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Unread 08-16-2014, 07:17 PM   #1
underpowered
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HP30 swap...now Death wobble?

Swapped in a HP30 from a 92 XJ today.

No death wobble prior to the swap, but post swap i can't drive over 40 MPH. New control arms bushings, most front end parts are in good shape and only a few years old at most.

Suspension is all stock with only a 2" BB.

The only thing i can think of is my caster is off. XJ uses a cam bolt as the body end of the LCA, ZJ has it at the axle end. so using the XJ axle in my ZJ, i now have no caster adjustment using my stock LCA's. Is this the issue?

Want to be pretty sure before i spring for new adjustable LCA's that they will solve the issue.

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Unread 08-17-2014, 08:54 AM   #2
PolkaPower
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You are on to something there. Most people do not swap hp30's in without bigger lifts/tires and that usually means they have adjustable control arms. There is also the clearance issues with small or no lift that make it a poor choice to swap in.
The two biggest contributors to DW are the track bar and poor alignment. Other things can cause it too but bad castor and loose track bar will almost certainly guarantee DW.
Without the adjustability in the axle cam bolts there is no way to align it either.
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Unread 08-17-2014, 09:50 AM   #3
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i have no clearance issues, i cycled the suspension to be sure.

Track bar is not new, but 4 years old at most and seems to be in good shape. I ordered some adjustable control arms that will be installed as soon as they arrive that i hope take care of the issue.

also found a bad sway bar end link, so going to be making a new set of those as well.
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Unread 08-17-2014, 04:00 PM   #4
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A few degrees change in caster can make a huge difference in death wobble. On my rig 5 degrees positive seems to be the sweet spot. Two degrees either way and wobble will happen.
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Unread 08-17-2014, 04:10 PM   #5
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Thanks. I'll start there as soon as my new arms arrive
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Unread 08-18-2014, 01:09 AM   #6
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Quote:
Originally Posted by Technohead View Post
A few degrees change in caster can make a huge difference in death wobble. On my rig 5 degrees positive seems to be the sweet spot. Two degrees either way and wobble will happen.
^- this exactly.

Incorrect alignment not only causes DW, it also causes bad handling. Caster angle a couple degrees off from the sweet spot of your lift height/ tire size can make your steering from being good, responsive and calm, to "squirrelly" or wandering all over the road.


Have you already checked toe-in?
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Unread 08-18-2014, 05:17 PM   #7
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that is what i assume. as the caster is the only thing that has changed really in the swap. I am pretty confident the adjustable arms will solve the issue.

anyone know what stock caster spec is on a ZJ?
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Unread 08-18-2014, 10:31 PM   #8
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Quote:
Originally Posted by Timo_90xj
^- this exactly. Incorrect alignment not only causes DW, it also causes bad handling. Caster angle a couple degrees off from the sweet spot of your lift height/ tire size can make your steering from being good, responsive and calm, to "squirrelly" or wandering all over the road. Have you already checked toe-in?
How does one adjust their caster from home for your lift/tire size? I had an alignment done, but I still notice the passenger tire sticking out and the too and leaning in at the bottom. I have a weird wobble and I'd say that's probably the issue.

Not trying to thread jack, but I've tried searching. Also, this is using the lp30, on 33s, with all adjustable arms...
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Unread 08-18-2014, 11:54 PM   #9
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How does one adjust their caster from home for your lift/tire size? I had an alignment done, but I still notice the passenger tire sticking out and the too and leaning in at the bottom.
You mean how can you adjust caster at home? Adjustable UCAs and LCAs are the best idea, cam bolts only offer you some adjustment. You need an angle finder, and start cranking the arm lengths to find the sweet spot.. when doing that, you get really good at unbolting CAs, adjusting length & rebolting

How do you know the right caster for a certain lift height/ suspension setup/ tire size? You don't. You should start with close-to-stock-specs, and adjust it as necessary.



Quote:
Originally Posted by underpowered View Post
anyone know what stock caster spec is on a ZJ?
IIRC stock caster spec. is 5.5*- 7.5*, and stock setup is about there in the middle. On lifted Jeeps this value may be different to achieve proper handling and no DW. However one needs to prioritize pinion angle to avoid DS vibes.
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Unread 08-19-2014, 10:02 AM   #10
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Quote:
Originally Posted by Scopez View Post
How does one adjust their caster from home for your lift/tire size? I had an alignment done, but I still notice the passenger tire sticking out and the too and leaning in at the bottom. I have a weird wobble and I'd say that's probably the issue.

Not trying to thread jack, but I've tried searching. Also, this is using the lp30, on 33s, with all adjustable arms...
Axle rotation causing a camber problem.... Do you have an angle finder?
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Unread 08-19-2014, 10:08 AM   #11
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Quote:
Originally Posted by PolkaPower
Axle rotation causing a camber problem.... Do you have an angle finder?
Could be...makes sense. I do have all adjustable arms btw. I don't have an angle finder, but I have the app on my phone. I'm sure a few buddies would have one I could use.
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Unread 08-19-2014, 10:53 AM   #12
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Caster and camber are not independent. To see that this is true just imagine adjusting your caster by 180 degrees. The camber will be exactly the opposite from when you started.
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Unread 08-19-2014, 03:26 PM   #13
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i'll start near stock and see where that gets me.



and Toe was not checked, but it was also never adjusted as i used my stock ZJ steering on the new XJ axle, and AFAIK the tie rod distance is identical between a HP and LP axle.
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Unread 08-19-2014, 04:59 PM   #14
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I have found that little things like balljoints can affect tie rod length. My toe was out of whack after replacing the balljoints.
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Unread 08-27-2014, 04:30 PM   #15
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toe is close, not within spec but close. tried adjusting but count not get the bar to turn.

got the new arms on to adjust camber and they do not offer enough adjustability. i cannot shorten them enough as they are, but it is close. the shorter i get them the better the DW gets but then i ran out of room. so now to modify the brand new arms to allow for more adjustability. I think if i can get one more turn from them i will be golden, so going to start by just milling the jam nut down, if that does not get me enough they will be cut, shortened and welded.
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