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This a 3:08 open rearend , it has the big M on top of the cast iron center section , i have not found any axle codes yet . The casting number of the center section is 393820 , it has the flat bolt retained spring pads that appear to be original , after i clean it up i can post pictures . It came out of a 1967 El Camino , i will have to confirm that from the guy who wants it rebuilt . It is the bolt in retained axles , the yoke is a o-type , it has some more little ribs in the castings the i have not seen before . I have anothe big M casting rear end the is also a 3:08 open but it has the std spring perches as any A body . This housing with the flat spring perches maeasures 54.5 inches back to back of the backing plates . Any ideas ? The rear cover is a 12 bolt O-axle std cover , 12 bolts . Ring and pinion are o-axle with the 10 bolt 7/16 bolts . Date code is 164 .
This a 3:08 open rearend , it has the big M on top of the cast iron center section , i have not found any axle codes yet . The casting number of the center section is 393820 , it has the flat bolt retained spring pads that appear to be original , after i clean it up i can post pictures . It came out of a 1967 El Camino , i will have to confirm that from the guy who wants it rebuilt . It is the bolt in retained axles , the yoke is a o-type , it has some more little ribs in the castings the i have not seen before . I have anothe big M casting rear end the is also a 3:08 open but it has the std spring perches as any A body . This housing with the flat spring perches maeasures 54.5 inches back to back of the backing plates . Any ideas ? The rear cover is a 12 bolt O-axle std cover , 12 bolts . Ring and pinion are o-axle with the 10 bolt 7/16 bolts . Date code is 164 .
This a 3:08 open rearend , it has the big M on top of the cast iron center section , i have not found any axle codes yet . The casting number of the center section is 393820 , it has the flat bolt retained spring pads that appear to be original , after i clean it up i can post pictures . It came out of a 1967 El Camino , i will have to confirm that from the guy who wants it rebuilt . It is the bolt in retained axles , the yoke is a o-type , it has some more little ribs in the castings the i have not seen before . I have anothe big M casting rear end the is also a 3:08 open but it has the std spring perches as any A body . This housing with the flat spring perches maeasures 54.5 inches back to back of the backing plates . Any ideas ? The rear cover is a 12 bolt O-axle std cover , 12 bolts . Ring and pinion are o-axle with the 10 bolt 7/16 bolts . Date code is 164 .
Bob - Were really going to need to see the perches and other areas to see if this was an original perched rear or not. FROM all we have ever parted out we have seen 2 M housings and both were raised spring perches NEVER flat... So we need to see if someone welded them from another rear or this was stock or??? Pictures are going to say thousand words here. Jim
J D
The shop owner came with the car owner yesterday to pick up the rear end , he said it was a 1966 El Camino which explains the flat spring perches . He will bring the El Camino by when he gets it done and then i can get the build date .
The shop owner came with the car owner yesterday to pick up the rear end , he said it was a 1966 El Camino which explains the flat spring perches . He will bring the El Camino by when he gets it done and then i can get the build date .
I'm not sure the Chevy ever used an O Type Olds rear axle. Unless the Chevy was a big block car,it probably had a 10 bolt unit.
In all of my 40 years,I've never heard of a Chevy having an Olds O Type rear axle. I always keep an open mind tho.
I agree with this man.I have been involved in muscle cars and building rearends for 40+ years and have never encountered an "O" rear in a Chevy.Also the early 10 and 12 bolt Chevy's with the flat spring pad,(64-66 only)had a squared off leading edge on the spring pad not rounded like in the pics.Additionally I did a refurbish on a friends very late production 66' 442 and it had an "O" type 12 bolt with the flat pads and was dated nicely to the car, so I believe some late 66' 442's got this rear.I remember this clearly because we put a 455 in the car and removed the "O" rear and put a Chevelle 12 bolt posi W/ 3:55's in the car.I may even still have this rear as I have around 500 GM muscle car rears.I don't recall measuring the width of the rear.I would like to add that when a rear is measured you need to visualize a place on the backing plate that is in the same plane as the welded flange that the backing plate is bolted to.Simply measuring backing plate to plate is not an accurate measurement.That housing doesn't look messed with
I have seen them in different 1970 cars only. EL Camino, GTO even the Monte Carlos had a 10 bolt Pontiac rear under them FROM THE FACTORY. I talked with old timers that worked in the plants and they said the strike in 1970 cause division mash parts. Like Pontiac rears in Chevys and olds rears in Chevys anything to complete the car. This still does not answer the flat perch on the 12 bolt olds and the vehicle it was removed from.
Possibly GM was going to offer a heavy duty version in the El Camino being a CAR TRUCK... Then some one through a STINK at a meeting and it was canned but not before some were built. Does happen sometimes...
Your taLKING ABOUT 40- 45+ YEAR OLD CARS THAT HAVE BEEN beat ON OVER YEARS...mOST ARE never ORIGINAL BY THIS TIME. Very few... Sorry bout the caps...not looking up as i peck at the keys...lol
I’m down to rebuilding the reared on my 66-442. Trying to determine if this is the original reared or if it was a replacement.
In reading the above thread it makes me wonder if it was a replacement out of Chevy.
Casting #393820, ‘M’ stamped on top of the housing, ratio 3.23, 28 tooth axle splines, ‘125’ stamped on the housing(date code? If so, what’s the date, ‘CFD and CE also stamped on the housing, looks like standard coil spring pads (not flat plates’
J
Joe, thanks for the response. I figured the ratio/code were correct. The bigger question was about the ‘M’ stamped on the housing and the ‘125’ which I think might be the date code but need confirmation on that, and also if that would have been the original rear end or a replacement.
The other thing I forgot to mention was the width of the ring gear, 8.5. There seem to be a lot of ring and pinion sets for 8.2, with a 3.23 or 3.55 ratio, not so much for an 8.5…….still searching though.
Still wondering if anyone has run into this M reared housing on a 66-442. In a quandary whether this is original to my car when built or changed/added somewhere down the road. Was thinking about changing ratios to a 3.55, but could only find a 3.42 ratio for the 8.5. Any help/info is appreciated.
Still wondering if anyone has run into this M reared housing on a 66-442. In a quandary whether this is original to my car when built or changed/added somewhere down the road. Was thinking about changing ratios to a 3.55, but could only find a 3.42 ratio for the 8.5. Any help/info is appreciated.
The 8.5 71/72 rear axle is the best choice for any car that's not going to be a totally correct car. They are plentiful and parts are readily available and way cheaper than a O type rear axle. The 8.5 is the same width as the 66 A Body axle.
So, are you saying my ‘M’ axle is not original to the car? Most everything I’ve read says the 1966 442’s had an 8.2” ring gear width. The 3.23 ratio ring gear I pulled out is an 8.5” width ring gear……no ‘c’ clips. They are bolt in axles.
Ah, another thing I didn’t mention…..the car had a Redaway two speed automatic in it. I’ve converted it to a four speed.
So, are you saying my ‘M’ axle is not original to the car? Most everything I’ve read says the 1966 442’s had an 8.2” ring gear width. The 3.23 ratio ring gear I pulled out is an 8.5” width ring gear……no ‘c’ clips. They are bolt in axles.
Ah, another thing I didn’t mention…..the car had a Redaway two speed automatic in it. I’ve converted it to a four speed.
I'm not sure who you are directing your question to but the O Type 12 bolt cover 10 bolt ring gear was available in 1966 A Body models. So yes your car could very well possibly have a O Type rear axle. They call the ring gear a 8.5 unit but they are often confused with the 71/72 8.5 corporate rear axle. I explained that rear axle is a direct bolt in option and parts are plentiful unlike the O Type which has very limited gear ratios and parts available. The only thing you would have to do is use a 1" shorter driveshaft to use in your 66. If originality is a must for your car pull out the wallet and buy the either 3.42 or 3.91 gear sets or find used original ratio of your choice. Same goes for the posi, buy the converted Phord unit or find an OEM O Type used unit. The 8.2 B or P axle was commonly used in the 442's in 66 but the O Type was used in some.
There is a good chance it is stock to your car. I went from a 2.78 open to a 3.08 Yukon posi, a .3 improvement on my 1970 factory 12 bolt O axle. It sure wasn't cheap but everything has gone up a lot. You only get .19 going from 3.23 to 3.42. A 3.91 will really boost off the line, if highway rpm doesn't bother you. Depends on what it costs to pick up a used 71/72 axle, if it offsets the extra expense of upgrading the 12 bolt 8.5" Type O.
Still wondering if anyone has run into this M reared housing on a 66-442. In a quandary whether this is original to my car when built or changed/added somewhere down the road. Was thinking about changing ratios to a 3.55, but could only find a 3.42 ratio for the 8.5. Any help/info is appreciated.
So the spring perch mounts are a DEAD give away to a 1966 era rear end. I personally did not know 12 bolt Oldsmobile 8.5 ever came with the flat cup and bolt perch.... BUT 7 to 10 years ago there was a post we were all in and trying to figure out if that was a real 12 bolt cover 10 bolt ring with flat perch housing... SOoooo I guess they did produce the 1966 12 bolt cover rears.... I always though they were 67-70.... BUT when there is ACTUALLY Physically a person that has one with factory welds you can not DENY it exists. I have been doing rears for almost 40 years now and STILL learning and discovering things exist out there. Jim
JD Race
So the spring perch mounts are a DEAD give away to a 1966 era rear end. I personally did not know 12 bolt Oldsmobile 8.5 ever came with the flat cup and bolt perch.... BUT 7 to 10 years ago there was a post we were all in and trying to figure out if that was a real 12 bolt cover 10 bolt ring with flat perch housing... SOoooo I guess they did produce the 1966 12 bolt cover rears.... I always though they were 67-70.... BUT when there is ACTUALLY Physically a person that has one with factory welds you can not DENY it exists. I have been doing rears for almost 40 years now and STILL learning and discovering things exist out there. Jim
JD Race
I'm pretty sure I was involved in that discussion about the 66 O Type rear axle. It's even listed in the 66 assembly/PIM manual in the rear axle section. I have personally parted at least 3 66's that had them.
Jim
