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Stupid Suspension Question

Goatman

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Can you just leave off the passenger side the front control arm and have a 3 link for better articulation without breaking everything? Does a 3 link make that much of a difference in terms of articulation to want to do it?
 

dbbd1

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Hmmm, no.

2 links on the drivers side, one on the passenger side? No bueno!
 

jjvw

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It's been done. I know a guy with a 3 link on stock mounts. Both lowers and the upper diff mount. Articulation comes from the shocks. If your setup is articulating more than stock, you probably shouldn't be using the stock arms or bushings. If you are using a decent set of aftermarket arms, then articulation shouldn't be a meaningful problem to begin with on the front 4 link.
 
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kmas0n

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3 link front suspensions are common. But I wouldn't rely on a stock control arm or mounting point. Most people that go with a 3 link front do it to increase the length of their control arms (mid arm) and use a bridge or truss for the upper mount. While you could probably get away with the factory mount on the diff and a strong control arm like a savvy, there is not going to be any real benefit.
 

jjvw

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3 link front suspensions are common. But I wouldn't rely on a stock control arm or mounting point. Most people that go with a 3 link front do it to increase the length of their control arms (mid arm) and use a bridge or truss for the upper mount. While you could probably get away with the factory mount on the diff and a strong control arm like a savvy, there is not going to be any real benefit.
The issue is that the single mount is now experiencing double duty to control the axle. Even with the Johnny Joint kit, that joint really isn't strong enough for that job.

The answer is to put a bigger joint there, which means finding a way to replace the stock mount. If you are replacing the stock mount, then maybe it should be positioned elsewhere and also be a part of a larger redesign of the control arms.
 
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kmas0n

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The issue is that the single mount is now experiencing double duty to control the axle. Even with the Johnny Joint kit, that joint really isn't strong enough for that job.

The answer is to put a bigger joint there, which means finding a way to replace the stock mount. If you are replacing the stock mount, then maybe it should be positioned elsewhere and also be a part of a larger redesign of the control arms.
I'm pretty sure we are saying the same thing. My biggest concern with the stock cast upper control arm mount is that it is cast. I'm far from an expert but doesn't that make it more brittle and likely to crack? This is the way I did mine. You can see the tabs from the original cast mount protruding through the truss for "extra" strength





99082
 
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jjvw

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The strength concern is with the bushing or joint, not the diff side mount itself. If a large enough joint could be fitted then the remaining concern would be the location. The same concerns would apply to the upper frame side mount, as well.
 
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Goatman

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My thoughts were cast mount strength. Would definitely use superior control arms. I keep seeing adds in the 4x4 magazines for ?Rock Island? Bolt in 3 link that appears to bolt to the stock mount with a long arm set-up to their skid plate. Stock 4 link flex is the reason we all change our control arms, right? So a good pollyurathne bushing in the top link and away we go! Seems too easy and simple or everyone would do it. Didnt think about the frame side mount. Could weld plate over it for extra strength. Any experts here wanna chime in and tell me what is wrong with the idea? I've put in plenty of suspensions, but my rocket science skills are somewhat lacking. 🤯
 

mrblaine

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I'm pretty sure we are saying the same thing. My biggest concern with the stock cast upper control arm mount is that it is cast. I'm far from an expert but doesn't that make it more brittle and likely to crack? This is the way I did mine. You can see the tabs from the original cast mount protruding through the truss for "extra" strength





View attachment 99082
Cast does not mean brittle, it does not mean malleable. It only means it has been made in a mold of some sort using molten metal that is poured in, no more, no less. The various iron alloys can be formulated to achieve 100's of variations with as many properties. If you believe that the casting is too brittle to handle the duties of locating the axle via a control arm, how do you reconcile the thin tubular sections that the axle tubes press into? If brittleness was an issue, wouldn't they just crack right off the side of the main structure? Not to mention that is an interference fit which is trying to expand the tubular part and crack it wide open.
 
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mrblaine

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My thoughts were cast mount strength. Would definitely use superior control arms. I keep seeing adds in the 4x4 magazines for ?Rock Island? Bolt in 3 link that appears to bolt to the stock mount with a long arm set-up to their skid plate. Stock 4 link flex is the reason we all change our control arms, right? So a good pollyurathne bushing in the top link and away we go! Seems too easy and simple or everyone would do it. Didnt think about the frame side mount. Could weld plate over it for extra strength. Any experts here wanna chime in and tell me what is wrong with the idea? I've put in plenty of suspensions, but my rocket science skills are somewhat lacking. 🤯
The stock cast mount for the upper control arm on the diff section is probably the single strongest section of the casting with the exception being the areas inside where the bearings sit. It has the smallest area with the largest amount of material and the only reason it is as wide as it is has nothing to do with anything except that is how much surface area is needed for the press fit on the bushing.

If anyone believes that the upper arms are capable of handling the loads well enough to double them up on one arm, make a set of lowers using upper control arm bushings and see how long they last when you use them on the lower arms. The upper mount is roughly twice the distance above the centerline of the axle tube as the lowers are below it. That means the lowers see twice the load of the uppers. There is a reason why the uppers are about half the size of the lowers. They don't see the same loads.
 
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kmas0n

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Cast does not mean brittle, it does not mean malleable. It only means it has been made in a mold of some sort using molten metal that is poured in, no more, no less. The various iron alloys can be formulated to achieve 100's of variations with as many properties. If you believe that the casting is too brittle to handle the duties of locating the axle via a control arm, how do you reconcile the thin tubular sections that the axle tubes press into? If brittleness was an issue, wouldn't they just crack right off the side of the main structure? Not to mention that is an interference fit which is trying to expand the tubular part and crack it wide open.
I never thought about it like that. Thanks for clearing this up.
 

mrblaine

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I never thought about it like that. Thanks for clearing this up.
Think about it another way. The most common issue with the Dana 30 fronts are not enough preload on the carrier which lets the gear set walk out of pattern due to housing flex.
 
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jjvw

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My thoughts were cast mount strength. Would definitely use superior control arms. I keep seeing adds in the 4x4 magazines for ?Rock Island? Bolt in 3 link that appears to bolt to the stock mount with a long arm set-up to their skid plate. Stock 4 link flex is the reason we all change our control arms, right? So a good pollyurathne bushing in the top link and away we go! Seems too easy and simple or everyone would do it. Didnt think about the frame side mount. Could weld plate over it for extra strength. Any experts here wanna chime in and tell me what is wrong with the idea? I've put in plenty of suspensions, but my rocket science skills are somewhat lacking. 🤯
Again, the strength concern is not specifically the mount. You can plate and and brace the upper driver's side frame mount all the way over to the passenger side and still have an inadequate bushing or joint.

You'll need to be more specific on what a good polyurethane bushing or joint is fully compromised of.

I'm not at all familiar with Rock Island, but the bolt on feature is an immediate red flag. As is the attachment to the skid plate. Ask yourself if the new mount locations are where they ought to be. What are you really trying to accomplish with a 3 link, since we know that articulation is not necessarily the primary purpose.
 

mrblaine

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Again, the strength concern is not specifically the mount. You can plate and and brace the upper driver's side frame mount all the way over to the passenger side and still have an inadequate bushing or joint.

You'll need to be more specific on what a good polyurethane bushing or joint is fully compromised of.

I'm not at all familiar with Rock Island, but the bolt on feature is an immediate red flag. As is the attachment to the skid plate. Ask yourself if the new mount locations are where they ought to be. What are you really trying to accomplish with a 3 link, since we know that articulation is not the primary purpose.
I helped a guy with a HP 30 front that was going to the mid arm at some point. We installed the truss only and then built a correct length short upper out of a Savvy DA lower. I cut the outside of the frame mount off, built a new one for the wider joint and welded it in place. Drilled out the inside hole for the 9/16" bolt and sent him on his way with a 3 link short arm.
 
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