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rstrucks
01-13-2010, 11:03 AM
My 3 year old trailer has a tendancy to sorta bounce at about 30-35mph. Not too much but enough to make my one ton truck's suspension move up and down what seems like a couple of inches. It also has a somewhat cyclical vibration at highway speeds ~ 70mph. It has done it behind my truck and others. I have had someone pull up beside my trailer and watch what it was doing while it was happening and the boomerang shackle was jumping around. I have since cut off spring mounts and squared them up with the frame along with making sure both axles where parallel - which they weren't. The tires have been replaced and balanced too.

Any suggestions?

ATL ZJ
01-13-2010, 11:44 AM
What kind of trailer? Car, boat, utility, dump?

Other than the obvious check-over to make sure everything's tight and straight, I'd suggest putting shocks on it. I hear that adding shocks to a trailer will greatly reduce the risk of tire failure, so there would be a dual benefit.

paulkeith
01-13-2010, 11:50 AM
does it do this loaded/unloaded/both?

what tire pressure are you running?

are you noticing any weird tire wear?

rstrucks
01-13-2010, 12:17 PM
Its my car trailer and it does it loaded or unloaded. I usually run about 45 psi. No weird tire wear. Hmmm shocks, that sounds like a good idea. Never even crossed my mind.

CrawlerReady
01-13-2010, 12:28 PM
But what shocks are you going to find to make a difference when loaded? The deck of my trailer weighs 1600# and the ZJ weighed in at 5300#. Sounds like a good idea, but I don't think any regular vehicle shocks would do the trick for ~7000#

ATL ZJ
01-13-2010, 12:52 PM
But what shocks are you going to find to make a difference when loaded? The deck of my trailer weighs 1600# and the ZJ weighed in at 5300#. Sounds like a good idea, but I don't think any regular vehicle shocks would do the trick for ~7000#

My titan exceeds 7000 pounds quite regularly when I have passengers and something in the bed and the original "regular vehicle shocks" on it work great. Shocks slow down suspension movement by forcing oil to pass through small holes in a piston.

You don't need anything special or expensive, just a little damping.

paulkeith
01-13-2010, 01:26 PM
Feel like that's kind of a bandaid though. Would want to make super-sure there wasn't an underlying cause.

Have you tried going up or down in tire pressure? What's the max psi on the tires?

ATL ZJ
01-13-2010, 01:45 PM
Feel like that's kind of a bandaid though. Would want to make super-sure there wasn't an underlying cause.

Tracking that down could be as fun as chasing deathwobble.

IMO every swaybar on the road is a bandaid for inadequate suspension design and tuning but that doesn't mean they shouldn't be there.

If ryan really enjoyed tweaking his towing setup he'd be out hitching up and testing different variables. I won't name names, but I know people who enjoy that sort of thing and I just don't understand how that's possible. Since Ryan posted up here for help, I'm guessing he just wants the thing to stop bouncing. And shocks are a pretty sure way to accomplish that. even one per side would probably work wonders... it's on my long list of things to do to mine.

grandf4
01-13-2010, 01:50 PM
My 3 year old trailer has a tendancy to sorta bounce at about 30-35mph.

It also has a somewhat cyclical vibration at highway speeds ~ 70mph

Any sort of cyclical vibration I would say would have to be related to the rotating assembly, ie: tires, wheels or hubs. One of them must have excessive runout. The rule of thumb in the tire industry is low speed vibration(30km/h) is a tire issue, mid speed(60km/h) is a wheel(or possible hub) issue, and high speed(100km/h and up) is a balance issue. A bent wheel or hub may cause a high speed vibration as well. Of course there are always exceptions but this is the general rule

Try jacking it up and spinning the tire to see if you can see any sort of wobble.

ATL ZJ
01-13-2010, 02:11 PM
I've always been told that trailer hubs aren't balanced so balancing trailer tires is pointless. But I've also heard (anecdotally) that balancing trailer tires can smoothen the ride and reduce blowouts. However, a friend of mine blew a brand new, properly inflated E range trailer tire that was balanced, so I'm sure it depends on all the other factors like hubs, temperature, load, and road surface.

paulkeith
01-13-2010, 02:22 PM
I'm just saying, I've done a decent amount of towing in a pretty wide range of tow vehicles and trailers, in everything from a 25 year old POS uhaul to a brand new $5k gooseneck and never had a problem with trailer bounce, and none of them had shocks. I agree that it would probably fix it, but there's gotta be a cause if so many trailers don't bounce and don't have shocks, knowmsayn?

zjeepin
01-13-2010, 02:43 PM
My trailer has vibrations mostly when unloaded, and when the load isn't balanced well. It has similar cyclical vibrations as well , whats worked to eliminate 95% is fine tuning where I park the rig on the trailer, just a few inches front to back has made a big difference..

CrawlerReady
01-13-2010, 02:58 PM
My titan exceeds 7000 pounds quite regularly when I have passengers and something in the bed and the original "regular vehicle shocks" on it work great. Shocks slow down suspension movement by forcing oil to pass through small holes in a piston.

You don't need anything special or expensive, just a little damping.

Hmmm...good point haha. For some reason I was thinking that the shocks on trucks don't handle that much weight because of the coil spings/leaf springs....guess what I remembered though?! Trailers have springs too! :smt041:finga:

zjeepin
01-13-2010, 02:59 PM
Hmmm...good point haha. For some reason I was thinking that the shocks on trucks don't handle that much weight because of the coil spings/leaf springs....guess what I remembered though?! Trailers have springs too! :smt041:finga:

thats some funny shit right there!!

SirFuego
01-13-2010, 03:20 PM
My trailer has vibrations mostly when unloaded, and when the load isn't balanced well. It has similar cyclical vibrations as well , whats worked to eliminate 95% is fine tuning where I park the rig on the trailer, just a few inches front to back has made a big difference..
I never really gave too much thought into how my trailer handled unloaded because I figured it was designed to haul heavy loads and wouldn't ride like butter without a load on it.

Getting the tongue weight is key to eliminating bouncing. Too much and it constantly bounces. Too little and it sways every which way.

I've also found that not compressing the suspension on the towed vehicle (i.e. tying it down by the axles only -- which seems safer to me anyways) dramatically helps ride quality since the rig soaks up most of the bumps.

But maybe saying this in regards to Ryan's problem is apples to oranges, so take it for what you will.

rstrucks
01-13-2010, 04:13 PM
Just to give a bit more info. The trailer has done this since new. I used to to my race car ~ 2600lbs, with my ZJ when it was stock. I just assumed it had something to do with the less than ideal tow rig set-up and soft coils - even though I was running air bags.

The boomerang shackle is the only visible spot that is an indicator of something wrong. It oscillates back and forth when the vibe is occuring.

I need to remeasure the spacing of the frame mounts and the shackle mounts to ensure they are even and square. About 6 or 8 months ago I rewelded the passenger side rear frame mount so it was even with the driver side as it was off about 5/16ths. I thought that would solve the problem thinking the rear axle was "hopping" as it tried to crabwalk away from the front axle and then scrubbing/jumping back in line. It obviously didn't fix it.


Any sort of cyclical vibration I would say would have to be related to the rotating assembly, ie: tires, wheels or hubs. One of them must have excessive runout. The rule of thumb in the tire industry is low speed vibration(30km/h) is a tire issue, mid speed(60km/h) is a wheel(or possible hub) issue, and high speed(100km/h and up) is a balance issue. A bent wheel or hub may cause a high speed vibration as well. Of course there are always exceptions but this is the general rule

Try jacking it up and spinning the tire to see if you can see any sort of wobble.

I will triple check everything. I have adjusted wheel bearings and the shop that balanced my tires never mentioned anything about bent wheels. I will try to verify everything though. And what is this km/h stuff?:D


I've always been told that trailer hubs aren't balanced so balancing trailer tires is pointless.

Yeah, I've run the trailer with both balanced and unbalanced tires and didn't see/feel a difference.


My trailer has vibrations mostly when unloaded, and when the load isn't balanced well. It has similar cyclical vibrations as well , whats worked to eliminate 95% is fine tuning where I park the rig on the trailer, just a few inches front to back has made a big difference..

I have towed a number of things on my trailer from light ATV's to my pig ZJ with the same results. Do your vibes seem to fade in and out or is it fairly constant?


I've also found that not compressing the suspension on the towed vehicle (i.e. tying it down by the axles only -- which seems safer to me anyways) dramatically helps ride quality since the rig soaks up most of the bumps.


That's how I tie my stuff down too.


Oh yeah, my trailer sits just about level loaded and unloadeds.

Thanks for the input and help guys.

zjeepin
01-13-2010, 08:21 PM
my vibes fade in and out when they occur but when the load is balanced they are non existant..

you may check the bushings in the spring eyelets and equalizer bars.. the factory may have welded all the spring mounts on with with the springs in the mounts and melted the bushings allowing for misalignment...

have you checked how well placed your axles are? are they square to the trailer? is the frame of your trailer square? how close to 60/40 are the axles?

Pearce
01-13-2010, 08:41 PM
I would try and take a closer look at tire wear to try and figure out which tire/wheel/spring it might be starting from. Seems like everything mentioned above are good places to look. Maybe an out of round tire but you did say tires have been replaced so maybe an out of round wheel? And always run your trailer tires at max psi mine are 50. Another idea, have the right sized bolts in the boomerang shackle and leafs? Just seems like something should be showing a bad wear pattern because its not functioning correctly.