anybody ever try the 26 spline axles for the 7 5/8 rearend. also how much power have you put through them????? need to know ASAP

 

Get 28s. The 26s are weak, and if you're going to step up to Moser axels anyway you're better off improving the strength. You can swap out the 26 spline side gears in your stock posi for peanuts. Or if you're getting an aftermarket posi just order it for 28 spline. If you've already got one send it back and swap it out. If you threw out the box buy a new one, then send the old one back in the new box (yes, I have done that before). Be kind and mark the new box with the correct part number so someone else doesn't get screwed down the line.

The stock 28 spline axels are considered a weak link in the 8.8 Ford rear. Most serious guys step up to 31s in that rear. You've got a heavier car that makes more torque with a smaller axel. See what I'm saying? The 26s weren't any good stock. That's why GM upgraded them to 28s as the years went on.

 

thanks for the comments. I am building a 33 spline 9" but wanted to go racing saturday. broke the stock 26's but figured the moser axles would hold up a bit better. 260 for the week end didn't sound too bad. I got the itch, wanna run it again. didn't want to wait till August on the 9".

 

33 spline? for a 9" is overkill for a street car. I only need 31 spline in my car although I may be getting close to needing 35 spline. Large axles unless you spend the big bucks for gun drilled axles are heavy and need lots of power to turn them.

A street car can easily survive on aftermarket 28 or 31 spline ford 9" axles. Even the factory ford 28 spline axles are stronger than Chev 28 spline.

 

Yeah, the problem with the factory GM 28-spline axels is that they are undercut. The Mosers aren't, and are a lot stronger, even with the same spline count. The material and heat treatment is also superior to a factory axel.

 

Stephen, nice ride, but you ever look at a torque curve on nitrous. its pretty much twice the HP increase value. After I get the car running right, thats the next stop. the other side of the story is if you can equally plant the axle on the ground, if not you could have a torque rate of near 10,000 ft-lb's to one axle. On motor yes, your probably safe, but thats got a lot to do with the suspension set up too. So what kinda torque does your car make, looks high r so I am gunna guess 650 @ 4500...or closer to 800 @5500 maybe. oh, not exactly a street car legally, OSCA type more or less.

 

tko, see thats part of the reason i was thinking of doing this for the time being. don't the 28spline and 26 spline use the same alxle bearings??, I thought they did so i figured I would be improving by just the constant DIA shaft and the fact its brand new and better quality than stock using the 26 spline.

 

Yes, they use the same axel bearings. A GM axel tapers down right after the bearing though, and then necks down again before the splines.

Ideally, a properly made axelshaft will be the same thickness as the bearing seat all the way. The splines will actually have a slightly larger diameter than the shaft (not always possible given the constraints of the bore in the differential). This allows the axel to have the maximum amount of strength. The splines are not cut into the shaft, but hobbed on a section that is larger in diameter, so the splines do not weaken the end of the shaft. This allows the entire shaft to absorb the shear load, as opposed to creating a localized weak spot at the end of the shaft, which is where the shaft would fail.

Think of an axelshaft as a spring. When load is applied it actually twists the shaft, as if you were taking the shaft in your hands and trying to twist it like a braided pretzel. The shaft slowly snaps back into shape, as long as there isn't enough load applied to push the shaft past the point where it is permenantly stretched and cannot return to its original shape. If that happens the shaft will fail in short order.

This is the reason why an axelshaft isn't through hardened. The inner core is softer, and more malleable. This allows it to spring back into shape, where a through hardened shaft would snap. Harder is not always better, because the harder outer surface is more brittle. So, the surface is hardned to prevent stress risers from forming, which would eventually cause failure. The inner core is softer to allow the shaft to twist and not fatigue, which would eventually cause failure. It's the best of both worlds. This is actually how samurai swords were made hundreds of years ago. The outer metal is folded hundreds if not thousands of times, which makes it incredibly strong, and capable of holding a razor sharp edge. The inner core is softer and flexible to allow the sword to flex and not just snap in half when it contacts another sword.

 

Good answer, but you only covered carbon steels, alloys are through hardened to bring out the strength. You were refering to yield strength or stress for the point of permanent deformation, and ultimate strength for point of fracture.

 

Not bad a guess. Dyno 2000 puts the new engine at 759 @ 5500.

Don't forget that I'm also using a 1.76 first gear powerglide. Because I don't launch in a lower gear ratio like with a TH350 or TH400, the torque multiplication isn't as high.

759 x 1.76 x 4.56 = 6091 pounds of torque to the wheels. According to the Moser web site's axle calculator, 31 spline axles can handle 7000 pounds each so I'm still under the requirement by about 900 pounds.

33 spline axles are good for 8200 pounds and 35 spline axles are good for 9600. If I was using a TH400, I would need 35 spline axles because of it's 2.48 first gear.

 

Correct, yeild strength is the point of permenant deformation. Some materials have a short fatigue life too, which is why you wouldn't run aluminum rods in a street engine for example. Over so many loading cycles the material begins to work harden, and this will lower its yield strength. Eventually the yield strength will be less than the working load and the component will fail. This isn't a problem with a high end race engine where the rods are replaced after so many passes as a matter of course, because they are changed well before they have seen enough cycles to lower their yield strength.

Typically this is only a problem with aluminum and other similar metals. The working life of a steel alloy, like that used in an axelshaft should last the life or the car and then some.

Most aftermaket alloy shafts are made from a completely different material than the stock shafts, which are actually just a basic steel. Even a lot of "alloy" aftermarket shafts are not a true alloy. In steel carbon is not an alloying element (the percent of carbon is what distinguishes steel from iron). Some manufcaturers misrepresent the material as an "alloy", when in fact it is just steel. An actual alloy like 4340 will have alloying elements like molybdenum, chromium, nickle, or manganese. The numbers give you information about the type and quantity of alloying elements. Then heat treatment can alter the material's characteristics further. You will see aluminum often noted as 6065 T6 or such. The T6 refers to the specification of the heat treatment.