Control arm separation

hosejockey61

hosejockey61

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I'm in the middle of building a HP30 and using all new brackets etc.

My understanding is that it is optimum to have our TJ's control arms parallel to each other. Out of curiosity and to further my suspension education (specifically @mrblaine 's knowledge does not equal understanding), I checked three different stock TJ's and found that in stock form there is approximately 3 degrees different from back to front (the front has more separation). Why did the engineers do that? @jjvw speculated that it could be due to packaging but I don't see it.

Is it better to keep the minor separation difference or would it be better to make them parallel? I can make it work either way, but want to do what is most beneficial.

By the way, Artec brackets suck. Wish I would have known the drawbacks prior to purchasing. I'm abandoning the lower mounts and reworking the other parts.
 
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hosejockey61 said:
I'm in the middle of building a HP30 and using all new brackets etc.

My understanding is that it is optimum to have our TJ's control arms parallel to each other. Out of curiosity and to further my suspension education (specifically @mrblaine 's knowledge does not equal understanding), I checked three different stock TJ's and found that in stock form there is approximately 3 degrees different from back to front (the front has more separation). Why did the engineers do that? @jjvw speculated that it could be due to packaging but I don't see it.

Is it better to keep the minor separation difference or would it be better to make them parallel? I can make it work either way, but want to do what is most beneficial.

By the way, Artec brackets suck. Wish I would have known the drawbacks prior to purchasing. I'm abandoning the lower mounts and reworking the other parts.
Click to expand...
The only parallelism I care much about is when viewed from the side. Overhead view I do not care about in the least.
 
One of the things we compared was stock to the Savvy mid arm. The mid arm is parallel from the side, or very close to it. Factory is less so, with the axle side having a bit more separation than the frame side. Artec does the opposite of the mid arm in that the axle side lowers are lower than stock. This is dumb for several reasons.

My argument that day was to at least mimic the factory lowers, but work towards making the upper and lower arms parallel even on a short arm lift.
 
jjvw said:
One of the things we compared was stock to the Savvy mid arm. The mid arm is parallel from the side, or very close to it. Factory is less so, with the axle side having a bit more separation than the frame side. Artec does the opposite of the mid arm in that the axle side lowers are lower than stock. This is dumb for several reasons.

My argument that day was to at least mimic the factory lowers, but work towards making the upper and lower arms parallel even on a short arm lift.
Click to expand...

I'm trying to leave any bracketry out if it. Think in terms of stock mount locations. That will help me determine appropriate bracketry. Only question is why Jeep engineers added the approximate 3 degrees of separation when looking at side view.
 
hosejockey61 said:
I'm trying to leave any bracketry out if it. Think in terms of stock mount locations. That will help me determine appropriate bracketry. Only question is why Jeep engineers added the approximate 3 degrees of separation when looking at side view.
Click to expand...

The question is whether to duplicate the factory or is there an improvement to be made to the front short arm geometry after a 4" lift. This is on a shaved axle awaiting brackets.
 
jjvw said:
The question is whether to duplicate the factory or is there an improvement to be made to the front short arm geometry after a 4" lift. This is on a shaved axle awaiting brackets.
Click to expand...

Yes and no.

The original question is, why did Jeep engineers opt to have greater separation at the front instead of having the arms parallel.

Your second question is valid... Is there a better bracket set up (axle side only at this point) when going to a 4" lift.
 
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hosejockey61 said:
I'm trying to leave any bracketry out if it. Think in terms of stock mount locations. That will help me determine appropriate bracketry. Only question is why Jeep engineers added the approximate 3 degrees of separation when looking at side view.
Click to expand...
Because that was enough parallelism to hold the caster angle change within a tolerable range versus suspension travel to keep everything out of trouble. As you increase travel, that needs to be paid more attention to. It also gets harder to do as you increase arm length.
 
jjvw mentioned this frame end spread controlling the pumpkin roll during swing. i took almost all the spread i could at the top end, but it's not what Savvy holds.

i tried to play with a model for this with hole positions to try and find a control point that would keep my pinion in the same relationship it is at rest for as deep into droop as i could. or to roll it up some as it drooped out and away.
 
someguysjeep said:
jjvw mentioned this frame end spread controlling the pumpkin roll during swing. i took almost all the spread i could at the top end, but it's not what Savvy holds.

i tried to play with a model for this with hole positions to try and find a control point that would keep my pinion in the same relationship it is at rest for as deep into droop as i could. or to roll it up some as it drooped out and away.
Click to expand...

Parallel arms that are the same length will maintain the caster throughout the travel. I think the emphasis on maintaining the pinon throughout the travel is misguided.
 
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someguysjeep said:
tried to play with a model for this with hole positions to try and find a control point that would keep my pinion in the same relationship it is at rest for as deep into droop as i could. or to roll it up some as it drooped out and away.
Click to expand...

We're you able to determine anything from your model? I was going to tack my "like stock" brackets in different positions to see what the results would be. That be based on if I have time or not. It'd probably be easier to make a cardboard sample and do it that way. Then I could draw lines of travel and compare the difference. I know I wouldn't be the first to do this but it would be interesting to see the results.
 
jjvw said:
Parallel arms that are the same length will maintain the caster throughout the travel. I think the emphasis on maintaining the pinon throughout the travel is misguided.
Click to expand...

Interesting thought.

The whole pinion takes precedence over caster is simply to eliminate vibrations. The locking hubs is the solution IMHO. I'm surprised there isn't more aftermarket support in that area. It would be nice to maintain stock caster numbers and not have vibes.
 
hosejockey61 said:
We're you able to determine anything from your model? I was going to tack my "like stock" brackets in different positions to see what the results would be. That be based on if I have time or not. It'd probably be easier to make a cardboard sample and do it that way. Then I could draw lines of travel and compare the difference. I know I wouldn't be the first to do this but it would be interesting to see the results.
Click to expand...
Hmm...I might be able to mock up a quick sketch tomorrow at work, assuming my day doesn't go to hell. I have solidworks...the dimensions might not be relatable to an actual axle, but I can definitely mock up the parallel vs non parallel and see what it does to pinon and caster...

no promises on timing though. Going on vacation next week...
 
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peg board works well......................yah pinion control for castor while driving, slow speed makes it not super critical to retain for crawling. but i started with a deficiency of angle at the pinion into my driveshaft. so not making it worse during travel did have some use to me.
 
hosejockey61 said:
We're you able to determine anything from your model? I was going to tack my "like stock" brackets in different positions to see what the results would be. That be based on if I have time or not. It'd probably be easier to make a cardboard sample and do it that way. Then I could draw lines of travel and compare the difference. I know I wouldn't be the first to do this but it would be interesting to see the results.
Click to expand...
for me it was similar to the suspension calculator the info was only a teaching tool to learn what movements gave what results and what was gonna happen with the set-up i had space to produce.
 
hosejockey61 said:
I'm surprised there isn't more aftermarket support in that area. It would be nice to maintain stock caster numbers and not have vibes.
Click to expand...
How many choices do you need? I know of at least 4, maybe 5 options.
Omix-ada
Milemarker
Yukon
Solid Axle Spin free kit
And some oddball damn thing that uses a bizarre unit bearing.
Some may be out of date but they weren't not long ago. I think even Alloy USA dabbled in one for a bit.
 
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jjvw said:
Parallel arms that are the same length will maintain the caster throughout the travel. I think the emphasis on maintaining the pinon throughout the travel is misguided.
Click to expand...
they are connected and the relationship cannot change, so castor control is pinion control and vice n versa, no?

i had set axle mounting points and only played with what would be the frame end mount points.

we are pulling the lower off the riser up front it ends up a little lower below the frame rail this suffices to lowering that angle back into the chassis. this and your BL then allow all that separation to the upper mount, yes?

what would happen if we strung a line from our link bolts on the axle end 30" out, inline through the frame connection points?
then pull the lower line down to where we can attach the bracket on the rail, and then bring the upper down keeping it in the same relationship.
 
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