1969 4-speed, what gear would you choose

ABC123 · Uber Guru

RE: 1969 4-speed, what gear would you choose

65 SD L79 · Canadian Poncho Superstar!

3.31 non posi

ABC123 · Uber Guru

Screenshot 2024-02-05 141306.png

seventy2plus2 · Canadian Poncho Superstar!

Does the 09 27 date code match up with your car?

ABC123 · Uber Guru

Not even close.

October 1968 car.

09 27 should be a 1970 model

65 SD L79 · Canadian Poncho Superstar!

09 27 is September 27 completely lines up with your car in the corner of the rear end you will see a date code in the casting

-- Edited by 65 SD L79 on Monday 5th of February 2024 03:44:16 PM

-- Edited by 65 SD L79 on Monday 5th of February 2024 04:04:24 PM

seventy2plus2 · Canadian Poncho Superstar!

DD is 3.31 gears for 66-69. 09 27 is September 27, K is McKinnon Industries.
Casting # on Center Section will be 3852980, the casting date will tell the story.
Casting date looks to be on the bottom of the center housing, facing forward.

So far I'd say it looks like it might be the corrrect one for your car. But, the bracket for the brake hose is missing.

If you've got the Protect-O-Plate, the engine, transmission & differential #'s will be on it.

What gears are in it now?

ABC123 · Uber Guru

Quick run out to the shop.

Numbers are in !

41 teeth

And this surprise

I really appreciate all the feedback.

More please

seventy2plus2 · Canadian Poncho Superstar!

That's the 3852980 casting number that I knew we'd see, but what about the date code in the casting? And it sure looks like a posi unit to me.

I think the hand written numbers on the side of the ring gear are the setup tolerances, etc.

41 teeth on the ring gear, how many teeth on the pinion?
41 tooth options are: 2.56, 2.73, 3.42 & 3.73, depending on how many teeth on the pinion.

-- Edited by seventy2plus2 on Monday 5th of February 2024 07:10:18 PM

65 SD L79 · Canadian Poncho Superstar!

seventy2plus2 wrote:
That's the 3852980 casting number that I knew we'd see, but what about the date code in the casting? And it sure looks like a posi unit to me.
I think the hand written numbers on the side of the ring gear are the setup tolerances, etc.
41 teeth on the ring gear, how many teeth on the pinion?
41 tooth options are: 2.56, 2.73, 3.42 & 3.73, depending on how many teeth on the pinion.

-- Edited by seventy2plus2 on Monday 5th of February 2024 06:59:45 PM

casting location of date code for 69 gm rear axle - Search (bing.com)

look for this Randy

4SPEED427 · A Poncho Legend!

It looks like a posi unit with an aftermarket ring gear spacer behind it. That posi will have originally been used on a 2.73, 2.56 or 2.29 gear set. It will be fine for the street but on a 2 ton car with sticky tires on a racetrack guys shear those longer ring gear bolts off that are required when you use that spacer.

Magician40 · Poncho Master!

My 64 CS has a M20 Muncie with 3.50 rear ratio. Good for all driving situations. i run it about 2600 rpm on the highway so 65 mph.
works for me.
Brian

seventy2plus2 · Canadian Poncho Superstar!

65 SD L79 wrote:
seventy2plus2 wrote:
That's the 3852980 casting number that I knew we'd see, but what about the date code in the casting? And it sure looks like a posi unit to me.
I think the hand written numbers on the side of the ring gear are the setup tolerances, etc.
41 teeth on the ring gear, how many teeth on the pinion?
41 tooth options are: 2.56, 2.73, 3.42 & 3.73, depending on how many teeth on the pinion.

-- Edited by seventy2plus2 on Monday 5th of February 2024 06:59:45 PM
casting location of date code for 69 gm rear axle - Search (bing.com)
look for this Randy

On the 70 diff I have in the alley the casting date appears to be on the very bottom of the casting, facing forward. The passenger side facing forward didn't have anything.

It's on saw horses, and has the pinion facing the wall. I crawled under for a look, but had some lights shining in my eyes so I couldn't make out the casting date.

-- Edited by seventy2plus2 on Monday 5th of February 2024 07:36:43 PM

seventy2plus2 · Canadian Poncho Superstar!

In the wide shot you provided showing the internals of the diff (and the posi carrier), on the left of the posi carrier will also be its casting number:
ED 32088 2 series 2.73:1 & down,
30140PM1 3 series 3.07:1 - 3.73:1,
EDB 30174 4 series 3:90:1 & up.
As Carl says, spacers can be used to put the wrong gear set on another carrier.
The 3 series carriers are the ones that are worth money. I think I have both empty 2 series & 4 series posi carriers in the garage.

ABC123 · Uber Guru

I ran out to the shop.

Before the radio show starts biggrin

More hieroglyphics !

10 teeth on the pinion.

41 gear- 10 pinion

Is that not 4.10s ??

seventy2plus2 · Canadian Poncho Superstar!

41 teeth on ring ÷ 10 teeth on pinion = 4.10:1 gear ratio.

Not sure what the carrier is though as a spacer is being used. However, and I'm not a diff expert, is that ring gear looks pretty skinny for 4.10's.

seventy2plus2 · Canadian Poncho Superstar!

Here's a 2 series posi carrier.

4SPEED427 · A Poncho Legend!

Strictly a guess but I'm thinking it's a set of thick 4.10's made to fit a 3 series carrier. Then, because he didn't have a 3 series carrier he got a 2 series carrier and use a spacer to make it equivalent to a 3 series carrier. Make sense?

cdnpont · Canadian Poncho Superstar!

Now I'm curious if it's a 3 series ED 30140 PM1 carrier,

Look here Randy,

ABC123 · Uber Guru

That would explain the hieroglyphics.

A machinist was involved.

So it looks like I opened a can of worms.

Now I may need a carrier for the 3.31s

seventy2plus2 · Canadian Poncho Superstar!

The hieroglyphics are standard fare, they're the factory specs for installation.

4SPEED427 · A Poncho Legend!

ABC123 wrote:
That would explain the hieroglyphics.

A machinist was involved.

So it looks like I opened a can of worms.

Now I may need a carrier for the 3.31s

If it does turn out to be a 2 series carrier you can just keep the posi unit you have and use the 3.31's with the spacer. It will be fine for what you are going to use it for.

cdnpont · Canadian Poncho Superstar!

If you have a 3 series posi, then rebuilding it would be the way to go. If you have to go and buy one, then rebuild it, then I'd just spent the extra and get a new Eaton 3 series posi.

https://www.summitracing.com/parts/etn-19554-010

I know it's pricy, but by the time you buy one, do the clutches, plates, spiders, bushings, pin, springs, you'll be up there anyway.

ABC123 · Uber Guru

seventy2plus2 wrote:
In the wide shot you provided showing the internals of the diff (and the posi carrier), on the left of the posi carrier will also be its casting number:
ED 32088 2 series 2.73:1 & down,
30140PM1 3 series 3.07:1 - 3.73:1,
EDB 30174 4 series 3:90:1 & up.
As Carl says, spacers can be used to put the wrong gear set on another carrier.
The 3 series carriers are the ones that are worth money. I think I have both empty 2 series & 4 series posi carriers in the garage.

It's a 4 series

seventy2plus2 · Canadian Poncho Superstar!

Here's the date code casting from the diff in my garage. I think it shows F 16 9, which would be July 16 1969, sounds good for a 1970 Impala. This date code is on the very bottom of the case facing forward.