CRAZY sway when brakes applied

[Simon A]

So, you know the drill - get home from work, run around like an idiot, packing the bikes/toys/dogs/beer/etc etc etc. All is done and we were off to the Shushwap.....

Hit Armstrong (coming from Vernon), and I applied the brakes and the trailer immediately violently started swaying - fishtailing - back and forth. Obviously we pulled over, onto a side road.

My first thoughts were that I had a flat tire? Nope. nothing. So drove along this side road to test it out. Sure enough, did it again - only at certain speeds. And when foot taken off brake and gas, still sways excessively till at a stop. It almost feels like the thing is going to rip off the hitch!

I am towing a 21.5 Bigfoot with a f350. I usually have my brake controller (stock) at 5 - 6 depending if water loaded. Today I had it at 5.5. I tried lowering it down to 4 and still same thing happening.

We turned around, not risking any damage to trailer / ourselves.....I figure brakes must be not braking evenly or something. Will make some calls to some brake shops in the AM then try to head out again.....

Any suggestions??

Thanks

Simon

PS I forgot to mention that yes, I do have sway bars....

[floyd]

tongue weight?
Broken brake wire causing only one side to grab?
Bad seal with grease in the brakedrum on one side??
Cracked frame or axle mount, which can cause the axle to move when brake is applied?
Do you have a torque flex type axle?
If it is leafs, then a broken leaf or shackle, or axle U-bolt?

[Perry J]

I think you don't have enough tongue weight.
You should have 10% to 15% of the gross trailer weight on the tongue.
John

[Simon A]

I have been towing this trailer with this truck for over 4 years now. Over mountain passes, glaciers, highways, winter, summer, etc etc etc. Never an issue 'till now.

I will check wiring in AM. By the time we got back home it was dark. Axle, frame, u-bolts all seem OK. Tows fine just when brakes applied it does this. And seems to only do this when at a certain speed ("sweet spot") - roughly 60 km per hour.

I am leaning towards the wiring issue. because IMO it would make sense if only one side was 'grabbing' then this would happen.

[Donna D.]

Simon, the palms of my hands got sweaty just visualizing this. Hope you get it figured out soon and will feel comfortable once again towing your Bigfoot!

[BCDave]

Of course, if it continues to be a threat to the life safety of you and your family, I will rescue you by taking it off your hands - just to save you of course!

On a more serious note - there are a number of things that could cause this- ranging from a brake lining coming unbonded from the shoe and wedging itself at certain speeds, to a brake magnet that this not fully engaging fully (possibly a bit of grease on the facing of the drum). A spring hangar could be broken or a bushing is shot. As noted earlier a wire that is shorting could do it. If it is brake failure on one wheel or one side, it would likely not sway back & forth - more likely just pull to one side only - but I have been wrong before! (maybe it does just pull to one side and then "rebounds" against the hitch?)

Something as "silly" as a castel nut coming off, allowing the hub to move on the spindle?

From your description, it is hard to tell, but is it possible that an axle is actually moving on the spring, relative to the trailer frame?

However, having been a trailer dealer (for medium duty construction flatdecks in the 7 - 12,000 lb GVW range) and having had the occasional trailer make a serious attempt to pull out and pass me at speed, I can relate to the feeling. It is a real sphincter-tightener!

[Mike Magee]

Here's a test to try. When traveling at that 'certain speed,' apply only the trailer brakes (not the truck brakes). If sway occurs, this would seem to indicate a problem with the trailer brakes (and the reverse situation, applying truck brakes without trailer brakes, should be sway-free). If not, look for other causes.

[Simon A]

Update (long over due):

Long long long story short ended up being both my leaf springs (mains) had snapped! Only noticed when I took one of the wheels off.

put new leaf packs in (used). All good. Still peaved multiple mechanics / rv techs had no idea what the problem was....

[Emily R.]

So glad YOU noticed it...Sorry you had to pay to have the mechanics find nothing. Glad everything turned out okay.
Cheers! Emily

[floyd]

Originally Posted by Simon A

Update (long over due):

Long long long story short ended up being both my leaf springs (mains) had snapped! Only noticed when I took one of the wheels off.

put new leaf packs in (used). All good. Still peaved multiple mechanics / rv techs had no idea what the problem was....

Thanks for the update,It doesn't always happen,and it's nice to hear back on how the story ends.