Quote:
Originally Posted by SS427
I cannot speak for F bodies but some of the A body plants received differentials that were not painted. I commonly see Baltimore, Arlington and Atlanta cars that are all natural and have a fairly large database showing this.
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Below pertains to Chevelles only - not Firebirds. I know nada about Pontiacs!
As to A-body Chevrolet axles, I have owned and/or studied and photographed very, very many 65, 66 and 67 survivors from every assembly plant except 67 Framingham (not many survivors left around from up there!). Both 10-bolts and 12-bolts. There is no question that ALL 65-67 Chevelle axles were painted black at the axle plant, end to end, including the drums (but with a mask over the pinion yoke). The wheel studs also had some sort of sleeve (I assume cardboard or tubing) slid over them before the paint was applied, so the threads did not get painted. You can see a donut of bare metal on the drum face around each stud, that shows where the outer diameter of the sleeve was.
(On I side note, I also have one survivor 67 Camaro LOS car, and its axle is black, and was very clearly black before it was installed.)
As to 68-72 axles, I can't claim to have first hand knowledge, other than from looking at all the low-mileage survivors I have seen while on the lift in Vintage judging at MCACN, which have all been black.
But I do have a Sept. 1, 1972 "Chevrolet Dealer Service Information Bulletin" (previously called "Technical Service Bulletins) which says (quoting):
"the chassis black paint as previously applied to axle housing assemblies has been deleted on 1973 Monte Carlo, Chevelle and Vega models effective with the start of 1973 production."
That is pretty strong evidence that Chevelle and Monte axles WERE painted black BEFORE the 1973 model year. If they hadn't been, then a Service Bulletin like that would have been issued earlier, whenever the black painting was stopped. I have every single TSB/DSIB issued from the beginning of the 1963 model year through the end of the 1973 model year, and there is no mention anywhere of deleting the black axle paint until the Sept. 1, 1972 Bulletin noted above. And again, I know for sure they were black in 67; so if they stopped in 68, 69, 70, 71 or 72, logic says there would have been a Bulletin issued. (Or at least there would have been no reason to issue a Bulletin in September of 1972 that says "effective with the start of 1973 production".)
Also, note that whenever an axle assembly was blacked at the axle plant (whatever years that applied to), there would be no variation in that paint based on which VEHICLE final assembly plant the car was built at. Variation could exist from one AXLE plant to another (and from one day or worker in the axle plant to another), but not between two final vehicle assembly plants that were getting their axles from the same axle plant. (Just like orange on an engine - variation may exist from Tonawanda to Flint, but not based on where the car was built.)
The original axle black on 65-67s appears to be pretty cheap oil based paint, and quite thin. A rag with WD-40 on it will just about wipe it all off. So unless a car has low mileage, it is easy to see how a lot of that paint (or even all if it) would "wash" off over time with engine and trans leaks and road grease washing back onto the axle for several decades, giving the false impression they were bare when new. I have pulled axles out of 66s and 67s that there was no sign of paint, until you get them out and there is paint hidden up in the control arm brackets where it was protected from leaks and road grime.
With that said, even with the axle already fully covered in black paint when it arrived in the vehicle assembly plant, the vehicle assembly plants did (again, at least in 65-67) still apply some additional chassis blackout around the rear suspension. It is common (at least in 65-67) to find it on the bottom half of the spiral shocks and on the tail pipes behind the axle. That obviously resulted in some overspray on portions of the axle too, which WOULD create some variation from one vehicle assembly plant to another, and from one car to the next. And that extra coat of paint would also slow down the degradation of the axle plant paint in those areas, creating even more variation over time (as some cars were exposed to more oily fluids underneath than others).
On a related note, I have two low mileage Baltimore 67 Chevelles that also have blackout on the front suspension, erratically covering the front and lower sides of the front sway bar and outer tie rods, and the lower part of the front of the springs and shocks (as well as overspray onto the front of the lower control arms). And I know that was factory applied, because there are copious amounts of runs and "drip-tits", which all defy gravity and go straight toward the sky -- because it was sprayed on while the frame was still upside down on the assembly line. So it didn't happen at the dealer, or after the car was sold.