Differential Differences??? 12 Bolt / 10 Bolt

[Jamie F.]

I am very familiar with the typical Chevy 10-Bolt, 12-Bolt rear ends.
I always assumed that on Corvettes the HD rear-ends for Big Blocks had the 12-Bolt carriers (12 bolts holding the ring gear) like the 12-bolt standard live axles, and small blocks had the 10-bolt carriers. Hence the axle code differentiation between 350/427 on C3's.
Am I correct?
It doesn't seem like anyone out there selling gears or carriers on ebay and the other sites differentiate between the two. They just list gear ratios and years.
Also can someone tell me if the housings are different between the two? Or will any C3 housing accepting either carrier?
Inquiring minds want to know...

[Joe L.]

Re: Differential Differences??? 12 Bolt / 10 Bolt

I am very familiar with the typical Chevy 10-Bolt, 12-Bolt rear ends.
I always assumed that on Corvettes the HD rear-ends for Big Blocks had the 12-Bolt carriers (12 bolts holding the ring gear) like the 12-bolt standard live axles, and small blocks had the 10-bolt carriers. Hence the axle code differentiation between 350/427 on C3's.
Am I correct?
It doesn't seem like anyone out there selling gears or carriers on ebay and the other sites differentiate between the two. They just list gear ratios and years.
Also can someone tell me if the housings are different between the two? Or will any C3 housing accepting either carrier?
Inquiring minds want to know...

Jamie-----


Your assumption is totally incorrect. 1963-79 Corvettes use neither a Chevrolet "10 bolt" or a "12" bolt rear gear unit. Those two units were used on other Chevrolets, but never Corvettes. 1963-79 Corvettes use a special, unique rear unit, although it does use a "10 bolt" configuration ring gear. Most components of the Corvette rear gear unit are NOT interchangeable with regular Chevrolet "10 bolt" or "12" bolt rear unit.

1963-79 Corvette rear gear units are all very similar although there were a few mostly minor changes over the years. The ONLY difference between units used for big block and small block applications for any given year was the type of yoke axle used (u-bolt versus cap). Otherwise, the units were identical for big block and small block. Some 1970-79 small blocks also used the cap-type axles.

Some small blocks were available without positraction; all big blocks were equipped with positraction.

[Jamie F.]

Re: Differential Differences??? 12 Bolt / 10 Bolt

Joe,
Thanks for setting me straight! And the knowledge imparted.
Regards,

[Gary R.]

Re: Differential Differences??? 12 Bolt / 10 Bolt

Joe is correct, no surprise there. If I may add there are some differences to the vette diff's over the years. Some were improvements others were not.

As Joe stated the RG were/are unique to corvette. Presently there are only a few aftermarket suppliers of this gear set for the 63-79 iron units.

The side yokes in BB used the caps and are referred to as "HD" yokes. The U bolts used in SB cars.

Posi was an option until 1970. The early posi cases(63-64) were Dana's and were weak. Many by now have been blown up and replaced with Eaton posi's. Parts are rare and not worth rebuilding.

Eaton posi's were used from 65-79. The first design, '65-68, had a small sq window in addition to the large window. These often were prone to cracking and if not found would split apart like and egg and break everything inside the carrier.

The later, 69-79 Eaton posi cases are much better. They crack as well but in general hold up much better. The spiders used from 65-70 are 10-18's referring to the # of teeth. They're ok but the later 10-17's are much better. For HP use aftermarket heat treated 10-17's are available. The clutches used in the 65-70 are sollid steels and much better then the 71-79's slotted clutches that I coined the phase "snowflakes" I've found many posi's with broken snowflakes.

All Eaton posi's use 4 springs and 2 preload plates. These in addition to spider backlash during setup will cause clutch hammer on a lot of cars. I set them up without these springs/plates and they out perform the stock setup with less wear.

The side yokes used from the 75-79 period are soft and wear out fast. If left unchecked the yoke will wear down and grind the housing(carrier) by the seal and wreck it. I've been able to save some that didn't hit the seal but once the seal is torn up then the housing is shot. When I find the time I'm going to machine some repair sleeves to save these worn housings.

Also of note, the RG bolts used on the late 76 to 79's are flanged head botls,no washers or loctite. They tend to back out from the RG more then the earlier shouldered RG bolts and hardened lock washers. ARP makes a similar 12 pt bolt with shoulder that I've used on a lot of diff's if you get to that point.

Hope this helps

[Jamie F.]

Re: Differential Differences??? 12 Bolt / 10 Bolt

Thanks Gary for the info! Lots of good information there!
Would you know if the input yoke is unique to Corvette, or is it shared by other GM rearends? Are there any differences in these yokes?

[Joe L.]

Re: Differential Differences??? 12 Bolt / 10 Bolt

Thanks Gary for the info! Lots of good information there!
Would you know if the input yoke is unique to Corvette, or is it shared by other GM rearends? Are there any differences in these yokes?

Jamie----


The pinion flanges were NOT unique to Corvette; they were shared with other Chevrolet models. Basically, there were only 3 flanges used from 1957-79 FOR CORVETTES. These were:

1957-64= coarse (10?) spline, 1280/1310 series u-joint

ALL 1965-67 & 68-70 with manual trans= fine (26) spline, 1280/1310 series u-joint

68-70 with THM and all 71-79= fine (32) spline, 1330 series u-joint

[Joe L.]

Re: Differential Differences??? 12 Bolt / 10 Bolt

Correct me if I'm wrong, please.

For decades, now, I've been under the impression that 63-82 Corvette differentials are based on Dana-44. Ring and pinion, carriers, posi parts, etc.

This assembly is a common, robust, inexpensive to manufacture, with high torque capacity. Commonly used front axle assembly in 4X4 domestic trucks in the 60s-80s.

I believe the diff internals in my 85 4+3 are Dana 44 as well.

Dave-----


Well, if you've been under that impression for decades then you've been under the wrong impression for decades. Pretty much, anyway. 1963-79 Corvette rear gear assemblies are NOT based on the Dana 44 or any other Dana design. They are of completely GM design and are unique to 63-79 Corvettes in most respects.

1980-82 Corvettes do have a Dana 44 based rear gear assembly.

There exists NO parts interchangeability of the 63-79 Corvette rear gear assemblies and the 80-82 Corvette rear gear assemblies.

1984-96 Corvettes have either a Dana 36 or Dana 44 rear gear assembly. Generally, those equipped with manual transmissions have the Dana 44; those equipped with automatic transmissions have the Dana 36. There may be some exceptions to the aforementioned, but the Dana 36 and Dana 44 were the only rear gear assemblies used for 84-96.

[Jamie F.]

Re: Differential Differences??? 12 Bolt / 10 Bolt

Joe,
Thanks for the detailed info. I guess it brings up another question;
You stated:

ALL 1965-67 & 68-70 with manual trans= fine (26) spline, 1280/1310 series u-joint

68-70 with THM and all 71-79= fine (32) spline, 1330 series u-joint

What is the difference between the 1280/1310 u-joint and the 1330 joint?

If I have a '69 manual transmission and I by a original Ring & Pinion from a '70 Automatic car I guess I would need a different pinion flange and,,,
What type of U-Joint???
Thanks!!!

[Joe L.]

Re: Differential Differences??? 12 Bolt / 10 Bolt

Joe,
Thanks for the detailed info. I guess it brings up another question;
You stated:

ALL 1965-67 & 68-70 with manual trans= fine (26) spline, 1280/1310 series u-joint

68-70 with THM and all 71-79= fine (32) spline, 1330 series u-joint

What is the difference between the 1280/1310 u-joint and the 1330 joint?

If I have a '69 manual transmission and I by a original Ring & Pinion from a '70 Automatic car I guess I would need a different pinion flange and,,,
What type of U-Joint???
Thanks!!!

Jamie-----


The difference between the 2 u-joints (and width of the saddle on the yokes) is the finger width. The 1280/1310 is 3-7/64" wide; the 1330 is 3-5/8" wide. The bearing caps are the same OD on both joints.

The ring and pinion are the same configuration regardless of what type yoke is used. So, if you are just buying a ring and pinion, all you need to know is that you need a 65-79 style. The pinion yoke you would then need would be GM #3878972. Unfortunately, it's GM-discontinued. An equivalent might be available from other sources like Tom's Differentials or Randy's Ring and Pinion.

[Jim T.]

Re: Differential Differences??? 12 Bolt / 10 Bolt

Gary Ramadei as Joe mentioned in his post some SB used caps. My 70 original owner 350/300 turbo 400 still has the original caps it left the factory with.

[Jamie F.]

Re: Differential Differences??? 12 Bolt / 10 Bolt

Joe,
Didn't you say that some pinion flanes/yokes have 26 splines, and some have 32 splines?
Would the pinion gear also have to have either configurations?
So they would be different?
I'm confused.

[Wayne M.]

Re: Differential Differences??? 12 Bolt / 10 Bolt

Joe,
Didn't you say that some pinion flanes/yokes have 26 splines, and some have 32 splines?
Would the pinion gear also have to have either configurations?
So they would be different?
I'm confused.

Jamie -- I believe we're confusing yoke locations here. Here's the diff input yoke off a '65; it has 30 splines (not 26). The '986' is the cast # for the GM part #3878972. Joe L. has said (and questioned his count) 10 splines for the early diff yoke (up to '64). Wish I'd paid more attention when I had one in my hands, but I'd say 14 splines for that one [part #3741822, with cast '823']; and yes, it required a different pinion gear. Don't know what the TH400 diff yoke spline count is.

Now the 26 and 32 spline yokes are for the OTHER end of the driveshaft (trans output shaft).

[Joe L.]

Re: Differential Differences??? 12 Bolt / 10 Bolt

Jamie -- I believe we're confusing yoke locations here. Here's the diff input yoke off a '65; it has 30 splines (not 26). The '986' is the cast # for the GM part #3878972. Joe L. has said (and questioned his count) 10 splines for the early diff yoke (up to '64). Wish I'd paid more attention when I had one in my hands, but I'd say 14 splines for that one [part #3741822, with cast '823']; and yes, it required a different pinion gear. Don't know what the TH400 diff yoke spline count is.

Now the 26 and 32 spline yokes are for the OTHER end of the driveshaft (trans output shaft).

Wayne and Jamie------


Yes, I don't know why I said 26 and 32 splines in my previous post. My thinking must have gotten "reversed" for a few minutes. The 26 splines applies to the transmission output yoke for all 65-67 and 68-70 with manual transmission. The 32 splines applies to the transmission output yoke for 68-70 with automatic trans and most (but, not all) 1971-81.

The differential pinion yokes for ALL 65-79 Corvettes are 30 splines. All 65-67 and 68-70 with manual trans use the 1280/130 series flange and u-joint. 68-70 with auto trans and all 71-79 use the 1330 series flange and u-joint.

[Wayne M.]

Re: Differential Differences??? 12 Bolt / 10 Bolt

.... What is the difference between the 1280/1310 u-joint and the 1330 joint? ....

Jamie -- here's two old eBay pics; the 14-spline diff input (up to '64) and the WIDE 1330 U-joint (30-spline) that Joe L. describes.

Also, third pic is a better shot showing a June '65 3.70 pinion gear (RH) with the stepped shaft and the small ('64 and prior-type) crush sleeve. Compare with a Nov '65 gear (LH) from a 4.56 set; uses longer crush sleeve. Both pinion gears are 30-spline.