Rear End/Transmission - Pontiac GTO Forum
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post #1 of 6 (permalink) Old 11-23-2017, 04:55 PM Thread Starter
 
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Rear End/Transmission

Trying to figure out what rear end is in my 1967 GTO. I know it is posi traction but don't know the axial ratio. This is the only number I could find on the axial,

9783393 and above this number was the number F226. Now the first 2 was smaller than the F and the last 26. I have been told that there should be other numbers close to the brake drum etc etc. but I could not find any.

No for the 4 speed transmission. I would like to know what trans I have. It is a General Motors trans because it has a patent number 3088336 and above the number it says General Motors.

These are the numbers off of the trans. On the main case #3885010 on the smaller back portion of the case #3846429 , on the shift fork cover #3884S85 .

I'm sure there are experts on this site that will know the answer to these two questions.

thanks in advance.

Alan
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post #2 of 6 (permalink) Old 11-23-2017, 05:57 PM
 
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The center housing casting number 9783393 is a '66 & 67 gray iron Pontiac 8.2 piece. This particular gray iron casting center housing was used in standard performance 8.2 10 bolt rears for '66 & '67 Pontiac A-body's, as well as many '66 Olds A-body's (Olds usage 8.2 10 bolts rears had their own stamped ID codes). This particular gray iron casting center housing was also used in the mfg of '67 Firebird base rearends. In the gray iron '67 Firebird 9783393 casting rears, there will be no rubber control arm bushings in the cast upper control arm bushing area. Being a gray iron 8.2 housing, the date code will be alphanumeric, Fxx5 through aprox Fxx7. 1966 housings are easily spotted as they have coil spring mounts that use the bolt on "ears". Pontiac & Olds used the gray iron 9783393 housing rears for its highest performance '66 8.2 rears with factory 3.90 or 4.33 Safe-T-Track (Olds used the Anti-Spin jargon). For 1967 models, these lowest geared 4 pinion cone posi rear were built off a Nodular iron Pontiac 8.2 housing. Later in the '67 model year, Olds A-body's began to recieve their own rearends, the "Type O" Olds 10 bolt (12 bolt smooth cover).

On the Muncie 4speed, the "010" casting case was used in following GM production:
-extremely late '65 production
-all of '66 production
-all of '67 production

If you can clean the upright areas of the main case on the passenger side, good chance you will be able to view the Muncie date code.
Following is a good read, & has illustrations & pictures.

Muncie 4-speed

Last edited by Pinion head; 11-23-2017 at 06:08 PM.
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post #3 of 6 (permalink) Old 11-24-2017, 08:19 AM
 
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Garage
The axle code, which is a two-character code, is stamped on the front passenger side axle tube to the left of the carrier case. You may have to really scrub to see/find it as they are not stamped real deep and can be easily covered with grease, rust, paint. Took me a while to reveal mine, but I did find it. Here are the axle codes that show your '67 and what you will be looking for. https://www.thepartsplaceinc.com/dat...%20Decoder.pdf
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post #4 of 6 (permalink) Old 11-24-2017, 09:20 AM
 
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If you cannot find the code and simply just want to know the ratio it is relatively easy with a posi. Get the rear end up, mark the u-joint with a piece of tape or marker. Rotate the tire and compare the number of revolutions of the u-joint to the tire. For example, if you rotate the tire 10 revolutions and the u-joint rotates slightly over 32 revolutions you have 3.23 gears. (32.3/10=3.23)
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post #5 of 6 (permalink) Old 11-24-2017, 08:55 PM
 
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Quote:
Originally Posted by johngto1967 View Post
If you cannot find the code and simply just want to know the ratio it is relatively easy with a posi. Get the rear end up, mark the u-joint with a piece of tape or marker. Rotate the tire and compare the number of revolutions of the u-joint to the tire. For example, if you rotate the tire 10 revolutions and the u-joint rotates slightly over 32 revolutions you have 3.23 gears. (32.3/10=3.23)


For a Posi rear end: Jack both wheels off the ground. Turn one wheel 1 complete turn.
- Count the turns on the drive shaft.

For a Non-Posi rear end: Jack one wheel off the ground. Turn the wheel 2 complete turns.
- Count the turns on the drive shaft.

If it takes about 2 and three-quarters turns, it's around a 2.73 gear ratio. If it's a little more than 3, you have 3.08s. If it takes about 3 and a quarter turns of the driveshaft, you have 3.23. If it takes more than 3 and a quarter turns of the driveshaft, but less than 3 and a half turns, then it is a 3.36. If it takes 3 and a half turns of the driveshaft then it is 3.55. Very close to 3 and three-quarter turns, 3.73 gears. This method won't work very well on a posi that's worn-out and won't spin both tires equally.
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post #6 of 6 (permalink) Old 11-24-2017, 09:15 PM
 
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If you're lazy, there is a formula for figuring it out on the internet, as long as your car runs......Something like,...Your rear tire diameter or height, a running speed (Like 45mph), your tach (RPM) reading at that speed, 4th gear or D (1:1 ratio)...Doesn't take long, and effortless....Hope this doesn't screw you up ! Best, J......(.I think it's ANGELFIRE.Com)

Last edited by JNYBOY; 11-25-2017 at 02:29 PM.
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