Front Axle hop??? and rear end thunking

This has been a problem for a few yrs now. When I try to climb a sand dune, the front end starts violently shaking when the front wheels start spinning. As the title says, it feels like axle hop, but from up front. Needless to say, this causes an immediate loss of forward momentum.

Things replaced:
All new bushings in stock suspension - no effect.
RE LCAs with first iteration of lift - nothing
RK 3 link, uses new frame side control arm mounts and all hard joints - just tested it yesterday on a dune, problem still there.
Along with the 3 link, I also put in some Brown Dog poly motor mounts. Stock mounts (driver's side really) were shot anyways.

I'm running an HP30 with 4.88s, open and stock axle side control arm mounts with RE5.5" coils and blown RE monotube shocks.

Out back are RE 3.5" leafs with JKS 1" Boomerangs and 2 more blown RE monotubes. Not too impressed with the shocks...They're only a year and a half old. Leafs are the same age and I have developed gangster lean. My sagged, warped stock leafs did the same. Both leafs appear fine, but they didn't lean at all a year and a half ago...this is a fairly new development. Also, there's a loud thunk over any kind of "whoops" (smooth and less than a foot high) at anything over a crawl. Sounds like bottoming out, but I'm not sure that's possible with the amount of travel I tend to get back there. But, this is also a new development. The thunk is loudest on the pass side, same side it leans to.

Any ideas?

I'd start with your shocks. I bet that will help immensely.

My TNT setup up front contributes to this (Radius arms vs. 3 link). It's like it's dancing up a hill :roflmao:

I'd bet you're bottoming it out in the back, put some paint on the bumpstop ends and while it's still a little tacky, cause the thunk and see if the paint ends up on the axle tubes. Dunno on the axle hop though.

Climbing dunes ? What is your tire pressure at?

Jeff

MoparManiac said:

I'd start with your shocks. I bet that will help immensely.

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agreed

MoparManiac said:

I'd start with your shocks. I bet that will help immensely.

My TNT setup up front contributes to this (Radius arms vs. 3 link). It's like it's dancing up a hill :roflmao:

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It's done this with the stock shocks as well. However, new shocks are on the list...SO once I can afford them, I will report back. Come to think of it, it did it with the stock shocks after the boost...might've killed them and then it started. Hm...

kastein said:

I'd bet you're bottoming it out in the back, put some paint on the bumpstop ends and while it's still a little tacky, cause the thunk and see if the paint ends up on the axle tubes. Dunno on the axle hop though.

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I've never had bottoming out back before, but I also didn't have gangster lean before. Would bad leaf spring bushings be a possible cause?

JAS said:

Climbing dunes ? What is your tire pressure at?

Jeff

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This time, it was at full street pressure. With 30's, stock suspension and spacers, it happened at about 15-20 as well.

i would be willing to bet that the thunk is your shackle hitting the back of the shackle box. mine is doing the same thing, although i have factory shackles, not boomerangs. i would still check it out though

I'll look for signs of contact although I thought the Boomerang was supposed to prevent that. But maybe I need to adjust my bumps.

Darky said:

This time, it was at full street pressure. With 30's, stock suspension and spacers, it happened at about 15-20 as well.

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Cut that 15-20 PSI down to about 8-10 PSI and try again. Yes there could be some problem parts, but running too high of a tire PSI in the dunes will cause all kinds of fail when climbing.

I run just a small 31x10.50 tire and run in the 6-8 PSI in the dunes... If I do not I get a bunch of hop and bad vibes from smaller hops.

Interesting. I've never run that low in the sand. But then , prior to my XJ, both vehicles were IFS, and therefore I'd imagine it'd be a lot harder to get vibes/hopping from the front end.

If you do run that low get a good 0-20 psi gauge... that you trust.... It darn near impossible to tell the difference between 10 and 15 PSI on a 0-100 gauge that they sell for 99 Cents at the quicky mart.


Does not have to be a liquid filled dial either... I run with about a $5 pencil type that reads 0-20 PSI.