[Toby Mack]

Driving down the M3 yesterday and I noticed a vibration through the wheel Thinking I had shed a wheel balance weight I slowed down expecting it to go away. It didn't, it got much worse to the extent I decided to pull over.
I immediately noticed the left front wheel was smoking slightly so I removed the wheel and found the smoke coming from the grease round the axle nut. The caliper also appeared to be dragging and was very hot so I assumed a siezed caliper. 10 minutes later I went on my way (keeping my speed down) and it is behaving fine now.
I was going to change the caliper but thinking about it I am not so sure.
- The wheel bolts were at least as hot as the caliper
- the smoke was coming from the axle area, not the brake
- the wheel was difficult to turn but without and graunching or funny noises.
- no sign of slack in the suspension or bearing.

I'm suspicious that it appeared to be the hub that was hottest, not the disc, could all this point to a siezing wheel bearing rather than a siezed caliper?

 

[Derek]

A friend recently had exactly the same symptoms, it was the caliper which had seized.
How do you know that the hub was hottest inless you measured it? I think you would find that the hub appeared to be hotter because of smoke from the grease in the bearing and the hub splines but the disc being free of grease wouldn't produce any smoke although it may have been nearly red hot.
If the bearing was really seizing up, once it had cooled down it would still be stiff to turn and certainly feel very rough. You would need to remove the brake pads so that there is no drag from them to be sure.

 

[MikeH]

My money is on the bearing,when they go they go properly,last one I changed had totally disintigrated.
Mike

 

[Toby Mack]

Well, Just been for another drive and checked it again. I didn't get any vibrations but the wheel did get hot again. This time (checked more carefully that last time!) it looks like the hottest bit (by a long way) is the disc. Caliper and wheel nuts about the same temperature and axle nut slightly cooler. Looks like it is the caliper after all.
Derek- thanks for the confirmation a siezed caliper can cause wheel vibrations. I've never come accross this before.
Mike- I was thinking wheel bearing but in my experience with bearings that have gone you can feel/hear roughness in the bearing. Can't in this case.

Anyway, thanks guys, I'll replace the caliper and if that doesn't fix it, wheel bearing is next on the list!