Oops... I did it again (Broke another CV Shaft)

[87-Z28]

This is the benefit of staying within 2" right? That you don't overextend the CV and put all the extra wear on the suspension and steering systems.

A 5” lift at the wheel requires about 3.25” of lift at the shock for the oem LCA. The oem extended shock length is 23.3”. The max shock length the oem CVs can handle is another inch on top of that, so >24.3 is getting problematic.

Hopefully this 5” wheel lift doesn’t have a 3” shock spacer. More likely a spacer plus spring collar to add preload. Total of 3”.

with this lift you have most definitely pushed the limits of allowable shock length. But also are riding around with significant preload and thus limited your available rebound travel. This setup causes the suspension to cycle around an equilibrium ride height that is closer to the max shock extension.

I doubt that when the cv broke was the first time the suspension was fully cycled in rebound. This suspension setup will surely add significant premature wear on the CVs as it cycles and likely fail sooner than expected.

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[5GENIDN]

Staying in the 2" range certainly helps preserve the CV angle but coilover travel contributes to over extending the CV angle. Some of the aftermarket coilovers have way more travel than the CVs can handle. A spacer on top of the coilover makes the probelm worse. Limit straps should do the trick IMO.

And this is why Accutune offers a limiting shim on the Kings, because the front travel was slightly too much and put the CV in bind... So they add (if you want it) a 0.30 inch shim inside the shock to limit it's travel.

 

[87-Z28]

And this is why Accutune offers a limiting shim on the Kings, because the front travel was slightly too much and put the CV in bind... So they add (if you want it) a 0.30 inch shim inside the shock to limit it's travel.

For those that are not aware. Here is a list of shock lengths from different manufacturers. Take a close look at all of the extended front lengths. Adjusting king shocks with 0.3” shim. Notice a trend.

 

[5GENIDN]

For those that are not aware. Here is a list of shock lengths from different manufacturers. Take a close look at all of the extended front lengths. Adjusting king shocks with 0.3” shim. Notice a trend.

Seems that 24.3 is a popular limit.... with a few thinking a little more is okay... After the testing Accutune did, I liked their answer. Even kept their own in house shocks at 24.3 after all the testing.

 

[RIDE]

This is what jeep avoids by using a solid front axle. I think of all my old trucks, jeeps, FJ40, scouts and even older bronco's. A broken front axle would of never occurred to me to even be a risk.....

Funny you mention that as it took me a sec to think through why I haven’t had this issue on my lifted trucks before. Then it dawns on me the diff drops along with a lift on solid axle thus giving me the epiphany this is my first truck with cv’s. Now, If we start talking driveline angle failures, I’m well-versed there. Haha.
I’m finding this thread real enlightening tho, fo sho.

Edit for clarity: And BTW, no previous trucks of mine were Jeeps (with exception of an old Willys on our place that’s not street legal). Haha. I’m not endorsing Jeeps solid axle here in any way shape or form.

 

[87-Z28]

Seems that 24.3 is a popular limit.... with a few thinking a little more is okay... After the testing Accutune did, I liked their answer. Even kept their own in house shocks at 24.3 after all the testing.

yes indeed. According to accutune, for the kings at 24.6” under full droop, you can feel some binding when rotating the wheel by hand. Doesn’t mean the cv explodes immediately under first full extension cycle, but definitely outside the cv design parameters. And surely causing premature wear.

 

[SierraBronco]

For those that are not aware. Here is a list of shock lengths from different manufacturers. Take a close look at all of the extended front lengths. Adjusting king shocks with 0.3” shim. Notice a trend.

Shoot. We need to add Rock Krawler to this list. Front compressed 17.5” extended 24.5” as best as I could measure.

 

[BigMeatsBronco]

Diff drop for the win! the extra 1.25" DOES help reduce wear and breakage especially at the travel limits.

 

[87-Z28]

for sure. A small diff drop can be a big benefit, 1-2” or so. There is a limit though, not sure exactly where this is.

the CVs have limits wrt there operating angles and also tolerances for axial movement in extension and compression (or CV plunge). For instance, let’s call our suspension at ride height or static equilibrium optimal when LCA angle is perfectly horizontal, shock travel is at midpoint, CV angle is horizontal, and CV plunge is at midpoint.

Now when suspension cycles and LCA pivots, the CV length extends as shock rebounds (LCA moves downward). Likewise the CV length compresses as shock undergoes jounce (LCA moves upward). Likewise CV angles change accordingly.

when suspension becomes a bit unbalanced due to lift, the LCA angle necessarily increases positively downward. This induces increased CV angles but also results in increased CV length. Dropping the diff helps reduce CV angle and also helps reduce CV extension. CV gets happier because it has better angles and plunge gets back closer to midpoint.

all is good. Except now during jounce the CV needs to compress further than it did when suspension was more balanced and it may run out of available plunge at full jounce. A diff drop unbalances the CV design geometry in favor of better behavior at full shock extension. A good thing for sure. But at some point this unbalanced behavior will cause issues during jounce.

the oem CVs just have a very tight design tolerance wrt geometry. The are not nearly good enough for what most of us are trying to do.

 

[popo_patty]

There was a local guy that kept blowing CV axles with a 7" rough country. The spacer used on top of the struts is to long and rough country hasn't bothered to fix the issue. Same as running to big of a top spacer. Need to differentiate between lift and adding length to the strut.

Yea that guy eventually sold his Bronco because he thought it was junk because he snapped 3 axles. We all told him it was the massive spacer lift and improper technique (he was new) but he didn’t care and left the off-road scene. Oh well it was Fords fault and he wanted them to warranty his axles which they obviously wouldn’t do.

 

[popo_patty]

for sure. A small diff drop can be a big benefit, 1-2” or so. There is a limit though, not sure exactly where this is.

the CVs have limits wrt there operating angles and also tolerances for axial movement in extension and compression (or CV plunge). For instance, let’s call our suspension at ride height or static equilibrium optimal when LCA angle is perfectly horizontal, shock travel is at midpoint, CV angle is horizontal, and CV plunge is at midpoint.

Now when suspension cycles and LCA pivots, the CV length extends as shock rebounds (LCA moves downward). Likewise the CV length compresses as shock undergoes jounce (LCA moves upward). Likewise CV angles change accordingly.

when suspension becomes a bit unbalanced due to lift, the LCA angle necessarily increases positively downward. This induces increased CV angles but also results in increased CV length. Dropping the diff helps reduce CV angle and also helps reduce CV extension. CV gets happier because it has better angles and plunge gets back closer to midpoint.

all is good. Except now during jounce the CV needs to compress further than it did when suspension was more balanced and it may run out of available plunge at full jounce. A diff drop unbalances the CV design geometry in favor of better behavior at full shock extension. A good thing for sure. But at some point this unbalanced behavior will cause issues during jounce.

the oem CVs just have a very tight design tolerance wrt geometry. The are not nearly good enough for what most of us are trying to do.

I swear every time you post I have to read very slowly and still, my mind hurts haha. All I know is I’m still on my original CV’s after 57,000 miles and I wheel a ton. No issues but I’m careful with technique and locker usage. I treat it like my Jeeps Dana 30

 

[RIDE]

Shoot. We need to add Rock Krawler to this list. Front compressed 17.5” extended 24.5” as best as I could measure.

Thats nuts.
And since you have em, did you ever run numbers on cost of adding a lift, modding suspension and steering to accommodate, dropping the diff, and then cost of dropping transfer, adding limiting straps (plus then factoring the inevitable premature wear and subsequent early repair cost of your CV’s, diff and drive shafts and likely transfer) and put all that up against the cost of just running Portals? I mean, portals are steep for sure, but I’m curious how out of whack they are compared to the alternative?

 

[87-Z28]

I swear every time you post I have to read very slowly and still, my mind hurts haha. All I know is I’m still on my original CV’s after 57,000 miles and I wheel a ton. No issues but I’m careful with technique and locker usage. I treat it like my Jeeps Dana 30

I think you are close to the 24.3” shock extended length with those fancy coilovers. So less wear on your CVs for sure. Ultimately technique is king. Anything can be broken.

 

[userdude]

Thats nuts.
And since you have em, did you ever run numbers on cost of adding a lift, modding suspension and steering to accommodate, dropping the diff, and then cost of dropping transfer, adding limiting straps (plus then factoring the inevitable premature wear and subsequent early repair cost of your CV’s, diff and drive shafts and likely transfer) and put all that up against the cost of just running Portals? I mean, portals are steep for sure, but I’m curious how out of whack they are compared to the alternative?

SierraBronco's an all-of-the-above kinda guy.

 

[5GENIDN]

Thats nuts.
And since you have em, did you ever run numbers on cost of adding a lift, modding suspension and steering to accommodate, dropping the diff, and then cost of dropping transfer, adding limiting straps (plus then factoring the inevitable premature wear and subsequent early repair cost of your CV’s, diff and drive shafts and likely transfer) and put all that up against the cost of just running Portals? I mean, portals are steep for sure, but I’m curious how out of whack they are compared to the alternative?

So... what you are saying is that what he is doing is a bad idea??? And yet he has ONE OF the most capable broncos on the road.... hhhmmmm... will it wear parts out faster? will there be complicating problems? nah... I think you might have forgotten steering racks, tie rods, that 4 link and it's frame mounts needing reinforced... Hell you cant even get a good +70 wheel offset. AND the big one... the Brake shims!!! probably have to design your own and have to have them custom made.

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