Flat plates welded to trailer axle and spring mount points.

[troopy196]

Good evening everyone

I bought a trailer fitted with electric brakes the other day and while underneath it I noticed one of the flat plates welded to the axle and spring mount points had cracked.

I pointed this out to the manufacturer and he stated that the primary role of the plate was to hold the axle in place during assembly and that the 'U' bolts prevented the axle from rotating when the brakes are applied.

I accepted this explanation until I was told by another manufacturer the exact opposite regarding the plates.That is, that the primary role of the plate was to stop the axle from rotating.

My experience tells me that the 'U' bolts are there to hold the axle in place and to prevent it from rotating.

Does anyone have the definitive answer?

Regards Bob

 

[desertfox]

Hi troopy196

Can you post a picture? for easier if we can see your problem.

desertfox

 

[troopy196]

Not a problem I will post photos late tomorrow or early monday.

Bob

 

[Ron]

Some plates are welded to the axle tube, while others are only bolted. Those that are bolted depend on the U-bolts to prevent rotation, since the plates are attached to the spring which prevents the plate from rotating, but doesn't prevent the plate from flexing (which is the likely cause of your cracking). Plates are sized to the axle capacity, and thus the spring capacity.

When the brakes are applied, the front of the spring dips and the rear of the spring catches to prevent further dipping. This attempts to rotate the axle, but since the plate is bolted to the axle, the friction of the U-bolts against the axle tube resists rotation. When you have a plate welded to the axle tube, it is usually done so with gussets under the plate and conforming to the tube radius. When brakes are applied to this configuration, the welds are subject to radial shear to prevent rotation. The intent here is to prevent rotation of the plate around the axle, to lessen the bending in the spring. The spring works best when load is applied in the same direction on both shackles. When braking, the load on the shackles is not the same, in fact one is usually up and one is usually down.

Either system can assist in the trailer assembly as the plate defines "top dead center" of the axle tube.

 

[MintJulep]

Does it matter? A cracked weld on a new trailer is not acceptable. Insist on a replacement.

 

[dhengr]

Real good explanation Ron. I generally agree with MintJ, and would be particularly concerned if the weld crack could propagate into the axle.

 

[Ron]

In most trailer applications, there really isn't an axle...just a spindle connected at the ends. The tube that holds all this is just a convenient means to hold the spindles.

Since the tube is perpendicular to the plate, there's not as much chance for cracks to migrate into the tube...usually isolated to the plate.

I got the impression this was a used trailer. If new, I agree...don't accept with cracked plate.....even used, have them fix it.

 

[troopy196]

Thankyou for your assistance gentlemen.

Yes, it is a second hand trailer and yes they will now be welding the plate and redoing the other side as well.

Have a safe and enjoyable Christmas.

Regards Bob