Fish tail

[214skier]

Just picked up 2020 MHC 376fl. At 60 mph this rig fishtails. Took back to dealer who lowered hitch 2” rig is still probably 2” high from level. It still fishtails on occasion and it gets pushed around by passing semis. No chance to drive above 60 (not that we would).

No water in tanks—black and grey empty.

Wheels with correct tire pressure

Help. Any chance the axels are out of alignment?

[Ram Montana High Country]

try increasing rear axle tire pressure 5 lbs and see if any change occur - it might be little things to tune this in

One of the things Morryde does when installing the iS (independent suspension) is to level it with truck

[Theunz]

Doesn’t sound right to me. I’ve had four fifth wheels over the last 35 years ranging from 27’ to 37’ and have never had a fishtail once. Have never been affected by semi’s either. Get a long STRAIGHT two by four and lay it across both tires on one side and then do the same on the other side. The two by four should touch each tire on both the leading and trailing edges. If there is a gap then you have an alignment issue. Check your spring hangers and see if they are bent or if any suspension bolts are loose.
How much of a fishtail are you getting? Are you nervous when towing and perhaps over correcting for minute movements by gripping the steering wheel to tightly?
You should be able to drive 65 mph and not even notice the trailer is behind you.

[shorthauler]

What are you pulling it with?

[WeBeFulltime]

Not enough pin weight.

[Dixie Flyer]

Originally Posted by WeBeFulltime

Not enough pin weight.

Rear kitchens are famous for this, too much weight in the rear. If your fifth wheel is a rear kitchen model there may not be a fix for this,

[WeBeFulltime]

Originally Posted by Dixie Flyer

Rear kitchens are famous for this, too much weight in the rear. If your fifth wheel is a rear kitchen model there may not be a fix for this,

We fulltimed for 6 years in a 2012 3585SA which is a RK and never had a problem with pin weight. One can always shift items to front storage to compensate. We've had 3 Montanas and it was the best pulling of all 3.

[Jester]

Originally Posted by shorthauler

What are you pulling it with?

I have the same question.
Check tire pressure in tow vehicle .

[mlh]

How much pressure do you have in all the tires, truck front and rear and the trailer tires?
Lynwood

[Slow Hand]

I would echo tires as well. Sidewall flex is sometimes a problem. Once the trailer starts to sway it's hard to make it stop. It would be very dangerous to drive it this way. I have a 34' er and haven been in all sorts of wind and mine doesn't sway. Trucks have no adverse effect ether. IO have towed at 75 and mine is rock solid. Please no speed police, thanks

[rmthelen]

Without knowing what the tow vehicle is, it is difficult to troubleshoot on this forum.
There is not enough information to accurately problem solve.

[jimandlaurie]

Sounds like a weight distribution problem. Along with all the other ideas posted, much investigation needed.

[bshgto]

From: Theunz

You should be able to drive 65 mph and not even notice the trailer is behind
you.

This is true. Trailers that I`ve seen fishtailing are either over loaded or tires are real low on air. Yes it was me and it was a loaded car trailer. I don`t think miss alignment would cause this as there are many many post on here about miss-aligned axles and don`t remember any mentioning fishtailing just crazy tire wear. Are the trucks tires up to the task or low on air? Are the camper tires over loaded. I`m 2 inches nose high and don`t fish tail or get bothered by trucks but I have a dually. This needs to get worked out or it will ruin your travels cause of stress. what`s the truck? don`t tell us it`s a 1/2 ton and the dealer said it would be fine.
Why would the dealer send you out 4 inches nose high if you had adjustment left to use to help correct this?

[Dave W]

Our MHC 343RL used to wallow badly over interstate bridge approaches and departures which in turn started sway. I had to level the trailer as well as add a heavier set of springs. I also found that the OE U-bolts were barely finger tight and the OE nylon spring bushings shot at about 4K miles. Then those crappy China Bomb tires had to go. I used the springs plus a 1" thick block to level the unint. No more wallow, sway ar other unexpected movement. A tow vehicle sway bar also will help sway plus correct tire pressure on the trailer and truck

[214skier]

Tow vehicle is a 2018 F350 platinum. E rated tires with 5k wear. Computer monitored for tire pressure +\- 1 ~ 2 PSI. Running with firestone airbags with 30 lbs filled. Trailer 3” higher in front than back.

This layout with rear bedroom and two exterior storage behind axle has to be pin light.

The modified suspension and upgraded tires good suggestions.

[DadsHemi]

Is your tv and trailer level when loaded, also what model are you towing

[shorthauler]

Sounds like you have enough truck to pull it safely but before making modifications to the rig I would pull it with a different vehicle just to make sure your problem is in the 5th wheel and not your tow vehicle. You have a short bed with a 13k 5th wheel that's almost 42 feet long. The weight distribution for this combo might not work especially if the rig is pin light.

Ralph & Nadine
2020 3120 Legacy
2016 F-350

[WeBeFulltime]

Originally Posted by 214skier

Tow vehicle is a 2018 F350 platinum. E rated tires with 5k wear. Computer monitored for tire pressure +\- 1 ~ 2 PSI. Running with firestone airbags with 30 lbs filled. Trailer 3” higher in front than back.

This layout with rear bedroom and two exterior storage behind axle has to be pin light.

The modified suspension and upgraded tires good suggestions.

I believe I mentioned not enough pin weight earlier. I learned a little about weight distribution while trucking 20 years and 3,000,000+ miles. You need to weigh and calculate pin weight which should be 20-24%. With my 3791RD with all the behind axle storage had to be very careful not to overload rear.

[fulltilt]

30#'s of air in the bags, with the trailer off the truck or weight on ? I ran 8#'s in my Jimmy with weight off, that translated into 28# weight on. Any higher & my Jimmy suspension was not doing any work, I may as will have placed blocks of wood in the suspension. The springs need to travel or it will become dangerous.

[DebNJim B]

Originally Posted by 214skier

Tow vehicle is a 2018 F350 platinum. E rated tires with 5k wear. Computer monitored for tire pressure +\- 1 ~ 2 PSI. Running with firestone airbags with 30 lbs filled. Trailer 3” higher in front than back.

This layout with rear bedroom and two exterior storage behind axle has to be pin light.

The modified suspension and upgraded tires good suggestions.

We have a 3731FL, similar floorplan at least front to back though maybe a bit heavier, and similar tv. We have never had any sway or fishtail though I have felt movement in strong gusty cross winds. My experience with bumper pulls is any fishtailing is nearly always not enough pin weight. Our f/w tank is in the rear and even with it full have not had a problem. Unless you are loading the rear storage with bricks you should have enough pin weight. I'm thinking you being 3" high in front is the issue. We don't have air bags and our rig runs level. Unless your truck is modified and is very high you should be able to get it level w/o sacrificing bed clearance. I'd also start with a trip to the scales then you will know just what your pin weight is.