rear end casting code - Pontiac GTO Forum
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post #1 of 14 (permalink) Old 07-22-2015, 03:57 PM Thread Starter
 
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rear end casting code

The casting code on my rear end is 385914N

Put in in Google and everything points to a 65 chevelle

Would the GTO be the same?
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post #2 of 14 (permalink) Old 07-22-2015, 04:50 PM
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I don't think so, 65 GTO axle codes are here.

GTOAxleCodes
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post #3 of 14 (permalink) Old 07-22-2015, 04:54 PM Thread Starter
 
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Thanks Goatroper. I suspected this was a chevy rear end,,,, don't really care that much, just curious
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post #4 of 14 (permalink) Old 07-22-2015, 06:38 PM
 
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Originally Posted by 65gto View Post
The casting code on my rear end is 385914N

Put in in Google and everything points to a 65 chevelle

Would the GTO be the same?

Just to clarify. You said "casting code." The codes listed for the GTO's are the stamped letter codes found on the axle tube. This is different than the "casting code." I am no expert by any means, but it is possible the casting code on the housing center section may be the same as the Chevelle as it is a GM piece, but all else is specific to a Pontiac spec'd rear axle when it was built/assembled.
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post #5 of 14 (permalink) Old 07-23-2015, 03:33 AM
 
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So this stumped me for the better part of the day.

I spent quite a bit of time looking around. And I can not find a definitive answer.

To begin I think you are missing a zero in the cast code. I think it should be 3859140N instead of 385914N.

What I did find is that that differential cast code was used by GM on Chevelle 12 bolt rear ends. The N indicicates it was cast at the Neenah foundry in Neenah, WI. I found 2 guys that both have that differential, One with a 66 GTO and one with a 67 GTO that have 3859140N differential's in them. They swear up and down that they were original to the car. Both of their cars were built in Fremont California. Chevelle's were built in the same factory for those years. But what confuses me is that I keep reading about Buick, Olsmobile, Pontiac (BOP) specific parts. GTO's are supposed to use BOP parts. Now I called this old timer that I met at Good Guys in Pleasanton a while back. He used to work at the Fremont Plant in the 60's and 70's. He told me the differentials came to Fremont as empty housings and they were actually out together in Fremont. The guts that were put into the housing were BOP parts.

But this is from his mouth and I cant find anything supporting this claim.

What I would do is look for the 2 digget code stamped onto the axle and compare it to the list above. If it matches up then I would be comfortable stating that it was original.
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post #6 of 14 (permalink) Old 07-23-2015, 09:25 AM
 
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The only "Chevy" casting number rears installed in US built Pontiac musclecars were McKinnon plant built 12 bolts, used in factory '70-72 Pontiac 455 application A bodys as well as '70 GrandPrixs with 400 4spds. The center housing casting numbers on these were 3969278, 3969278N, & 3969278NF. These exact same center casting numbers were ALSO used on same era ('70-72) 12 bolts cast out of two other GM axle plants, but those axle plants cast the center housing differently with a large casting date in the RH lwr webbing.

Early Pontiac A bodys all received PONTIAC 8.2 10 bolts.
PONTIAC 8.2 10 bolts had their own center housings, own style ring and pinion, own design carriers, and own axle tubes that flared out to accept Pontiac bolt in axles.

Chevrolet 8.2 10 bolt had their own round 10 bolt rear cover with a splash lip on it. Chevy 8.2 10 bolt rears axle tubes neck down on the ends, as the axles are are retained with c-clips inside the carrier sand do not have flared out axle tube ends. Chevy 8.2 10 bolts took their own style chevy 8.2 carrier and ring and pinion. The chevy 8.2 10bolt pinion gear has less splines and requires its own pinion flange which uses the small Spicer 1310 ujoint.

The only uses for c-clip axle Chevy 8.2 10 bolts in US production Pontiac chassis were:
-multileaf 8.2 Chevy 10 bolt in base 1970 Firebird
-mono leaf 8.2 Chevy 10 bolt installed in all production '71 Ventura II's.

If a '64-72 Pontiac A-body has a c-clip axle 8.2 Chevy A body (Malibu-Chevelle-Elco) rearend in it, someone other than the original assembly plant has installed that rearend in the car. It's that plain and simple. I've done it many times in Pontiac partscars in order to be able roll them around. Across the country, many folks over the years have been happy to find the early configuration A body rear they needed to get what had been a bolt-in axle A body going. Original rears often spun an axle bearing, the early ('64-early 66) length bolt in axles have often been hard to find and thus the early Malibu 8.2 rear that was avail for $50 made it under another Pontiac. Other than installing an adapter ujoint in the rear of the driveshaft, the 8.2 Chevy rear was cheap and easy fix, and worked for them. That is exactly how 8.2 Chevy rears end up under early Pontiac A bodys.

As a GM differential builder, I personally do not like the 8.2 Chevy rears, as the lack pinion support and have cclip axle retention. I seldom build them unless a customer asks me to. Chevrolet deemed the 8.2 Chevy cclip rears weak enough that when a '65-72 Chevy product had more than 275 gross HP and aprox 325 ft lbs of torque, a standard issue 12 bolt was used. Most of the stock 12 bolts Chevrolet used also had their own weaknesses... am straying from the original topic.

Hope this helps.
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post #7 of 14 (permalink) Old 07-23-2015, 09:39 AM Thread Starter
 
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This is interesting stuff, thanks everyone. To Tony, you're right it is 3859140N. That was a typo on my part when I entered it.
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post #8 of 14 (permalink) Old 07-23-2015, 09:53 AM
 
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Quote:
Originally Posted by tonyskala View Post
So this stumped me for the better part of the day.

I spent quite a bit of time looking around. And I can not find a definitive answer.

To begin I think you are missing a zero in the cast code. I think it should be 3859140N instead of 385914N.

What I did find is that that differential cast code was used by GM on Chevelle 12 bolt rear ends. The N indicicates it was cast at the Neenah foundry in Neenah, WI. I found 2 guys that both have that differential, One with a 66 GTO and one with a 67 GTO that have 3859140N differential's in them. They swear up and down that they were original to the car. Both of their cars were built in Fremont California. Chevelle's were built in the same factory for those years. But what confuses me is that I keep reading about Buick, Olsmobile, Pontiac (BOP) specific parts. GTO's are supposed to use BOP parts. Now I called this old timer that I met at Good Guys in Pleasanton a while back. He used to work at the Fremont Plant in the 60's and 70's. He told me the differentials came to Fremont as empty housings and they were actually out together in Fremont. The guts that were put into the housing were BOP parts.

But this is from his mouth and I cant find anything supporting this claim.

What I would do is look for the 2 digget code stamped onto the axle and compare it to the list above. If it matches up then I would be comfortable stating that it was original.
Tony,
The N or NF deal, I don't believe has ever been conclusively determined that the Neenah foundry cast the center housings. On several of the later McKinnon cast center housings they have he N at the end of the casting number but were cast in house.

Also own several Pontiacs built out of Fremont. From my exhausted research, not that much done differently on one other than different style bolt head markings, different placement of the partial VIN on the block, and a date code stamping on the side of the original hood. On a chevy 10 bolt being factory installed in a early GTO, GM didnt use adaptor style ujoints. Such a build would have required its own driveshaft, one with spicer 1310 ujoint ends on each end. There would be engineering documents supporting that use and the special application driveshaft would have made it into the '67 assembly manual, there would be a notation in the upper box. Short of that happening, I just don't see the chevy 8.2 rears being original to those two cars. Both GTO's in stock form also made way more torque than what 8.2 Chevy rears were put behind Over the years, I've across many owners that want to state something being original but there memories were often hazy... just throwing this out.
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post #9 of 14 (permalink) Old 07-23-2015, 10:06 AM Thread Starter
 
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post #10 of 14 (permalink) Old 07-23-2015, 10:26 AM
 
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Nodular iron was used in select Pontiac 8.2 10 bolts from '67-71. There is a big N on the nose of the center housing along witha specific casting number. The 8.5 housings also used nodular iron construction. No nodular iron in in low horse Pontiac 8.2 housings or Chevy 8.2 housings, both used gray iron.
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  Pontiac GTO Forum > The 1964-1974 Pontiac Tempest, Lemans & GTO > 1964-1974 Tempest, Lemans & GTO Undercarriage, Frame, Transmission and Differential Discussions.

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