Tracking down possible wheel hub failure

Hey guys, SWMBO's rabbit has been making a throbbing cyclical sound for a while now. I suspect it is a wheel hub because it is speed dependent; isn't affected by applying the brakes, but does *seem* to "miss" when load is removed from the wheels (like when travelling over a bump at speed that lifts the car and falls away quickly). My issue is at near $150 a hub, I don't want to guess which it might be.

I was thinking maybe of employing a dyno/rolling road to verify if it's front wheels or back wheels related. Good idea? A simple push/pull reveals nothing, and there isn't really a discernible roar coming from any specific wheel. Nor is any wheel getting hotter than any other (that I can feel anyway).

Is there a dyno day or anything coming up? I heard the prices are cheaper when a group gets together to do that kind of thing.

Have a great day!

-Piff

i might start by trying cheaper things.. have you rotated tires, checked brake/caliper, checked lug nuts ... i'd suspect a trip to one of the suspension alignment shops could determine the issue more cost efficient than a trip to the dyno... ymmv

I've seen people just rotate the hub by hand very slowly and ~feel/listen~ for play and or resistance in the hub itself. Seems like you would be able to determine the culprit that way, assuming it is the hub that is making noise.

When the hub went out on our Miata, I took the wheel off each corner and rotated it by hand. I could feel the bearings dragging in the bad hub.

Also If you are cornering does the sound go away or get stronger? It should lessen/go away as you are turning to that side and the suspension unloads as weights shifts to the opposite side.

Short answer:

I guess I’m in for some hot manual labor. Not the world’s biggest problem. The dyno idea was just to isolate front/rear and cut the potential work in half. But it probably isn’t worth it for the price (just found out that dyno shots can cost about $60 for a couple of runs.)

Long answer:

When I’ve had the wheels on, drag was hard to gauge. It’s a front wheel drive car, and with the tires off, it’s hard to turn the hubs on either side (of the front) as the axles have to be rotated along with the assembly. In other words, getting them up to any kind of speed by hand to hear anything hasn’t worked so far. But I’ve never dealt with a bad hub before, so maybe I just don’t know what I’m looking/listening/feeling for yet. There isn’t really the obvious kind of “roaring” people say they hear while driving. It’s a cyclic thrumming that can be heard, but not felt (even through the steering wheel).

I guess I’ll have to knock the axles out, remove the rotors and feel them by hand. I read on VW Vortex some guy had the same/similar issue. When he took it all apart, he could feel about a quarter inch play in his hub. Maybe I’ll get lucky and find it first shot.

OMG will this post ever end answer:
Car has 50k miles. Never tracked. Never driven hard (although I did drive it through Chicago once… maybe that counts).

Rotate tires—
I've rotated the tires multiple times. I’ve even put the full-sized spare on in place of specific tires. Although the sound did seem a bit different while swapping tires, it wasn't definitive as to where the noise was coming from. Putting the spare on never eliminated the noise. I also had the tires checked/balanced at NTB. Not that they couldn’t have missed something, but this is the second set of tires since the issue started. I doubt a tire at this point.

Check brakes—
I changed the rear brake pads a few months back and no change to the throbbing. The old rears did not experience any weird wear.

VWs apply about 80% stopping power to the rear brakes, so there was plenty of meat on the fronts, and there shouldn’t have been any heat buildup issues to warp the rotors. However, though I doubt the brake rotors being at fault, I guess I can’t rule them out. I visually inspected them with a metal ruler, but not a run-out checking tool.

Regards,
Piff