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Measuring LCAs with flex joints and bends?

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Old 08-06-2017, 10:27 AM
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Default Measuring LCAs with flex joints and bends?

Today I'm pulling off my front lower adjustable arms because I wasn't happy with where my caster was. 2.9deg driver side, 2.4deg passenger.

With my lift height, most recommend of length of 23" to 23.5", where I originally dialed them in for 22 3/4". So it makes sense my caster is lower than expected.

However, when I was measuring them to adjust their length, I noticed something I hadn't really paid attention to when I originally installed them. When measuring from eye to eye, if I measure them on the outer side of the arm eye sides, the length is 22 1/4", and when I measure them on the inner side of the eyes they're 22 3/4".

Here's a picture to give you an idea of what I'm talking about. It might be hard to see and I'm sure the tape measures aren't laid in the exact position, but hopefully it still gets the idea across. The measurement is less on the side of the arms that the bend is towards.


When taking the measurements, I have the eyelets of the flex joints set so that they're centered within the joint. It seems like the reason the measurements are different between the 2 sides are due to the bends in the arms. I know I'm not the only one with arms with bends and flex joints, but I have never heard anyone mention how to measure given that situation.

So what is the proper way to take measurements on a LCA which has a bend and flex joints?

Last edited by Rednroll; 08-06-2017 at 10:30 AM.
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Old 08-06-2017, 12:08 PM
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I don't know if there is a proper way, but if it helps, i have the Synergy adjustable, and they're bent like yours, i measured them at 23 1/8", with the bent on the outer side, i have 5.2* caster with 3" lift in the front.
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Old 08-06-2017, 12:16 PM
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Originally Posted by rsmwrangler View Post
I don't know if there is a proper way, but if it helps, i have the Synergy adjustable, and they're bent like yours, i measured them at 23 1/8", with the bent on the outer side, i have 5.2* caster with 3" lift in the front.

Good to know. I was considering measuring so it was 23 1/4 on one side which should make the the other side 22 3/4", and therefore splitting the difference, in the middle would be 23".

I have about 2.5" of lift, so based on where you're at, I may go with 23" with the bend on the outer side, unless someone else has some other advise.

Thanks!!
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Old 08-06-2017, 03:58 PM
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Place jack under pinion, remove arms. Jack pinion to 1-2 at the flange, adjust one arm to mounts, remove, place next to other arm and adjust to match (slide bolts through both holes, tighten jam nuts, install, done.
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Old 08-06-2017, 04:07 PM
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Also the joints have to be straight no matter angle of housing.
When matching lengths center the joints first before sliding bolts through.
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Old 08-06-2017, 07:46 PM
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Originally Posted by kjeeper10 View Post
Place jack under pinion, remove arms. Jack pinion to 1-2 at the flange, adjust one arm to mounts, remove, place next to other arm and adjust to match (slide bolts through both holes, tighten jam nuts, install, done.
This I wish I knew how to do in understanding on how to measure the pinion angle


Originally Posted by kjeeper10 View Post
Also the joints have to be straight no matter angle of housing.
When matching lengths center the joints first before sliding bolts through.
This I can do.
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Old 08-06-2017, 09:16 PM
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Pinion is pinion angle. The stock axle has around 6 between the two angles (stock 2 pinion and 4 caster) so setting pinion to 1-2 will get ya 4-5 caster.
I like to measure straight off the flange where the DS Mounts. Theres room to get a angle on there just make sure its flush.
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Old 08-06-2017, 10:24 PM
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I was taught similar to Kjeeper10... almost.

1. Measure your ride height between the bumpstop pad on the axle and the bumpstop on the frame (where the OEM foal bumpstop inserts). Remember this measurement.

2. Support the axle with jacks. Remove control arms and the coils. Position the axle so that it's centered under the frame-side bumpstops and at the distance from the frame-side bumpstops that you measured in #1

3. Install the lower control arms and snug the bolts (but don't torque to spec). Install one upper control arm (just so the axle won't rotate the pinion up)

4. Install the coil springs. Put the wheels back on and put the vehicle on the ground on its tires. (upper CA installed was just for safety)

5. Use your jack under the differential just behind the pinion to get the axle to the point that the upper control arm can be unbolted from the axle.

6. Set your pinion angle to desired setting which means you're setting your caster (6 degrees between the two, so -2 degree pinion is 4 degree caster)

8. Install upper control arms while the axle is set to the desired caster.

9. Let the jack down so the vehicle is on its own weight. Bounce the suspension around a bit. Torque everything to spec.

It helps to have gotten a proper caster reading on an alignment rack (this is the only time I subscribe to getting an alignment). Then park in your garage and read the pinion angle off the axle flange. Doing this gives you the ability to measure your own caster in your garage.

Example:
Alignment Machine Caster = 3 degrees
Measured Pinion (in your garage) = -1 degree
Calculated Caster (in your garage) = 5 degrees (because there is 6 degrees of separation in an OEM JK axle)
Correction Factor = Calculated Caster - Alignment Machine Caster = 2 degrees

If you want a caster of 5 degrees, then you set your pinion angle (in your garage) at 1 degrees.

Measured Pinion + 6 degrees = Measured Caster (before correction) = 7 degrees

Actual Caster = Measured Caster - Correction Factor (2 degrees in this case) = 5 degrees of actual caster

#########

Like I said, this is what I was taught and did to mine. When I took it back to my friend who has access to an alignment rack I was within 0.1 degree of what I thought I had set my caster to.

The piece you may wonder about.... By setting my control arm lengths this way, when the axle makes its arc toward the frame (compression) how far from center am I between the frame-side bumpstop and the axle side bumpstop.

I took the springs back out and the shocks off. I used jacks to bring the axle to full compression (frame-side bumpstop meets the axle-side bumpstop) and it was off, but not enough to make me worried.

That said, I'm running 3 1/8" of actual lift... so the amount I'm off would grow with more lift.

Now... I'm hoping Dirtman will weigh in on this as I really don't know if this is the best/worst/okay way to get to a correct control arm length.
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Old 08-06-2017, 10:36 PM
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Pretty much did the same with all 8 CA's ^^ my instruction was for the two lowers only.

I set my lowers matching (to start) and installed. Then adjusted both uppers to the mounts with jack under the pinion. Rear i left alone front i was off a degree on the alignment rack. Axles were both square, all i ended up doing was shortened my front uppers to add a degree caster .
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Old 08-07-2017, 10:02 AM
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I wish there was a youtube video showing how to best measure the pinion angle since I'm having trouble getting my head around this part. I knew what my caster was until I pulled that LCA shown above off.
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