So this has little to do with the other current 8.75" narrow rear end thread, but got me thinking.

I'm wondering, does a narrowed 8.75 give the center section a tougher time in high HP applications, in that the narrower the rear, the less "spring/twist" in the axles, and I have never heard this as a strength criteria mentioned when we have the monthly threads on the safe power range for an 8.75"?

So we should now include narrowness of the rear in the discussion regarding car weight, tire size/width/compound, gearing, application, back brace, billet caps, etc?

I agree, the torsional distortion is a shock absorber, but how much? Would reducing the diameter mid way allow more rotation?
Bill Jenkins remarked on the 12 bolt 50 years ago that he painted a stripe along the axle, and it was safe to use until the stripe went half-way around.
!!!!

Years ago,after putting in a detroit locker, I broke 2 stock axles, both snapped right next to the splines and the only twisting was only about an inch long by the splines. I don't think the length would of matter. just my .02 worth. Race axles from DR.Diff sloved that problem!

I’m sure it’ll break somewhere else being an 8-3/4, axels are the least of the problem

I've broken two stock A body 8 3/4 axles, both broke after twisting less than 3 splines
I advice a friend who had a set of the early Mark Williams 30 spline axles and spool in his 1971 Demon two rotate the left side twisted axles to the passenger side to untwist it
It broke, shattered between the twist in the splines and the bearing end, it was a really ugly break , after about three time trails runs.
He called Mark Williams and they told him to NEVER swap axles from side to side on any rear end
He ended up buying a set of Yukon race axles instead of buying some of the better American made brands

If longer axles actually increases their torsional twist, wouldn't that promote the amount and rate of twist that takes a "set" and eventually leads to breakage?

I'm thinking along the lines of bending a wire back & forth until it eventually breaks. It's easier to bend a long wire so it will heat up faster and break sooner. The shorter wire has the same diameter, but despite the same force being used, it's harder to bend and creates less heat and fatigue. It seems that something will last longer the less it bends/twists.

But I agree with a previous post.....the 8 3/4" has other weak spots, especially the ring & pinion teeth. So anything made stronger in the "chain" of parts will reveal the weakest "link" sooner.

I also read that it's a bad idea to swap axles side to side. Same applies to torsion bars.

A narrower rear axle housing is more resistant to bending enough to steer the car; the dragster guys figured that out in the '50s.
Melrose Missile VI on big tires actually steered itself into the right lane fence at Famoso, it's even on video.
Come to think of it, the car also crossed the return road.
Whether housing distortion leads to broken axles is probably debatable, but would seem possible.
I would think that axles made of softer material could also be less brittle, yes ?

Many years ago I went to a Direct Connection Technical seminar. Tom Hoover, and Larry Shepard were the presenters and if I remember right Ron Mancini was there as well. The seminar was at Wise Speed shop in St. louis, bought my mopar bible, which I still have. So that kind of dates me I guess, anybody remember Wise Speed shop?

Rear axles came up and their advice was that axle tube flex on the starting line caused the most problems, they recommended a girdle across the back to strengthen the axle housing. All the 8 3/4 I ran I did this and never broke but one axle, and Moser said it was defective when I sent it back and replaced it no charge. As others mentioned most of the problems I have seen on other cars have been the ring and pinion breaking. I think the axles available today are just about bullet proof.

Why narrow a weak rear ? Lol
Any thing with decent power will destroy an 83/4 just because of housing flex alone .
What’s next ? Pinion angle ? !
Lmao

When an 8-3/4 center section breaks, I believe a lot of it has to do with the housing flexing which then allows the axles to essentially act as pry bars to distort everything in the case. The shorter the housing is, the less leverage the ends have on the center section, effectively strengthening the overall package. (My theory).

After breaking a relatively stock setup a couple of times, I finally backbraced the housing, installed an MW steel cap, and went with a 35-spline spool and axles. It’s still the stock length, and I’ve been beating on it for a number of years now with no issues.

Maybe my concern was not clear enough. It does not center (pun) around axle strength or breakage, its more about the hit, or lack of an axle shock absorber effect a shorter axle has, on what many consider already a "weak" 8.75, meaning the possibility a narrower housing has inducing greater shock loads on the CENTER section than a longer axled set-up.

The weld-in brace is almost a must if drag racing a 8-3/4. I worked on a car that did monster wheelstands past the 60' and only had a 8-3/4 rear with ladder bars and wheelie bars. Still there after 20+ years. Guy liked the rear end because he could make fast gear changes at the track depending on traction, running 1/8, 1/4, etc. The original 8-3/4 that was in the car broke because it didn't have the brace. The housing twisted and an axle broke. Changed the rear end with the braced one and has been fine since.

90% of the rears that I use are 8 3/4 but I also have a 9" in my Rampage.. on the race car it is shortened
and I have used ladder bars and a 4 link.. large dia axles on all of them I put a line on them the full
length to measure twist.. the biggest issue has always been that the axles will twist at the splines.. I
have seen it on axles as new as 1 week old and determined that they take a set right away and tend to
stay there.. I back brace right to the end of the housing.. if you look at a stock housing with leafs you
will see that the housing bends at the outer edge of the leafs(thus the brace on mine going full length
of the housing).. I have only broke 1 8 3/4 of all the years racing and I leave very hard 1.19 60