Rhythmic motion only when towing

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RamInfo

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2016 1500 Laramie, 5.7 and 3.92LSD. 15000 mi since diff fluid change at dealership.

I tow a single-axle aluminum flatbed dual MC trailer and loaded it’s only 2000lb or so. I’ve been getting a rythmic bouncing or surging feeling only when towing, and it’s worse when turning. Today I had the wheels balanced and runout checked on truck and trailer and added a cinch on my stinger to eliminate any slop there. Truck wheels were close on balance, trailer tires needed 3oz and 4oz to balance. I’m leaving on a 1500mi tow later this week—if the problem persists should I be looking at changing diff fluid again? I have occasionally noticed some “grabbiness” on the rear end when turning sharply.

thx,
DG
 

BWL

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Are you turning under braking and does the trailer have brakes? The only when towing thing makes me think trailer related. Bouncing trailer is pretty common. More tongue weight helps with that and more weight on the back end of the trailer makes it worse. Surging when turning may just be trailer brakes kicking in and out so check wiring and settings. Set too strong and the trailer will brake the truck more. Loose plug or general bad connection on the trailer can cause the braking to be more intermittent.
 
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RamInfo

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No brakes on trailer, it’s only 600lbs empty and 2k loaded. It just feels like something is engaging/disengaging, or not fully or steadily engaging; an odd feeling but it’s pretty regular and doesn’t change much with speed changes. I’m going on a test tow later this week; my longer tow has been moved to after turkey day.

thx,
DG
 

123 Redbeard

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My guess would be the balancing will solve it, if not look to see if a tire is out of round, or has a bubble or tread starting to separate ... Jack up the trailer and spin a tire ...

If you can't see anything, if you can have some one follow you to observe, and if possible come up beside the trailer to see what is the cause while going down the road ...

Also ... Just incase you may not know ... Most trailer axle manufacturer's require yearly bearing greasing ... If not done recently, I'd make sure the axle bearings are fresh greased before your trip.
 

Daw14

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Rear control arm bushings do not last very long, you may want to inspect all of them .
 

wgreggking

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as mentioned, it only happens when towing so look at the trailer vs. mechanical problem w/truck. Suggest moving the bikes forward on the trailer to add more tongue weight.
This above, back end heavy will sway horribly
also tighten all bolts , shackles ,frame , also trailer should be somewhat level, check hitch, may need to go to adjustable height setup
 

62Blazer

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As mentioned above if it only happens when pulling the trailer I would highly suspect it's the trailer. Any chance you could hook onto a different, but similar size, trailer and see if the problem is still there?

Generally a trailer tire being slightly out of balance (you mentioned 3-4 oz. and that is not extreme) will not be noticable. I would be looking at the run-out of the tire assembly on the trailer that may be caused by a bent hub or axle. Simply jack the trailer tires off the ground, spin them by hand, and see if they look wobbly in any direction.

As far as tongue weight and sway........you are only talking about 2,000 lb. fully loaded trailer. I doubt you could physically load it in a way to have too much tongue weight (unless it's some sort of homemade trailer with a weird tongue length or axle location).
 

tonynap

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smart folks do you think the ESC could be trying to compensate for the lack of trailer brakes and an underweight tongue?

i.e. DG takes a turn, the upward angled trailer pushes the back of the truck out, and the ESC compensates?
 

2003F350

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smart folks do you think the ESC could be trying to compensate for the lack of trailer brakes and an underweight tongue?

i.e. DG takes a turn, the upward angled trailer pushes the back of the truck out, and the ESC compensates?

Not having ESC I'm not familiar with how it works...but it's possible, especially since OP states it is only when towing. Did the 2016 have this option? I don't know.
 

2003F350

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As mentioned above if it only happens when pulling the trailer I would highly suspect it's the trailer. Any chance you could hook onto a different, but similar size, trailer and see if the problem is still there?

Generally a trailer tire being slightly out of balance (you mentioned 3-4 oz. and that is not extreme) will not be noticable. I would be looking at the run-out of the tire assembly on the trailer that may be caused by a bent hub or axle. Simply jack the trailer tires off the ground, spin them by hand, and see if they look wobbly in any direction.

As far as tongue weight and sway........you are only talking about 2,000 lb. fully loaded trailer. I doubt you could physically load it in a way to have too much tongue weight (unless it's some sort of homemade trailer with a weird tongue length or axle location).
I'm sure it's not an issue of too much tongue weight but rather too little tongue weight. Since it's a motorcycle trailer I'd suspect this is part of the issue, the bikes should be moved as far forward on the trailer as possible, since IIRC many of these trailers are built to keep most of the weight on the trailer axle (similar to a boat trailer). Not putting the bikes all the way forward could actually put you in a position where the tongue is trying to LIFT off the ball as you go down the road...which COULD be OP's problem. If, as they are cornering or hitting bumps, the weight is shifting OFF the tongue, then it is possible that the trailer could eventually come unhitched.

I've...actually had this happen once, or rather happen in a vehicle I was riding in. When I was a kid on a hunting trip with my dad and his friends to Montana, we stopped at the mouth of a mountain river for a short while. These guys liked to collect rocks as momentos of where they've been, and they piled all of these rocks (probably a good 300-400 lbs of rocks) in the very back of the trailer (a small 8 ft trailer made from the old box of a pickup truck). No one looked or checked the tongue weight, and over the course of nearly 2000 miles of almost constant driving (stopping only for fuel and food), the tongue lifting up on the ball finally snapped the catch off the tongue. The safety chains kept the trailer in check long enough to get down from highway speeds to about 25 mph, before those also gave and the trailer took a little tumble before coming to rest on its wheels.

That incident was enough to teach me at a very young age that loading and weight distribution is VERY important, and that what seems like an insignificant amount of weight added improperly to an already close-to-improperly loaded trailer can spell disaster.

Thankfully, no one was hurt, nothing in the trailer was damaged (only the side of the trailer was scratched/dented), and we were able to limp it to a nearby hardware store to make repairs for the final 60 miles home.

The rocks were left on the side of the road, thrown way off into the ditch. They recently re-did that section of highway, so I'll bet they're gone now.
 
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RamInfo

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Clarifications: truck has nearly new Michelin Defenders installed and rear diff serviced within last 15k. Trailer is new Aluma with less than 500mi on it, sits level within 1/2” when hitched, and the wheel chocks were mounted by me approx 6” forward of the normal location, far enough forward that I’ve had to install tie-downs forward of the ones that came on the trailer. Tongue weight is not at all an issue nor is sway—the trailer tracks true as an arrow. All wheels on tow and trailer are freshly balanced. Hitch stinger has a cinch installed and no play. Connecting the trailer to another tow vehicle results in a smooth tow.

What I am experiencing doesn't feel at all like it’s coming from the trailer—it feels more like LSD engaging/disengaging or torque converter locking/unlocking, or something along those lines. It’s not noticeable until a trailer is attached.

I’m going to put the rear on jackstands this weekend and see if I can spot any issues. I am still suspicious of the dealer not installing additive when they serviced the diff…

Thanks for the inputs,
DG
 
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RamInfo

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Wrapping this up…
Found one truck wheel with a very small amount of runout; my tire shop (excellent place) deemed it too small to create an issue. Took the trailer for a 30mi test tow and am not getting the issue now. The only changes made were balancing truck and trailer wheels and adding a cinch on the tow stinger. It’s possible the out-of-balance trailer wheels were setting up a motion that was picked up or amplified by the slight play in the stinger... dunno. At any rate, all is well and thanks for all the suggestions!

best,
DG
 

mtofell

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I have occasionally noticed some “grabbiness” on the rear end when turning sharply.
My 2500 does this quite severely, especially under heavy load. I've complained to the dealer, changed the fluid and finally have just accepted that it's just the way it is. So, at least that part of your problem is potentially "normal". I agree with the others about making sure you have plenty of weight on the tongue. Nothing causes poor towing like a trailer with a light tongue.

Obviously, the load isn't near your limits (unless you are also carrying a bunch of weight in the bed) but you might consider something to stiffen up the rear end. Either replacement springs or airbags, etc. The rear suspension on these trucks is just so soft to give a nice ride but it can wreak havoc on towing.
 

turkeybird56

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BOIRD rides one of these, tho not related to OP's thread:

DSCN0321a.jpg
 

800steve

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Have them check the runout on the trailer, not the balancer. These small trailers that use stamped steel wheels have issues. The center holes are often off center. most balancers use that hole to balance the tire. Its very hard to find a shop that has the equipment to do these junk wheels.
 
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