[alanmay0]

My car is a 1967 GTO. The engine numbers match the car. PHS documents show this car to have been made an automatic. Some where along the line the trans was changed to a 4 sp. Now I have been doing research on the transmission and the rear axle. Here are the numbers: Trans Main case #3885010, Date code P0714, Extension tail housing #3846429, shift cover plate # 3884685, also on main case # 9783393. You try and figure out what year Muncie transmission is.

Next the build sheet shows this car was a automatic turbohydromatic transmission with a YC code 2:93 rear axle ratio. The stamping on the rear axle on my car is YH code meaning a 3:55 axle ratio.

Now when I rotate the drive shaft and count the rotations it comes out just shy of 3 turns of shaft vs one turn of tire meaning a 2:93 rear axle ratio.

So how could the axle be stamped YH and the build sheet says it's a YC. Could you but 2:93 gears in a 3:55 rear axle housing???

thanks
alan

[Tom Vaught]

Just taking a guess here but:
If I remember correctly and I am a Old Guy,
The 2.93 Gear was thicker vs the 3.55 Gear.
Housing would allow the interchange because the support bearings were the same.

But I think to put the 3.55 gear in the 2.93 housing you had to install a custom steel spacer
to put the ring gear in the right spot.

Have you actually looked at the rear to see if there is a spacer on the posi unit?

Tom V.

[Chief of the 60's]

Numbers mean nothing. Ask any former GM employee or dealer mechanic. It is an old car and unless a person is the original owner from the moment it rolled off the line without an issue and it has never had any warranty or service work performed, no one knows what kind of life it had. Hell, I've seen original owner's stories change over time.

[Squidward]

My guess to the mystery: During the life of your car, some previous owner Speed Junkie wanted to mash through the gears in a manly fashion, and swapped the auto for a 4 speed. Now that brutal clutch drops were available, aforementioned Speed Junkie fragged the original rear end housing, and swapped in a different rear end housing. But, because the 2.93 gears were already on hand, the 2.93 carrier and gears were swapped into the axle housing. Speed Junkie now learned how to launch more carefully. Or, in Scenario B, wife made Speed Junkie sell GTO in favor of a sensible 4 door full size to haul the kids. Additionally, this kept Speed Junkie from cruising Central Avenue where all of the 19 year old hotties hung out.

This practice was also adopted with pets to control overpopulation.

It was my understanding that the 8.2 BOP housing was the same for all gears, but the differential carrier had 3 breaks: 2.56-2.78, 2.93-3.23, and 3.36+. But this is mostly from reading, since I have only played with a couple of 8.2 BOP rears - a 67 with 3.23's, and a 72 with 2.78's.

['ol Pinion head]

Alan, I would examine the rearend housing, see what 97xxxx casting number it has, along with date code. Years ago, I setup many factory 8.2 Pontiac gear sets in housings that coded something else, many others have done the same. Have also tore down tons of Pontiac 8.2's, typically the factory gear set jives with the two letter code (if legible) and the dates of the ring & pinion predate the housing by several months.

[dataway]

Yep ... I have a 2.93 .. it was my understanding that you could only go 3.23 without changing something more complicated than ring and pinion.

I like Squids explanation .... except for the "Manly" part. Manly is a nice five speed top loader in an Italian sports car With a large bosomed female in the passenger seat. I'm thinking Claudia Cardinaly.

[Formulajones]

You'll have to dig deeper. Pictures of the rearend code would help. Sometimes those stamps aren't what they appear, sometimes they are hit with debri etc...and sometimes people try to fudge numbers.
There are many instances that are documented where BE 4.10 rearends for COPO Camaros actually had 4.56's ordered and factory installed, but never got the BW code stamped.
Like Pinion head mentioned, I'd be pulling the cover, checking the gear dates and tooth count, the casting number on the housing etc....with good investigative work it can be determined what's going on or what happened.

[alanmay0]

So then what year is the transmission given the following facts found on the internet and numbers taken off of the transmission.
The trans main case # 9783393 equals a 66-67 Pontiac 8.2 10 bolt rear end with a YH code
The main case build date = P0714= Muncie July 14th. It is either a 65-66 because in 67 they came with the year, month, day not just he month day in 65-66
The extension housing # 3846429 = a 64 or 65 with the thick lower web which my tail housing has.
The shift cover #3884685 with "584" tail stud shifter shaft = 65-70 muncie

[Blued and Painted]

Alanmay0,
You may want to put a key word in the thread tittle so the topic can be acessed later by the search tool.

[Formulajones]

Originally Posted by alanmay0

So then what year is the transmission given the following facts found on the internet and numbers taken off of the transmission.
The trans main case # 9783393 equals a 66-67 Pontiac 8.2 10 bolt rear end with a YH code
The main case build date = P0714= Muncie July 14th. It is either a 65-66 because in 67 they came with the year, month, day not just he month day in 65-66
The extension housing # 3846429 = a 64 or 65 with the thick lower web which my tail housing has.
The shift cover #3884685 with "584" tail stud shifter shaft = 65-70 muncie

The shift cover with studs for linkage attachment stopped after 1968. In 1969 GM went to a bolt style attachment. So your shaft style side cover is correct for the early trans. From what you've posted it's a 65-66 transmission. We can narrow that further with more information.
66 was actually the first year for the larger 1" counter shaft pin, not 65 like some sites state. So knowing that would help to narrow down the year.
Also 1965 was the last year for the M-20 trans with the 2.56 first gear. In 1966 the M-20 went to a 2.52 first gear. Also An M-20 from 1965 with the 2.56 first gear will have no rings on the input shaft (like an M-22) These changes likely had something to do with the larger counter shaft pin change that same year in an effort to strengthen the transmission.

['ol Pinion head]

Alan, the factory stamped XH housing is a '67 nodular housing, by casting number. Nodular Pontiac 8.2 housings were only factory assembled with low ratio gear sets & 4 pinion Safe-T-Track carriers. Later in this rearends life, someone has set up a 2.93 Pontiac 8.2 gear set on a mid ratio Pontiac 8.2 carrier. Occasionally, such changes were made. Though this rear is not original to your car, consider the housing an upgrade to gray iron center housing.

Agree with Blue & Painted, a key word would help bring it up in any future search. this type of topic would also be best moved & posted in the '66-67 Tempest/GTO Forum as the entire subject has to do with original codes & usage.

['ol Pinion head]

Jones, actually some late '65 models received 010 case Muncies, have ran across several.

[TedRamAirII]

Originally Posted by Blued and Painted

Alanmay0,
You may want to put a key word in the thread tittle so the topic can be acessed later by the search tool.

I gave that suggestion, many questions ago, to no avail. A 50 year old car isn't going to have much original parts. I would just go with what you have, unless you have unlimited pockets to build a "correct" car. The next car I buy is going to be a Survivor, no resto's or pieced together cars.

[Chief of the 60's]

Originally Posted by TedRamAirII

The next car I buy is going to be a Survivor, no resto's or pieced together cars.

Great idea, still no guarantees though.

[Formulajones]

Originally Posted by 'ol Pinion head

Jones, actually some late '65 models received 010 case Muncies, have ran across several.

Yes entirely possible. Likely during the change over period late in the year. Would like to know dates.

With his being a mid July stamp and approaching the start of a new production year, I'd say it's perfectly acceptable to have the 010 housing with the larger counter pin shaft if we were talking about a late production 65 vehicle. Then one could also say this is possibly a late 66 transmission as well, since GM wasn't putting the year on these things until about 1968. Seems vehicle vin stampings were also hit and miss so sometimes difficult to document if they are in fact original to a particular car.

[alanmay0]

Sorry if I stated XH anywhere in my post
I meant YH

[alanmay0]

The 97 number is 9783393. What does this tell you?? above that is F226 with the first 2 being smaller than the following 2 and 6.