Throughout the life of the 9" axle assemblies the axle housings got stronger and

[Qikbbstang]

stronger with supposedly the Lincoln Versailles and later 70s F-series getting the most robust axle housings by design. Comparing the 9" early axle housings to late housings it's obvious that FoMoCo added strength by tapering and triangulating the pumpkin to axle tube sections. We've all seen the weld on girdle that reinforces the full width of the rear of the axle.
   Recently I was admiring a stock based drag car that employed the usual CalTracs and and all the matching goodies that scream full race drag car that will do  wheel-stand starts. It appeared to have a stock really early 9" axle housing.  I've never heard of anyone tearing up an axle housing though I've heard of ripping the spring peaches at the axle tubes on even mild street/strip cars which twists the complete housing/pinion etc that can really mess things up. But I've never heard of anyone having a failure on the pumpkin to tube areas of the housing?................................... 

[The Magic Ratchet]

It's not common but I have seen failures at the axle tube. The only one that immediately comes to mind was my own '75 T-Bird. That was probably a 9 3/8" but they were so similar that it's hard to tell them apart except when I was working on them every day. My wife called on her way to school, complaining the car was "all over the road." Sure enough; the housing was cracked at the axle tube, the tube was skewed, and both rear tires had excessive negative camber. I replaced it with a used assembly and never had another problem with it through mine and the subsequent owner's time with it.

Lou

[TomP]

They will rip the tube, the weld on the top of the left axle tube by the center section usually. That all depends on how the housing is attached. A pinion snubber won't do that but leaf springs with any sort of bars or ladder bars will transmit the force through the tube while trying to tip the pinion up.

 The stronger housings are also heavier so the tradeoff has to be considered. I like the earlier housings with a brace.
 If jumping ramps or carrying 8,000 lb loads was gonna happen i'd want the bigger tapered housing.

[fe66comet]

I was thinking of upgrading mine for my mini Ranger project but I want to save weight so I used a small bearing housing out of my Comet. I think with four link and a lightweight chassis I should be fine.  When I do the Comet I will upgrade to a Currie fabricated housing for the extra weight and torque I am planning for. They do make 4130 housings of which would be both lighter and stronger but of course cost goes up also, the weight of the cromo housing is considerably lighter and much stronger though. Eventually I suppose the strength of the pig itself becomes an issue then a Dana 60 is a better choice as the parts for the 60 drag rear ends are all monster strong and widely available.

[machoneman]

Actually, the factory backed, Logghe, built, Ford nitro burning funny cars of yore (think: the flip top Comets of Dyno Don, Eddie Schartman, et al) at about 1,200 hp used factory housing quite successfully! 

[fe66comet]

I have heard of limits of 800 HP all the way up to 1500 HP. I suppose chassis weight, transmission type and gearing has a lot to do with it but in the end total torque capacity is the real number that limits a parts strength. Also I suppose if you have 1500 HP and the front end comes off the ground with a ton of tire spin the applied torque is much lower.

[cammerfe]

Carl Holbrook once 'pretzeled' the rear end housing on his blue Mustang to such an extent that the car sat 'dog-tracked' by several inches. But he DID win his class.

KS