Rear Hub Wobble/Drum turning?

D

dmar836

Member
So I was going to turn some new cast drums on rear hubs to true them. While apart I quickly checked them on a lathe for excessive hub warpage but didn't detect any(using an old axle taper). After swaging the drums on, one has a wobble(about .015"). Checked a third hub with old drum and it was fine.
I was indexing off the hub bearing race/rear hub(with bearings removed) and a small cone on the outer, small end. it's one of the new drums that wobbles(measured at the face about where wheel touches). When indexed off the taper using the same small outer cone, it's pretty darned true for turning as are the others using the bearing race and small cone.

To me, the issue is the bearing is what the unit will use when on the car but the axle taper will then be off and the current drum wobble will remain. Truing the drum by indexing off the taper would fix the wobble but the drum would then not be concentric to the bearing. Hope this makes sense as it took me a while to trouble shoot.

Have you guys seen bad rear hubs where the taper and the bearing race are machined not concentric?
 
dmar836 said:
So I was going to turn some new cast drums on rear hubs to true them. While apart I quickly checked them on a lathe for excessive hub warpage but didn't detect any(using an old axle taper). After swaging the drums on, one has a wobble(about .015"). Checked a third hub with old drum and it was fine.
I was indexing off the hub bearing race/rear hub(with bearings removed) and a small cone on the outer, small end. it's one of the new drums that wobbles(measured at the face about where wheel touches). When indexed off the taper using the same small outer cone, it's pretty darned true for turning as are the others using the bearing race and small cone.

To me, the issue is the bearing is what the unit will use when on the car but the axle taper will then be off and the current drum wobble will remain. Truing the drum by indexing off the taper would fix the wobble but the drum would then not be concentric to the bearing. Hope this makes sense as it took me a while to trouble shoot.

Have you guys seen bad rear hubs where the taper and the bearing race are machined not concentric?
Click to expand...

Are you saying the machining was not co-planer, -or the hub was worn that way?

When the hub was manufactured, there was a reamer that brought the taper and the bearing race to final size as a simultaneous op. This would have ensured they were in alignment. Think about this. When new, if the hub race and axle taper had been out of alignment, it would have broken the axle due to the constant flexing since the weight of the vehicle would have been on the bearing and the axle shaft was floating.

FWIW, I have an aluminum plug that I made that I insert into the hub bearing race area. Then with my finger plugging the axle nut end, I quickly pull the plug out while listening for a vacuum 'popping' noise. If it doesn't 'pop', then I know that hub bearing race area is excessively worn and not worth reusing. Many hubs are worn beyond their serviceable life.
 
I'll have to look again. It didn't appear too worn but nothing I own is beautiful and much of it is worn out old stuff("ran when parked" type stuff). I think one was off a spare rear and one was off a running car. I wanted them to match, early vs late style. I tended to choose the matching hubs that exhibited the least amount of taper wear and thus fit further out on the axle.
What you guys say makes sense. I need to explore why it runs without wobbling on the taper but wobbles when on the bearing(that slight chamfer). I suppose either one or the other surface is damaged/worn. I just might have fallen for the vary assumptions/issues I tend to rant about.

Thanks for the ideas.

Dave
 
I true wire wheels for the Harley Davidson motorcycles. I shoot for .010" rim bead side clearance and get it with quality OEM parts. Aftermarket rims not so much. OEM specs were 1/32" or .032". I can get the Aftermarket rims to within that spec but just. I mount a tire and install them and they go down the road fine.

A lot boils down to the drum lathe when truing a brake drum. The bearing, the journal, and the hub inner race may have an issue with any one item and get some wobble or eccentricity from it. The taper really doesn't affect that all that much since the axles float and flex. I'm not saying the tapers aren't important but they should be good enough to function properly or better parts should be sourced for replacements and same with the hub bearing components. Worn parts wear on the good ones so get the best you can.
 
Thanks. Well to my surprise, I found three studs that allowed .004 - .010 gap under the hub inside the drum. So the hub is not completely seated to the drum on one side. When swaging I had all studs held with 1/4" thick washers and nuts but for some reason there must have been flex. I attempted to pull them tight with the same washers and they snugged up well(a ran pretty true on the brake lathe). I had assumed the studs would have expanded between the hub and drum a bit(as in poor standard riveting) but this wasn't the case. Unfortunately, the middle stud area will not stay tight once it's nut is removed for additional swaging. I can slide at least a .0015" feeler gauge under there. There might be some hub warpage but two on the opposite side are fine and I don't remember seeing warpage when lightly draw filing the hub face. I had it in a lathe but on an old axle taper and really didn't trust the setup for machining. With the pressures used I wouldn't doubt a bit from the process now that will complicate additional pressing.
I am using a DIY jig similar to what Vince Falter shows (https://www.fordgarage.com/pages/swaging.htm) and a 32 ton air over hyd jack in a 20 ton frame. This was my first time so I'll need to get better but not sure how to get that hub to hug the drum while in the press.

Dave
 
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Interesting. I mounted the offending drum/hub on a wheel - in this case a '32 wheel and torqued the nuts to 50ft/lbs. The gaps drew up with no measurable gap between hub and drum. They are clearly not "loose" as the sheared part of the shoulder is 3/32"+ and sits below the face of the drum.
I am actually growing confident to add nuts and washers and go ahead and true the drums. I know some say they tack their studs to the hubs and run the drums as slide-on style but I do not agree with that at all. That's not how the engineers did it. I digress.
Any thoughts?

Dave
 
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