and saw the problem.

On this particular lamp, there is a plastic piece on the base that the
lead wires from the filaments are laid on top of. Some flat springs in
the socket contact these wires when the lamp is installed. Apparently,
there was a poor connection at one of the contacts for the brighter
filament that caused the lead wire to heat up. The lead wire was
unbroken, but the plastic around it was pitted and melted. The wire had
sunk into the plastic, visibly lower than the other wires on the base.
After it sunk long enough, it no longer made reliable contact with the
contact in the socket. I applied 12 V to the lead wires and the bright
filament lit right up.

I couldn't see very well into the socket to see what might have been
damaged there, but I could see some markings on the affected contact. I
cleaned the contact as best I could with an emery board (it was handy),
blew out the dust, and bent the contacts a little more towards the center
so they would press harder on the lamp base. I then installed a
replacement lamp, and it's been working fine for a couple of months now.
I don't remember exactly the brand of the failed bulb. I know the tail
light assembly was made by Britax. I may still have the bulb around
here somewhere.

I thought this was kind of an interesting failure mode. A few years
ago, when these wedge base lamps started appearing at the auto parts
store, it seems to me that most of them had a glass base. The bulb was
simply extended down and pressed flat to form the base - there was still
a plastic ring around it to locate the lamp in the socket, and to stop
the wrong type of lamp being put in the socket, but the lead wires were
on top of pressed glass. All of these lamps that I have seen lately are
the kind where the base is mostly plastic, and the lead wires lie on top
of plastic. This style is probably easier or cheaper to manufacture,
but I think the glass base would have done better in this situation. On
the other hand, the heat generated might have tended to melt the plastic
socket instead, which would be much more expensive to replace. The
socket was part of a molded assembly with three other sockets; I'd
rather buy a $2 bulb than what is probably a $50 part at the dealer.

Matt Roberds
 
V

Victor Roberts

Jan 1, 1970
0
[snip]
I thought this was kind of an interesting failure mode. A few years
ago, when these wedge base lamps started appearing at the auto parts
store, it seems to me that most of them had a glass base. The bulb was
simply extended down and pressed flat to form the base - there was still
a plastic ring around it to locate the lamp in the socket, and to stop
the wrong type of lamp being put in the socket, but the lead wires were
on top of pressed glass. All of these lamps that I have seen lately are
the kind where the base is mostly plastic, and the lead wires lie on top
of plastic. This style is probably easier or cheaper to manufacture,
but I think the glass base would have done better in this situation. On
the other hand, the heat generated might have tended to melt the plastic
socket instead, which would be much more expensive to replace. The
socket was part of a molded assembly with three other sockets; I'd
rather buy a $2 bulb than what is probably a $50 part at the dealer.

There is an aspect of this discussion that is similar to one
we had just a short while ago regarding the incandescent
lamp with the switch chip in the base.

I have not seen the wedge lamps with the plastic bases, but
plastic cannot be used to replace a glass base. To keep
oxygen out of the lamp, a glass fusion seal must be used.
The type of seal used in these lamps is usually called a
pinch seal. In the older designs, the lead wires were just
bent back along the fusion seal and the seal was then
pressed into the socket. It is possible that the plastic
base was added on top of the fusion seal to provide a more
uniform base shape for insertion into the socket.
(I strongly suspect that Daniel knows the answer to why this
was added.)

--
Vic Roberts
http://www.RobertsResearchInc.com
To reply via e-mail:
replace xxx with vdr in the Reply to: address
or use e-mail address listed at the Web site.

This information is provided for educational purposes only.
It may not be used in any publication or posted on any Web
site without written permission.
 
D

Douglas G. Cummins

Jan 1, 1970
0
Hello all!

A couple of months ago I helped a friend change one of the stop/tail
lamps on his '98 Chevy Malibu. It was a 3057 lamp - the "wedge base"
type where the base is rather flat, instead of the more traditional
round brass base. Anyway, I got it out of the socket pretty easily,
and noticed that the bulb didn't have any black or silver spots on it.
I held it up to the daylight and saw that the filaments looked OK -
tapping the bulb didn't result in loose filament ends flopping around.
Finally, I looked at the base and saw the problem.

On this particular lamp, there is a plastic piece on the base that the
lead wires from the filaments are laid on top of. Some flat springs in
the socket contact these wires when the lamp is installed. Apparently,
there was a poor connection at one of the contacts for the brighter
filament that caused the lead wire to heat up. The lead wire was
unbroken, but the plastic around it was pitted and melted. The wire had
sunk into the plastic, visibly lower than the other wires on the base.
After it sunk long enough, it no longer made reliable contact with the
contact in the socket. I applied 12 V to the lead wires and the bright
filament lit right up.
< snip >

All the bulbs I'm familiar with (mostly the OEMs) use thermoplastics
with a maximum operating temperature of at least 250°F, so the bulb and
socket would have to be hot enough to boil water for their bases to
melt. Usually its the socket and/or the lamp assembly that melts when
the lamp overheats. Was the Britax lamp that the bulb was in the
original equipment or a replacement?
I thought this was kind of an interesting failure mode. A few years
ago, when these wedge base lamps started appearing at the auto parts
store, it seems to me that most of them had a glass base. The bulb was
simply extended down and pressed flat to form the base - there was still
a plastic ring around it to locate the lamp in the socket, and to stop
the wrong type of lamp being put in the socket, but the lead wires were
on top of pressed glass. All of these lamps that I have seen lately are
the kind where the base is mostly plastic, and the lead wires lie on top
of plastic. This style is probably easier or cheaper to manufacture,
but I think the glass base would have done better in this situation. On
the other hand, the heat generated might have tended to melt the plastic
socket instead, which would be much more expensive to replace. The
socket was part of a molded assembly with three other sockets; I'd
rather buy a $2 bulb than what is probably a $50 part at the dealer.

The 3057 comes in two different styles - an S-8 bulb style which has a
plastic base that holds the glass envelope that's been pinched closed
and a GT-8 bulb style which pinches a longer glass envelope to form a
base and only a little plastic is used to position the bulb so that the
filament is in the right focal plane of the lamp.

Current US and European cars will typically use bulbs like the 3057 with
a plastic wedge base. Most Asian cars use a different style bulbs - the
7440 (W21W) or 7443 (W21/5W) - which are an all glass wedge base. These
bulb styles are not interchangeable.

In my experience, the plastic base bulbs are higher quality with better
filament positions and the glass base bulbs are cheaper. But then again
I need bulbs that fit extremely tight tolerances so I'm biased toward
the best. For the average consumer, it probably doesn't make too much
of a difference.
 
Victor Roberts said:
I have not seen the wedge lamps with the plastic bases, but plastic
cannot be used to replace a glass base.

Right. I know that both the "newer" and "older" bulbs are sealed by the
glass bulb being fused to itself.
In the older designs, the lead wires were just bent back along the
fusion seal and the seal was then pressed into the socket.

Like this: http://secure.cazbah.net/product_images/catalog19590/3057_200.jpg

The bulb that failed, and the one I replaced it with, looked like this:
http://www.hardwarestore.com/media/product/112192_front500.jpg
It is possible that the plastic base was added on top of the fusion seal
to provide a more uniform base shape for insertion into the socket.

I wonder if it might also have been to allow for a better retaining
mechanism. On the second picture, there is a groove in the plastic base
just under the "12V32/2CP" stamping. This might let the socket have a
spring "finger" to fit into that groove and retain the lamp better, or
for the really paranoid, allow for a wire retaining clip to be added.

Matt Roberds
 
Douglas G. Cummins said:
Was the Britax lamp that the bulb was in the original equipment or a
replacement?

The housing (colored lenses, reflectors, plate with sockets) was made
by Britax and is original to the car. I believe all of the lamps were
original. I _think_ they were Sylvania lamps but I don't remember for
sure.
The 3057 comes in two different styles - an S-8 bulb style which has a
plastic base that holds the glass envelope that's been pinched closed
and a GT-8 bulb style which pinches a longer glass envelope to form a
base and only a little plastic is used to position the bulb so that the
filament is in the right focal plane of the lamp.

_That's_ the difference I am talking about. Perhaps the Asian makers
started using the GT-8 style sooner than the US and European makers
started using the S-8 style; I remember the GT-8 kind showing up first
at the auto parts store.
In my experience, the plastic base bulbs are higher quality with better
filament positions and the glass base bulbs are cheaper.

The root cause of this problem could very well be the socket (poor
contact spring tension?) instead of the lamp. However, most of the
damage appears to have been done to the lamp. It was hard to see down
into the narrow slot in the socket where the lamp seats, but I could see
that there was some discoloration on the socket contact. I don't know
if the plastic around the contact had been damaged.

The housing looked like this one
http://auto-headlights-taillights.com/index.cfm?fuseaction=products.detail&product_id=633
but it was original to the car. The lamp that failed was the inboard
stop/tail lamp. I remember pulling out the (working) outboard stop/tail
lamp and inspecting it for damage, but it was fine.

Matt Roberds
 
V

Victor Roberts

Jan 1, 1970
0
Right. I know that both the "newer" and "older" bulbs are sealed by the
glass bulb being fused to itself.


Like this: http://secure.cazbah.net/product_images/catalog19590/3057_200.jpg

Sort of - but the wedge base lamps I am most familiar with
have no plastic at all.

--
Vic Roberts
http://www.RobertsResearchInc.com
To reply via e-mail:
replace xxx with vdr in the Reply to: address
or use e-mail address listed at the Web site.

This information is provided for educational purposes only.
It may not be used in any publication or posted on any Web
site without written permission.
 
D

Daniel J. Stern

Jan 1, 1970
0
A couple of months ago I helped a friend change one of the stop/tail
lamps on his '98 Chevy Malibu. It was a 3057 lamp

Apparently, there was a poor connection at one of the contacts for the
brighter filament that caused the lead wire to heat up. The lead wire
was unbroken, but the plastic around it was pitted and melted. The wire
had sunk into the plastic, visibly lower than the other wires on the
base. After it sunk long enough, it no longer made reliable contact with
the contact in the socket.

This failure mode is commoner than it ought to be. There are several
potential causes:

1) Low-quality, off-brand bulb: Improper plastic base material used,
insufficient thermal stability and temperature resistance and/or improper
corrosion resistance of contact wires. Subpar contact causes high
resistance which causes high localized heat, which increases resistance
and softens the plastic, worsening the contact and increasing the heat,
and the cycle carries on until failure occurs.

2) Improperly-designed socket. This was a major problem with late-'90s
Volvos. Basically, socket factors cause the same heat cascade described in
(1) above.

3) Properly-designed socket with dirty or deformed contacts: Same result
as in (1) above.

As you note and D. Cummins confirms, there are two different designs for
the 3057 bulb. Wagner, whose predecessor Tung-Sol devised this type of
bulb in the mid-1970s, uses the GT8 design, in which the bulb is all
glass, top to bottom, with a small plastic collar (usually these days a
golden/transparent Ultem polyetherimide) to position the bulb within the
socket. That design looks like this:
http://www.donsbulbs.com/bulbs/g/ib/3157~usa.jpg

Then there is the design marketed by Sylvania, Philips and others, which
is an S8 glass with a full plastic base. That design looks like this:
http://www.donsbulbs.com/bulbs/g/ib/3057~usa.jpg

Both designs work well when properly designed and when the correct
plastics are used for the temperatures that will be reached by that
specific bulb in whatever application. Some of the bulbs in this family
have variants that are identical in terms of power consumption, light
output, lifespan, color of light, etc., but have bases of different
plastic for applications with more or less severe operating conditions.
There's nothing about either design concept that makes it superior to the
other. Implementation is another matter, and a poor implementation of
either design is not as good as a good implementation of either design. D.
Cummins is probably correct that certain of the GT8 bulbs are less precise
in terms of e.g. filament placement, but he's also correct that this only
matters for such exacting tasks as lamp certification or approval testing.
As long as you stick with a major brand, pick the right bulb for the
application and check the socket for condition and cleanliness, you should
be fine.

It is worth noting that there were two fixes for the problematic Volvos
mentioned above. Some of the cars were recalled and retrofitted with
bayonet-base bulbs and matching sockets. For those not severely enough
affected by the problem to warrant that, the fix was to replace the
plastic-base S8 bulbs with all-glass-with-plastic-collar GT8 bulbs.
I think the glass base would have done better in this situation.

It very well might have; glass is, after all, harder and more heat
resistant. If you prefer the all-glass design, you're most likely to find
it in a Wagner or GE package. Try to avoid "econo" brands like CEC,
Eiko/Wiko, and of course the many pretend-brands that pop up and disappear
in a space of months.

DS
 
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