Adjustable control arm length

I installed a Teraflex 3" lift (with all 8 adjustable arms) in my 2013 JKRU and followed TF's specs for control arm length.

Here are TF's specs for a 3" lift:

Front lowers: Driver - 23 7/8"; Pass 24 1/8" (factory front lowers are both 22 5/8") [TF wants the passenger side lower arm longer to eliminate pull to the right.]
Front uppers: Driver and Pass - 19 1/2" (factory front uppers are both 18 3/4")

Rear lowers: Driver and Pass - 20 3/8" (factory rear lowers are both 19 3/4")
Rear uppers: Driver and Pass - 18 3/8" (factory rear uppers are both 17 7/16")

When I set my passenger side front lower to 24 1/8, the axle was so far forward that the passenger side coil spring was touching the tip of the sway bar. So I cranked the adjuster back in so it was 23 7/8" to match the drivers side. The sway bar then cleared the coil spring by 1/4". I have been running the Jeep that way for about 2k highway miles and all is well, steering is fine, tracks straight, no bump steer or other problems. No off road yet.

I have recently read posts saying Teraflex's control arm specs are not correct, various lengths are mentioned all shorter than TF's specs. I also asked a local 4x4 shop and they said that they setup TF lower arms at 24.0".

I am in the process of installing EVO Plush Ride springs and might as well adjust the control arms while I am at it, if necessary.

So my question is what length should I set my control arms, especially the front arms? Are they too long now at 23 7/8" for the lowers and 19 1/2" for the uppers?

Thanks

See my write up that I did for a 4" TF lift here;

http://project-jk.com/jeep-jk-write...rangler-4-flex-arm-lift-installation-write-up

Even though they were for a taller lift, the numbers I have listed should be closer to what you want.

Thanks for the link and the write up. I actually used that exact write up when I was doing the 3" lift kit install, and it was super helpful.

But I still have a couple questions.

In your write up you said the control arm measurements (23" for front lowers and 18 7/8" for front uppers) were "a starting point". Don't know whether you ended up keeping those numbers or changed them after you tested the Jeep's performance over time?

And your write up is dated Feb 2, 2009 so I am wondering whether my 2013 Jeep has changes that require longer control arms compared to the Jeep used in your write up?

Thanks.

I am wondering the same thing, your advice will be greatly appreciated. By the way, great forum.

wwood said:

Thanks for the link and the write up. I actually used that exact write up when I was doing the 3" lift kit install, and it was super helpful.

But I still have a couple questions.

In your write up you said the control arm measurements (23" for front lowers and 18 7/8" for front uppers) were "a starting point". Don't know whether you ended up keeping those numbers or changed them after you tested the Jeep's performance over time?

And your write up is dated Feb 2, 2009 so I am wondering whether my 2013 Jeep has changes that require longer control arms compared to the Jeep used in your write up?

Thanks.

Click to expand...

The numbers used are good across the board for all JKs. It's a starting point so depending upon how much lift you have you could be perfect at those starting point numbers or you could need to lengthen them or shorten them to get your caster right.


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Don't concern yourself so much on the measurements, worry more about caster, tracking. You could also work with just 3 of the 4 control arms. Leave off the upper driver control arm. Make all your adjustments, drive your Jeep up and down the driveway, and then reattach the 4th control arm.

supra_launch21v said:

Don't concern yourself so much on the measurements, worry more about caster, tracking. You could also work with just 3 of the 4 control arms. Leave off the upper driver control arm. Make all your adjustments, drive your Jeep up and down the driveway, and then reattach the 4th control arm.

Click to expand...

Don't think I understand the idea behind your 3 of the 4 arms idea. Could you elaborate?
I am not really worrying about the measurements, just trying to learn. I like to understand how/why stuff works.

Control arm length is confusing because factory arms are not adjustable yet Jeep puts them in every Jeep. Therefore the frame and axle brackets on every Jeep must be pretty accurately placed by the factory.
Obviously if you lift a Jeep (raise the frame in relation to the axles by installing longer springs) you are going to need somewhat longer control arms or you will be drawing the axles closer together and messing up caster, pinion angles, etc. But why are there different specs brand to brand and mechanic to mechanic for aftermarket control arm length? Why is there not a standard CA length for a 2" lift, 2.5" lift, 3" lift, etc. Factory CAs are all the same, so why are aftermarket CA's not all the same length for a given lift amount.

I put a 3" TF lift kit in my 2013 4 door. TF says, for example, that the front lower CA's should be 23 7/8" and the front uppers should be 19 1/2". But Eddie says the front lowers should be 23 and front uppers should be 18 7/8 for a 4" TF lift. Those differences are significant. Why would TF's numbers be longer for a smaller lift? It looks like TF's numbers are wacky and this is confirmed by other brands who also spec shorter front arms. Metalcloak says you should set their front lowers to 23 1/16 and front uppers to 18 3/4 for a 3.5" lift. These numbers are also significantly different from Teraflex for a 3" lift. Rock Krawler says front lowers should be set to 23 1/8 and you can use the factory uppers for their 3.5" Flex lift.

Presumably, all aftermarket CA makers test their numbers to make sure their kits work? And that caster and pinion angles, etc come out in the ballpark. But since we are putting aftermarket arms in factory bracket locations which are proven to be consistent, the variation in aftermarket CA lengths does not make sense to me.

Many folks say pay attention to caster, not a specific CA length. OK, that makes sense but why is that necessary? Factory caster is set at about 4.1. There is a CA length combo (upper and lower) that will produce 4.1 caster for all reasonable lift amounts. Why is that length not standardized and known to all of us?

Plus caster is not the only factor. When we change caster we also change pinion angle. Since there is only 6 degrees of separation between caster and pinion on the D30/D44 factory axles it is difficult or impossible to get 4 degrees of caster and enough upward pinion angle to avoid driveline stress and vibration for lifts over about 3". On my Jeep caster came out to 3 deg using TF's recommended CA lengths. My pinion angles up about 3 deg as well and I do not get any driveline vibration and luckily my Jeep steers well, tracks well, not flighty at all. But according to TF's specs my caster should be 4. But it ain't. Why?

And there is another factor. TF's rather long front lower CA setting pushes my front axle farther forward than stock. As a result my passenger coil spring almost hits the tip of the sway bar, I had to move the sway bar bracket forward to get adequate clearance. Also the spring perches on my front axle are not centered under the upper spring perches. So, at full stuff, the upper factory bump stop hangs over the rear edge of the axle perch. If I set my front lower CA shorter, say back to 23 instead of 23 7/8, my upper bump stop will land well centered on the axle perch at full stuff. If I do that I will also need to make the front uppers a lot shorter to get my caster back to 3 or a little more. Don't know if there is enough adjustment range in the front uppers to do that.

Right now my Jeep is up on jack stands with the springs out, all CA's loose waiting for parts. I am switching to EVO 3" plush ride springs and would like to get the control arm situation settled at the same time. I still not sure what to do. I don't want to leave the CA's at TF specified lengths even though the Jeep rides well because of the spring perch issue and 3 deg of caster, would prefer more caster but don't want driveline vibrations or other problems. I have a Coast 1310 front drive shaft installed, rear shaft is factory. Hopefully someone can confirm that shortening the front CAs will not cause problems.

Thanks for any feedback.

Newbie question: 2.5" lift - front upper control arm length

I'm installing a 2.5" MC DUAL RATE suspension. It comes with their FRONT UPPER CONTROL ARMS. What should be the
length of the control arms OR what guide should I use to determine the correct length.

Thanks,

JEEP671GUAM said:

I'm installing a 2.5" MC DUAL RATE suspension. It comes with their FRONT UPPER CONTROL ARMS. What should be the
length of the control arms OR what guide should I use to determine the correct length.

Thanks,

Click to expand...

Their length will be determined by your caster angle.