Actual torque ratings or sound theory, how much was that small change supposed to help?

 

keep it under 250hp...

 

It doesn't sound like much but it does make a difference. The 8.5 10 bolt and the 12 bolt only have 3/8 inch difference between them. There is only 1/8 difference between the 12 bolt and 9 inch.

 

Biggest improvement was the change to 28 spline axles

 

Fail. LS1 guys are putting 500 hp through 7.625s, and this does not answer the question

 

Because once they upsized the ring gear, the 26 spline shafts became the weakest link, then once they upsized the shafts, the ring gear size was once again the weakest link. Still does not answer the question.

 

The 12 bolt has never been proven stronger than an 8.5 with the same spline axles. The Ford 8.8 is proven stronger than the 9 inch and the 12 bolt. So this is not very helpful.
Does no one have the numbers or the engineering formulas?

 

So you're trolling? That seems to be the answer.

You just said something was "proven," but I don't see any "data" on how the 8.8" is stronger than the 12-bolt or the 9" either? Where was that study done? Tehcnically, the same is true of the conventional wisdom. With the notable exception that it bears out in practice of people racing who would rather not have a broken rear end than be right about the proof of 8.5 vs 12-bolts.

The bigger the gears, the stronger the gear set. The stiffer the case, the stronger the rear end. Stiff case + big gears = strong rear end. (Ever see the MW 11" ?)

Almost all of the things we "know" (like 9" + rears are stronger) are anecdotal and empirical. We know, because thousands (maybe millions) of us have run the parts and blown them up, then found ways to not blow them up. There are far too many variables for most people to make anything that looks even remotely like scientific method happen with this stuff. You simply can't control for everything.

The only thing you could do, with unlimited time and resources, is to build rear ends for the same car with the same brand (and allow) gears, axles, and bearings. All with the same size/spline axles. Then run them all in the same day on the same tires.

And there will still be things you can't control for, like the setup tolerances in the rear ends.

Or, you could just stop worrying about being "right" and having the numbers so that you can say, "Well, actually ... " And save yourself thousands of dollars and hundreds of hours and simply accept the empirical evidence of countless racing sessions that rear axle A is stronger than rear axle B 99.999% of the time.

If you want to be technical, nothing is ever truly proven. But if you're insistent on being right, by all means use an 8.5" 10 bolt in stead of a 12 bolt or a 9" and enjoy.

 

I completely disagree with that. The 12 bolt is stronger than the 8.5. Axle splines have nothing to do with this. The ring gear diameter has always been the one thing that makes the most difference in the strength of a rear end. Yes, a 28 spline axle is going to be stronger than a 26 spline axle, but a 7.5 with 28 spline axles is no where near as strong as a 8.5 with 28 spline axles. Any increase in the diameter of the ring gear will make the rear end stronger. You can always upgrade axles, but you can not upgrade the size of the ring gear. You must step up to a better rear end to get the larger ring gear. It's simple physics, the longer the lever (radius of the ring gear) the more power it can transfer.

 

Incorrect!

The weakest part of these rears is the ring gear, followed by the pinion, then the axles.

I did wipe one out by spinning the pinion race in the housing, causing damage that was unrepairable, but never heard others having the same issue.

When one goes it is majority of the time a ring gear failure - if you go by the numbers.

 

I'll make it simple, not enough to matter.

 

I broke a ring gear in one 7.625" with 26 spline axles. Axles didn't fail
I broke pinion gear in another 7.625" with 26 spline axles. Axles didn't fail
I now have a ford 9" with 31 spline axles. No failures.

The ring and pinion gear sizes are the main things to strength or weakness of a rear end. Then I would say housing and next axles.
Any increase to ring gear sizes adds some strength. How much, I can't say but every little bit helps.

 

Why chime in since none of you know?
Curiousity Isn't trolling, or there wouldn't be a sub-forum for history / originality. And there's a production-housing max-effort 8.5 living at 900 RWHP, in a 3500# car with a trans brake on drag slicks, while a Strange 12-bolt in the same car broke without the trans-brake, on drag radials, so how is the 12- bolt stronger? It isn't.

 

If you want a complete scientific thesis on this subject you'll need to look elsewhere as most here can not give you that but .375 (3/8ths) difference in the 8.5 and 12 bolt ring gear isn't much. It's similar to failures in the 7.5 vs 7.6.
What I can give you is almost 35yrs of experience building/servicing/racing and even blowing up rearends of all different types.
Any rearend can break for any number of reasons, casting flaws, machining issues, clearance issues, bad bearings, axles, internal diff issues, ring/pinion problems or even assembly issues.
A "weak" rear could live forever behind insane power and a "built" rearend could blow right off the bat with low power and no real reason.
Build the best you can. If you are worrying if a .125 bigger ring gear is enough to be safe (or whatever reason), you are doing it wrong.

 

Now that I think of it, why did I bother. Go find an engineer and ask him.

 

Right. And there are people running 10s on a T5. But that doesn't mean it makes sense or it's a good idea to try.

You know what it takes to find this out, as it's been discussed by several people in this thread. If you want real data, you're going to need a budget, a lot of parts, and a lot of time, and to go out and collect it yourself.

We have the anecdotal/empirical evidence for which rears are stronger.

 

Why ask the question, when you don't have both lined up in preparation of making a purchasing decision?

 

There is no reason I can see, for me to read anything any of you have posted since I last posted in this thread, since if any of you had any answer close to correct you would have posted it to begin with. It is stressful watching you boys behave like you are still in grade school.
PLEASE, for everyone's sakes, from now on lets all stick to correct tech facts, independently verifiable, before drifting into opinion, which should be identified as such, before getting into it.

 

Wow. So you started this whole thing just to hear yourself talk then?

What were you expecting? Someone to have a peer-reviewed study vetted by an academic publication on the as-tested strength of the popular rear axles used in drag racing?

Your focus on the superiority of your position and accusation of others doing exactly what you're guilty of in this thread is borderline ridiculous. How about this; do not ask questions that you don't want the answer to.