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Thread: Lifting a JK - introduction

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    Trip Coordinator/Association Delegate Dru's Avatar
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    Default Lifting a JK - introduction

    Kerry and I have spent some time working through what a lift does - very often learning the hard way. It's a topic that ask 10 Jeeper and you'll get 20 different answers - so go easy on me. Just my thoughts.

    First, let's start with a pretty decent introduction to the components and key issues when modifying your Jeep.

    https://www.youtube.com/watch?v=ZttaTkR2OLk


    Then we can talk about how the typical lift systems in Australia relate.

    Note that
    a) the this does not at all apply to the IFS/IRS Jeeps: WK2, Trailhawk etc.
    b) but the themes completely apply to all live axle jeeps, TJ and probably the JL too.

    Dru'n'Kerry
    Last edited by Dru; 2 Weeks Ago at 10:05 AM.

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    Trip Coordinator/Association Delegate Dru's Avatar
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    OK summarising what happens when we lift a Jeep:

    1. Because the jeep is higher off the ground the wheels, and with the wheels the axle drops lower away from the Jeep chassis. Because the live axle does not travel straight up and down, but rotates around the control arms (forward and back), as the axle drops the front goes backwards a bit, and the rear goes forward a bit.

    2. Not only the wheel base is shorter, but the angles of everything that controls or attaches to the axle just changed. As that geometry was optimised by Jeep for ride control in the factory and before you started mucking around with it, your Jeep is no longer optimal! The bigger the lift, the more extreme the issue. Two keys for the front end: caster angle and pinion angle.

    3. Caster angle: Take the front wheel off a push bike with the forks and handle bars. Now position it so that the forks are totally vertical. It is easy to see a vehicle engineered like that is going to be really manouverable, but any road input or bump/bounce will also turn the wheel. So easy to turn but not easy to keep going straight. Now set it up like easy rider with the wheel way out in front on a long angle. Engineered like this the vehicle will stay straight, isnt going to get off line _ _ _ AND wont go around corners.

    That is caster angle. In a JK lift kit, the caster is either a) not adjusted and you get what you get; b) has brackets that are designed to adjust in the factory but have no further adjustment; c) are fully adjustable, and (if you know what you are doing) should be really good. Once you lift the Jeep it changes the caster so the steering is flighty and wont stay straight and cruisey like easy rider. We want to shift the angle forward for better handling.

    The problem is, with limited adjustment depending on your kit and how good the guy setting it up is - as you make improve the caster - YOU STUFF UP THE PINION ANGLE. They kind of go together.

    4 Pinion angle: Draw a line through your axle out through the uni joint and along the drive shaft up to the transfer case. Obviously in the perfect world to reduce wear and tear (in the worst case, vibration, whine and heat build up) you want that line to be perfectly straight. But if you increase the caster the line is bent at the uni joint. If your are really pushing your lift, say 6" - the only way to solve it is a new axle that is manufactured with a different pinion angle!

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    Trip Coordinator/Association Delegate Dru's Avatar
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    Here are another two matters to keep an eye on: track bar and drag link.

    1. Track bar: As earlier, when you lift, the axle drops lower (and rotates so that the Jeep track is shorter). But look at things from the front of the Jeep. As the axle is lower, it is held side to side by the track bar. The track bar has to be long enough to allow the axle to travel up and down. So it is NOT mounted onto the jeep in the middle. So it is another suspension component that does NOT travel straight up and down but rotates around a centre point. The effect is the axle is no longer sitting in the middle of the jeep but has become offset to one side.

    So you will want to adjust the new position of the axle.

    3. Drag link: This connects the steering to the front wheels. Set up in the factory, the drag link is parallel to the axle and moves up and down with it. With the lift, it is no longer parallel so as the axle ides up and down, the drag link changes from not parallel in one direction, through parallel to not parallel in the other direction. This has the effect that the steering is not in harmony and going straight - over a bump - the steering will lurch in your hands. So you want the drag link adjust to be parallel with the axle and all working together.

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    Trip Coordinator/Association Delegate Dru's Avatar
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    So what does it mean with the lift kits common here in Sydney?

    MINOR LIFT

    First let's take a minimal approach. Just see what we can get away with no attempt to make geometry correction. YES, these sort of lift is not uncommon in Australia! Not to be fair too much with Wranglers.

    Probably this would be done with either spacers (between the coils and the chassis). Typically you would only go 1 inch more than that is asking for trouble. In theory the geometry changes might be minor and you might get away with it. Cost is low, sometimes the dealer may offer something like this. If you are going through a cheaper lift from an Aussie brand just check out what they do for the geometry.

    Avoid these lift kits if you can. Not recommended.
    Last edited by Dru; 2 Weeks Ago at 11:24 AM.

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    Trip Coordinator/Association Delegate Dru's Avatar
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    STANDARD 2' OR 2 1/2' LIFT.

    Available from pretty much all Jeep mod manufacturers but the big three are probably AEV (American Expedition Vehicles), Terraflex, Synergy.

    What these kits do is try to keep the cost down by lifting as much as they can withOUT needing adjustable everything. Adjustable stuff is expensive to manufacture. Typically it invloves beefed up brackets that are pre-drilled to ensure that the geometry correction is sorted out automatically. There is some adjustment eg the track rod but on the whole the kit should be "set and forget".

    As it so happens, these kits will let you install 33" on the 2' lift so that you are at the legal limit and do not need to get certification and engineering in NSW.

    Another advantage is that, other than bolting it all together, there is nothing to adjust, no fine tuning knowledge required - bolt it together and go wheeling!

    You can see why this lift system is considered something of a "go to" at the SJC. Very effective, sensible, and with an experienced driver a huge step up from stock. And the Jeep was good stock anyway!

    Highly recommended.

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    Trip Coordinator/Association Delegate Dru's Avatar
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    3" 3.5" 4" Lift - typically AEV, Terraflex, Synergy.

    This stuff is NOT "plug and play". Everything needs adjusting and there is more than enough room to build in strife - or to really fine tune things. The kit is a lot more expensive and takes a lot more time to build.

    You need it for 37's, I'd recommend it for 35's though plenty of Jeepers disagree.

    I don't think it's enough to leave this with the mod shop - you are on a journey here and will want to be directing how you want it looked after. Quite likely that it is not perfect the first time - these systems need fine tuning. Sensational ability off road, should be great on road. Just more work.

    Recommended? Yes but expect to need to work it through.

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    Trip Coordinator/Association Delegate Dru's Avatar
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    Other advancements?

    Off set to new wheels - in essence making the Jeep track wider so that it is less tippy after lifting. A great improvement for road handling, but resolving clearances to rubbing tyres can be painful and new mud guards may be required.

    Want to go extreme? It's a Jeep there is ALWAYS more you can do if you insist.

    Long Arms: Longer control arms which means that the radius the axle uses is longer - much more straight up and down. Also more movement available. Problems? More movement the suspension just has a little more "slop" so engineering is a little tougher, road handling not quite as tight.

    4 Link rear: I mention it in passing but it removes off centre with the rear track bar so the axle stays centred. Jose has this on his TJ. I suspect it
    will challenge road handling though Jose's TJ seems wonderful!

    Coil Over: The shock absorbers are inside the coils. Allows longer travel but shock maintenance is more involved.

    If you are considering any of this then you will know what is going on and will be running with your own recommendations.

  8. #8

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    Great summary Dru
    Our newer members will be looking for more tips and advice I believe.....thanks for sharing!


    Sent from my iPhone using Tapatalk

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    Trip Coordinator/Association Delegate Dru's Avatar
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    Quote Originally Posted by isherz View Post
    Great summary Dru
    Our newer members will be looking for more tips and advice I believe.....thanks for sharing!


    Sent from my iPhone using Tapatalk
    Yeah, I';m not sure it's very organised, more "stream of consciousness:" but I did promise to nail our experiences, lol.

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