sammicurr86

Like the title says. Just curious. Anyone running one with high hp/tq ratings?

Fun71

Well, the O-Type held up behind the 455 W-30 and 350 W-31 engines with manual transmissions running on the drag strip, so are making more horsepower/torque than those? If not, don't worry.

I recall one of the Daves (Bunch or Hialeah?, they ran these on the drag strip back in the day) saying he did 5500 RPM clutch dumps on the drag strip, so again, if you're not going to that extreme, don't worry, you'll be OK.

joe_padavano

Of course, the tires also matter. If you can't put the power to the ground, you aren't really going to hurt the axle, just spin the tires.

JohnnyBs68S

A lot of folks claim the Chevy 12-bolt (8.875 ring gear dia?) is the strongest GM put in any '60s vintage musclecar. But is that true?

Joe is spot on, max torque transferred by the rear gears is a function of how much traction you get.

I contend that the limiting factor of the rear end strength is not the number of bolts holding the ring gear to the differential (has anyone sheared-off these bolts??), but rather the axle splines or housing.

Certainly, a 7.5" 10-bolt (ala 3rd & 4th gen F-bodies) is way weak compared to a 8.5" 10-bolt (ala "O" and "corporate" 8.5" units), and I believe the reason for this is since the smaller ring gear applies more force on the pinion due to the torque acting on a smaller radius than in a 8.5" rear, more stress is induced in the housing (the pinion has less leverage on a small diameter ring). But the difference between the 8.5" and 8.875" "Chevy 12-bolt" is much smaller.

I'm not familiar w/ the axle spline count differences between the 12-bolt and either of the available "O" axles (28 & 31?), more splines on a larger axle the better IMO.


So, IMHO, the Chevy 12-bolt may have a slight advantage in ultimate strength vs. the "O" axle w/ 31 splines, but this is more likely due to the slightly larger ring gear diameter and possibly higher axle spline count, and NOT the 2 extra bolts holding the ring gear to the diff.

Ryan 1969 Chevelle SS396

Casey Marks at PSMCDR went 12.83 in the quarter with 4.66 gears with an "O" Type. His 1970 W31 was/is Automatic.


Ryan

VC455

That confirms what an axle specialist told me. The weak spot is the small size of the pinion shaft. For example a F**d 9" has a much beefier pinion shaft.

However, I agree that the "O" axle does have good strength.

olds 307 and 403

The pinion diameter is smaller than some of the other rears out there. But some of the other strong rears also have this flaw and hold up fine, as I was told. I was told 500+ ft/lbs is no issue. I was told 8.5" 71-72 Type C 28 spline axles stock or aftermarket will fit the 70 rear with an aftermarket posi. That alone should add a lot of strength. There is also a girdle cover available.

sammicurr86

500+hp/600+tq dynoed. I'm assuming with an automatic that's 20%-25% loss in power on a chassis dyno.

GEARMAN69

This sounds way wrong. The BOP and C 10 bolt 8.2 rears (and 7.5) have a smallish 1.438" diameter pinion. The Corp 8.5 and 12 bolt C (car) axle has a beefier 1.625 diameter and the Type O at 1.626"

The Ford 9" pinion is smaller than both at 1.313" but yet the ring gear is bigger

I am pretty sure the pinion diameter is of least concern on the Type O

As far as I am concerned the great GM Corp 8.5 was basically evolved from The Type O as it appeared as the immediate replacement in 71 while they still did the Type C thorough 72. The Type O guts of the diff are identical to the Corp 8.5 and both were bolt in axles and the 70 to 71/72 axles are interchangeable. Else where here someone mentioned maybe the carrier itself may be a touch weaker but since you can upgrade to 31 spline axles it seems to be the rears could handle a ten second A body car all day long if one ran a full spool (w 31 sp) or true trac .

My cheap mini spool type O 3.08 did a good many 1.6 and 1.7 60 fts on 28 spline axles at a heavy 4250# and did not break. A lighter normal weight car say 3400# should handle 11's but if running taller slicks I would go to 31 spline.

A taller slick 28" + is going to put more leverage against the axle versus a 26" slick.

I agree on the 600 ft lbs 500 hp reference.

I feel mine was close to that at the flywheel.

joe_padavano

The 9" has two advantages. The larger ring gear lowers loads in the pinion teeth. The added pinion nose bearing in the 9" significantly reduces pinion shaft bending loads, which are the stressing case for the pinion. These two factors are why the pinion shaft on the 9" is smaller.

GEARMAN69

That makes sense since we know than can take a hell of a load

But the 57-64 Olds Pontiac is the grand champion !!! 1.875” dia 9.3"

monzaz

14 bolt semi floater 9.5 rear has all the same diameter as the 9.3 we custom build them for camaros nova anything leaf spring. 33 spline axles we install Moser 7900 end and race axles in them.... all posi units are available for these rears. true trac eaton auburn power trax etc.

Trying to find time to custom up a A-Body version....time eludes me....
THEY are plentiful as the 4x4 guys want the FULL FLOATER 10.5 14 bolt rears which are just WAY over kill for a car rear...LOL. Jim

J D

GEARMAN69

That 14 is Bad Ace !

11971four4two

dana 60



trying
to
get

axle out

Run to Rund

Ford 9" gear sets in 9310 alloy are available with 35 spline, 1.5" diameter pinion.