Y Code Tech: 1972 Climate Controlled Combustion System

                                                                         By: Patrick Smith        

   Emission controls became a necessary part of the automobile since the late 1950s when smog from the Los Angeles basin became prominent. The early systems are laughably primitive now. The road draft tube found in pre 1961 cars was devised to allow engine crankcase vapors to escape via vacuum created by exposure to passing air from the bottom of the engine bay. This set up eased blowby and got the vapors out of the engine bay and passenger compartment, but added to the pollution by creating about 20 percent of hydrocarbon emissions. California State did away with road draft tubes in cars sold in that State by switching to a closed system with a tube from the crankcase to the intake manifold with a valve in between to control the flow of fumes. This was the start of the PCV valve. By 1963, the other 49 States started using PCV valves as well.

   Now on these early systems there was no way for the hydrocarbons to leave the crankcase. It was theoretically recombusted until the output was spent, burnt hydrocarbons. The exception to this was at wide open throttle when the intake manifold had no vacuum to draw pollutants into the engine. At wide open throttle, the engine breathes through the oil filler cap on the filler tube. This was changed in 1966 with a closed PCV sytem on California State cars. 49 State cars gained this set up by 1968. The closed combustion System (CCS) allowed zero hydrorcarbon gas escape. They did it by drawing the pollutants into the engine through suction in the air cleaner element.  Let's look further into the General Motors version of closed combustion system, or CCS as it was called.

The basic closed combustion  setup: At first glance, there doesn't appear to be much difference between an open PCV and closed PCV system.The main difference is the way the fresh air entrance is rigged. Fresh air enters from the air cleaner into a hose or other connection to the crankcase. The normal route is fresh air entering a PCV filter inside the air cleaner, then going into a hose to the rocker cover. This way it doesn't pass crankcase fumes into the air at wide open throttle. When operating under manifold vacuum, the air flow goes from air cleaner to rocker cover. At wide open throttle, the air flow is by crankcase pressure through the fresh air hose from rocker cover back to air cleaner. Once inside the air cleaner they are sucked into the carb for re entry.  With these closed combustion systems you will see a PCV filter at the end of the fresh air hose. Frequent loading up of the filter media tells you blow by is heavy from taking excess fumes.

Transmission Controlled Spark- 

  

The TCS system when used on Pontiacs, may differ in operation particularly with the way the
solenoid is activated. Some years the valve is energized ON, other years energized OFF. Look up the
right year to make sure it works correctly,

    In a nutshell, TCS works by having vacuum to the distributor cut on or off by a vacuum solenoid. The solenoid gets current when the ignition switch is on and normally it is fused in with the car fuse block. The solenoid is grounded at the tranny in certain gears and ungrounded in others. One trip up in diagnosing TCS is there are two types of solenoids; normal open to vacuum and normal closed to vacuum. The first one allows vacuum flow when not energized and the second one allows vacuum flow when energized. The earliest set up used normal open solenoids so it would allow vacuum advance at all times should a fuse blow or something happened to break the electrical circuit.

Top image shows you the transmission controlled spark components found in Pontiacs. The bottom image is of
the Combination Emission Control set up found only on Ventura II cars usually with Chevy engines.

  The Pontiac TCS system controls distributor vacuum by an oil pressure sensitive  transmission switch connected to a solenoid valve in the carb to distributor vacuum line.Whenever the tranny operates in other than high gear, the tranny switch and solenoid valve are both closed, shutting off vacuum to the advance unit. When the transmissions goes into high gear, oil pressure in the direct clutch circuit causes the transmission switch to open, cutting the signal and opening the solenoid valve, allowing vacuum flow to the unit. A temperature switch allows vacuum to reach the unit below 85 degrees F or above 220 degrees F. With manual transmission cars, the set up is similar but the switch is externally mounted and operated by transmission linkage position.

A close up of the CEC solenoid and position adjustment.

Combination Emission Control System CEC: 

 This set up was used on the Ventura II for 1971 instead of TCS. When the CEC solenoid is energized, the solenoid plunger moves outward against the throttle lever. This speeds up engine and allows ported spark vacuum to the advance unit.It can be energized three ways: a transmission shift into 3rd or Reverse gear, a temperature override switch at temperatures below 82 degrees F, a time delay relay allowing vacuum advance for 15 seconds after turning on ignition during temperatures above 82 degrees F. The CEC solenoid is vented to purge any vacuum that may hold the distributor advanced wen the trans is in 1st or 2nd gear. An idle stop solenoid prevents run on  by allowing the valves to close beyond normal idle position when ignition is turned off. That means two throttle positions are required; a curb idle and  emission control setting.

The 1971 Thermal Vacuum Switch  Set Up (455 HO Engines)

  The high output 455 round port engines used a thermal vacuum switch connected to a throttle actuated spark advance. This set up gives no vacuum advance at idle unless engine coolant temperature is above 230 degrees F, when full advance is applied to allow the engine to circulate coolant faster to maintain normal operating temperature.

The 1972 Pontiac CCS System: This year's CCS set up was redesigned.A new Speed Control Spark Advance operation was added by combining bits of the older TCS and CEC set ups. The new acronym for Speed Control Spark Advance is SCS.If it's a four speed manual transmission car, it will be using the older TCS system, If it's running a straight six or Chevrolet 307 V8 it will use the CEC system but without time delay relay.Vacuum advance is allowed 20 seconds after the transmission goes into high or drive gear. Advance is allowed whenever engine temperature is below 82 deg F.
   The SCS system has a vacuum advance solenoid valve and temperature sensing switch. The TCS switch is replaced with a speed control spark (SCS) switch. The SCS restricts vacuum spark advance to road speed above 38 mph. The TCS/SCS temp sending switch was moved from the top of intake manifold to the right of the rear cylinder head between plugs 6 and 8. The switch was recalibrated to allow vacuum advance at engine temps below 95 deg F and above 230 deg F. Air cleaner operation is unchanged from 1971.

Component Diagnosis: We have included a few flow charts of diagnosis for vehicles with partially imoperative systems. This may help you get the car running for emission testing or help prevent a roadside FAIL from MOE boys.

Although basic, this chart should sort out what parts needs work or replacing.

                                             

Evaporative Control System ECS:  There is a purge valve on the intake manifold besides water outlet housing which prevents canister purges until coolant temperature reaches 170 deg F. This makes the exhaust emissions better during cold starts. This set up is not used on Chevy 307 V8s or inline six cylinder cars.

Air Injection Reactor (A.I.R): Some cars due to the State they are sold in such as California, or due to a dirtier camshaft profile, need to run an air pump. The inline six engines use air pumps of the positive displacement vane type. They are belt driven and use a diverter valve, check valve and silencer. The check valve is behind the diverter valve and is a one way diagpragm designed to prevent hot exhaust gas from backing up in the hose and damaging the pump if the belt fails or hose rupture or excessive system pressure. The diverter valve releases air from system during deceleration. It is vacuum actuated.This takes care of the CCS system up to 1973. The following year incorporates a lot of changes and will be covered in a future article.

  * Article (c) 2017 by Patrick Smith, images from PHS MEDIA ARCHIVES. This originally

             appeared in expanded form on phscollectorcarworldblog April 2017. used with permission.

PHS Y Code Registry Certificate Program is Ready to Roll...

                                                                       By: Patrick Smith


  After many months of talking, I have been able to obtain a nice Certificate of Authenticity document for the Y Code Registry. The Certificate shows that the vehicle in question is a genuine L75 equipped  GTO or LeMans model and a member of this registry. Initial set up and production of the proof document and certificate number one has been the expensive part of the process. Mailing and verification also takes time and effort. If it could be done for free, I'd do it gladly. Consider it an investment in the car. Having it in a registry and a source of authority can only benefit your ownership experience. Whether your car's ready to drive show piece or a project car, every owner gets valuable information to put these rare, big bore machines back to Day One status.

   Shown below is a copy of the certificate. This is my own car. I left the signature, date and full VIN off for protection. Your copy of course, will be set up with your full VIN and the field description matching your car. Once I confirmed the car is indeed a genuine factory built Y Code, the date is placed on the document.  About the Certificate program. This isn't a rubber stamp, cash- money deal. I need proof the car is what you say it is.If it's numbers matching, show me the engine partial VIN and transmission VIN.

  The L75 or Y Code 455 is obscure compared to the X Code round port 455. The latter had an entire performance package built around it and was quite expensive if ordered that way as a WW5 car. Not every round port was a WW5, however. There were some very basic similarities between the cars especially in automatic transmission form which allowed clone artists to fake a round port using a Y Code car. This page helps keep the two models distinct and separate as well as document thoroughly as possible, the nuances that went into building the last of the 1968-72 A body big bore Pontiacs.

  The Certificate of Authenticity is part of a program of documentation and verification of these rare cars, called The Y Code File.  It's a complete documentation process involves a few hours time, plus travel and related expenses and produces a complete package verifying what equipment the car has and what is missing and or required for complete, show ready status. The Y Code File isn't a cheap process and I don't recommend it for cars missing their original drive lines. This is more suitable for well optioned, original cars either in excellent unrestored condition or a new restoration. For most owners, a PHS 1972 Y Code Registry COA  is sufficient.

   If you believe you own a genuine Y Code car and are interested in having it entered in the registry as an authentic car, contact me at phscollectorcarworld AT gmail DOTcom

   Be sure to place an automotive topic in subject header or the post will go into the spam file. Alternatively we can be reached by snail mail at:

 30 Moultrey Crescent, Georgetown, ON L7G 4N5 Canada

 

Y Code Parts Dept:1980s Replacement Gauges & Sender Unit Part Nos.

                                                                        By: Patrick Smith

   Those of you seeking GM original NOS (New Old Stock) parts have probably learned by now they're pretty scarce and cost a lot when they do show up.It may cheer you up to learn the Ac Delco replacement parts Division issued a catalog late in 1988 listing some replacement gauge and sender units part numbers alongside their brand new pieces for showroom Fieros, Trans Ams  and older Pontiac 6000 and J2000s. I have taken the trouble of recording these numbers for you and listing them here in case you come across some for sale online at Crag's Lust or evilBay. This way you can compare the list number against what's offered online and decide whether it'll work for you. My only warning is the Ac Delco list was active in 1988 which is  many years ago and the list wasn't updated. Some parts already were no longer in inventory such as the in dash tachometer, speedometer and hood tach assemblies. I have included their part numbers here as a reference in case you see some assemblies offered for sale.In the words of Walt Kelly, creator of Pogo, "We Promise Nothing!"
  A Word about the listings: The images can be right clicked for larger size and easier reading.
    

Either image can be right clicked for larger size and easier reading.

Notes About the PNs for Instrument Panel Part Numbers
 These were collated during the mid 1990s by Paul Zazarine and Chuck Roberts back when many of the GTO parts weren't being reproduced yet. A lot of external goodies like body panels, interior trim and engine pieces were being done but not crash stuff nor electrical goodies. It was assumed the junk car supply was stable enough to handle this so the part numbers were pulled off existing units. Some panels may have replacement revision numbers stamped there with the older original number cancelled out.
1971  Air Conditioned Instrument Panel 483517
1971 non A/C              Instrument Panel  483516
1972 Air Conditioned Instrument Panel  546619
1972 non A/C              Instrument Panel 546614
 * Early 1972 cars may have 1971 non A/C block off plates which will bear the word "Pontiac" on it. Later 1972 cars will have plain black A/C block off plates. Both types have been observed in the cars.
  

Some early build 1972 GTOs without air had instrument panels with the older 1971 style
"Pontiac" script block off plate. Most 1972 block off plates were plain black. This car was built in December
of 1971. A reproduction instrument panel was installed after gauge clean up and is waiting for the rosewood vinyl transfer.

1971 Instrument Panels used a vinyl film transfer of Castillian Leather. 1972 Instrument panels had vinyl film transfers of Brazilian Rosewood. Both are available as reproductions as are the instrument panels.

Hood & Instrument Cluster Tachometer Accessory #       and Part Numbers:
1971 Hood Tach                                           989919                           pn 5657094 
1971 Inst Cluster Tach                                 na                                   pn 5657064
1972 Hood Tach                                           989919                           na
1972 Inst Cluster Tach                                 na                                   pn 5657922
Note: In 1972 Pontiac stopped installation of hood tachs at the factory. The hood tachs sold were by the dealer and installed either by the dealer or by some aftermarket installer. This is why there is no part number for the 1972 hood tach. Likewise instrument cluster tachs were part of a 3 pod gauge assembly as shown above in the Ac Delco gauge listings and not sold separately.

UPC Code U30 rally gauge cluster with clock order code 714
UPC COde U15 rally gauge cluster with tach order code 721
 *Article (c) 2018 by Patrick Smith / PHS 1972 Y LeMans & GTO Y Code Registry
                                                    


  

Y Code Parts Dept: 1972 LeMans & GTO grille inserts

                                                                          By: Patrick Smith
       

   Since 1972 was an extended production year with a carry over body, Pontiac had to come up with a few visual changes to make the 1972 LeMans and GTO stand out from last season's stock. The extra wrinkle is they had to do it on a budget because the budget was small. No one wants to spend big outlays on an outgoing model. It's not prudent and the chances of making any returns on the tooling are nonexistent. One change Pontiac did make was to the grill. They made new deep white metal grill surrounds (called bezels) but kept the basic shape of the grills. Instead of bright checkerboard plated grilles mounted up front, the 1972 grill inserts were recessed deep behind the metal bezels which were painted argent and held in place with speed nuts.
 

This grille GTO emblem is a one year piece as well. Part # 546501. It was no longer available from GM by 1983.

  A little die cast GTO logo went on top of the driver side grille insert, also held in place via speed nuts. These grille inserts were made of aluminum and somewhat fragile in nature. A bird strike can easily damage the egg crate pattern and permanently distort it. Given part number # 486397, the part number applies to a single piece and since it is reversible, there is no LH or RH part number. You merely ordered two of the same part number, plus the GTO call out if yours was missing or the "Arrowhead and LeMans" call out if your car was a LeMans with the T-41 option. The grill inserts have been out of stock at GM since 1983 according to the parts catalog issued that year.
 

The 1972 Pontiac Endura grill nameplate is the same piece used in 1971 cars and uses the 484606 replacement parts number.

  T-41 option was a $41 extra feature which could be ordered for your LeMans Sport to dress up the car and make it look like a GTO. It was quite popular and a lot of cars had this. The part number for the 1972 GTO grille call out is pn 546501. They are available in original and reproductions. The part number for the "PONTIAC" callout is pn 477741 7002(c)2. It is the same piece used in 1972 Endura grill cars and shares the replacement number 484606. The 1970 "PONTIAC" grill nameplate is a different piece.
The arrowhead is a separate casting held by two lugs and speed nuts and is pn 478649 13342. 

The LeMans T41 PONTIAC script and arrowhead were cast separately for easier handling
of the part. Both items were held in place with nuts.

                         

Here, the part number can be seen on the arrowhead underside.

   It may surprise you to learn they weren't one piece but making such a big casting in one piece with three dimensional clarity would have cost more than doing 2 separate pieces. Since GTO sales were falling fast, cost cutting was needed to keep profits rolling in. That meant a cheaper method of casting parts where possible. They basically re used the 1971 PONTIAC nameplate and although the 1970 version looks the same it bears a different part number. The same goes for the 1969 vesion.
 

Flimsy "butcher paper" wrapping was all that protected the grills during shipping. Shelf wear of corners
was a problem as well.

   The NOS grilles themselves are somewhat scarce being a one year only part and shipped in rather flimsy "butcher style" brown paper with turquoise GM logos and ink stamped part numbers. The corners are often dented and shelf wear is definitely a problem in some cases. Fortunately there is a reproduction alternative available. The Parts Place in Chicago is selling these pieces again. I have ordered a set in for the project Y Code GTO and will be doing a product review and comparo to the original pair from my car.  National Parts Depot catalog shows a part number for 1972 grill inserts but beware. The part number is identical  to the reproduction 1971 barbecue style grill inserts. A photo shows you the piece isn't at all like the 1972 item. This is why I ordered it from Parts Place.

Parts are made of fairly soft aluminum and are held by speed nuts onto grill surrounds. 

   While we're at, let me address the issue of grill color. All the 1972 cars got gray grilles, whether they were 455 HO, striped cars, plain jane or loaded. No blacked out grills existed for the 1972 LeMans or GTO. Blackout grilles are listed for the 1971 GTO Judge and they have their own part number. The Judge was dropped in winter of '71 and didn't return. Gray is the correct color. It is very common to see them painted black which is fine if you want to customize the look of your car. It isn't concours correct however.

Availability and Pricing: The grill inserts are reproduced and so is the GTO 1972 only call out. Original GTO call outs are also available as they often show up on evilbay and local CL listings. The GTO call out and 1972 grills have been discontinued since 1983 so it's nice to have new ones offered. The arrowhead and PONTIAC call out for the LeMans cars with T-41 also show up and in theory should be easier to find than the GTO call out. Somehow that isn't holding true in real life. I suspect the reason is due to it being a 2 piece affair. More prone to rattling off from road vibrations and bird strikes. By the way, the parts manual suggests gluing the emblem in place with Dow Corning epoxy. Pricing isn't a big deal for these parts. NOS grille inserts are being offered in original wrapping for mid $400 a set, but I don't see anyone snapping them up at that price.

Yes, that's how they look out of wraps.Those little irregular tangs at the top and sides distinguish them from
the regular LeMans non T-41 grille inserts which aren't big enough to fill the white metal grille surrounds on a T-41 car.

  The call outs are inexpensive, GTO averaging mid forty dollar range for a nice condition piece. The arrowhead is offered as a reproduction and some NOS stuff is available as well. Just price shop until you find a deal you can live with.
 

1972 Grill bezels aren't reproduced yet and are difficult to find in show condition.
The argent silver paint is available and very light pitting can be sanded and painted over. Broken
studs, cracks and pitted brightwork affects value considerably. Excellent pieces can be $220 each or more.

  The grill surrounds for 1972, (called bezels in the GM parts book) are harder to find. The LH part was out of stock by 1983 and the RH piece was in the same situation later that decade. Neither part is being reproduced at present. They are;  LH486394, RH 487747. When they come on the market they range from $150 to $220 each depending on condition. The usual issues are broken speed nut studs and pitting of the white metal inside the surrounds and argent paint loss. The chromed external surface is prone to pitting as well and affects value. Paint loss is repairable with correct paint and minor pits can be removed.

  * Article (c) 2018 by Pat Smith for PHS 1972 Y Code Registry, special thanks to Scott Sheppard and Craig Eckhart for assistance.

Tail Lamp Lenses: What was correct for 1972.

                                                                         By: Patrick Smith

  One of the hang ups of restoring a 1972 Pontiac GTO is it was a "build out" model year. What that means is it's the last production year of an old body style before the plant is shut down for retooling for a new body style. In practical terms, it means some parts are going to be in short supply and if a car is being assembled needing those parts to complete the job, a couple of things may happen. The best case scenario is if the assembly line gurus in charge of production logistics are doing their job and spot that supplies of certain parts are too low to assure the quantity of cars being built will have the necessary goodies, the job order gets delayed. In effect the data processors for production orders would  hold off or "block" the order and enter it when adequate supplies of parts were in storage to do a build of cars. In the ideal world that's how it's supposed to happen.

The LeMans, LeMans Sport and GTO got smooth tail lamps for 1972. In the real world, a few GTOs, LeMans and
even LeMans Sports got some ribbed lenses. It's unknown whether it was due to carelessness or supplies running out
as cars in early and late production have been observed with incorrect lenses.

The 1972 Luxury LeMans got ribbed tail lamps from 1971 which were "First Job"
GTO lamps according to the 1974 parts catalogs. After Job lamps were smooth and minus silver paint. 

  In reality, a couple of problems made it difficult to guarantee a steady supply of all the goodies to all the plants. One problem was a GTO required a lot of extra parts not used on the LeMans body. The front end is completely different, including the hood, fenders, bumper, grilles and rad header panel. The front end was also available as a option on the LeMans Sport as the T-41 front end. It was quite popular that year as it was promoted in special 2 page color ads. GTOs also had a few special bits here and there like engine turned metal lower dashboard trim, decals, a minimum engine displacement of 400 cubic inches with four barrel carb and either a manual three speed on the floor or automatic column shift TH400. These and other details meant  more logistics planning for data processors and build sheet orders. The last hang up was a dramatic fall in demand for GTOs that season. Production dropped from 10,532 to about 5,673 cars that year.

   Considering how many different parts had to be thrown together to make a GTO instead of a LeMans it made sense for the data processors to bank a bunch of GTO orders and build them together in "batches" to prevent jamming up the line. After the initial season kick off of orders started filling the pipeline they waited for dealer orders...and waited....and waited. They got T-41 LeMans Sports orders but few GTOs. A decision was made early on to batch build the GTOs by storing up orders until enough could be run off to make it worthwhile. Sales were poor enough that the batch build order was amended to include LeMans T-41 cars as well since they used the same front end as a GTO.
 

A survivor Y Code in Georgia shows the "After Job" lenses did get silver paint, contrary
to what the parts book stated in 1974.

   Since it was the last year for this body style, re orders for parts were done  early. Whatever wasn't used near the end of production was used for parts inventory.When you're getting product out the door on the clock, you're not going to fool around searching for the correct tail lamp to complete your build. Jamming up the line was bad and God forbid if you shut down a line because you didn't have smooth tail lamp lenses for the GTO in your pit! No way, if you didn't have smoothies but a bunch of ribbed tail lamps were sitting handy, that's what went on the car. Technically it's wrong, but it happened. Presently our registry has  many entries and only two had ribbed tail lamp lenses, one was an early build convertible, the other a hardtop assembled in the last week of May. It's possible that one  was a build out car.

The 1970 only version included chrome bezel trim. Part number is different as well on box.

The part number for a 1970 GTO tail lamp RH assembly.These are reproduced now.

Part Numbers & Styles:
  Next thing we need to do is look at what was available for lenses in 1972 and what was used on the line. The 1970 GTO-Tempest lens were marked 5962274 RH and 5962273 LH. These were superceded by #5964078RH and #5964077LH.
For 1971 the parts book shows a new design described as "First Job w/3 exposed vertical ribs and silver paint along periphery" The part numbers for First Job 1971 lenses are: #5964570 RH and #5964569 RH. Below this is a listing for 1971 lenses described as "After Jobs-Less 3 exposed vertical ribs and less silver paint on periphery." The part number for "After Jobs" lenses are different from First Job lenses as well. They are: #5964078RH and 59647077 LH. There is no specific 1972 lens part number for the LeMans or GTO. They used the "After Job" assemblies listed under 1971 in the parts book. Also it should be noted the description of "less silver paint" is wrong as well. Survivor GTOs and LeMans clearly show silver paint on the edges. 
     

The box for 1971 tail lamps with part number. These babies in good condition sell for a lot of money. Reproductions
are available now from The Parts Place.

A pair of  New Old Stock "First Job" 1971 tail lamps. Note the silver painted accents and vertical ribs. Some have been
used on 1972 GTOs. Only the Luxury LeMans cars were supposed to get them that year.

Applications:
  As for applications, the ribbed vertical lenses were used on 1971 GTOs and for 1972 they were used on the Luxury LeMans as a dress up item. The 1972 GTO and LeMans models were supposed to use smoothie lenses which would be "After Jobs" pn 5964078 and 5964077. In theory that's how it was supposed to go. In practice this wasn't the case. Since both styles of lenses were available at the plant from roll out of production, it appears any GTO or LeMans that got the ribbed lenses were just assembly line errors and not true "build out" cars which would be the case from half way through the production year when supplies did run low. Another problem is the confusing terminology of "FirstJob" and "After Job". This relates to the 1971 redesign and the major strike that happened at GM, delaying roll out of 1973 models by a whole year. Since Pontiac needed to make the GTO last one more season, they contracted a cheaper lens design without ribs and chrome trim. It became a footnote in the 1974 Parts Book. There are other instances where the 1972 is merely considered an extension of the 1971 model year.


   We do have a few instances of 1972 cars with ribbed lenses but with so much time lapsing from production to the present, it's only prudent to consider survivor cars or ones with a solid documented history establishing these parts were present when new.We will update the article when we get solid evidence of deviations on early production 1972 GTOs.

   The NOS ribbed babies aren't cheap. They're selling for almost two grand once you include shipping. Luckily they're reproduced now.1971 GTOs used them as standard  issue so a few top drawer restorers will pull the trigger on these survivors if the car warrants it.The smooth 1971 and later lenses have no chrome bezel either. They got silver paint instead.Those are correct for 1972 GTOs and LeMans. The station wagons had their own lenses and housings. The numbers are included in the chart below for reference, just in case you're restoring a Y Code wagon. I wanna hear from you if you are!

Chart showing housings, lenses part numbers and notes for same. This is a 1974 parts book.

  I have included a chart to show you the application numbers and notes issued on tail lamps, housings for the 1970-72 era GTO and LeMans cars for reference purposes.

The Takeaway:
Pontiac used three styles of tail lamp lenses on their 1972 LeMans cars, a smooth tail lamp, a vertical ribs lamp and a separate completely different station wagon lens.

The vertical ribbed lenses were only supposed to be used on the Luxury LeMans cars for 1972. They were first used on 1971 GTO cars. "After Job" lenses were smooth and listed for 1971 GTOs and Tempest cars in the 1974 parts catalog. This, along with the "less silver paint" description are errors and should have been listed as 1972 because they were contracted for that model year.

Some 1972 GTOs and LeMans did get vertical ribbed lenses. Some got them early in the year like one convertible in our registry, others like mine got them late in the year. It could be a "build out" supply problem or an assembly mistake. Technically, ribbed lenses on a 1972 LeMans or GTO are mistakes. A few cars got them however so if you have documentation to prove it was original, by all means keep them.
        *Article (c) 2017 by  Patrick Smith for PHS 1972 Y Code Registry