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Many general control arm questions, joints, material, etc and basic geometry rules.

Rob50lx

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May 29, 2020
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I screwed up and should have used the 4-link calculator!!!!!!!!!


So I decided to raise the rear control arm brackets to restore geometry and simulate MetalCloak DB3 frame drop brackets for the rear of my JK while improving ground clearance at the rear axle. I thought it would be relatively simple and this is my first major non bolt in project. The UCA bracket on the frame is the only bracket I'm not wanting to modify and use as my reference point. The UCA bracket on the axle is already welded on permanently but has 3 holes for adjustment. To clear the axle bearing retainer bolts I had to clock the UCA brack back further than the control arm can adjust, so I need to look at new UCA at the minimum. If I use the upper hole in the UCA mount I can still use my Metalcloak Duraflex joint. If I need to use the lower holes than I need to use a joint with less deflexion during articulation (heim, JJ, etc).



General control arm selection
questions:

1. Thread engagement of joint, 1.5 times diameter is the general rule. So with 1 1/4" x 12tpi shank does that mean 1.25"x1.5=1.875" of depth x 12 threads per inch = 22.5 threads minimum engagement?

2. Does this rule change or become more strict if using aluminum links?

3. Local shop does 6061 aluminum links, most online places do 7075 links: Does it matter?

4. What is minimum wall thickness for tapping threads with steel vs aluminum?

5. Joint selection, my prefered joint is MetalCloak Duraflex as vehicle is daily driver but a may need to use a heim or other joint for packaging reasons. My thoughts are that a rubber based joint may allow for slight geometry or control arm placement errors due to rubber deflexion vs the rigid articulation of heim, JJ, etc?

6. I have a control arm that I would like to cut off fixed joint and hand tap, is this possible? 1.5" DOM 3/16" wall 1 /14" 12tpi tap

7. Does anyone besides MetalCloak make a joint with an angled shank in 1" or 1.25" shank?

8. Tapping DOM vs: using weld bung? Is one better than the other?

9. Who makes custom bent DOM control arms?


Basic geometry rules: (I screwed up and didn't use 4-link calculator)

A: Joint separation should be 25% of tire diameter, Does this matter for both front and rear axle?

B. My application has 8.5" joint separation at rear axle and I'm running 37s and may step up to a true 37" or 38" tire, is this OK with rubber joints or heim joints?

C. My current control arm brackets are at centerline of axle and 8.5" above centerline, does this induce more axle wrap vs 2" below centerline and 6.5" above centerline?

D. My current mock up has the upper and lower control arm lengths almost equal (stock rear LCA was about 2.25" longer than UCA), Do I need to look at lengthening the lower arm 2.25" to get better pinion angles through articulation?

E. I was told I need to raise my LCA frame bracket a little to get better geometry, Should I follow this advice?

"your links are nearly parallel with each other which drives the instant center very far forward and produces a corresponding very low anti-squat, potentially "too" low? The good news is that you shouldn't have to move the frame end LCA mounting point up very much, maybe 3/4" to make a noticeable difference. Run it and see what happens, that is part of the fun for interesting projects such as this"

F. Any other basic tips I should follow besides I was a DUMBASS FOR NOT USING 4-link calculator?

20210118_121647.jpg


20210118_105042.jpg




This is how the arms will be at ride height.
20210118_201607.jpg
 
1) yeah if can get that much engagement which is easy to do, have at it. won't hurt to be more or less than that. less shank showing is better as the shank will be what bends, but with a light rig I doubt you'd bend them

2) AL doesn't change thread engagement factor for all intents and purposes, if anything, more is better

3) 7075 is superior to 6061 in this application, better columnar strength in the material and better resistance to rock damage and better spring back. steel is obviously the cheap do very well option

4) you'll want more wall thickness for AL vs ST because AL takes threads like shit, so we make up for that with diameter. i'd have to look, but more is better than less and why 2" steel links are common while over 2" AL is common

5) properly setup, it doesn't matter if you are using rubber or rigid joint as long as it all moves freely. if using a mix, make all your frame side or all your axle side one type and all of the other the other so that they don't fight each other. if you like the duraflex, use the duraflex. a rigid joint puts less stress on the mounts.

6) yes it's possible, but using an insert is easy and serviceable which is nice and nets a better "product" for not much money.

7) I can't think of a good reason to use an angled shank in all honesty.

8) welded bung is better than tapped control arm. you can use a thinner wall for the whole arm and have greater thickness at the joint, which saves weight and improves strength of the fitting. plus it is serviceable and the bung can be cut out and reused with a new arm when the old one gets wore out.

9) cutom bent arms would be a local fab shop type thing, find somebody with a bender or break out the torch and heat/bend yourself. better yet, cut out whatever is in the way and use a straight arm.

A) 25% is a rule of thumb for both front and rear, due to typical climbing driving and car design, it is easier to hit in the rear than the front.

B) it will be fine, the added stress is on the mount and not on the joint so much, so make your mounts properly braced and rock on.

C) no. axle wrap is controlled by the upper and lower links, where they are relative to the axle centerline will again make a difference to how the axle "wants" to drive around those brackets, but with sturdy brackets it will be well controlled and is unimportant.

D) define "better" pinion angle rotation. Does your pinion go where you don't want it to and overextend your driveline U Joints? if not, don't worry about it. Does your pinion point into your oil pan at any point? that wouldn't be good, metal on metal contact in that sense is not good. Does your pinion point into the rocks when flexed out? probably not good. overall, don't worry about it much unless you plan on doing lots of high speed whoops where the pinion will be flopping fast and often through a large range

E) I dunno, play with the calculator and see what it does to your "numbers" it might be better, it might be worse, it might be physically impossible. IN GENERAL, if you can make it fit, raise the frame side is usually not bad advise, but it depends on the relation to your lowers and desired anti-squat performance. This is also why adjustable upper frame side brackets are very common. ~1" spacing makes for quick and easy options to play with.

F) there are way more 4 links out there built around "what fits" than there are with math behind them, it will be fine. the calculator is a great guesstimating tool for general notions on how things might react and change, but it is all based on assumptions. build what you've got in mind, make some adjustments available in your mounts, change it if it doesn't do what you want it to do



those are all just my thoughts, take it for what you paid for it :beer:
 
after noticing your last picture "at ride height" i'd honestly probably lower your upper frame side mount 1" and see what happens. again, make the mount where you have it, then another hole 1" up and another 1" down and see what you like.
 
D) define "better" pinion angle rotation. Does your pinion go where you don't want it to and overextend your driveline U Joints? if not, don't worry about it. Does your pinion point into your oil pan at any point? that wouldn't be good, metal on metal contact in that sense is not good. Does your pinion point into the rocks when flexed out? probably not good. overall, don't worry about it much unless you plan on doing lots of high speed whoops where the pinion will be flopping fast and often through a large range

E) I dunno, play with the calculator and see what it does to your "numbers" it might be better, it might be worse, it might be physically impossible. IN GENERAL, if you can make it fit, raise the frame side is usually not bad advise, but it depends on the relation to your lowers and desired anti-squat performance. This is also why adjustable upper frame side brackets are very common. ~1" spacing makes for quick and easy options to play with.



after noticing your last picture "at ride height" i'd honestly probably lower your upper frame side mount 1" and see what happens. again, make the mount where you have it, then another hole 1" up and another 1" down and see what you like.

Thanks for the advice.

D) Since I have a 2 Door this vehicle is already sensitive to pinion angle changes. From what I have started to read, I may want to keep the UCA and LCA closer to the same length to have a more stable pinion angle during travel.

E) What is a decent range for anti-squat? I would like the vehicle to climb a little better and feel more stable on climbs.

Should I go with crankshaft centerline or top of bellhousing for COG, This seems to change my anti-squat value by 20 points. Playing with COG and the simple mods I can do; my anti-squat range is between 53%-120% using the old simple 4-link v3.1 calculator.
 
Thanks for the advice.

D) Since I have a 2 Door this vehicle is already sensitive to pinion angle changes. From what I have started to read, I may want to keep the UCA and LCA closer to the same length to have a more stable pinion angle during travel.

E) What is a decent range for anti-squat? I would like the vehicle to climb a little better and feel more stable on climbs.

Should I go with crankshaft centerline or top of bellhousing for COG, This seems to change my anti-squat value by 20 points. Playing with COG and the simple mods I can do; my anti-squat range is between 53%-120% using the old simple 4-link v3.1 calculator.

Something like upper arms at 70% of length of lower arms will hold the pinion at the least amount of rotation through travel. equal length "points" the pinion towards the T case i.e. rolls up on droop and points down on compression. somewhere between all those is more ranges of travel. The calculator should have a "pinion change angle" if you put in travel amounts. If not the version you have, there is a new version of the calculator posted by TreeFrog in General4x4 and i believe the "Articles" section way up on top of this site.

it is reasonable to try to keep pinion angle change in the single digits.

antisquat about 75-90% sound good? sure :) top of the bellhousing is probably a reasonable place to guess from, but like you can see the COG plays a huge role and it's all a reasonable guess on paper and very real in real life. hence making it adjustable, a range from 53%-120% to be able to change pretty easily on the vehicle should be fine. Start in the middle, see if it does what you like. set it to one extreme, drive a bit, set it to the other extreme, see the difference and then you'll have real feedback from how it really is.
 
Something like upper arms at 70% of length of lower arms will hold the pinion at the least amount of rotation through travel. equal length "points" the pinion towards the T case i.e. rolls up on droop and points down on compression. somewhere between all those is more ranges of travel. The calculator should have a "pinion change angle" if you put in travel amounts. If not the version you have, there is a new version of the calculator posted by TreeFrog in General4x4 and i believe the "Articles" section way up on top of this site.

it is reasonable to try to keep pinion angle change in the single digits.

antisquat about 75-90% sound good? sure :) top of the bellhousing is probably a reasonable place to guess from, but like you can see the COG plays a huge role and it's all a reasonable guess on paper and very real in real life. hence making it adjustable, a range from 53%-120% to be able to change pretty easily on the vehicle should be fine. Start in the middle, see if it does what you like. set it to one extreme, drive a bit, set it to the other extreme, see the difference and then you'll have real feedback from how it really is.

Upper arms the same length as and parallel in side view provides the least pinion travel. 70% is generally about the point where antisquat increase as the suspension compresses and decreases as in droops out. Pinion angle change is usually good in the rear as it can help with angle extremities and keeping the pinion out of stuff. Its under Resources up top. If memory serves, 3.1 has travel, but the newer versions are a bit clearer about it.

Regarding antisquat, I would say that in V 3.1, try to stay under 90% at full compression, this gives some leeway with regards to the front being fully extended. This will keep it from going over 100% when climbing. If you do go to a newer calc version, 50% drive bias works for flat ground, 100% rear bias is the same as all weight off the front when going up.
 
Upper arms the same length as and parallel in side view provides the least pinion travel. 70% is generally about the point where antisquat increase as the suspension compresses and decreases as in droops out. Pinion angle change is usually good in the rear as it can help with angle extremities and keeping the pinion out of stuff. Its under Resources up top. If memory serves, 3.1 has travel, but the newer versions are a bit clearer about it.

Regarding antisquat, I would say that in V 3.1, try to stay under 90% at full compression, this gives some leeway with regards to the front being fully extended. This will keep it from going over 100% when climbing. If you do go to a newer calc version, 50% drive bias works for flat ground, 100% rear bias is the same as all weight off the front when going up.

thanks for straightening me out :beer:
 
So after more playing around I have come to the conclusion that my numbers are not so good. I think I'm going to give it a go with these numbers so I can see if I feel a difference. I'm really limited by the short length of my control arms. UCA=20" and LCA=22" These short length arms limiting my placement and joint separation of 9" on the axle. If I move the arms much or increase separation I get binding of the joints and limited articulation. I may have the ability to lower the UCA mount on the frame to improve the numbers, but I think I want to drive it this way and try it out before lowering the UCA mount.

I did go to a car lot and measure a stock JK and a 3.5" lifted jk to get an idea of numbers. I used the same weight and wheelbase settings and used the front body mount height on all vehicles for COG measurement. I believe that may be a little low, but it seems to be about 1" above the crankshaft bolt. This at least keeps it consistent.

The combo I will try and drive for now.
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My proposed change with lowering UCA 1.5"
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Stock JK for reference:
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3.5" Lifted JK for reference:
Click image for larger version Name:	my jeep.jpg Views:	3 Size:	49.6 KB ID:	289845
 
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