# 1965 GTO Engine, Transmission, Diff Codes



## propuckstopper (Jan 20, 2012)

Hello everyone. I am hoping to find a real 1965 GTO expert here. I feel I have done my homework, but before I pull the trigger on a 1965 GTO I am considering buying, I just want to make sure my homework has been done correctly.

I have my own set of PHS documents and so far, all matches up. The car has a few desirable added options, but nothing taken away, at least according to PHS.

Firstly, this is a Pontiac, Michigan built car dated 03A (first week in March, 1965). It is a PHS documented Tri-power four speed, and the block code is WS. I checked the date code, and it is C55, which indicates March 5, 1965. The block part number is 9778789. Obviously, the block was cast in the exact week the car was built. Is this possible? Would production have been that "tight" in March of 1965?

On to the cylinder heads. They are a 77 cast with a cast date of C25, which indicates March 2, 1965. This date is almost spot on with the block code, but again, is this too tight to the car build code?

The distributor is the correct 1111054, which looks correct according to my research. Sound good?

Alternator is a 37 Amp unit, but very hard to read the numbers. I am not real worried about the alternator, as it is a replaceable part and the original may very likely be gone.

The center Tri-power carb bears what looks like the original tag of 7021575, which matches my research exactly. However, the front and rear carburetor tags are slightly off. The front carb bears tag number 7025178, while research suggests a tag number of 7024178. Similarly, the rear carb indicates 7025179, while research says it should be 7024179. While these numbers on the front and rear carbs appear incorrect, it seems they are consistent in the fact that they both use a "5" in their tag numbers rather than a "4". Could this be because they are actually the correct 1965 carbs? 

Intake is the 9778818 unit, which seems correct. I don't have the date code as I forgot to look; I will be getting that information tomorrow.

Now on to the M-20 Muncie. The exact vehicle VIN is stamped on the top of the transmission, which is good. Also, the casting numbers on the Main Case (3851325) and the Tail Housing (3846429) match up perfectly. However, the production code doesn't quite jive. I am reading a code of P0305, which to me indicates P (Muncie aluminum 4 speed for passenger applications), but this is where the code goes weird. The "0", at least to me, indicates 1970 production. The third digit should be a letter (as in month), but it is reading as a "3". Lastly, the "05" has me lost. I would think that a sort of appropriate code for my car build date may look like this: P5C2. But as you can see, it is nowhere close. However, every other number jives perfectly. What gives? *EDIT....SEE MY POST BELOW!!!*

Lastly, the differential, which should be a YH code 3:55 Safe-T-Track. I can find absolutely no YH code anywhere, and we looked hard. It does have a raised cast part number of 9773925, which I really can't research as everyone talks about the "YH" that I can't find. However, we put the car up on a hoist and spun the rear wheels and watched the driveshaft. It didn't seem to equate to a 3:55 to 1. It seemed more like a 3:36. I have since googled this subject and it appears that this may be a 3:36 unit out of a 1968 GTO. It is also important to note that the car has a rear sway bar and boxed lower control arms. Somebody has been in there with a wrench for sure, and I am pretty convinced they might have changed the whole rear end. Any ideas?

I apologize for the wildly long post, but I really want to make that right call on this car. It has been a dream of mine for over 27 years to own a 1965 GTO, exactly as long as I have owned my current 1968 convertible. I bought the 1968 27 years ago due to its extensive option package, but have really longed for a 1965 GTO all the while.

I sincerely appreciate anything you may have to offer. Thanks so much!


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## extinctmake (Feb 8, 2011)

I think if you examine the right side axle tube next to the carrier on the side facing the rear of the car, you will find the differential code. 

It may require some scraping of paint or scale to find it, but it should be stamped there.

Sounds like you got yourself a good one.


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## 05GTO (Oct 6, 2004)

Also, In mid year 1966 Pontiac increased the width of their rear ends, here are those measurements;

Size for the standard mid-year1966 and later GTO differential is as follows:

Axle flange to axle flange is 60 15/16 inches.

Backing plate to backing plate is 55 1/2 inches.

Spring perch centerline to centerline is 35 inches.

Shock mount centerline to centerline is 49 1/4 inches.

Subtract 1" from above measurements for mid-year 1966 and earlier

Here is more information I found for the location on the 65 GTO axle code;

http://www.nh-gto.com/GTO Axle Codes.htm



> A sticker with the code was applied to the left brake drum.
> The code was also stamped on the axle housing directly to the right of the carrier case and below the brake line clip.


Also, look for a single letter code of " F " below the brake line clip,

The code on the Muncie P0305 is the date code (P=Muncie 4 speed, 0305 = March 5th) If the code were P0305N it would indicate the transmission would have been built on the night shift.

Regarding the tri power carbs;

7025178 is a Front Tri-Power 2bbl carb for a 1966 GTO with a manual transmission,
7025179 is a Rear Tri-Power 2bbl carb for a 1966 GTO with a manual transmission,

Something else, on the 1965 Pontiac and Kansas City built GTOs the GTO option was listed on the data plate, on the ACC code line at the bottom of the plate you will have a letter "N" in the 5th group.


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## jmt455 (Mar 26, 2012)

puckstopper, in my opinion those block and head date codes are a little "tight", but certainly possible for a car assembled at Pontiac.


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## propuckstopper (Jan 20, 2012)

It is indeed a 5NW code, stamped in plain view on the data plate.

For the information of all, I have primarily been using the GTO Association of America's Pontiac GTO/GT-37 Illustrated Identification guide. I bought this guide just a few months ago at the GTO Nationals in Loveland, CO.

I have already found a couple of pieces of information that are inaccurate, and I am not writing this to slam the publication, but I am writing this so I can inform yourselves and inform the GTOAA as well (I will show them this thread; this way, I only have to write it once).

The first piece of seemingly inaccurate information is found on page 102 at the bottom, which discusses "How To Read Production Code Numbers. This information, coincidentally, is found on the same page 102 where the 1965 transmissions are discussed.

Anyway, without typing the whole darn thing, it basically says this: P2E17 A.

P means passenger, 2 is model year (1972), E is month (May), 17 is day, and "A" is a suffix code for the ratios. From what I have found, this information is entirely true for LATER year GTOs, but not for the 1965 in question. The P0305 actually means third month fifth day, as evidenced by this commentary at Medatronics Corporation's 5 Speed Home page!

_Serial numbers for Muncie 4 speeds always begin with the letter "P". P stands for Muncie Plant. Not for passenger car as some self proclaimed specialists may think. The letter M was used to ID the Muncie plant for the Muncie 3 speed, so P was the next logical letter. The letter O would add confusion since it resembles zero. The serial number is a date code the transmission was built for a particular year. *Serial numbers from 1963 to 1966 included only the month and day.* P0101 would indicate January 1st. From 1967 to 1968 the serial number got a year designator and a letter designator for the month such as P8A01, meaning January 1st 1968. One important point is that if you have a Muncie dated with a December build date it was actually built the prior year. An example would be the date code P8T13. This is for a 1968 production car. The T stands for December and 13 is the day. To confirm this simply look at the VIN number. It will usually begin with a 18S101350 or a 28N12950. This means the Muncie was assembled December 13, 1967 for the 1968 model year. The VIN number will usually be a low number. 1969 to 1974 Muncies got a ratio designator at the end of the serial number. An example would be P4D23B. This equates to April 23, 1974, M21 ratio._

Imagine my horror just about an hour ago when I discovered the date code makes sense on this 1965 GTO's Muncie. Today, I was looking at the car and found the VIN number perfect, the two production numbers perfect, yet the date code looked weird. Anyway, I spent a gross amount of time on the transmission codes today and now find out that the GTO publication needs to clarify their explanation.

Trust me, please. This is certainly not a rant. It is only to provide information. It just goes to show that not everything you read (or sometimes see) is true.

I realize that the 5speeds.com site may also be inaccurate, but the "0305" just makes too much sense here. 

On another note, the GTO I.D. book lists a R.H. exhaust manifold as part number 9779325. And although I am not nearly as confident as I am with the transmission deal, all literature I can find shows that part number indeed belongs to a 1968 GTO. Now, you may say that I should go verify that on my own 1968 GTO, but mine is an H.O. car and as a result uses a different part number altogether.

At any rate, I want to thank all of you for your responses thus far. Please keep them coming. I have always viewed forums as a wonderful place to learn something new, and this forum is no exception.

Thanks again!


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## BearGFR (Aug 25, 2008)

Jump on it! Sounds like you've found a car that has been mildly touched by someone who knew what they were doing. The tri-power end carbs for 66 were larger than the ones in earlier years and it was a not-uncommon modification to swap them onto an earlier unit to get the associated performance boost. The boxed lowers and sway bar are more evidence of that. Since you've had your other one for 27 years, and have been dreaming about a 65 the whole time, how much do you really care about resale value?  You know you're going to keep this car forever, and it sounds like to me that you've found about as perfect an example of a 65 you'll ever see, with all the best options to boot. The only ones better are going to be in museums or will be show car trailer queens.... 

My dream GTO is one just like you've found. Ifn' I'd found that one, I wouldn't have let it out of my sight until it was MINE!


Bear


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## propuckstopper (Jan 20, 2012)

Thanks Bear. You just emptied my wallet! I just initiated the wire transfer and will pick up the car tonight. Thanks for helping me get over the edge. My wife is going to love you!

Ha Ha!

Thanks everyone!


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## Rukee (Feb 8, 2007)

This thread is worthless without pictures!!  :cheers


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## 05GTO (Oct 6, 2004)

Rukee said:


> This thread is worthless without pictures!!  :cheers


:agree


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## propuckstopper (Jan 20, 2012)

05GTO said:


> :agree


I'll get some posted tomorrow!

Thanks.


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