What Could Cause Vibration At 50 MPH On Trailer W/ New Axle and Hubs

Question:

Hello, I currently have this Kenda 4.80-8 tire on my small boat trailer but with load range B. The trailer is extremely light, probably 100lbs, and the boat is also very light. The overall weight of everything loaded is probably still less than 500lbs. The trailer had a very old 1.5inch round axle from 1959 with odd hubs and spindles, and I was having nothing but problems with it. I actually asked a question about it here a couple months ago but dont know how to link it. The problems I had were with leaking grease seals and worn out spindles, but the wheels and tires were always smooth even at 65-70 mph. I typically cruise at 60mph with this trailer and never have any problems. Last week I finally replaced the axle and hubs with a new Dexter 2inch square galvanized axle and two brand new galvanized hubs with new bearings. The install was smooth and very simple, and I made sure to pack the new bearings properly STP marine grease and installed everything properly with the castle nut just hand tight with no play. While up on a jack the wheels didnt turn as easily as with the old hubs, but the bearings were smooth and no apparent issues. I figured maybe the new grease seal was just doing its job or the grease was still fresh and thick. I took it out on its first trip yesterday, using the exact same tires and wheels, and the first thing I noticed is anytime I go over 50mph I get what I can only describe as a very slight, hardly noticeable vibration with a very low, loud, deep hum. Enough to give you a headache. It sounds like Im towing a freight train behind me, and is only at 50mph or higher. Ive double checked everything and the hubs have no play or anything, and the castle nut is still only hand tight...not overtightened at all. The new u-bolts are all tight and situated properly, and the only thing that is loose back there is the leaf spring bushings are shot...but they always were. Ive already ordered new springs, bolts, and shackles but like I said they have always been this way and I dont see that causing the issue. Im curious what your first thoughts are and if theres something Im overlooking. This only started as soon as I installed the new axle and hubs. The tires are still almost brand new and I cant imagine them just coincidentally going bad right after installing a new axle. Could I have gotten a defective axle? The spindles came welded on to the 2inch square tubing but from the naked eye they looked straight. Or does it sound more like a hub or bearing issue? Im still new to this and not sure how I would test or pinpoint the problem. Any advice is much appreciated. Thanks!

asked by: Jake H

Expert Reply:

That is definitely odd, but I would lean towards a hub/bearing issue.

I didn't see you mention this step, but when installing the new hubs/bearings did you tighten the castle nut nice and tight to seat the bearings fully, and then loosen it up to get the correct bearing preload?

If not I would start there and complete this step and see.

The hubs should not free spin, but should have very minor resistance.

If that all checks out, I would make sure all of the U-bolts holding the new axle are tight, and that the dimple in the spring is not moving around in the spring seat causing additional movement.

If these steps do not fix the issue I would take the trailer to a local axle shop and have them take a look at the axle.

expert reply by: Samuel C