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Discussion Starter #1 (Edited)
I'm revisiting a project that I have worked on off and on over the years, and I think it's at a point where I'm happy with it as a potential production part.

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Inverted ball joint (and converted to spherical bearing) makes them adjustable for roll center height, and dramatically reduces the stresses in the control arm and strut rod making this sort of design possible. Also adjustable for camber and caster of course. I am considering adding double adjuster pieces between the rod ends and the aluminum parts to both increase the range of adjustability and also allow for adjustment without disconnecting the arm from the car. At the very least the front caster arm will likely get one of these, same as I use on my current adjustable strut rods.

The ball joint adapters will have built in roll center adjustment equal to my geometry kit (1.75" front / 1.25" rear), so the rest of my geometry kit hardware will be required to complete the setup (everything minus the RCAs). Flipping the ball joint like this also means that this amount of roll center correction should fit in 15" wheels, for those who are into that.

Weight is ~4-5lb per corner less than stock arms.

Price looks like it will be around 600 per pair for the fronts, 650 for the rears (due to some more expensive rod ends required there). Any interest?
 

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I would be interested, especially if camber can be adjusted without having to unbolt the arm from the car. What effect does eliminating the rear arm center bushing have?
 

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Do I understand correctly that it would be $600+$650+Geometry kit to be able to use these control arms?

I would be interested, especially if camber can be adjusted without having to unbolt the arm from the car. What effect does eliminating the rear arm center bushing have?
+1 that it would be awesome that these allow camber adjustability without having to move coil overs.
 

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Discussion Starter #4
I would be interested, especially if camber can be adjusted without having to unbolt the arm from the car. What effect does eliminating the rear arm center bushing have?
Any time you eliminate a rubber bushing you get less suspension compliance (alignment change as a result of suspension loads), and a little bit more ride harshness as a result. In my experience it's not bad, but it IS intended for track cars and the like.

As far as adjustability goes, it may end up being that the pivot bolt has to be removed in order to rotate the rod end.
The inline adjusters that are available simply weaken the assembly too much (this style).
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There is also the sleeve style where the RH and LH threads are concentric and of different sizes, but this gets difficult to package and the availability of parts is somewhat limited, so I might need to make them custom. Making custom hardware is never my first choice! And I still have some concerns about the strength. But removing the pivot bolt to adjust that rod end isn't too inconvenient in my experience, especially since that isn't really meant to be your primary camber adjustment.
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Do I understand correctly that it would be $600+$650+Geometry kit to be able to use these control arms?

+1 that it would be awesome that these allow camber adjustability without having to move coil overs.
Correct. Well, if you don't have the geometry kit it would be around 140 cheaper than normal since you don't need the RCAs, being that they are built into the control arms.
 

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Generally interested.
My car has more obvious places to lose weight, but taking away (partially) unsprung pounds never hurt anyone. More front caster adjustability than the '91 arms would be good too.
 

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@Alex W as mentioned on the book of faces, I am definitely interested in this as long as I can get an inch extension over the stock arm length.
One thing to watch out for when extending rod end shanks on arms like this is that the shank is in bending. The more you thread it out, the worse it gets. This can cause fatigue cracks to form in the root of the thread next to the jam nut.
 

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One thing to watch out for when extending rod end shanks on arms like this is that the shank is in bending. The more you thread it out, the worse it gets. This can cause fatigue cracks to form in the root of the thread next to the jam nut.
Ideally, I would prefer an arm that is an inch longer before any extension, but I don't think that is what Alex is trying to do here.
 

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Discussion Starter #11
One thing to watch out for when extending rod end shanks on arms like this is that the shank is in bending. The more you thread it out, the worse it gets. This can cause fatigue cracks to form in the root of the thread next to the jam nut.
Agreed, it's definitely something I wouldn't want to over do. But it's also something I can analyze and if the stresses are low enough I'm not too concerned with cracking a 3/4" chromolly rod end, even if the threads do pose a stress concentration.

Ideally, I would prefer an arm that is an inch longer before any extension, but I don't think that is what Alex is trying to do here.
Making these as a machined aluminum part certainly has it's plusses and minuses in this respect. On one hand it avoids a lot of fabrication time like you would have with an arm like Hux offers, which I think is why I should be able to offer them cheaper. But I have to have them made in relatively large batches to get that price to work. However my machinist is pretty nice about doing small variations in parts as part of a larger batch without charging too much extra for it, so it may be possible to special order a couple that are an inch longer, as long as I do it while I am making a bigger batch.

One option I am considering that addresses both of these is to do a two piece arm similar to the Porsche GT3, but instead of a bolt on bearing housing it would just be a bolt on block with threads for the rod end. That way length can be adjusted by shimming between those two pieces, or by making a longer version of the bolt on block which is at least a small and relatively cheap part to make two versions of. Not sure yet if I want to go this route or not, but it might be an option.
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If you do a bolt on housing, definitely put a spherical bearing on the inner portion and then shim it. I was going to bring it up as an idea, but it’s definitely more expensive.

I’ll say that if you analytically look at a REIB, it won’t pass for infinite life, or even last the 100,000 cycle fatigue rating the expensive stuff passes.

Even if it’s a $500/piece 13-8 PH H1025 AS spec aerospace bad boy. The Kt of a thread root of a modified UNFJ aerospace thread profile can exceed 8-10, A normal UNF thread profile, it’s probably 16+.
 

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What load is causing significant bending in the inside rod end threads? I'd be a hell of a lot more worried about the outboard threaded rod in shear and bending than the inboard rod end.
 

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Discussion Starter #14
One thing to watch out for when extending rod end shanks on arms like this is that the shank is in bending. The more you thread it out, the worse it gets. This can cause fatigue cracks to form in the root of the thread next to the jam nut.
Looking at my analysis, if I extend the rod end an inch and load it up for 1.4g braking taken entirely by the control arm (ie no help from the strut), you do start to get into a fatigue concerning load on the threaded area. It's only around 30ksi, which wouldn't be too big of a deal if it weren't for the threads...

Which gave me an idea. If the point of failure is next to the jam nut, why not move that point out closer to the bearing? Basically if you are going to extend the rod end run a regular nut instead of a thin jam nut, or just put washers or a spacer between the nut and the end of the arm so that when you tighten the nut you bear down on the washers and some of the bending stress from the rod end is transferred back to the arm. Or even just double nut it. Anything to move that first exposed thread closer to the end.

Of course if it's taking 1.4g braking to cause concern, it's going to take a while to develop a lot of cycles of that, it's not like a rotating part that can be cycled a lot in a short amount of time. And any way you look at it a rod end is a wear item that will be replaced occasionally.

What load is causing significant bending in the inside rod end threads? I'd be a hell of a lot more worried about the outboard threaded rod in shear and bending than the inboard rod end.
The problem is that the strut rod attaches in the middle of the control arm, so the acceleration and braking loads put the entire control arm into bending. The worst of the bending stress is in the middle of the control arm, but it's extra wide in order to handle it. But where it necks down to the rod end you get some bending stresses, and as Def mentioned the problem is that the threads create stress concentrations.
 

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Any issues with moving the strut rod pickup point further outboard so that you don't see as much bending in the rod end?
 

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That is a lot of good information from your quick analysis Alex. You created the extreme top mounts because you found that they essentially made the suspension geometry better. Would there be any benefit or negative to a control arm that is an inch longer? I keep stressing "an inch longer" because it's based on the width of the wheel and tire, and offset that I eventually want to run on the front of the car. Most people just go with a lower offset but I would like to keep my offset as high as possible to keep the scrub radius to a minimum.
 

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Mmmmm, made some guesses on lengths and rod end sizes and did the math. Running the rod end out an inch puts you in a serious pickle :oops:
 

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Discussion Starter #18
Any issues with moving the strut rod pickup point further outboard so that you don't see as much bending in the rod end?
You can do that to some extent, but eventually the strut rod ends up in the space that the tire is trying to occupy.

That is a lot of good information from your quick analysis Alex. You created the extreme top mounts because you found that they essentially made the suspension geometry better. Would there be any benefit or negative to a control arm that is an inch longer? I keep stressing "an inch longer" because it's based on the width of the wheel and tire, and offset that I eventually want to run on the front of the car. Most people just go with a lower offset but I would like to keep my offset as high as possible to keep the scrub radius to a minimum.
There are geometry benefits to extending the control arm, but I don't think I have calculated how much if you go that far. But a little helps with front tire clearance, camber curves, etc. But most people wouldn't be able to use much extension without buying different wheels, and it can make it tricky to get rid of the excess static camber...

Mmmmm, made some guesses on lengths and rod end sizes and did the math. Running the rod end out an inch puts you in a serious pickle :oops:
Unfortunately we don't REALLY know how big of a pickle without knowing details on the material strength. FK lists only axial strength for rod ends, and for the one I would use it's ~28,000lb. Material is listed as "alloy steel" and "heat treated". That could be anything from about 97ksi ultimate strength for normalized 4130 to 160ksi ultimate for quenched and tempered 4130.
 

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There are geometry benefits to extending the control arm, but I don't think I have calculated how much if you go that far. But a little helps with front tire clearance, camber curves, etc. But most people wouldn't be able to use much extension without buying different wheels, and it can make it tricky to get rid of the excess static camber...
Well, whenever these are set to go into production, pencil me in for a set that is an inch longer than stock front and rear.
 

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@Alex W All of these ball joint suspensions on the market require the use of the 93+ strut rod brackets. However, because these cars are so old these parts aren't available from Toyota anymore and are super rare used. So I realize as much as I would love this suspension, it will not work on my 91. Do you plan on also producing the strut rod bracket to make these work on 92 and older cars?
 
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