 streets
"14th Year" Silver Supporting Member
Posts: 245
Loc: Central Illinois
Reg: 05-30-04
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09-16-23 06:10 PM - Post#2862600
Just picked up a 1966 Impala 12 Bolt. And I have been looking for a while.
Got it home and started cleaning it up.
Can someone who knows these tell me if these are cracks at 12:00 & 6:00 or are they seams from forging?
There is NO indication of external leaks.
Thanks for your help.
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bobb
Super Senior Member
Posts: 6413
Loc: paradise
Reg: 09-05-03
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09-17-23 10:27 AM - Post#2862616
In response to streets
if they are cracks brake cleaner will bleed through. i dont think they are cracks. make sure your bearing caps have a nice mating surface and are not fretted. i would clean the housing out with a pressure washer. you never know what happend in the past. make sure to get the correct pinion seal that does not sit too deep.
| 70 L camino, grampa engine, g-force 5 spd, road rage suspension. Pray first before all else fails. |
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Shepherd
Valued Contributor
Posts: 3090
Loc: Lake George, NY
Reg: 11-11-15
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09-17-23 12:26 PM - Post#2862621
In response to streets
Sure looks cracked, also, if you tap on the side of the "crack" with a hammer and oil squeezes out, it is a crack, do this on the larger one. Do this before the brake clean test.
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Jynx
Poster
Posts: 96
Loc: Australia
Reg: 03-01-11
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09-18-23 06:17 AM - Post#2862629
In response to streets
Looks like a casting mark to me. I say that because when you look at the photo that's on angle, where it's shown above the axle ends, you can see that there's no depth to it shown in the chamfer machined into the casing.
You can also see that it was there during manufacturing. If you zoom in on it you can see when the chamfer was machined it's not perfectly the same depth in it's full circumference, it's slightly different exactly where the mark is, as though the two sides of the casting were filled with molten metal from different sides of the mold creating a very slight ledge from one side compared to the other.
The bottom photo looks worse, but the mark is also being reflected in the small amount of oil still coating the lower casing.
Edited by Jynx on 09-18-23 06:24 AM. Reason for edit: No reason given.
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Shepherd
Valued Contributor
Posts: 3090
Loc: Lake George, NY
Reg: 11-11-15
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09-18-23 07:18 AM - Post#2862635
In response to Jynx
Your point is well taken, but I've never seen these marks on other diffs I've rebuilt. The tap test we used to use on GM gear boxes that had chronic leaks under the top cover. On close inspection, it does look a casting seam, tough to be sure though.
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streets
"14th Year" Silver Supporting Member
Posts: 245
Loc: Central Illinois
Reg: 05-30-04
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09-18-23 08:02 PM - Post#2862656
In response to Shepherd
Update-Today I performed both the oil and brake cleaner tap test. Absolutely NO seepage 
Then I took it to 3 different tenured (old guy) mechanics who have worked on several of these. Everyone of them said these are seams from when the casting was forged. Some comments were: "if it were a crack it wouldn't be in a perfectly straight line."
"All these axles have them, some are more pronounced then others." "do you see how there is no depth to them? cracks have depth." "Notice how both the top and bottom seams run all the way to the rear cover." After much scrubbing they do (attached.) Want to thank you-bobb and Shepard for your input and insight. Thank you Jynx for your in-depth observations on the photos. One Major Headache Avoided. Hope this helps someone in the future.
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Shepherd
Valued Contributor
Posts: 3090
Loc: Lake George, NY
Reg: 11-11-15
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09-19-23 05:25 AM - Post#2862664
In response to streets
That pic shows it's a seam, good info all around. 
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