Front End Bounce

[Hiredgoon]

Hi guys

I'm having a curious thing happen, and I'm hoping to narrow it down before I take it in--I'm currently in a place with a parkade that doesn't allow mechanical work done, so I can't spend any time underneath (definitely too cold outside) and I'm hoping maybe there will be some insight here, to save me a bit of money on exploratory mechanical work.

About a month ago, I replaced the stock shocks with a set of adjustable ranchos, and at the time, added a 1 1/2" lift with a set of low coil spacers on the rear and a torsion bar adjustment on the front. The shop that did it had a heck of a time getting the torsion bars to move, but apparently they worked it out because it ran beautifully and smoothly. For about a week. Suddenly, about 2/5 of the times I go anywhere, I get a huge bounce from the front end. It's not triggered by anything specific as far as I can tell--has happened at several speeds, while turning in either direction, or not turning at all, and in a couple of different (only forward so far) gears. It bounces about 10-12 times, and feels like my wheel is WAY out of alignment. If I am in a position to stop and pull over, it stops. If not, it runs that 10-12 bounces, and then straightens out.

The (16" snowflake) wheels are torqued to spec, the tires are all full to 32 (although the less than 2 year old General Grabber AT2s have felt extremely slippery this winter, needed a push to get out of a slightly inclined parking lot on a bit of ice, even in 4L, likely unrelated), I'm not missing any lugs, and as far as I can tell when it's sitting still everything looks fine. I've tried reefing on the tires to see if there's any play, but there's nothing that I have been able to discover.

Any ideas? The only thing that I can think of is that maybe the CV joints/axles got messed up do to the lift, but the angle is NOT extreme looking and all the boots are intact and dry.

Any help at all would be welcome, I'm making an appointment to get it into a shop asap.

Thanks for your time!

[PK]

I am having trouble with your description of the problem.

"Front end bounce" to me describes the vehicle bouncing up and down as it would if you went over a hump in the road and the shockers were stuffed. Easy to see and easy to fix.
But some of your description sounds like the front wheels are shaking in and out, which would be described as a "steering shimmy" or "wheel wobble". This is normally (but not always) felt in the steering wheel, and there are a few things that can cause it -
Tie rod ends
Drag link joint
Upper and/or lower control arm bushes
Upper and/or lower ball joints

A good suspension place or general mechanic would easily test and isolate the problem.

Good luck with it.

PK

[Hiredgoon]

Thanks for your response!

I don't really know how to describe it better. It's not tugging the wheel from side to side, other than as a by product of one of the wheels--and I can't even tell which, if it's not just both--wobbling vertically and it's definitely not tied to any terrain I'm driving over. Nowhere I've looked has given me much to go on, because of how weird it feels and how hard it is to describe. The closest I've found is on jeep forums where they describe something they call a death wobble.

If I had to try and find an analogy, imagine if the hub were suddenly off centre by an inch or so but statickly so, resulting in a very out of balance kind of thing, where every revolution of the wheel went up and down, like a child's wobbly toy. It does this crazy exaggerated bounce a dozen times, and then *something* slips back into place and it's gone. It's sudden, and violent, and gone.

It's regular though, like the bounces are even and almost timed, and they don't *seem* to get bigger or smaller or anything, and there's a clunk that comes with it, but that may even be a by product of the shocks bottoming out or something. I'd take it back to the shop where I had the lift done, but literally a week after my work, they stopped answering their phone, and google lists them as permanently closed, after something like 40 years in the city.

Anyways, thanks again.

[PK]

Just a weird hunch, but try pulling out your ABS fuse and driving. Might be a bad ABS sensor sending false messages.


PK

[Hiredgoon]

Hunh. I'll give that a try, thanks!

[Nikad92397]

Mine just started doing it. But mine is a vibration. On the freeway going 70.
Nothing crazy or with noises, just a vibration for like 5 seconds and then it stops for like a minute and it comes back.
I KNOW I need axles ( mine just started popping) but I was thinking tire rotation (BFG mudders) or both.

[Y33TREKker]

Mine just started doing it. But mine is a vibration. On the freeway going 70.
Nothing crazy or with noises, just a vibration for like 5 seconds and then it stops for like a minute and it comes back.
I KNOW I need axles ( mine just started popping) but I was thinking tire rotation (BFG mudders) or both.

Yeah, I would think either tire rotation or wheel/tire rebalancing might help. Wheel weights sometimes fall off after balancing.

[Igor]

When it is cold outside my steering wheel will wobble but only in the 50-55mph range. After 15 minutes of driving the wobble is gone in that range. I've had the tires rotated and balanced but it still happens within the first 15 minutes of driving only. Any ideas?

[Y33TREKker]

When it is cold outside my steering wheel will wobble but only in the 50-55mph range. After 15 minutes of driving the wobble is gone in that range. I've had the tires rotated and balanced but it still happens within the first 15 minutes of driving only. Any ideas?

When it gets colder outside, the air pressure in your tires will decrease a pound or so for every 10 degree drop in temperature.

As a result, your tires will have more of a chance of developing something of a flat spot after sitting overnight in the cold. That flat spot becomes pretty evident once you start driving, but after a few miles, the tires warm up enough for that "flat spot" to go away and the tire to feel smooth again?

I don't know that this can be TOTALLY counteracted even if you maintain the correct tire pressures when it's cold, but the closer you DO maintain them to proper operating pressure (32 psi - or whatever the recommend factory pressure), the less pronounced such flat spots will be and the sooner any associated vibrations will go away once the tires have warmed up from driving.

Just a theory of mine anyway.