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

[TSiAWD666]

Keep in mind steering rack changes may necessitate power steering pump changes as different racks have differing operating pressures.

 

[99gst_racer]

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One good fix for this is a K brace as shown in green. It isn't easy to fit in but Mitsubishi did it with an aftermarket K brace in Japan that fits in similarly. It also prevents distortion in other directions but the one I'm showing is probably the most likely.
First off, thanks for the post. It's very much appreciated.

As much as I'd like to have bracing directly between the LCA pick-ups, it's just not possible. The transmission and t-case are parked right in the way and sit in extremely close proximity. And if I built a brace to go beneath those things, it would have to sit incredibly low. I just don't see a way to do a k-brace without having the engine and trans sitting a bit more forward.

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The XZ plane can distort vertically as I'm trying to show in this pic. It is a little confusing since the picture isn't straight on but the distortion should be perpendicular to the firewall as in the fender moving up and down. The green brace I drew in would help prevent this distortion much like a fender brace does.

I had planned to add a similar brace as your green line there, for the road race version. Although it can't be nearly as long/large as shown in your image due to interference with the steering rack. It would moreso have to follow the path of either of these lines:

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Another suggestion I received was to replace the single joining piece with a double "boxed in" configuration or with an "X". If I did the X, I'd have to use smaller diameter tubing with a heavier wall thickness. Either would offer more resistance to twist, but I think I'm leaning more toward the boxed in config.

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[counti41]

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The plane of the firewall (YZ plane in my coordinates) is very well braced. A lateral load (red arrow) won't distort it much if at all.

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The XY plane isn't as well braced against distortion. A lateral push can create shear as represented by the red box.

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One good fix for this is a K brace as shown in green. It isn't easy to fit in but Mitsubishi did it with an aftermarket K brace in Japan that fits in similarly. It also prevents distortion in other directions but the one I'm showing is probably the most likely.

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The XZ plane can distort vertically as I'm trying to show in this pic. It is a little confusing since the picture isn't straight on but the distortion should be perpendicular to the firewall as in the fender moving up and down. The green brace I drew in would help prevent this distortion much like a fender brace does.

I hope all that makes sense now. None of it may be necessary but I see those as weak points that could be improved upon.

How about gusseting all the intersecting joints would that not reduce twisting and increase regidity?

can you show a picture from front to rear of subframe with a centerline at the bottom or middle of the subframe???

 

[99gst_racer]

The Ford pinto design steering rack is popular in the V8 custom sommunity for its size and its different length options, it can also be had with a hydraulic assisted steering option as well. would you also be able develop a tubular front core support with a front subframe connector that works with your new front subframe. it would be cool if you can redisign the whole front suspension with lighter components(chromoloy, etc... to help take some weight off the front end. i have lots of ideas just no time equiptment or resources to get it all done. PM me and maybe we can exchange ideas.

IIRC, The Pinto rack is several inches shorter than the Mustang II rack. And the Mustang II rack is already ~4" shorter than our OE rack. And Mustang II power racks are available as well.

A tubular core support is something that is best built on the car in person. Should be a piece of cake for any local chassis shop though.

I will be doing chromoly lower control arms to go along with this k-member. I'd also like to eventually build a tubular compression arm. I just need to figure out a design for an inboard bearing that does not allow the arm to roll.

 

[turbosax2]

Paul, this is the brace I believe eclipsh was referring to. Round tube would not be good here.

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[greengoblin]

The bends would have to be even more extreme on his unit because the pick up points are so much higher. I just don't think that is a good solution and really is only a band aid for a poor design. Where Paul is headed a lower brace will not be need. He just has to make sure the tubing is properly sized and configured .

 

[99gst214]

If the pick up points are too high on the unit, why not just fabricate drops that lower the mounting points to hold lower tie bar? I like the idea of having a lower tie bar added as well as also being able to utilize a north south tie bar, similar to the factory one (in a tubular version of course).

One idea I had was, combine the lower tie bar and north south bar as "one" solid unit. Meaning that instead of being separate bolt on pieces, make it one solid piece with four mounting points, that offers better yields to preventing deflection in all directions.

I may be underestimating the overall potential of the current design, based on its rather small size, I would just rather push to see as much bracing to the design as possible and then remove it as necessary. Rather then having to add on later due to failure or over flex issues.

Just my thoughts. Im sure some have already crossed your mind, but never hurts to rethink something that was once considered a bad idea.

 

[99gst214]

Any updates Paul?

 

[99gst_racer]

Had to push this aside briefly to get a rear subframe done for someone.

The k-member is done. As are the control arms. But I discovered the Mustang II rack won't work afterall, due to it being front steer rather than rear steer. I've picked up a Pinto rack, so I just need to cut off the old rack mounts and fab up some new ones and it will be ready for powdercoat. I'll have that all squared away sometime next week.

 

[99gst214]

Good deal. I'm more interested in the road coarse style kmember, but progress is progress. Take your time and we will al be anxiously awaiting updates.

 

[99gst_racer]

Got the k-member back from coating yesterday and got everything weighed today. We'll be installing it on John's car tomorrow.


OEM k-member = 41.2 lbs.
4130 k-member = 15.2 lbs.

OEM LCA = 5.0 lbs.
4130 LCA = 3.1 lbs.

OEM steering rack = 18.6 lbs
Pinto steering rack = 10.4 lbs.
_________________________________

TOTAL savings = 38.0 lbs!

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[talont3t4]

Pretty sure the OEM is 34 or 36lbs!

 

[99gst_racer]

I weighed John's OE k-member today. With the lower plates and roll stop attached, it tipped the scale at 41.2 lbs. So with the Pinto rack and fabbed arms, that brings the total weight savings to 38 lbs.

 

[91stocker]

that brings the total weight savings to 38 lbs.

Holy shit thats light

More weight loss then a cf hood with many more benefits.

 

[Miasma]

Hey paul,

Would you be willing to make a 420a version? The rear transmission mount on 420a variations, is on the opposite side as on the 4g63 models.

I am swapping my platform to a long rod 4g64 with an evo 8 head, and I am going to have clearance issues when trying to run the t-case through the factory 420a subframe. SO I was thinking about going with a custom tubular subframe, just in time for you to have developed this to save me the work haha.

 

[Jon Lane]

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Nice. This looks interesting to anyone tired of replacing arms.

The outer joint is going to see big static loads and even bigger dynamic loads. Have you considered accommodating a rebuildable conventional ball joint? Something like this? They're inexpensive.

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[99gst_racer]

Nice. This looks interesting to anyone tired of replacing arms. The outer joint is going to see big static loads and even bigger dynamic loads.

Have you considered accommodating a rebuildable conventional ball joint? Something like this? They're inexpensive.

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Thanks for the post.

I do plan to re-do the outside connection on the arms. Though I am very confident the 5/8" bearing on these is fine for John's drag car. I know for sure I'll need something with a greater axial load capacity for dynamic loads from road race and auto-x applications. On the heim in the image, its radial capacity is rated for just under 15,000 lbs. And the axial capacity is 15% of that.

For the next set of arms I do, the outboard heims are out. I have two ideas and I'm not yet sure which I'll go with. The first idea was to use a bearing cup and 3/4" bearing like I did for the shock mount. That would afford roughly 3200 lbs of radial load on each corner and it would be quick and easy to use a long 3/4" balljoint stud and use spacers to shim it as the desired height to get the desired arm angle. The only downside being its 3200 lb. radial load capacity. That's plenty for most applications, but I'd rather overbuild something like this.

And the other idea is to just run a balljoint like you've suggested. I'm leaning heavily more toward this idea. I still need to take some measurements to make sure there's room for a BJ sleeve (there should be) and I'd have to figure out the best way to attach it to the shock mount bearing cup on the arm with such close proximity. The BJ I had in mind is adjustable for height. It would definitely add quite of bit of cost to the arms, but I feel it's the best route for strength and adjustability.

Allstar Performance - racing and high performance car parts, accessories and specialty tools.

I'll see if I can dig up load capacity specs on this BJ today.

Also, in regards to using GM balljoints; I believe we're pretty much limited to running upper balljoints on the lower control arm due to stud diameter. The stud on a GM lower like in your link has a taper that begins at around .755" diameter. That would take a ton of reaming to fit our spindle.

 

[Jon Lane]

That's a really considered reply and I'm sure others will appreciate it as much as I do. The challenge probably lies in finding the right combination proper stud dimensions and taper in a tension joint.

In sum, if you design a strong new lower arm, and if it allows heavy-duty, rebuildable ball joints, then you'll have accomplished the first real fix for this critical problem. Even as old as these cars are, I'm sure some owners would even be able to save money over three or four conventional replacements while getting the peace of mind not possible from the OEM-spec part. Nice job.

 

[99gst_racer]

Well, the GM upper BJ idea isn't working as planned. The stud fits pretty well though. It's a hair too small in diameter and the taper protrudes through a little bit, so a small spacer would be needed underneath the nut.

But there's an issue with with the diameter of the housing/sleeve. It's too large in diameter and interferes with the compression arm. The housing on the OEM LCA measures 1.870" in diameter. The OD of the threaded sleeve for a GM upper is 2.250". 2.000" is probably the largest diameter that will fit without interference.

Back to the drawing board.

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[snowborder714]

Holy crap that's a massive ball joint!

 

[99gst_racer]

Holy crap that's a massive ball joint!

As far as domestic stuff goes, it's actually pretty small. Any GM lower is massive compared to this upper. Ours is just tiny in general.

I really like this one though. I wish it could be used...

 

[super95awd]

Get ahold of me and we can work on something to fix that issue.

 

[99gst_racer]

Get ahold of me and we can work on something to fix that issue.

I meant to call you last night and got busy in the garage. I'll hit you up sometime late tonight.

 

[BLACKCARBON]

would something like this work

 

[Boosted6]

I would loooooooooooooove to get something like this for my 1g.