el jefe

"look what you did...LOOK! "

"you've over tightened the fuckin' thing! it's plastic, goddammit; the screw doesn't need to be torqued down. Jesus Christ—get the hell atta here before I break my foot off in your ASS!"

there wasn't anyone there. 

I was yelling at the headlamp cover hoping that, somehow, by telepathy or Hermes' ghost, the message would be delivered to the oaf.
this 968 is 22 years old and that's a lot to ask of daily driven plastic. but, shit...he, she, or both could've been a bit more observant, used some finesse.

"'ang on a minute...no metal collar molded into this bore to stop the screw from cracking the plastic; best to go easy when I re-tighten it."

maybe the last line of my outrage should be directed at the Porsche project manager 2 Pfennig short of making a better part; the bullshit spacer washer falls short with those less delicate — making the housing out of PC/ABS only aggravated things.
look at the three shots above. 

the top one is how it looked before and after being removed for the first time. the housing won't come off without some thought which is why you can't just slip it off. there's some twisting, prying, and turning involved; give too much of those three verbs, and it'll crack. I managed to get the old one off without further injury, but I wanted to dry fit the thing a few times to get the angles right when time came to put  on the new one — and this is when I completely split the old housing open. even at a humid  90­° (32,2°C), the plastic wasn't very pliable. UV rays, the environment, and the headlamp's heat cycles all took turns stripping the plastic's flexibility over the years.

now...every plastic component Porsche makes has a date stamp, a part number, and Porsche's triangular seal of authenticity; it also has a tattoo of its composition. in the case of the housings and retaining rings, they chose PC/ABS — PolyCarbornate/Acrylonitrile Butadiene Styrene.

this is considered an "alloy." synonymous with  metal alloys, plastics use the moniker for the same reasons; to describe a blend or poly-blend of materials formulated for a specific performance. this blend capitalizes on each of the material's best characteristics to make a superior plastic. in this case, Polycarbonate (PC) brings stiffness, hardness, toughness, with extraordinary impact strength and weathering. the Acrylonitrile Butadiene Styrene (ABS) contributes rigidity and strength of Acrylonitrile and Styrene, which also adds shine to the plastic, while the (poly) Butadiene adds rubber to the mix for flexibility, heat resistance, and ruggedness. ABS also has strong chemical resistance and physical impact strength and is easily paintable.

"and forget the workshop manual, you may as well use the pages therein to wipe betwixt thine buttocks because they're utterly and purposely fucking vague — shit...IKEA instructions pack more logic."

PC/ABS is what the housing/retainer rings are made of. it's a Thermoplastic that, by definition, melts into liquid form at a low temperature (around 221°F) making it easy to injection mold and re-heated without significant degradation. and because of its ability to melt back into a liquid, it's a perfect candidate for recycling. 

what I questioned was why Porsche didn't use PUR-RIM, Polyurethane Reaction Injection Molding, for these headlamp pieces. they did on the 928 with fantastic results; our 38 year '28 still has the original headlamp housings, no cracks or imperfections in the paint. then I gave the problem some thought.

Porsche had been using PUR-RIM on the 911, 914, Carrera GT, and 928 since 1969. it matches and in some cases surpasses PC/ABS' qualities. it's got superior tensile strength and super-high impact resistance, even in extreme temperatures. Porsche conducted tests where the material (with paint) was folded 180° in -20°C to 100°C conditions showing no cracks or loss of composure. so why didn't they use this nearly indestructible composite on the 968's headlamp housings? the answers have to do with economy and ecology.

Porsche's financial situation was in the shits by the time the 968 began production. this was a new model intended to be a stopgap in the hopes of keeping enthusiasts entertained while the 986 Boxster was being conceived. the 968 has heavily redesigned and re-engineered which meant new tooling, dies, molds, this sort of thing and with production moving back into Zuffenhausen, the expenses were piling up. when you figure in a slump in overall Porsche sales, and no chance of the costs being amortized with such a short model life, every Pfennig count, which meant corners had to be cut in the most inconspicuous places — the housings were one such place.
Picture
PC/ABS stamping on the headlamp housing...
Picture
and on the retaining rings
PUR-RIM is an expensive method of producing plastic components, not only in raw materials, but also in the machinery involved in molding these parts; they're much more robust to handle higher pressures. PUR-RIM components are also more dense, and naturally heavier than a more modern plastic like ABS; although their individual weight is negligible, when a car like the 928S is nearly 20% PUR-RIM, and the 924 Carrera GT nearly 25%, the weight adds up. this taxes fuel economy and the ecology which were becoming important issues to address in the 90's.

on the subject of ecology, PUR-RIM is nearly as bad as Styrofoam. the problem is that Polyurethane is a thermoset plastic, similar to a 2-part epoxy; once you mix the reactive materials together and allow them to set, it's done and irreversible. you can't remelt the finished product back into liquid form, trying doing it and it'll burn, and this makes them bad candidates for recycling. 

naturally, Porsche realized the attributes of PUR-RIM didn't jibe with their economical situation nor those of the green party and granola gangsters which is why I suspect they chose the lighter, cheaper, and reconstitutable PC/ABS. it easily met and surpassed the 10-15 year life expectancy of their product (the 968) with exceptional performance. let's face it, why spend more money on a product to last twice as long when the market was evolving to one of perpetual change, fickleness, and disloyalty. this wasn't the 911/928 market of the seventies.when you consider these points, it's hard to complain about cracked plastics on a 22 year old mass-produced Porsche.

getting back to the repair, I've yet to hear of any owner whose 968 had the same problem. but I don't suspect this was an isolated case, which is why I've documented the process.

luckily for Porsche, they still offered both headlamp covers and retaining rings; the paint is your problem.

you'll need to order these:

  • 944 750 121 00 - housing (2 pieces )
  • 944 750 151 00 - retaining ring front (2 pieces)
  • 944 750 153 00 - retaining ring rear (2 pieces)
before you take anything apart, flip each light up by hand and examine the retaining rings. the slender-fingered effete can slide their manicured digits between the fender and top of the headlamp, and pull forward. filthy sausage-fingered apes; on the inside of the fender, directly behind the lock release, is a hole big enough for your fingers sneak in and push the headlamp forward — look at the shots below, you'll see.
my hand in the shot above is on the spring loaded lock-out lever (workshop manual calls it a release). pull the headlamp up until it stops, then pull the lever out (inwards towards the center of the car) and hold it out as you pull the headlamp out some more (pulling the lever out allows maximum extension of the headlamp until it's vertical as shown in the shot). 

next, release the lever letting it spring back into its original position; the lever has now locked the headlamp in a vertical position. bingo — you've successfully positioned the headlamp in "service mode."

familiarize yourself with the headlamp and its mechanism; look at how the retaining rings and headlamp housing are held in, how, and where the Phillips head screws are attached. there're also two 5mm (maybe 6mm, memory eludes me) holding the bottom retaining ring, and three behind the swivel frame to remove the headlamp assembly.
Picture
top part of the housing, screw removed but spacer intact
Picture
the cheap fucking spacers that do jack shit in protecting the housing from cracking.
Picture
shot from the rear of the assembly with upper retainer removed. the 5mm hex head screws holding the lower retainer can be seen.
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close up of the lower retainer's right side (looking from behind) showing the threaded brass insert that the upper retainer screws into
Picture
the assembly without the goddamned housing and upper retainer
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shot of the headlamp swivel plate where the headlamp assembly bolts into. three 5mm screws (their bores in plain view here) holds the headlamp in. you now have clear view of the lower retainer for the attack.
Picture
a housing-less headlamp assembly shot from behind
if you're looking for me to tell you exactly what to do at every step, forget it; a rundown is more than adequate. those confident enough to work on their Porsches shouldn't have any problems figuring the shit out. and forget the workshop manual, you may as well use the pages therein to wipe betwixt thine buttocks because they're utterly and purposely fucking vague — shit... IKEA instructions pack more logic. 

begin by removing the upper retaining ring (N°16); two Philips head screws hold it in place (N°23). the threaded brass inserts (visible in the seventh image from the bottom) may have broken off the lower retainer (N°15) and may come out with the screw. don't worry about those, the new lower retainer ring comes with them and a few spares.

then go for the housing (N° 17) by removing the three Philips head screws 
(N°19)...and be careful not to lose the spacers (N°20), you'll be transferring them over to the new housing. if they're missing or have become victims of carelessness, here's the part number to order them: 

951 505 157 00

you can cannibalize the spacers from the screws that hold the under-chin liner to the front bumper cover, just remember to replace them. and remember what I said, practice re-installation and removal of the housing to get your technique down for the new ones.

you now have the guts of the headlamp exposed.  unbolt and remove the headlamp assembly from the swivel plate (three 5mm screws) in order to remove the lower retaining ring that's held by two 5mm hex head screws; be mindful that the headlamp wiring may be tie-wrapped to the retainer and the swivel plate, cut it loose and remember to replace it when re-installing. mine retaining ring was cracked where the screws attached, so nothing was holding the retainer onto the swivel frame.

alright...there should now be a housing, an upper and lower retaining ring, and a headlamp assembly on the floor.
the two shots above are comparisons of the new and old parts; the three above those were excitement-enduced error...hubris, pompous grammaticians might say. you see, you can't put the housing on the headlamp UNTIL the headlamp is bolted back onto the swivel frame which happens AFTER you install the lower retaining ring. got it?

our headlamp covers and retainers were sprayed by Paterek Brothers; these guys know exactly how the factory applied paint, what kind of paint they used, and how they cured it. when we started talking about the grain of car's paint and how the first few 928s produced were rejected because the direction of the metal flakes on the bumper didn't match those of the car, well hell...it was the beginning of a beautiful relationship.

Porsche used single stage on the non-metallic colors which means that the clear is mixed in with the paint while metallics of this 968's vintage were done in two stage; the color (base coat) goes on first followed by a coat of clear. if your non-metallic, single stage painted car had any paintwork in its past, it may have been done with a two stage paint process since lots of shops prefer it. not sure what have? when you wax your car and the cloth you're using to apply wax with is stained with the car's color, it's single stage. 

when you get down to it, talk to your painter to make sure you're getting exactly what you want. if, like me, you prefer everything to be done as the factory did, trust in someone's knowledge, experience, and expertise is non-negotiable. 
so...let's put the new ones on.

first, the lower retaining ring gets bolted to the swivel frame...don't forget to tie-wrap the headlamp wiring to it and the frame. the naked headlamp assembly gets screwed in next, followed by the headlamp housing...careful with that thing, and remember the trick you've learned while fitting-removing-refitting the old one. you needn't worry too much about cracking the new one since it's a bit more pliable than the old one, but don't push your luck — and don't force the goddamn thing, either.

make sure to put the three spacers back into the housing's bores, and use two fingers to twist the screws back in...that's all the torque they need.  finish up by screwing in the upper retaining ring and disengage the headlamps from service mode laying them back into the fender.

if your 968 is to remain in your care for the next 20 years, I suspect this'll be the last time you'll ever have to do this job. while the bulbs won't last that long, remember to use finesse when removing and replacing the headlamp housings, and for chrissakes...use two fingers of torque on those three screws, will ya?
 


Comments

MICHEL DUPUIS
10/21/2016 07:57

such a great piece of info with all the sarcasm needed on 1 of the 968 least understood part (i've owned three of them...all were f....g cracked) thanks for the help!!!

Reply
el jefe
10/22/2016 19:27

Salut Michel! glad you enjoyed the article...and you had three 968's with this problem!

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