C3 Diff Paint Markings

[Sheldon S.]

I have just finished disasembling the diff and found some paint markings. First the dark blue on the driveshaft yoke and the top of the carrier. Also on the driveshaft yoke-one side was painted a pink color. Any specific meaning for this. Then on the inside, one of the carrier bearing caps had orange painted on the top surface. Was this to identify right or left or something else?
The other question I have is what finish are the u-joint retainers, bolts appear to be black oxide or phosphate but can't tell if the retainers are natural or BO/BP.

Thanks
Sheldon

[Chuck S.]

Re: C3 Diff Paint Markings

I have just finished disasembling the diff and found some paint markings. First the dark blue on the driveshaft yoke and the top of the carrier. Also on the driveshaft yoke-one side was painted a pink color. Any specific meaning for this. Then on the inside, one of the carrier bearing caps had orange painted on the top surface. Was this to identify right or left or something else?
The other question I have is what finish are the u-joint retainers, bolts appear to be black oxide or phosphate but can't tell if the retainers are natural or BO/BP...

Well...where are the pics?

For universal joints with U-bolts, the U-bolts are black phosphate with black oxide cut lock washers and hex nuts. Opinions of black phosphate vs. black oxide finish use on chassis applications vary, but that is my opinion based on my observations.

If by "retainers", you mean your universal joints have straps instead of U-bolts (LT1 & LS5?), I can't offer much help there and there's nothing specific in the 70-72 TIM&JG. Without better information, I would probably have to assume the same finishes were used for the strap configuration, i.e. straps are black phosphate, bolts and lock washers are black oxide.

[Tom P.]

Re: C3 Diff Paint Markings

I also would like to know about paint markings on rears, except the ones I rebuild are 62-earlier. I've been rebuilding the 56-62 (55-64 for pass cars) rears for 40+yrs and never paid much attention to paint markings, but it is now becoming more and more of a concern for people who are expecting exacting restorations. I've already inquired earlier with ZERO replies. So, since the issue has been brought up again, I'll give it a second effort.
Below are some before/after pictures of a rear from a 57 Vette (3.36 non-posi) that appeared to have never been touched. The owner and I examined and discussed the colors and jointly concluded how it was to be finished.

[Edward J.]

Re: C3 Diff Paint Markings

Sheldon, I just finished doing a original 70 rear axle and my own 72 rear diff, both the cars had the blue on the driveshaft yoke and rear housing, the half shaft flanges both sides had white paint, and a dab of yellow on the pinion flange nut. these marking where used as balance points I believe as the half shafts were marked with dab of green paint, and the driveshaft had a few different colors used.

the bolts I believe were black phos. and straps were natural on my 72 and the 70 axle I just finished. these cars were with the H/D axle shafts not the u- bolts.

[Gary C.]

Re: C3 Diff Paint Markings

Tom, just curious - what was the assembly stamping on the non-posi housing in your photos? Gary....

[Tom P.]

Re: C3 Diff Paint Markings

Tom, just curious - what was the assembly stamping on the non-posi housing in your photos? Gary....

The casting date is I286, assembly code/date is AE1004. This fits the car. It is an EARLY production 57 PG car with 3.36 gear, plus the R&P stamp dates are also early, 9-56.

[John H.]

Re: C3 Diff Paint Markings

Also on the driveshaft yoke-one side was painted a pink color. Any specific meaning for this.

Sheldon -

The paint mark on one side of the rear driveshaft yoke was to be aligned with the paint mark on one side of the pinion yoke, as noted in the Assembly Manual.

[Gary C.]

Re: C3 Diff Paint Markings

Tom, thanks for info. Unusual to see red oxide primer on a 56-7 Corvette rear end. Have tried since the 70's to find documentation for the different paint marks on 56-7's and my theory is; Yellow paint marks are identification paint marks to indicate Corvette, White was for passenger cars, Blue is to signify pinion nut was torqued. Others markings on gears, ring & pinion, etc. some are alignment marks and others? JMTCW, Gary....

[Tom P.]

Re: C3 Diff Paint Markings

Tom, thanks for info. Unusual to see red oxide primer on a 56-7 Corvette rear end. Have tried since the 70's to find documentation for the different paint marks on 56-7's and my theory is; Yellow paint marks are identification paint marks to indicate Corvette, White was for passenger cars, Blue is to signify pinion nut was torqued. Others markings on gears, ring & pinion, etc. some are alignment marks and others? JMTCW, Gary....

As best as I've been able to understand, all 55-56 and early 57 cases were painted with red oxide----------inside and out.
Just by observation, when I clean up the cases, it APPEARS that the case is painted red oxide BEFORE machining is done. Correct, BEFORE the machining processes. On this rearend case, I especially examined it closely. It is painted EVERYWHERE, EXCEPT where machining has been done. Thus, that means it was done BEFORE the case was coded or designated as either pass car or Vette use. I get VERY FEW 55-56 rears, and in the past, I've not paid extremely close attention to how they were painted, but as best as I recall, all 55-56 rearend cases that I've touched were painted red oxide. The 55-56 Chevy guys who do exacting restorations, are insistant that the 55-56 case is painted.
Below is a 56 rear, that had a posi added BEFORE I touched it, and as you can see, it has remnants of red oxide.
By the way, the bearing caps of these rears have not been painted.