2G Tubular front k-member build - share ideas!

[99gst_racer]

Thanks for the posts, guys.

Great news is that Jon Lane has brought to my attention a GM upper balljoint that I believe will work perfectly. It's O.D. is small enough to avoid contact with the compression arm. And it's a true balljoint, so it's far stronger than a monoball bearing in a cup. And it's rebuildable with extra length studs available for roll center adjustments. The 772 stud is about as close as we're going to get. The taper matches, but it will require a small washer/spacer below the nut. Far better compromise than requiring a ton of reaming for a much larger stud. The 772 stud is also commonly available and will be forever, so that's a great thing.

I have two of these on the way right now. If I find time this weekend to tack up a prototype, I'll share pics.

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[Jon Lane]

Credit where it's due: This part came from the 1G thread. They're always two steps ahead...

 

[greengoblin]

Good work. Maybe we found the unicorn.

 

[99gst_racer]

Well, here she is. All teflon-lined sphericals. The ball joint is rebuildable and externally greasable. And it does fit the spindle and clear the compression arm with ease.

Stud fit:

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Arm disassembled:

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Arm assembled:

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Balljoint/compresson arm clearance:

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[Blurred Talon]

Bad ass!
Can't wait to see more.

 

[Atuca]

Looking good indeed!

 

[gho5tone]

Hazzah! One step closer to making it happen!

 

[gixxerdrew]

Here was another quick and very rough drawing. Andrew you can tell me if it is what you where talking about. I do think this could work too.

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Yes that was exactly what I meant, awesome update from Paul though!

 

[greengoblin]

Those look great Paul!

 

[boosting88]

That's actually very impressive.

 

[gofer]

You going to be selling those separate or only with the subframe?

 

[99gst_racer]

I'm glad you guys like it as much as I do.

You going to be selling those separate or only with the subframe?

I'm going to offer them separately as well. I just have to whip up some standoffs for the inboard heim so that it will fit the OE k-member.

 

[Jon Lane]

And one DSM Achilles Heel is solved. Fantastic!

Some questions:

The Coleman ball joint comes with up to +0.75" more depth, or half of the typical -1.5" drop not including the joint's dimensions themselves. The joint's rebuildability and the arm's weight and flexibility are enough to warrant the mod, but are there a few more fractions of an inch in arm drop in the way the stud meets the spindle, Paul, or in the joint itself compared to stock?

With even 0.75" drop in the joint, is your tubular arm short enough eliminate upper A arm camber adjusters and put adjustment down in the LCA?

Lastly, are there any options for the spindle purchase point? Maybe poly for the street?

 

[99gst_racer]

The Coleman ball joint comes with up to +0.75" more depth, or half of the typical -1.5" drop not including the joint's dimensions themselves. The joint's rebuildability and the arm's weight and flexibility are enough to warrant the mod, but are there a few more fractions of an inch in arm drop in the way the stud meets the spindle, Paul, or in the joint itself compared to stock?

Good question! I haven't measured it to be exact yet, but due to the dimensions of the stud and where the ball pivots, the "stock" stud that comes in the BJ assembly will yield roughly .500-.650" drop compared to the OE arm. So any other stud would be in addition to this amount.

With even 0.75" drop in the joint, is your tubular arm short enough eliminate upper A arm camber adjusters and put adjustment down in the LCA?

Another good question. I guess I'm not sure how much shorter it would need to be. But I can make it any length. Unfortunately, there's not much available adjustment with the heim while maintaining proper thread engagement. The heim has 1.700" of thread, the jam nut is .450" thick, and there needs to be roughly 1.125" of thread engagement (1.5x diameter). That leaves an adjustment range of .125" (or up to ~1/4" if you rob a little engagement in the tube). So I'd have to get the length pretty close to begin with rather than rely heavily on adjusting the heim to get to the desired length. I guess we just need to figure out the ideal length of the lower to be able to eliminate adjustment at the upper arm.

Lastly, are there any options for the spindle purchase point? Maybe poly for the street?

Use poly for which part?

 

[Jon Lane]

...due to the dimensions of the stud and where the ball pivots, the "stock" stud that comes in the BJ assembly will yield roughly .500-.650" drop compared to the OE arm. So any other stud would be in addition to this amount.

Then adding a +0.75" stud option, the tallest one from Coleman, actually gets the LCA geometry dropped between 1.25" and 1.4", or close to original for moderately lowered cars.

This informs the answer to the next question, which is if the new tubular LCA can absorb enough shortening to eliminate upper A arm camber adjusters.

I guess I'm not sure how much shorter it would need to be. But I can make it any length. Unfortunately, there's not much available adjustment with the heim while maintaining proper thread engagement. The heim has 1.700" of thread, the jam nut is .450" thick, and there needs to be roughly 1.125" of thread engagement (1.5x diameter). That leaves an adjustment range of .125" (or up to ~1/4" if you rob a little engagement in the tube). So I'd have to get the length pretty close to begin with rather than rely heavily on adjusting the heim to get to the desired length. I guess we just need to figure out the ideal length of the lower to be able to eliminate adjustment at the upper arm.

Without a model to confirm by, I'd guess that if the long stud Coleman part can restore the outboard LCA point to within a half inch for some average drops, the adjustment might already be in the proposed tubular arm: Just cinch it all the way in and see where that lands you.

This said, if cinching it in all the way still leaves an undesirable negative camber angle, then now would be the time to consider how best to shorten it more, while leaving the adjustment range +/- a sufficient range.

Easy to say, but difficult to calculate.

Use poly for which part?

CORRECTED: The spring and shock point, at the bottom of the shock and spring.

Relative to that, this next bit could be interesting. With three sphericals, the tubular LCA is currently free to rotate around its axial center, excepting for its angle about the spring/shock point restoring it when under weight. It's probably not going to bang around against the limits of any one spherical, but wouldn't it be the case that if a limit is reached, and if due to the enormous loads on the arm and its components it gets reached with some force, a spherical could be damaged by a hard unintended twist?

Given that the arm doesn't have to rotate (the stock LCA is centered on its axis by hard rubber), how about making the center spring/shock point fixed? A simple through bushing to carry the bolt? Then the arm is positively located with regard to axial twist and all axial angles relative to either spindle or chassis are free to seek their centers via the sphericals at those respective ends.

The advantage is potentially greater strength, less complexity and cost, and maybe even a single straight arm tube from end to end, whose only disadvantage is a higher lower spring/shock point, meaning slightly less shock travel. If these arms get used in cars with adjustable spring perches and top shock hats, which is a fair assumption, even that may not be that great an issue...

 

[eclipsh]

Then adding a +0.75" stud option, the tallest one from Coleman, actually gets the LCA geometry dropped between 1.25" and 1.4", or close to original for moderately lowered cars.

Too long and I'd start to worry about the extra torque on the knuckle mounting tongue. Wouldn't want that tongue cracking or breaking under heavy side loads.

Given that the arm doesn't have to rotate (the stock LCA is centered on its axis by hard rubber), how about making the center spring/shock point fixed? A simple through bushing to carry the bolt? Then the arm is positively located with regard to axial twist and all axial angles relative to either spindle or chassis are free to seek their centers via the sphericals at those respective ends.

This is a great idea and an easy place to put in a urethane or brass bearing. The current bend in the arm should prevent it getting out of position (possibly the reason it is there?) The weight bearing on it will force the alignment to stay oriented.

 

[greengoblin]

I regards to putting a bushing in the lower shock mount location.


I would be hesitant to put a bushing or even hard poly in this location. The OEM rubber there is pretty soft. We know that just adding the Prothane poly bushing here has caused shock failure because it limits the articulation of this joint causing the shock rod to bend . It could "possible" work if the user has a functional coaxial spring hat. Even then a bearing would still be ideal to eliminate stiction and prevent an unwanted spring at the end of your dampener. The 2g front dampeners move around a lot (around 15*) just by turn the wheels lock to lock. You can certain give it a try but make darn sure you cycle the suspension in all direction and to all extremes.

 

[Jon Lane]

I would be hesitant to put a bushing or even hard poly in this location ... The 2g front dampeners move around a lot (around 15*) just by turn the wheels lock to lock.

I didn't know that - that's a shocking amount of twist. It may bring the compression arm's ball center into question too, that is if that joint remains at stock height.

Last idea: A rectangular tubular arm. Improves vertical strength a little, may improve weld area to the ball cylinder, and allows the shock mount to go slightly lower in what could be a straight arm. Downside seems to be the inboard fixing point, where a threaded heim needs to join the rectangular opening somehow.

And how about a simple curved tubular compression arm to accept the same ball as the straight LCA, lowering it to the same depth?

 

[greengoblin]

I didn't know that - that's a shocking amount of twist. It may bring the compression arm's ball center into question too, that is if that joint remains at stock height.

Last idea: A rectangular tubular arm. Improves vertical strength a little, may improve weld area to the ball cylinder, and allows the shock mount to go slightly lower in what could be a straight arm. Downside seems to be the inboard fixing point, where a threaded heim needs to join the rectangular opening somehow.

And how about a simple curved tubular compression arm to accept the same ball as the straight LCA, lowering it to the same depth?

I think "if it is need" strength could be added simply by increasing the OD and wall thickness of the tubing. Also simple finger plates could be added over the top of and bottom of the bearing cup for the shock pick up point and around the ball joint cup.

With the compression arm it is going to be hard because the arm wants top twist/flop down with out the inboard pickup point being rubber. That and the dogbone design mounting point. This can be over come by changing the mounting points on a custom crossmember and using poly/rubber in some form as a stop to hold the arm in correct position while in droop.

Also will two ball aftermarket ball joints fit the space that is currently there. I have seen oem arms that have a small amount of excessive casting flash cause binding problems.

 

[99gst_racer]

CORRECTED: The spring and shock point, at the bottom of the shock and spring.

Relative to that, this next bit could be interesting. With three sphericals, the tubular LCA is currently free to rotate around its axial center, excepting for its angle about the spring/shock point restoring it when under weight. It's probably not going to bang around against the limits of any one spherical, but wouldn't it be the case that if a limit is reached, and if due to the enormous loads on the arm and its components it gets reached with some force, a spherical could be damaged by a hard unintended twist?

Given that the arm doesn't have to rotate (the stock LCA is centered on its axis by hard rubber), how about making the center spring/shock point fixed? A simple through bushing to carry the bolt? Then the arm is positively located with regard to axial twist and all axial angles relative to either spindle or chassis are free to seek their centers via the sphericals at those respective ends.

The advantage is potentially greater strength, less complexity and cost, and maybe even a single straight arm tube from end to end, whose only disadvantage is a higher lower spring/shock point, meaning slightly less shock travel. If these arms get used in cars with adjustable spring perches and top shock hats, which is a fair assumption, even that may not be that great an issue...

There is no force to cause the arm to roll to the point of interference, so I'm very confident it will stay put for the most part. As well, the shock mount bearing and the inboard heim are teflon-lined and are pretty stiff, so they would do quite well at resisting roll due to vibration. Furthermore, I used a new (new to me) bearing cup on this arm that is longer than the ones used in the past. Once the shock mount standoffs are in place, maximum misalignment would cause the standoffs to contact the bearing cup, rather than cause any type of misalignment interference at the bearing or mono-ball housing/race itself.

So in a nutshell, none of the bearings themselves could ever be subject to misalignment interference due to how the shock bearing is situated. But even if that were not true and the bearings were subject to misalignment interference, I am extremely confident that no damage could result due to the virtually non-existant rolling force.


I very well could use a urethane bushing for the shock mount, but I believe most people would rather have a connection that didn't deflect at all.

 

[Jon Lane]

I think "if it is need" strength could be added simply by increasing the OD and wall thickness of the tubing. Also simple finger plates could be added over the top of and bottom of the bearing cup for the shock pick up point and around the ball joint cup.

I was thinking more about the simplicity of boring the shock wishbone bushing location, offset downward, through a single flat arm versus welding round tubing to both sides of a collar. Again, these are general ideas.

With the compression arm it is going to be hard because the arm wants top twist/flop down with out the inboard pickup point being rubber. That and the dogbone design mounting point. This can be over come by changing the mounting points on a custom crossmember and using poly/rubber in some form as a stop to hold the arm in correct position while in droop.

Also will two ball aftermarket ball joints fit the space that is currently there. I have seen oem arms that have a small amount of excessive casting flash cause binding problems.

Leave the compression arm's inboard point the stock dogbone configuration to stop droop.

The advantage to replacing this arm was weight savings and having it use a matching ball joint at the spindle, if a pair fit side by side. Whether it's important to correct the compression arm's ball-end geometry downward to match the load arm I do not know.

 

[99gst_racer]

Leave the compression arm's inboard point the stock dogbone configuration to stop droop.

The advantage to replacing this arm was weight savings and having it use a matching ball joint at the spindle, if a pair fit side by side. Whether it's important to correct the compression arm's ball-end geometry downward to match the load arm I do not know.

Aside from the weight savings, another huge benefit to an aftermarket would be the ability to ditch the rubber on the inboard end. I'm not sure if it would be worth building an aftermarket arm that maintained the exact same rubber inboard connection.

Andrew Brilliant and I once discussed a complicated type of bearing that could be designed to allow complete articulation while preventing roll. The compression arm would need something like that to have an arm without rubber bushings and without a rolling droop. And if I had my own verticle mill, I would definitely give it a whirl.

 

[Jon Lane]

Street restoration here. I'd be happy with standard rubber dogbones locating the inboard point on the compression arms. Getting the servicable - and lowered - ball joint is enough.

 

[greengoblin]

Any pics of the lower arms all welded up?

 

[99gst_racer]

Any pics of the lower arms all welded up?

They aren't welded up yet. I've been stupid-busy with 1G crossmembers lately, and just started in on Brian's k-member again. But I plan to get them welded up this weekend and to the powdercoater sometime next week. I'll post pics next week.