I purchased this car (1963 Convertible) in 1969 from the original owner. It was a 250 HP car with a 3-speed. He swapped out the 3-speed for a 4-speed and I suspect he also swapped out the rear because it had 3:70 gears in it when I purchased it. (I never asked him about a rear swap.)

In short order the rear started making a clicking sound with lots of back-lash so I purchased a complete rear with 4:56 gears. I was modifying it and... heck that's what we did back then... (It turned out that one of my half-shaft U-joints was missing all of its needle bearings and that's where all of the noise came from.) Since I was modifying the engine and already had the rear with little to hold me back, I swapped it in. I checked the play in both rears and the back-lash on the gears was just about perfect on both of them.

Now after storing the car since 1971 we're doing a complete frame-off and I'm wondering about the rear end. The car will probably see around 1000 miles or less a year so I'm considering re-installing the 4:56, at least for a while, since I have long since sold the 3:70.

These are the numbers on the bottom of the rear: 2 AM 11 7 67W. I'm not positive about the AM, but the rest of the numbers are very clear. Can you tell me what the breakdown of the numbers indicates? Someone posted a list of codes for these rears a while back, but after doing a search I could not find the post.

The rear axles do not have BB caps, they have U-bolts, so I'm beginning to suspect that someone swapped 4:56 gears into the carrier I have. Unfortunately other than checking the ratio and the lash, I didn't know enough to ask the genesis of the rear back then. Based on the date code, I also suspect it's out of a '68.

The engine is a CE short block with 11.5:1 pistons and used a Crane solid roller with Mondello heads and a rev-kit. That is being changed to a hydraulic roller with Dart heads. Any help would be appreciated.

GUSTO

 

It's a 3.36 Posi for a '68 small-block, made November 7, 1967.

 

John...even though the code says what it should be...should'nt one take the time to check the rotation of the drum in comparison the drive shaft to get the correct gears?

i don't know why...but... "someone" might have damaged the internals and put something else inside...

 

Thank you John, I was hoping you would comment.

It definitely has 4:56 gears in it. Does that mean that they changed the posi unit as well to get 4:56 gears in that carrier?

GUSTO

 

Yes, it does - the original 3.36 gear used a Series 3 Posi carrier, and the 4.56 gear requires a Series 4 Posi carrier.

 

John -- Remind me; is it the 3-series posi carrier that you can use with an aftermarket spacer to bolt-in a stock GM 4-series ring gear ?

Or is it the other way around , -- Wayne

 

Do not use a RG spacer. GM gears are long gone, so you need new ones or trust in a used set(not recommended). As john said the 456's use a Eaton 4 series case and you'll need a good used 3 series posi case or new one. You can get US made gears to fit the 3 series from 273,308,336,355,373,411 or even 456 to fit without the spacer normally required to go from a 3 to 4 series.

For a posi case there are some options.
A good used one, stay away from the 65-68's with sq window, they are crack prone. The 69-79 are better. If you buy a complete used posi then you should look over the parts. I always custom build them but you don't have to if you just want to put it in an go. The 71-79 clutches are weak, the spiders are good. (10-17) The 65-70 clutches are good and the spiders weaker(10-18) the best way is to build one from the best parts.

You can buy a new loaded Eaton from anyone. they are made in Mexico and have less clutches in them. They also used fiber coated clutches, (not recommended), and Heavy springs- also not recommended.

Also with a 63-68 housing you're going to find the side shims are thinner then the ones in all the kits sold-even though they are listed for 65-79's. If you change the gears you're going to have to reshim and these are expensive and not sold in 001 increments to properly dial in the backlash. I grind all my shims to size, never use "close to size" shims.

Replace the 5 line bearing cap screw with socket head bolts as well.

good luck