67 Rear End Ident?

[John C.]

I could use some help on identifying my 67 Rear end stamped AM 2 1 67. The car is a very stock 300HP A.I.R. 4 speed car. My confusion is that it is obviously a 3.70 ratio but stamped AM 2 1 67 that correlates with my mid Feb build 67. However AM rear end is noted as a 3.36 posi manual trans in John Amgwert's 53-67 Specification Guide. Not sure if "manual trans" means 3 speed? My 4 speed is stamped with correct VIN and corresponding date P7 A 23.
I'm pretty sure that this is the original carrier but definitely not 3.36 and not sure if it's open or Posi? jacking up one wheel it turns that implies Open but it could be a Posi with worn synchros? Doubt that anyone would change a 300 HP grocery getter from a 3.36 to 3.70.
Could it be mis-stamped at the factory as a 3.36 3 speed car? Want to change to 3.36 open or posi soon.
Any help greatly appreciated! John

[Tom E.]

Re: 67 Rear End Ident?

Just my .02 but unless you are the original owner and know the cars history it’s highly probable someone changed out the ring and pinion perhaps to try and get a little more performance.

My all original numbers matching 1967 327/350 had the same thing except instead of the factory 3:73 in the rear someone had replaced that with 4:10 gears. Fortunately they saved the original ring and pinion so it was an easy swap back.
Tom

[Mark F.]

Re: 67 Rear End Ident?

I could use some help on identifying my 67 Rear end stamped AM 2 1 67. The car is a very stock 300HP A.I.R. 4 speed car. My confusion is that it is obviously a 3.70 ratio but stamped AM 2 1 67 that correlates with my mid Feb build 67. However AM rear end is noted as a 3.36 posi manual trans in John Amgwert's 53-67 Specification Guide. Not sure if "manual trans" means 3 speed? My 4 speed is stamped with correct VIN and corresponding date P7 A 23. I'm pretty sure that this is the original carrier but definitely not 3.36 and not sure if it's open or Posi? jacking up one wheel it turns that implies Open but it could be a Posi with worn synchros? Doubt that anyone would change a 300 HP grocery getter from a 3.36 to 3.70. Could it be mis-stamped at the factory as a 3.36 3 speed car? Want to change to 3.36 open or posi soon. Any help greatly appreciated! John

Hi John,

As shown below, according to the 1967 GM-published Specifications Book, 300HP cars were equipped 3.08 or 3.36 axle ratios.

• 3.08 was available as a 3-speed (Base) or 4-speed optional - but positraction only.
• 3.36 was available as a 3-speed (Base), 4-speed optional, or Powerglide optional - all three w/ positraction or w/o posi.

As for "Not sure if "manual trans" means 3 speed?" my interpretation of GM's table is "manual" means either 3-spd or 4-spd because they are both showing up as "available" Power Team combinations...hope this helps!

Power Teams and Diff Codes 1967_002.jpg

[Thomas N.]

Re: 67 Rear End Ident?

Hi:
Manual transmission codes on a rear end are the same for a 3 or 4 speed. It is still a manual transmission.

The best way to determine what you have is get the rear cover off, look at the stampings on the ring gear, and look if it is a posi or non-posi carrier.

There appears to be marks between the rear cover and the main housing which might indicate that this has been taken apart.

I would find it highly unlikely that someone would change out a posi carrier for a non-posi unit, but stranger things could have happened.

[Mike E.]

Re: 67 Rear End Ident?

Not trying to be picky, but ratios were 3.70 and 4.11 rather than 3.73 and 4.10.

1967 327/350 had the same thing except instead of the factory 3:73 in the rear someone had replaced that with 4:10 gears. Fortunately they saved the original ring and pinion so it was an easy swap back.
Tom

[John C.]

Re: 67 Rear End Ident?

Thanks for the help on this: I was thrown by the term "standard transmission" thinking it meant 3 speed. It's a very original car but someone in it's lifetime must changed the 3.36 to 3.70? I assume that open and posi carriers are the same? John

[Tom E.]

Re: 67 Rear End Ident?

Not trying to be picky, but ratios were 3.70 and 4.11 rather than 3.73 and 4.10.

yep you are correct, must be the old brain cells mixing up numbers. Thanks for the correction.
Tom

[James G.]

Re: 67 Rear End Ident?

''AM'' is 3.36 positraction. std means it came with that differential. posi had to be specified on order.

[Joe L.]

Re: 67 Rear End Ident?

Thanks for the help on this: I was thrown by the term "standard transmission" thinking it meant 3 speed. It's a very original car but someone in it's lifetime must changed the 3.36 to 3.70? I assume that open and posi carriers are the same? John

John------


Yes, open and posi carrier are the same for C2/C3.

[Dan A.]

Re: 67 Rear End Ident?

Could it be mis-stamped at the factory as a 3.36 3 speed car? Want to change to 3.36 open or posi soon.

You have determined the probability that the dif is original to your car from the casting date and the build stamp. The rest of your questions should be answered when the unit is removed and opened. The ring gear is stamped with the number of teeth on the crown gear and the pinion, the part number and the date of manufacture. If the gears were changed out the probability of the date corresponding to your cars build is slim. If the gears are from an after market supplier again you will know the gear set had been changed. Posi or non posi will be obvious too. If a gear change occurred who ever did it had a couple of options which may muddy the waters regarding posi/open. Does your tank sheet have G81 listed?

[John C.]

Re: 67 Rear End Ident?

Yes, I believe that there is a tank sheet. Is there a way to view it without dropping the tank? Harbor Freight or other scope/camera?

[Dan A.]

Re: 67 Rear End Ident?

I have seen photos where owners have loosened the gas filler rubber boot. Moving it enough to see the tank sheet using a flash light. Whether it can be read is another question. I did find this picture on the net.

1967 427 tri power unrestored-original.jpg