Changing rear end gear questions - Impala Tech
Transmission & Driveline Transmissions & Differentials

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post #1 of 22 (permalink) Old 02-11-2018, 10:49 AM Thread Starter
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Changing rear end gear questions

Okay... I'm probably going to screw up the terminology so bear with me.

I have a 65 that codes out EP0424 B. As i understand it, it's a 2.73 gear ratio. My intention was to put 3.55 gears back there for various reasons. But as i started to consult Google, it turns out i have a TYPE 2 Carrier, and that I can't put anything higher than 2.73 without changing the carrier.

What does this mean? My limited knowledge of rear end gears and differentials is clearly obvious. If i got a type 3 carrier and 3.55 gears, would it all fit in the the diff/pumpkin?

I'm sorry for sounding ignorant.

At the end of the day, id like to put 3.55 positraction in the rear end of this car. Can this be achieved relatively easily?

Thanks
Mark

'65 Impala SS
'71 Super Beetle
2011 Dodge 2500 6.7L Cummins
2013 GMC Acadia
2014 Corvette Stingray
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post #2 of 22 (permalink) Old 02-11-2018, 01:47 PM
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In a Dana 60 or a Ford style Nine inch rear the different ring gear thickness are compensated by two spanner nuts that can shift the ring gear from side to side to mesh with the pinion gear (which gets smaller in diameter as the gear ratio increases numerically). In a Spicer rear end there are different series of carriers to mate the ring gear with the pinion and any minor difference in ring gear thickness is compensated for with shims.

The Spicer 12 bolt breaks are 2.55 and 2.73 for a two series carrier; 3.07 through 3.73 for a three series carrier, and 3.90 through 6.13 for a four series carrier. Here are some pictures to illustrate what I am talking about:

Pictured here is a two series carrier vs. a three series. Notice how the lip where the ring gear is bolted is at a different height (this is a S-10 rear end which is made by AAW, not Spicer, but the differences shown are the same).





Here is an aftermarket spacer with longer bolts to use a three series geaar on a two series carrier:



Big Dave
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post #3 of 22 (permalink) Old 02-11-2018, 03:29 PM
BA.
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Hey there Mark,
Answering the easiest question first, yes you could buy a 3 series carrier (eg. Auburn or Eaton posi) and a 3.55 gear and it will fit into your existing rearend/pumpkin.

But, to answer your other questions, 2 things stick out for me.

1. I hate to just assume or believe some 50yr old tag regarding your existing gear ratio. It's *SO* easy to do it manually in just 2-3 minutes. If you have a rear tire off the ground, car on a jack-stand, and a piece of chaulk or a helper, you can rotate the tire 2 revolutions and count the driveshaft rotations. The number of driveshaft rotations will be your ratio. You know what to expect, validation is crucial and easy!
2. If you aren't completely tied to a 3.55, and your existing carrier is good or you're saving $$$, they do make 3.42 and 3.54 ratio's that are thicker gear-sets to bolt onto a 2 series carrier.

WARNING: I don't know what rear-end you have but this link is just to show you that the 3-series gears are available for a 2-series carrier.
https://www.summitracing.com/search/...8%2B4294915092

HOW A NOVICE REBUILDS A 66 IMPALA CONVERTIBLE:
http://www.impalas.net/forums/blog.php?u=1432
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post #4 of 22 (permalink) Old 02-11-2018, 03:54 PM Thread Starter
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This is exactly the info I was looking for.

Once it stops raining, im going to jack up the car... spin the wheel and see what happens and count the rotations. Who knows?? Maybe someone else did all the work for me?

Lets pretend it's a 3.55 and its also not posi. What needs to be done to make it posi?

Thanks again.
Mark

'65 Impala SS
'71 Super Beetle
2011 Dodge 2500 6.7L Cummins
2013 GMC Acadia
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post #5 of 22 (permalink) Old 02-11-2018, 04:13 PM Thread Starter
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Spun the wheel twice, and I got about 2 and 3/4 turns of the Differential.

So.. by my eyeball, I suppose that would be close enough to 2.73

So.... it would appear I have two choices? Are you saying that a 3.42 and 3.54 gears can bolt in to a 2-series carrier? Seems like 3.54 is more or less 3.55.

Or... open up my pocket book, get a series 3 carrier, and gears to boot.

MB

'65 Impala SS
'71 Super Beetle
2011 Dodge 2500 6.7L Cummins
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post #6 of 22 (permalink) Old 02-11-2018, 04:18 PM Thread Starter
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Also... I forgot to add, I have a 12 bolt. I'm thinking, the series 3 carrier is where i need to go.

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post #7 of 22 (permalink) Old 02-11-2018, 05:30 PM
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To get a Posi you need to buy a Posi (which is a trade mark of Eaton Gear). Do not buy an Auburn gear limited slip differential (what a posi is referred to) as they are not rebuildable when they wear out. An Eaton posi is not only rebuildable, but you can modify it by adding clutch discs and stiffening the springs.

Here is an open differential:



Note how the only thing inside is two side gears and two spider gears on a cross shaft. Below is an Eaton Posi:



Note the coli spring pack (four springs with an Eaton Posi and five coil springs with a Borg-Warner differential).

Speaking of things you don't want: this is a Governor Lock used in miliions of Chevy trucks.



It works by a tire spinning in the dirt that causes the weight to fly out of the case and grab a pawl inside the rear end housing. On dirt it works fine; on pavement it will break first time every time.

I do not recommend a spacer and longer screws to adapt one series of gears into another series housing; as the bolts will shear, but a thicker gear will work just fine.

Big Dave
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post #8 of 22 (permalink) Old 02-11-2018, 05:33 PM
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I've got to think that a 2.73 12 bolt in a 65 is pretty rare. Mine has 3.08/ten bolt. It's a 327/250/glide car. What's your engine/trans?
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Two doors, four doors, wagons, and ragtops.
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post #9 of 22 (permalink) Old 02-12-2018, 09:59 PM
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I'm curious what engine you have as well.
Also curious what your driving habits are going to be? Are you going to be burning some rubber or cruise night only type of thing?
If you've got a decent motor and like to do some burnouts then yes I would say step up to a 3 Series posi carrier.

By the way, I am biased because that's exactly what I did.


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HOW A NOVICE REBUILDS A 66 IMPALA CONVERTIBLE:
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post #10 of 22 (permalink) Old 02-13-2018, 12:33 AM
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Someone may prove me wrong but I am quite sure 1967 was the first year for 2.73 ratio in a 12 bolt B body.
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post #11 of 22 (permalink) Old 02-13-2018, 12:30 PM
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Quote:
Originally Posted by Darth View Post
Someone may prove me wrong but I am quite sure 1967 was the first year for 2.73 ratio in a 12 bolt B body.
Yes, the 2.73:1 gears were installed in 1965 and 1966. Look here --> Drivetrain Decoding-Impalas.org and scroll down.

1967 Chevrolet Impala SS convertible - Ermine White C1
1967 Chevrolet Impala SS 396 - Marina Blue FF
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post #12 of 22 (permalink) Old 02-13-2018, 05:41 PM Thread Starter
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Ok. I've done a ridiculous amount of research on the motor, decoding all the tags and engine codes and rear end gear codes... the whole kit and caboodle.

Here's what i have. Car built in CA... Originally Maroon. Numbers matching 396 that when i got it was bored .30 over. I have done nothing to the boring of it since. I had the heads reworked and completely rebuilt as they were pretty wore out. There's a new Erson Cam in it... I dont have the spec sheet on me but if i remember right, @.050 it's 234/242. with .585 lift and 1.72 rocker arm ratio. i think that those numbers are off as it needed new valve seats so i think the rocker arm ratio is closer to 1.8 moving the lift to around .600??? maybe .608??? I really dont remember the actual lift numbers my engine guy said. And I dont really know how to calculate all that.

The Tranny is a TH400... off of a 73 truck that i have put a stage 2 shift kit in. The rear gears coded out to be 2.73 using the codes on it and referencing it off of 1965 rear end codes. But i want to put around 3.55 in there.

SO... I'll be running either a 3k stall or potentially a competition stall by hughes. Hughes suggested it, as they think 2500 would be too tight and 3k might be a little sloppy. I forget the exact description of it... its in my email quote at home. But whatever. I'm still not pulling the trigger on which stall yet.

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2011 Dodge 2500 6.7L Cummins
2013 GMC Acadia
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post #13 of 22 (permalink) Old 02-13-2018, 05:45 PM Thread Starter
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I've all but decided that i'll go with an Eaton Series 3 POSI @3.55. Ugh... now I'm curious if this is all out of my wheelhouse?? Is there anything else i should be doing to the rear end??? Axles? I keep remember seeing something about 30 spline? Also.. maybe a new drive shaft? I swear ive seen something before about stock driveshafts possibly not being able to handle the amount of rotation? But i may have been INTERNETING WAY TOO MUCH.

Its easy to get down a rabbit hole.

THanks y'all.

MB
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post #14 of 22 (permalink) Old 02-13-2018, 08:26 PM
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Quote:
Originally Posted by safetysoc View Post
I've all but decided that i'll go with an Eaton Series 3 POSI @3.55. Ugh... now I'm curious if this is all out of my wheelhouse?? Is there anything else i should be doing to the rear end??? Axles? I keep remember seeing something about 30 spline? Also.. maybe a new drive shaft? I swear ive seen something before about stock driveshafts possibly not being able to handle the amount of rotation? But i may have been INTERNETING WAY TOO MUCH.

Its easy to get down a rabbit hole.

THanks y'all.

MB


If you have as you say a nearly stock numbers matching car then you have the word of the engineers at Chevy who designed the car as you see it to know that everything will hold up just fine. This assumes of course you retain the small rock hard plastic tires of the sixties. Put on a set of large by wide supper sticky jumbo tires then dump the clutch and all bets go out the window.

You can look at the side wall of modern tires and compare Traction rating along with the Wear rating to know how well they will bite for any given size. Almost every new tire will offer more traction than a GoodYear PolyGlass 60 series raised white letter tire, if you could find one.

All 12 bolt rear ends have a 30 spline axle. How good of condition they are in I do hot know. The Spicer design (a copy of the Dana 44 rear end) was designed to use the axle itself as the inner race of the wheel bearing (the bearings rides on the cast iron axle instead of a forged steel inner race that every other rear end manufacture uses). Though the axle is induction hardened by a radio frequency transformer I designed and Jackson Products built it will eventually wear through the hardened surface and go to town on the raw metal of the axle. You will have to pull the axles to install any new differential, so look at them to see if they are still flat or have a groove worn into them by the tool steel roller bearings.

Before you do anything buy this book and read it:

https://www.amazon.com/Chevy-Differe...rolet+rear+end

I also recommend this book even though it isn't Chevy specific it does a better job of explaining the procedure to set up a rear end:

https://www.amazon.com/High-Performa...tials%2C+axles

I mention this because you only get one shot as setting up a rear end and it requires technique and tools to do it correctly the first time. Once a howler, always a howler.

I used to change and set up a differential once a week because I broke them one a week. This was in my 1953 2 door Chevy sedan with a 409 under the hood. As I got older I got wiser and paid others to do it for me (I actually changed my Chevy rear end out for an Olds rear and never broke it again; instead breaking B-W T-10 transmissions, which I became good at rebuilding). But 12 bolts or Dana 60 rear ends I took to a local shop that specialized in building them (my local Chevrolet dealership). I may have set up a half dozen or so myself but it is too bothersome and I lacked patience.

Big Dave
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post #15 of 22 (permalink) Old 02-13-2018, 08:49 PM
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With that motor you really should buy the new posi carrier. It would actually be ridiculous *not to* behind that 396 and great cam and decent gearing you'll have.

Your torque converter range sounds spot-on to me, I don't think you will be unhappy with either one to be honest.
If you had a Dyno sheet on the engine you could make a better choice based on your torque curve. I'd get the 3000 myself.
Either way, the smart money is to get yourself a trans cooler as well. Cheap insurance.



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post #16 of 22 (permalink) Old 02-13-2018, 08:51 PM
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Quote:
Originally Posted by BA. View Post
With that motor you really should buy the new posi carrier. It would actually be ridiculous *not to* behind that 396 and great cam and decent gearing you'll have.

Your torque converter range sounds spot-on to me, I don't think you will be unhappy with either one to be honest.
If you had a Dyno sheet on the engine you could make a better choice based on your torque curve. I'd get the 3000 myself.
Either way, the smart money is to get yourself a trans cooler as well. Cheap insurance.



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Damn it, I knew I forgot something.

I don't think you have to worry so much about the driveshaft itself but the U-joints at each end. Maybe update with new 1330 units.

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HOW A NOVICE REBUILDS A 66 IMPALA CONVERTIBLE:
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post #17 of 22 (permalink) Old 02-14-2018, 04:10 PM
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Changing Universal joints requires exchanging the front output yoke (part that slides into the tranny), drive shaft and the pinion yoke on the front of the rear end as the 1330 has a larger diameter than a 1310. If you are going to that expense jump top a 1350 as the cost is the same but a 1350 is larger still than the 1330.



A 1350 was standard on a one ton truck. You can reuse the drive shaft cutting it to length and take the tranny out put yoke verifying the spline count (TH400, 6L80, and 6L90) have 31 splines, while the 4l64 and 200R4 use a 27 spline out put same as the TH350, PowerGlide and Muncie.

Big Dave
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post #18 of 22 (permalink) Old 02-14-2018, 04:23 PM
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Quote:
Originally Posted by safetysoc View Post
.....Here's what i have. Car built in CA... Originally Maroon. ......
Sounds awesome! Could please post a picture of your cowl tag? I'm particularly curious about CA-built cars.
Thanks!

Edit: "CA" --> Do you mean "California" or "Canada"?

1967 Chevrolet Impala SS convertible - Ermine White C1
1967 Chevrolet Impala SS 396 - Marina Blue FF

Last edited by BigDogSS; 02-15-2018 at 09:24 AM.
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post #19 of 22 (permalink) Old 02-15-2018, 01:49 AM
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Quote:
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Yes, the 2.73:1 gears were installed in 1965 and 1966. Look here --> Drivetrain Decoding-Impalas.org and scroll down.
Interesting.

As you stated, I did find it listed for 1966 in my Canadian literature, contrary to what my brain told me. However, I can't find anything for 1965.
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post #20 of 22 (permalink) Old 03-04-2018, 12:38 PM Thread Starter
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Sorry, been away for awhile. Long story but my son in law is headed to Marine Boot Camp so my daughter and grandson are living at the house until he gets through boot camp and all his other training. Been a long few weeks traveling for work, flying to Oregon and getting the Grandson... Ugh... Busy busy busy. Some day i'll free up some time for the car.

BUt.... Here I am.

Okay... Cowl Tag. I've attached it.

Next.. U-Joints. That seems like an awful lot of work and expense right now. (I say that having just bought a ridiculous amount of parts lately.) Will my U-Joints not hold up?

Carrier. I'm getting a new Carrier. Right now i'm on the fence between Eaton and Detroit Locker (though that appears to be owned by Eaton as well.)

Axles. I'm still a bit JV on that topic right now.

Rear End. I need to find a shop that can do that for me. I really don't feel like "Learning" how to do a rear end at this moment. I dont mind learning new things. But man, it almost seems like a science project.

MB
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post #21 of 22 (permalink) Old 03-04-2018, 01:25 PM
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U joints are inexpensive and easy to DIY. I use a ball joint press, but they can be easily done with two sockets and a big vise or C clamp. For a street driven car: Eaton, not a Detroit Locker.

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post #22 of 22 (permalink) Old 06-02-2018, 09:33 PM
 
 
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I recently started researching and by no means verified but the table i saw had 2.73 all over 1965.
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