Over extending rear LCA - JeepForum.com

 
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post #1 of 13 Old 04-17-2014, 07:42 AM Thread Starter
JoeJackson
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Over extending rear LCA

I just installed my Rock Krawler 2.5 max travel lift over the weekend. The whole thing went pretty smooth overall.

The instructions from RK said to put the rear lower control arms to 19 5/8". I had to set these at 20 1/2". What could be the concequence for installing these LCA at a longer length? And how would i make the lower control arms fit if if wanted to shorten them?


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post #2 of 13 Old 04-17-2014, 07:56 AM
JIMBOX
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I haven't used Rock Krawler before, but


Quote:
Originally Posted by JoeJackson View Post
I just installed my Rock Krawler 2.5 max travel lift over the weekend. The whole thing went pretty smooth overall.

The instructions from RK said to put the rear lower control arms to 19 5/8". I had to set these at 20 1/2". What could be the concequence for installing these LCA at a longer length? And how would i make the lower control arms fit if if wanted to shorten them?
Unless you changed the UCAs, I would assume that by extending your LCAs---your Pinion angle is now very Negative and you'll get a lotta vibration-

Probably Rock Krawlers will tell you pretty quick-

I'm probably wrong !

Good luck

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post #3 of 13 Old 04-17-2014, 08:01 AM
duneslider
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What was the reason you had to set them 7/8" longer than recommended?

Is your pinion perfectly inline with the drive shaft at ride height?
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post #4 of 13 Old 04-17-2014, 10:56 AM
brianjw
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You aren't giving us enough information. You are asking what the consequence would be to shorten them, without telling us why you HAD to run them longer.
If you had to set then long for some reason, shortening them is going to affect whatever made you set them long...? Help us out here. Lol
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post #5 of 13 Old 04-17-2014, 11:29 AM Thread Starter
JoeJackson
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When i set the LCA to the recommended length they would not reach the axel, they were way to short. There is a vibration sometimes now in the rear while im driving. I have not driven it very far yet, just around the block a few times.

Ill have to look when i get home but im pretty sure that the pinion is not perfectly aligned from what i remember last night. How can i shorten the LCA and make them reach the axel?

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post #6 of 13 Old 04-17-2014, 11:40 AM
duneslider
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You need to rotate the axle to make the arms line up, it pivots. By lengthening the arms you are moving the axle out of alignment with the driveshaft which can create vibs and mess stuff up.

If you remove both lower arms and have a jack under the pinion area you can jack the pinion up and get everything aligned.
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post #7 of 13 Old 04-17-2014, 11:44 AM Thread Starter
JoeJackson
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perfect. thanks for the help. ill do that as soon as i get home.

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post #8 of 13 Old 04-17-2014, 11:51 AM
brianjw
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It is difficult without a friend. Block the front tires, remove the parking brake and put it in nuetral (level surface). You may be able to roll the axle forward with the tires. Or use a jack under the axle and push it. Or ratchet straps from the axle to frame, etc. lots of options but another set of hands helps.
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post #9 of 13 Old 04-17-2014, 01:04 PM
duneslider
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Agreed, I have done it both ways and when you have a buddy to help it does make it go easier. That way one can work on manipulating the axle and the other can stuff the bolts.
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post #10 of 13 Old 04-17-2014, 03:04 PM
222Doc
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unless you have a cardan drive shaft the rear pinion should be paralell to the out put of the trans.


the set up for a cardan


As you lift the jeep the arms tilt in shorting the wheel base a bit. Longer lower set the base a bit longer. But to adust the pinion at that point you need upper ca's.

Rotating the Pininon up rotates the springs and the track bar back, to much and they will contact the rear springs.

exception is the front. You set it for caster over pinion. Since the front in most cases is a NO load it wont viberate unless you are running a lot of gear and the angle is excessive. Off road with load the speed is slowenough to not be a issue. On big lifts it becomes an issue and the only fix is a custom fron axle housing with higher inion angle.

http://www.parker4wheelers.net
www.bullhead4wheelersinc.com
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post #11 of 13 Old 04-17-2014, 03:13 PM
SubAtomicGenius
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Quote:
Originally Posted by brianjw View Post
It is difficult without a friend. Block the front tires, remove the parking brake and put it in nuetral (level surface). You may be able to roll the axle forward with the tires. Or use a jack under the axle and push it. Or ratchet straps from the axle to frame, etc. lots of options but another set of hands helps.
Ratchet straps are your friend when doing work alone!
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post #12 of 13 Old 04-17-2014, 03:44 PM
222Doc
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Quote:
Originally Posted by SubAtomicGenius View Post
Ratchet straps are your friend when doing work alone!
off road too. We have used them to hold a axle in place after the control arm ripped off. If not for the 3" super duty type that would have been a nightmare to get him off that trail that day. We got him to town off a class 9 in cali. then had a guy weld him up. with nothing but the winch hold one side and that strap hold it the other way. i carry two of these every off road ride.

http://www.parker4wheelers.net
www.bullhead4wheelersinc.com
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post #13 of 13 Old 04-18-2014, 07:31 AM
brianjw
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Quote:
Originally Posted by 222Doc
unless you have a cardan drive shaft the rear pinion should be paralell to the out put of the trans.

the set up for a cardan

As you lift the jeep the arms tilt in shorting the wheel base a bit. Longer lower set the base a bit longer. But to adust the pinion at that point you need upper ca's.

Rotating the Pininon up rotates the springs and the track bar back, to much and they will contact the rear springs.

exception is the front. You set it for caster over pinion. Since the front in most cases is a NO load it wont viberate unless you are running a lot of gear and the angle is excessive. Off road with load the speed is slowenough to not be a issue. On big lifts it becomes an issue and the only fix is a custom fron axle housing with higher inion angle.
The factory rear driveshaft on mine had a CV on the transfer case. In this case the pinion should be inline with the driveshaft. Operationally it is the same as a dual cardan shaft. The u joint on the axle end should operate at no angle. If you have a single u joint on both ends then they should be at equal angles to cancel out the u joint movement.

If the springs are rotated back too much, you can add synergy coil wedges like I did. It does provide a small lift (1/2") but it keep the coils straighter. If you push the axle back too far you may run the bump stops into the track bar bolt or bracket, depending on the design of the extended bump stop.
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