H3 High-angle CV Axle Theory

[Sledder10]

So stumbled across some sick extended-travel CV axles for LB7-LMM Duramax's. They use a telescoping shaft and 8-ball joints, effectively doubling their maximum working angle compared to the stock tripod/tulip plunging joint. and they're only $200 a pop!! I thought, "dang, that must be nice. I wish our only extended-travel CV option wasn't $4,500 per side."
I got a little too curious and started brainstorming what it might take to make those DMax shafts work in our H3 application. The most obvious barrier to that is the fact that the 2500's shafts inner joints are a 6-bolt flange mount that bolts to a stub shaft that then couples into the diff. "Could I cut off that flange end and friction-weld an H3 splined shaft on? make a shorter/longer shaft? use differently splined shafts for the hubs?" I was thinking of all the possibilities, and how I would go about asking my school's shop manager to help me make some chop-shop CV axles.

So I looked up what spline count the LMM's stub shaft is: 28 spline--the same as our 7.6". "huh, that's interesting, but there's no way the hub splines will match." So I then looked up the 2500 hubs and they are 33 spline. I looked up our H3 hubs: also 33 spline... and the axle nut is even the exact same M24.
I searched around and found that the DMax shaft's overall compressed length--shaft end to flange mating face--is 21.75". A few inches shy of our ~25.4". But aha, that stub-shaft and its flange takes up some space as well. I'm estimating 2-3ish", as the stub shaft's overall length is advertised as 5" and a couple of those inches will be inside the diff. Might be be a little shy of our 25.4". But if you throw in a small CV-flange spacer (which is apparently common for lifted vehicles with flange-mount CV's) you could easily make the overall compressed length perfectly 25.4".

Maybe this has already been done before??? I can't possibly be the first to notice this.

I am no expert on this stuff; so please let me know if i'm crazy or completely missing something that would bar this theory from working. Currently my main concerns are the actual diameter of the 2500's stub shaft's spline portion compared to that of our CV axle's. They're both 28 spline but IDK if that automatically implies the same diameter and whatnot. I'm also concerned if the 2500's stub shaft would seal up in our diff properly and not leak gear oil.
And if anyone with an H3 also happens to also have a '99-'11 (i think those are the right years) GM 4wd with 6-bolt flange and 28 spline stub shafts, would you be willing to take out a CV axle stub shaft and check if it fits into your H3 diff? If it fits perfectly and seals up... I don't see why this won't work. And that would be huge news for lots of us.
Let me know what y'all know or think about this crazy theory.

https://www.drivetrainshop.com/GM_7_5_7_625_s/108.htm
https://www.drivetrainshop.com/GM_8_25_IFS_s/111.htm

 

[amrg]

Is there a taller one of those? Being 4" shorter the angles will go big on the cvs earlier since you have a shorter leaver. But they do have double the angles so why not.


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[Sledder10]

Wait a second. This popped into my head as I was trying to fall asleep last night. the H3's axle 25.4" compressed length is from tip-to-tail, like the very tip of the threaded & splined shaft in the hub, all the way to the very tip of the splined shaft that's in the diff. So if you theoretically were using a flange-mount CV with a flanged stub shaft, the equivalent measurement would be from the tip of the threaded/splined shaft in the hub all the way to the tip of the threaded end of the stub shaft that's in the diff.
Meaning, you would want your total compressed length of CV axle PLUS the entire stub shaft to be 25.4". These stub shafts are advertised as being 5".... i haven't found a dimensioned diagram yet. But we might be in trouble, as 21.75 + 5 = 26.75".
Ideas? knowledge?

 

[amrg]

Is there a 1.5" shorter one? Assuming it plugs into the diff and uses the same axle seal, it may work.
But overall, are those cvs stronger than the H3s cvs or weaker?

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[Big2dabank]

Thanks for posting this. I have not seen these yet. This is a great replacement for my H2. I am constantly having CV joint problems.

 

[amrg]

I dont know if the outer diameter is different, but the H2 ones are 33 splines and use the same nut. Rockauto shows them to be 17" long, so with the stub shaft thats 22" long, will need a 3" spacer though.
Here is the high angle one for it
GM8026XTT

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[atvspeed4]

Stock front diff is 28 spline for H3. Stock 2011+ 2500/3500 GM is 30 spline. You dont want to run a CV that short using a spacer you would have crazy axle plunge and vibration


The stub shaft you posted is for a 1500 which is a smaller 6 bolt flange and 28 spline as you mentioned.

Ive only broken one OEM CV shaft (ruined many china ones) but definitely destroyed two front diffs so I think this is chasing the wrong problem

 

[Sledder10]

I dont know if the outer diameter is different, but the H2 ones are 33 splines and use the same nut. Rockauto shows them to be 17" long, so with the stub shaft thats 22" long, will need a 3" spacer though.
Here is the high angle one for it
GM8026XTT

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Everywhere I've seen shows the Trackmotive GM8026 as being 21.73" overall compressed length. the XTT seems available to the US only thru rockauto, but the ET (which seems identical) is available on many sites. THey use the same graphics as the DMax website so I'm guessing that DMax is just selling trackmotive units (possibly with better boots?).

 

[Sledder10]

Stock front diff is 28 spline for H3. Stock 2011+ 2500/3500 GM is 30 spline. You dont want to run a CV that short using a spacer you would have crazy axle plunge and vibration


The stub shaft you posted is for a 1500 which is a smaller 6 bolt flange and 28 spline as you mentioned.

Ive only broken one OEM CV shaft (ruined many china ones) but definitely destroyed two front diffs so I think this is chasing the wrong problem

I have an open front diff so blowing that isn't a major concern. Also currently the issue with using these shafts is it being a little loo long now, as my hasty original calculation didn't account for the length of stub shaft that would actually be inside the diff. So really the joint would only be a liiiiittle bit farther from the diff. Yes there would be a little more plunging action, but this shaft design allows for a lot more unproblematic plunge than a tripod joint. but this extra 1.25ish" is probably going shoot this idea down unless there's a way to easily shorten the axle shaft. Maybe slide the two halfs apart, cut 1.25" off the inner half, and slide it back in? I've never had one of these apart before so IDK.

 

[amrg]

Probably a better idea would be to cut the stub shaft 1.5" and respline it (essentially making the middle section shorter). But that will add to cost.
Assuming the numbers you got are spot on.

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[Sledder10]

Probably a better idea would be to cut the stub shaft 1.5" and respline it (essentially making the middle section shorter). But that will add to cost.
Assuming the numbers you got are spot on.

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Possibly, but that stub shaft has to be long enough to make enough spline contact, and also that retaining ring has to snap in place.

 

[amrg]

From my end of the screen looks like it!

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[atvspeed4]

I have an open front diff so blowing that isn't a major concern. Also currently the issue with using these shafts is it being a little loo long now, as my hasty original calculation didn't account for the length of stub shaft that would actually be inside the diff. So really the joint would only be a liiiiittle bit farther from the diff. Yes there would be a little more plunging action, but this shaft design allows for a lot more unproblematic plunge than a tripod joint. but this extra 1.25ish" is probably going shoot this idea down unless there's a way to easily shorten the axle shaft. Maybe slide the two halfs apart, cut 1.25" off the inner half, and slide it back in? I've never had one of these apart before so IDK.

Sounds like you are new to the H3 platform. My "blowing up" of the diffs were both open. Locked or unlocked is not the problem its the tiny ring gear, pinion gear and aluminum housing.

 

[amrg]

For arguments (discussion actually) sake,

High angle cvs
Adjustable ucas (for camber) with higher articulation ball joint
Tie rods with heims

Can you just cut the uca metal stop 1" down and get more wheel travel upfront while being leveled to 24" and not worry about those parts for some time?

As for the diff, agreed. A CI diff with OD bushings is an upgrade but not bullitproof, but you make do with that. Im sure having more travel upfront reduces some of the bounce and may reduce the situations the diff blows up in.

Not a suspension guy, but I dont mind trying sometimes.

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[Sledder10]

Yeah you're right. I don't even an H3, actually. I've got a 2008 GMC Canyon that I did the H3 front suspension swap on. H3 arms, knuckles, hubs, brakes, CV axles, sway bar (that doesn't even get used, lol), shocks, all that stuff. So any questions I have about the front end, I ask the H3 folks. But anyways, after some digging I found some somewhat-useful cutaway and cross-section drawings of other ball-spline (telescoping shaft) style CV axles like the one in question. The drawings I've seen show some like clips or rings or seals looking things on the end of the inner shaft. I'm guessing that cutting those off to make the inner shaft shorter would probably f*ck it up. you'd also have to cut the outside tube, so it doesn't impact the CV joint when compressed. There looks to be some seals on the end of that one too, so keep grease in it. Cutting the shafts is probably a no-go unfortately. I will send DMax store an email inquiring about all this to confirm. If its true, then the only way this works is if they can easily make some 1.25" shorter shafts and throw their normal joints on and send em. If it turns out I'm wrong and that I could just cut the shafts shorter, we're in business.