Slight jerking below 40 mph

[greatlakes]

We just brought our ’04 25’ Safari home behind our 2010 4x4 Expedition. The Expedition has a 6-spd transmission, but has a “tow” mode selector to limit the top gear(s). The set up is an excellent match for power/weight. The WD hitch the trailer came with is a Reese/Draw Tite and it has also the matching anti-sway link. I set up both the TV and the TT to be level.

However, I noticed that at speeds below 40 mph there was some noticeable chatter (read: very slight jerking). Above 40-70 mph everything rode smoothly as glass. It was easy to forget that the trailer was there.

Anything in the anti-sway (friction-type) link adjustment that could be causing this? Any educated guesses?



Thank you in advance.

[ROBERT CROSS]

I used the same set-up on both our old Safari and the Classic when we first got it. Never experienced the concern you are describing.

Only happens when towing..straight line?

Doubt it could be caused by the friction bar, I would check for excess runout on wheels/tires both on the TV and trailer. Set tire pressures. Also inspect the trailer brakes for dragging and a possible brake drum out of round condition. Jack trlr and spin each wheel.

[greatlakes]

Only shows on straigh line towing at lower speeds. The TV is brand new, only 1500 miles, and the TT did not cause any vibration with the previous owner, I know that. All tire pressures are to spec. My only suspect is what's in between the TV and TT.

I kept the TV at the same attitude (dimentions to wheel well lips) as when not towing. Perhaps this vehicle needs a bit more tongue weight? I will take the rig to the scales to see what's going on, however.

[garry]

Make sure the 2 5/16 ball is tight a loose ball can give you this symptom.

[thecatsandi]

Originally Posted by greatlakes

We just brought our ’04 25’ Safari home behind our 2010 4x4 Expedition. The Expedition has a 6-spd transmission, but has a “tow” mode selector to limit the top gear(s). The set up is an excellent match for power/weight. The WD hitch the trailer came with is a Reese/Draw Tite and it has also the matching anti-sway link. I set up both the TV and the TT to be level.

However, I noticed that at speeds below 40 mph there was some noticeable chatter (read: very slight jerking). Above 40-70 mph everything rode smoothly as glass. It was easy to forget that the trailer was there.

Anything in the anti-sway (friction-type) link adjustment that could be causing this? Any educated guesses?



Thank you in advance.

What kind of hitch pin are you using? A bent end one? A strait one? Bent ones are hotorious for being a little to small.
My trailer will have very slight jerking. I have round out the hitch hole some with all the towing.

[ROBERTSUNRUS]

Originally Posted by greatlakes

However, I noticed that at speeds below 40 mph there was some noticeable chatter (read: very slight jerking). Above 40-70 mph everything rode smoothly as glass. It was easy to forget that the trailer was there.

Hi, at this speed I would look for an out of round tire on your trailer. [tread separation] what is the DOT code on these tires, they could be oringinal?

[barts]

I've had problems w/ hyper-active cruise controls - does this happen w/o the cruise control engaged? If you have disc brakes, make sure the brake actuator is compatible w/ your vehicle's brake controller.

- Bart

[ROBERT CROSS]

Originally Posted by greatlakes

Only shows on straight line towing at lower speeds..... My only suspect is what's in between the TV and TT.

That friction bar looks new...did the PO also use it?
Find a long, straight, smooth stretch of hi-way and take it off..see if the jerks go away.

[greatlakes]

RC: yes, the sway bar was used by the previous owner. On the way home I was passed by semis and I had no sway or even much of a hint of being passed by the 53-footers going at 70+ mph.

You all have come up with good points and I'm going to try the following today:

- re-tune my brake controller to the trailer
- run it w/ and w/o the sway bar
- re-check tire pressure on the trailer
- re-check the TV/TT attitude w/ regards to WD

I'm suspecting my new brake controller is not 100% in tune with the trailer. We'll see.

Thank you all for your input.

[ROBERT CROSS]

Frank,

POI...speaking from experience...watch out when making sharp turns. The friction bar can retract/extend all the way, bind up and bend the ball mounts...ask me how I know. I had to move mine back on our 63,(bar extended halfway when straight ahead) it's hard to tell, but in your pic the bar looks to be a little less than half extended. Could be the TV is not straight.

[HowieE]

If you can find a fairly long straight hill, 1 or 2 % grade like on an Interstate, go up that hill at the effected speed. If the problem still shows itself while on the hill it is most likely in the tires or a pulsing of the trailer brakes. Pulling the hill will cause constant tension on the hitch system thus eliminating any chance of mechanical reaction in the hitch.

[CanoeStream]

Expansion seams in poured concrete highways can have a harmonic based on speed and the length between your tow vehicle & the trailer axles. You can rule that out by experiencing the same jerking on a good condition asphalt highway.

This seam effect can get quite annoying as a concrete roadbed ages. Your term "slight" makes me wonder if this is the problem at all.

Michelle? Bent hitch pin? Intentionally bent or due to effects of age & wear? Frank, it is common that the hitch bar fitted into your Expy's receiver has an adjustment to allow about a 15 degree tilt toward the trailer. That is an angle specified by ... morning moment here ... hitch mfgrs? antisway mfgrs?

[Aage]

Bob,

I can attest to this effect. The 407 Highway (toll road, actually) near us is mostly concrete, and adds the jerking effect to the drive. It makes me think of riding a horse, actually.

In the over 6,500 kilometres (~4,000 miles) that we put on in November, that highway was the only one to display this rather disconcerting motion.

[ROBERT CROSS]

Got a stretch here on the 90 just east of the West Seneca toll station, about 4miles long, only way to make it bearable when towing... -40mph. or less.

[overlander63]

You have the transmission in tow/haul mode, which does not limit top gears. It only changes the shift points higher. You could well be feeling the torque converter engaging and disengaging, also known as "hunting". Try placing the shift lever in the next position down, usually marked "3", and see if the symptoms persist.

[Ag&Au]

Originally Posted by CanoeStream

.................................................. .............

Michelle? Bent hitch pin? Intentionally bent or due to effects of age & wear? Frank, it is common that the hitch bar fitted into your Expy's receiver has an adjustment to allow about a 15 degree tilt toward the trailer. That is an angle specified by ... morning moment here ... hitch mfgrs? antisway mfgrs?

I think she is talking about the cheap OEM type pins where one end is bent to form a handle and the other end takes a hair cotter pin or something similar. I have had the same experience with them being too small in diameter.

Ken

[greatlakes]

Well, after doing some soul searching prompted by your many suggestions, it seems like the problem may be solved.

I made sure all the tires in both the TV and TT were up to spec pressure, I found a few miles of dry, level, smooth road with no traffic. Yes, we have some of those here in FL at this time of the year -- albeit cooler than usual.

First w/o the sway bar I got the rig up to 25 mph and performed, once again, the brake controller (P3) adjustment per mfr instructions. Ran the rig for many miles at the speeds where the problem had shown up and varying the road conditions from smooth to bumpy -- no problem. Repeated the same cycle with the sway bar on -- same results.

Even over bridges with quite bumpy approaches, I could not get a jerk out of the trailer. Unless something else shows up next, I believe I did not do a good job with the initial brake controller adjustment and there may have been some erratic signals being sent to the trailer brakes. I'm happy.

BTW, I'm making a habit of anticipating very tight turns, as well as when backing in and removing the sway bar link altogether.

Again, thank you all for your excellent insights.