Broncoholic
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What is the minimum spline engagement you would want on 35 spline front axle?
Long unsupported spline sections are a weak point.
For maximum strength you want the male spline to match the female spline.
Long unsupported spline sections are a weak point.
I'm inclined to believe this as well.
I broke this (19 spline D44) RCV which had about an inch of unsupported splines. When I asked if it the length of unsupported splines were a weak point RCV stated that they were not; "Too long of splines won't contribute to the failure". I still am curious about whether it would have broken in the same spot if I was running a different drive flange that engage the full length of the splines (later found in my spare parts )
I'm inclined to believe this as well.
I broke this (19 spline D44) RCV which had about an inch of unsupported splines. When I asked if it the length of unsupported splines were a weak point RCV stated that they were not; "Too long of splines won't contribute to the failure". I still am curious about whether it would have broken in the same spot if I was running a different drive flange that engage the full length of the splines (later found in my spare parts )
You sprung for RCVs and didn't go 30 spline?
Rule of thumb is 1 diameter. So 1.5" 35 spline should have 1.5" of spline engagement. That rule gets bent all the time (drive flanges are a good example), but it's a good starting point. In general, more than that is pointless unless you need slip travel.
Originally posted by Tech Tim View Post
For maximum strength you want the male spline to match the female spline.
Long unsupported spline sections are a weak point.
This is a somewhat true, but highly misleading statement.
And you were mislead by the statement. As I said in my previous post, cut spline sections are only about as strong as a shaft of the same diameter as the root diameter of the cut spline section. It doesn't matter how much of the spline section is supported or not, the splined section will be the weak point if the rest of the shaft is of a thicker diameter than the root diameter of the spline section. A wider drive flange would have just pushed the failure closer to the end of the splines, and created even less flexibility in the shaft making it even more failure prone. That is a poorly designed shaft dimensionally and creates a less flexible shaft that results in a major stress concentration at the already weaker spline section.
It was a pretty accurate statement, just not expanded on to give all the info you wanted to see. I was just being short and to the point about spline engagement.
Most side gears in a differential are in the .75" to 1.5" thick. Stuffing a shaft in that side gear that has another 2" of spline sticking out (unsupported) is a problem waiting to happen.
Most shaft companies don't build shafts for ultimate strength; they build for ease and speed of manufacturing. Note I didn't say all, as you know, there are some great companies out there that will build shafts correctly.
The spline pic you posted from Carrol's book is pretty accurate when you get to shaft design in regards to the major and minor diameter. But as most shaft builders do not turn down the body of the shaft to a diameter smaller than the minor diameter of the spline, it is the spline that will see the majority of the stress concentration and I've seen way more unsupported long spline sections fail before a shorter splined section fail (all other things equal in the shaft design and make-up).
No, it's not. You can spline the entire shaft and it won't be any weaker than a smooth shaft with a diameter equal to the root diameter of the fully splined shaft. If the shaft doesn't neck down, as is the case with most aftermarket shafts, having that extra spline sticking out can actually help things because it will soften the stress concentration at the splines. Ideally, you want the shaft to have as uniform of a stiffness as possible.
That is completely anecdotal and lacks any real basis. Please explain the mechanism to me by which excessively long splined sections will fail before a shorter one?
If you have splines cut from the full diameter shaft that end right at the side gear/drive flange, you now have two stress risers placed right on top of each other with very little material in between to provide any give. If the splines are longer and "unsupported", you now have a section of the shaft that is more flexible between where the essentially rigid side gear/drive flange engages the shaft and the stress riser where the splines end and transition to the full diameter shaft. This helps dampen shock loads improve fatigue life, but will do noting to improve the maximum steady-state torque capacity of the shaft. It certainly is not a detriment though.
You can spline the entire shaft and it won't be any weaker than a smooth shaft with a diameter equal to the root diameter of the fully splined shaft. If the shaft doesn't neck down, as is the case with most aftermarket shafts, having that extra spline sticking out can actually help things because it will soften the stress concentration at the splines. Ideally, you want the shaft to have as uniform of a stiffness as possible.
Spline are essentially large cracks cut into the surface of the material, little reason you want them bigger then they have to be.
None of that is supported by any materials mechanics, that's all something that sounds good to people. You don't soften stress concentrations, you create paths so they don't produce cracks. Axle shafts you want to control where they twist. How I have mine cut they will twist in the areas that are profiled and not at the splines/spline ends. Spline are essentially large cracks cut into the surface of the material, little reason you want them bigger then they have to be.
Not true at all.
Those long peaks and valleys all the way down a shaft will be nightmare compared to a smooth round outer diameter.