Synergy Long Arm install - Rear Axle/Spring position - JKowners.com : Jeep Wrangler JK Forum
 
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post #1 of 10 Old 02-17-2019, 03:38 PM Thread Starter
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Synergy Long Arm install - Rear Axle/Spring position

Looking for some feedback on rear axle position/ spring angle after installing a synergy long arm kit with 6" springs.

Their recommended lower rear control arm length is 31 5/8 as a starting point for 4.5" lift springs so that is what I started with. Shortened it to just below 31 1/2" when I was setting the pinion angle. Compared to the factory position of the original arms, I am still about 1" further back where it sits now.

The synergy wedges for the rear springs were not enough and there is quite a bit of bowing of the spring to the back which can be seen on the drive side pics. I mocked up cutting the perches and spinning them on one side by inserting a spacer below the back of the spring (with the red strap hanging below in the pics, Passenger side) to help get rid of the bow in the spring which straightened it out.

Just not sure if I should shorten the control arms more to pull the springs in towards the factory location and get them vertical or if the axle position is ok. Thoughts anyone? Plan to cut the perches and spin them once I get things where they should be.
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post #2 of 10 Old 02-17-2019, 07:27 PM
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Subíd. Working on mine as well and Iím curious.
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post #3 of 10 Old 02-17-2019, 07:31 PM
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I would put a tire on and see how the tire sits in the wheel well at ride height.

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post #4 of 10 Old 02-18-2019, 03:03 PM Thread Starter
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Have to wait on the tires as I need to get the backlash fixed in the rear end and then get the axleshafts, brakes etc back on. Just going for approximate right now, I'll have to fine tune later on. With the 3-4" lift, short arms and 37's I already had to clearance the pinch seams, so pushing the wheel back a little bit as I have shouldn't hurt. I am just not sure how crucial it is that the springs are vertical. I know I do want the lower spring perch as close to parallel with the upper but I'll need to get my hands on some new weld on ones once I get things mostly in their place to correct for the axle twist to get the pinion angle correct.

I had read that you loose a spring rate if your springs are bowed, which makes sense since one side is getting more weight then the other.
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post #5 of 10 Old 02-18-2019, 03:27 PM
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If the rear springs are bowing a little bit due to the perches not being parallel to each other, the loss in spring rate is negligible. They have to REALLY be bowing to have an effect. The bigger issue is usually the coil springs getting into the rear axle side track bar bracket.

Just remember it is a dynamic system, so the perches are going to change relative to each other throughout the travel. Setting them parallel to each other at ride height with the correct pinion angle is typically a good middle ground and will keep them from getting too out of sorts at bump and droop. I would just tack them in until you have a chance to cycle with the tires mounted though. The tires are going to tell you where the axle position needs to be.

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post #6 of 10 Old 02-18-2019, 04:28 PM Thread Starter
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Thanks for the reply Chris, so the spring angle being maybe 5 degrees further towards the back at the bottom vs top instead of being vertical is still ok? If I get the wheels on, and to keep it centered in the wheel well, need to move the axle back even further you think that's ok?
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post #7 of 10 Old 02-18-2019, 04:56 PM
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Moving the axle back too far may cause issues with the track bar clearance. I would center the axle at ride height with the top perches. I just use a plumb bob. Then cut the axle perches off and rotate them so they are centered and level at ride height. I aways did like to move the rear frame side track bar bracket back about 1.5" and would recommend it if you are not running a good centered axle.

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post #8 of 10 Old 02-19-2019, 12:21 PM
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The axle being moved back is a bit of a misconception. When you lift the vehicle, the control arms will be at more of an angle and need to be longer to keep the axle centered at the new ride height. This works out because the height of your bump stop spacers is also affecting where your axle is at bump. You are just trying to keep the axle centered in the wheel wells and the range of your wheel travel has been spaced down. So, despite your arms being longer, your axle may not actually be moved back. With long arms, the arc of your wheel travel is larger, but the axle is still moving. Center your axle at ride height, set your pinion angle, then figure out where your spring perches should be. If you are actually moving your axle back even further, @thedirtman has some good advice. You may run into wheel well/fender clearance as well which may need to be addressed.

When we do builds with new axles, we typically get the axles bare with no brackets. Then we can set all the brackets in the correct locations for the ride height, pinion angle, and axle location. Otherwise, it is always a game of compromises where everything needs to be.

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post #9 of 10 Old 02-19-2019, 12:32 PM
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Quote:
Originally Posted by thedirtman View Post
Moving the axle back too far may cause issues with the track bar clearance. I would center the axle at ride height with the top perches. I just use a plumb bob. Then cut the axle perches off and rotate them so they are centered and level at ride height. I aways did like to move the rear frame side track bar bracket back about 1.5" and would recommend it if you are not running a good centered axle.
Please don't e-slap me for asking such a dumb question -- which reference points do you like to use when measuring axle ride height?
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post #10 of 10 Old 02-19-2019, 06:18 PM
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I generally use an angle finder on the pinion.

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