Pinion Height

[Lincoln]

I was looking at numbers tonight (for shits and giggles) and did a drawing so I could see the difference in pinion height when applied to drive shaft angles.

What I was thinking was since most of the time the pinion is rotated to set the angle to 0 degrees at the diff yoke that the actual height of the driveshaft doesn't change that much except in extreme cases. My theory was somewhat true.

What I did was took some ruff measurments from my junk and turned each housing up to set the driveline angle. I took a measurment to the centerline of the pinion joint and then one at about the midpoint between the centerline of the axle and the t-case output. The below is skewed a little because I did not take into account the way the CV curves the angle at the output. The measurements were to the yoke. All of the pinion offset and lenths were based off the info in True Hi9's site and I assumed a daytona pinion support for both the Hi9 and Low 9.

Centerline of axle to t-case output - 45"
Ground to centerline of axle - 17"
Ground to centerline of t-case output - 28"

The yellow looks like pink in the pic. I'll let you decide what that means.

 

[GSequoia]

So what is this saying?

You want a Hi-9?

It's so cute when Lincoln posts up to try to look smart

 

[Lincoln]

Of course I want a TrueHi9 but I need to justify it with numbers first. It's the accountant in me.

 

[CRASH]

Wow, your first tech post ever......how does it feel?

TH-9 is the bomb. Not only is way out of the rocks, but it keeps your CV alive and happy running at minimal angle.

 

[Root Moose]

Of course I want a TrueHi9 but I need to justify it with numbers first. It's the accountant in me.

On a budget, I'd say a HP 60 might be the way to go... But between that and a Hi-9 you'll probably be splitting hairs cost wise at the end. Time = money too. The 9" is stronger, but is it necessary? I don't wheel the south west so for me it'd be negligible.

For us lightweight wheelers, I'd say there isn't much difference in the LP stuff. Sure, the 9" is a touch lower but once rotated up there isn't a huge difference. I like 44s, just because I have a few lying around behind the barn. Have yet to break one.

 

[Lincoln]

Being the dumbass I am, I was trying to justify running a low 9 to get me by a while then swap it out for a Hi9 later to spread the cost some. I would have to build the low 9 as something that could be sold easily.

I'm thinking a better route would be to get a Hi9 with a spool and if I felt the need to swap it for an ARB later. But if I get a spool I would probably want 40 spline shafts which destroy's the ARB plan.

It won't matter for a while now. I bought a safe tonight and that took a good wack out of my axle budget.

 

[David Taylor]

Being the dumbass I am, I was trying to justify running a low 9 to get me by a while then swap it out for a Hi9 later to spread the cost some. I would have to build the low 9 as something that could be sold easily.

I'm thinking a better route would be to get a Hi9 with a spool and if I felt the need to swap it for an ARB later. But if I get a spool I would probably want 40 spline shafts which destroy's the ARB plan.

It won't matter for a while now. I bought a safe tonight and that took a good wack out of my axle budget.

Hi9 will tell you not to do a 40 spline. Bearings get to small. I tried when I bought mine.

 

[Lincoln]

Hi9 will tell you not to do a 40 spline. Bearings get to small. I tried when I bought mine.

My decisions just keep getting easier.

I have to know. Since you an Paul are the weight nazi's how much weight did you save by gun drilling your shafts? For $100/pr I think there is still a good 10-15 lbs weight savings to be had.

 

[David Taylor]

My decisions just keep getting easier.

I have to know. Since you an Paul are the weight nazi's how much weight did you save by gun drilling your shafts? For $100/pr I think there is still a good 10-15 lbs weight savings to be had.

Just what is "gun drilling"

For 10-15 pounds I would through down a Franklin in a heartbeat.

 

[XJ_ranger]

Just what is "gun drilling"

For 10-15 pounds I would through down a Franklin in a heartbeat.

the method of making gun barrels from solid stock - can be applied to axle shafts with out much of a strength reduction...

taking 1/2" or 3/4" out of the center of your axle shafts, then putting an epoxy plug at the end to keep dif fluid in would save a considerable amount of weight, and not reduce strength too much...

with the torsional loading that axle shafts recieve, the greater strenght comes from having the larger diamater shafts rather than just plane having more material...

looking at the equations:

for a solid circular piece loaded in pure torsion -
the polar moment of initria is:

Ip=(pi*r^4)/2 or (pi*d^4)/32

for a hollow tube (gundrilled axle shaft)
Ip=(pi/2)(r2^4-r1^4) where r1 = Inner Diamaiter after drilling and r2=outer diamiter...

both of these are applied to the torsion formula:

Max Shear Stress = applied torque * Outer radius / Ip
and obivously the lower the max stress, the better off you are... but running the numbers, the strenght isnt all that much decreased...

here is a pic that shows the subscripts in a little easier to understand fasion -

Thank god for strength of materials...

though if youre running hardened shafts, it may be hard to talk a machinist into doing that to his tools...


oh and Lincoln - it makes me sick to see a picture showing that i could gain pinion clearance by going to a LP60... Fawk my LP 9... skip this step - believe me - it sucks!

 

[Captain Ron]

Byran, I think you're missing the actual failure mode.

Look at the geometry of an ASE straight involute. Deformation here is where the problem would be long before a purely torsional failure. I have seen very, very few hollow involutes. Sure, lots of threaded ends, but not hollow without support in the types of potential shock loading situations involved with automotive applications.

Another thing you touched on. Gun drilling and broaching prehardened steels is highly impractical at a readily accessable level. A half inch gun drill job in a 35 spline shaft is simply not going to remove enough weight to make it worth the cost. It can be done, but me thinks you'll be paying far more than a reasonable shop rate for the work.

--ron

 

[Lincoln]

I order some Moser shafts for a kid a few months ago and noticed this on their site:

Gun Drilling (33, 35, or 40 spline only) 100pr

Get your calculator out and give use some weights. They told me they stop about 1" short of the bearing journal. I believe they only drill out the core material which shouldn't be that hard anyway.

 

[GSequoia]

huh huh huh, you said hard, huh huh huh

 

[XJ_ranger]

Byran, I think you're missing the actual failure mode.

Look at the geometry of an ASE straight involute. Deformation here is where the problem would be long before a purely torsional failure. I have seen very, very few hollow involutes. Sure, lots of threaded ends, but not hollow without support in the types of potential shock loading situations involved with automotive applications.

so with 35 spline stuff its the splines that fail before the shaft its self? i could see where it would deform inward much easier than the pure torsional twist failure...

and another thing to think about would be the shock loading like when airing the buggies out en route to the trail, and the side loading with the hollow shaft...

im not trying to say its the best idea or worthwile, more that it can be done, and that possibly lincoln does know a little about something, and it is a viable way to save weight...

i mean Ron - I installed one of your rear alxe shafts and that sucker was heavy... for the Mini Baja here at Sac state, we are going with tube for our front axle shafts, sure its an extreme ultralight and under powered to boot, but the concept should work...

-Byran (as my name is aparently spelled)

 

[CRASH]

I really think gun drilled shafts in off-road apps should be limited to full floating axle assemblies. This removes the side loads and deflection loads, and makes Opies calcs much more valid.

 

[FarmerMatt]

While you guys are at it you might as well cross drill them too. It works for rotors, why not axle shafts. It'll also keep them cooler to boot!!

 

[XJ_ranger]

While you guys are at it you might as well cross drill them too. It works for rotors, why not axle shafts. It'll also keep them cooler to boot!!

yeah! no more Axle Shaft Fade under extreme throttle aplications anymore!

 

[Root Moose]

Removing weight is a good thing but removing it from near the lowest part of the vehicle may not be the best place. What's ~15 pounds? If it bugs you that much go on a diet.

My experience with "light" axles is with Samurai gear (basically a scaled down Toyota mini-truck axle). I'd prefer more weight down low.

$0.02.

 

[Root Moose]

yeah! no more Axle Shaft Fade under extreme throttle aplications anymore!

Oh c'mon, EVERYONE knows that fire slotted shafts are better than cross drilled!

 

[Lincoln]

Questions for the smart people.

I'm not sure how deflection and side loading comes into play unless you gun drill through the bearing journal. I could see the end at the splines crushing easier but I don't think there is that much load there.

I've always thought that tube is stiffer than solid stock within reason. Say a 1.5" piece of solid stock vs. a piece of 1.5" OD x .5" wall tube. Or is that just the differences in materials? I'm still not sure that would even matter, it still relates to the above.

If the heat treating goes in 1/4" how much strenth does the core material actually provide. Gun drilling doesn't (or shouldn't) remove any of the treated material except at the splined end if you are using a semi float shaft.

If the shaft isn't drill through the bearing journal I can see how Ranger's math applies.

Since I'm "correct term" stupid am I correct in thinking Ron is talking about the end collapsing at the splines?

Oh and Moose, I think even with 1/4" tubes the housing weighs more than two sami axles.