Front axle of tandem trailer shifting

I can only go by what the dealer said was normal when I picked up the TT. Hard turns the wheels are not aligned; straight ahead the wheels come back in alignment.

If you have questions or need greater detail I would call the manufacturer.

myredracer wrote:

BubbaChris wrote:
I vote for normal. I did a lot of internet searches after it happened to me the first time earlier this year (also new to TT).

What set my mind at ease were the comments that you can see the same effect on commercial trucks and trailers if you watch for it.

Luckily it sounds like what happened to myredracer is not a common problem.

I guess unless you have had one of these frames as well as had it inspected by a gov't certified frame shop, you just won't know. It's more common than you think with these particular frames and a lot of owners don't know until something happens.

You make some good points. I don't know what kind of axles (leaf spring or rubber torsion) the OP has or what type of frame he has. I have built equipment trailers on and off for almost 40 years, and the leaf springs will flex in a turn, but not as much as your pictures show. I don't know what kind of a frame the OP has, but excessive flexing of the frame is not good. If the frame is flexing too much it will eventually fatigue. Many TT manufacturers are too cheap when it comes to the frames and axles, and they have been getting by with it for years. Your idea of a video camera under the trailer is a great idea to see if the frame is flexing too much, especially if the TT has the manufactured sheet metal frame.
When building equipment trailers I have used structural channels, rectangular tubing or "I" beams. I prefer the structural channel the most because of it's properties of strength with the thick flanges. They are basically half on an "I" beam with a thick web. They are also nice because they don't warp as much as the tubing when you weld them and you don't have to worry about rust on the inside.
The rectangular tubing frames will resist twisting more, and some folks think that is what you need for strength. The fact is that the frames are supposed to twist. You will notice that semi truck frames use a "C" channel of high tensile steel, but they aren't structural channels.
I have never used the "manufactured" sheet metal frames for the trailers that I have built. I imagine the TT manufacturers use them because they are lighter and cheaper. The problem is that if you are going to have some extra weight, it is best to have it in the frame. My estimate is that a TT with a quality frame and axles will probably only weigh about 200# more than a weak one, depending on the size of the trailer of course.

BubbaChris wrote:
I vote for normal. I did a lot of internet searches after it happened to me the first time earlier this year (also new to TT).

What set my mind at ease were the comments that you can see the same effect on commercial trucks and trailers if you watch for it.

Luckily it sounds like what happened to myredracer is not a common problem.

I guess unless you have had one of these frames as well as had it inspected by a gov't certified frame shop, you just won't know. It's more common than you think with these particular frames and a lot of owners don't know until something happens.

I vote for normal. I did a lot of internet searches after it happened to me the first time earlier this year (also new to TT).

What set my mind at ease were the comments that you can see the same effect on commercial trucks and trailers if you watch for it.

Luckily it sounds like what happened to myredracer is not a common problem.

I totally disagree on it being normal. Unless you have one of the versions that had a BAL frame for a short period last year, the frame has a "fabricated" I-beam that is made from 3 pieces of 1/8" mild sheet steel welded together that *looks* like an I-beam. These have excessive flex in them. Compounding that is the lack of any reinforcement where the spring hangers attach to the I-beam and the fact that the spring hangers are 6" tall versus 4" tall ones. The taller spring hanger brackets cause greater leverage force on them side to side when turning, especially in tight turns. When the spring hanger moves left or right at the bottom, it also causes the axle tube to bend and cause a change in the camber. The camber change is not good for tires. Everytime you turn a corner this is going to happen. This will also happen to a lesser degree when travelling in a straight line when the weight of the TT gets shifted left/right from lane changes, swerving, etc.

When doing a tight turn, because the axles have different turning radii, one set of tires is essentially dragged across the road surface. The lateral (sideways) force on one axle causes the spring hangers to bend. And yes, they can move in the order of 1 1/2" or so.

Without getting into a lot of details, eventually you will get fatigue cracks in the vertical web of the I-beam right above where the spring hangers attach to the I-beam. You should periodically inspect your frame. Cracks can be hard to see at first.

It would be a good idea to add gussets to the I-beams where the spring hangers are. Any competent frame shop can do this. Adding a longitudinal length of 2x2 tubing to the underside of the I-beams from the front hanger to the rear one (ie, under all 3) will help too. Another thing that helps is to tie the bottom of the spring hangers together from the left to right side of the frame with a cross-member. Mor/Ryde makes one or you can make your own. Adding shock absorbers will help to reduce vertical frame movement and reduce the risk of damage to the superstructure. You might consider installing higher rated axles.

I've seen these flexible I-beams on 5 or 6 other makes and models and it's not unique to your make. The vast majority of frames have a forged I-beam which is much stronger. If you have a camcorder, lash it to the underside of the frame and watch what happens to the spring hangers when you tow it somewhere.

Here's a few pics to show what happens. Pic 1 is a 90 degree turn in a CG. Pic two is at a frame shop and they pushed on the trailer sideways with a forklift. Pic 3 shows what happens to the bottom of the frame caused by spring hanger movement. This is on a fairly new trailer. Pic 4 shows damage that can occur to the superstructure from vertical frame flex and is a separated weld in the aluminum framing.

Normal. Drive straight on a super flat surface for 20 feet. if they look straight your good.

YEP...freaks one out first (second,third) time you see those axles 'twisting'

Perfectly normal trailer with more than one axle.

And as you noted it straightened out 'once on the road' (actually they straighten out as soon as you go in a straight line.forward or backwards)

2

Remember, When you are turning, backing or going forward. The pivot point on the TT is the axles. One axle tries to go one way while the other tries to go the opposite way. So the look out of line, which they are. But only as long as you are in the turn.

That is why I always back thru the sire, and then pull forward. To relieve the pressure on the tandems, before unhooking

Normal... Our fiver does the same thing in slow, tight maneuvering, and have seen many others do the same.