3500lb axles bad design
Probably most medium size trailers have the 3500lb axles and 10" brakes. The design of the spindles has little to no shoulder to locate the inner bearing. When I looked up the blueprints, I found th...
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Hi Lynnmor
I'm not arguing the fact of a small contact shoulder, its small. I'm just trying to help as I see something that is not right with the parts beyond the small shoulder.
As you described the bearing inner race is eating into the spindle. While a larger shaft shoulder will lower the psi contact pressure of the thrust load, a larger shoulder will not change the friction between the bearing race and the spindle shoulder. Bear with me a moment and think through what I am going to say/show.
Here is your spindle. We can see the galling going on. The shaft shoulder is galled and where the slivers are coming from.
I went and looked at all my pics when I had my smaller camper and I found this one. 3500# Dexter axles. I found these 2.
The assembly with the drum off and cleaned up. Nothing special on this one, just showing it.
Now a zoom in on the shoulder.
The zoom in shows no galling on the thrust shoulder. That is a key difference.
On yours, in order to gall steel in the pattern you have this points to the bearing race rotating. If you use a 10X loop or other magnifier you can see the score lines. They should be radial. If they are radial, the bearing was spinning. If the score lines are not radial, more jagged all over the place, then this points to maybe an impact loading smash which I'm not really thinking that's the case, it's more a radial gall.
That galling is the problem and I think you see that as I do. So the question is, where is the gall coming from?
The laws of friction do not have surface area in the equation at all. Force and the surface material coefficient of friction are the 2 variables that have to change. Not surface area.
Once that thought is realized, how did the gall happen?
The bearing bore, it is dead on center tolerance within 4 decimal places or is it sitting on the large end of the tolerance?
The shaft OD, it is dead on center tolerance within 4 decimal places or is it sitting on the small end of the tolerance?
You will need a mic to get that close, a caliper has more chances of error in it which I'm sure you know.
That would be my first place to look. It would not shock me in the least the shaft is ground small or the bearing race too big. Once the bearing starts spinning on the shaft under load, its all over and it's going to gall something. Yes, this is not an interference fit as it has to slide on, but the fit has to be right or the bearing will spin.
The other part of the equation is the coefficient of friction of the 2 steels changed. That is a lot harder to check. Hardness could be off or the steel itself. I would put this steel factor lower in odds of the issue, odds are much higher there is a bearing fit issue.
Again I agree the shaft shoulder is small, but that small shoulder is not changing the friction holding the bearing from spinning.
Hope this helps
John
I'm not arguing the fact of a small contact shoulder, its small. I'm just trying to help as I see something that is not right with the parts beyond the small shoulder.
As you described the bearing inner race is eating into the spindle. While a larger shaft shoulder will lower the psi contact pressure of the thrust load, a larger shoulder will not change the friction between the bearing race and the spindle shoulder. Bear with me a moment and think through what I am going to say/show.
Here is your spindle. We can see the galling going on. The shaft shoulder is galled and where the slivers are coming from.
I went and looked at all my pics when I had my smaller camper and I found this one. 3500# Dexter axles. I found these 2.
The assembly with the drum off and cleaned up. Nothing special on this one, just showing it.
Now a zoom in on the shoulder.
The zoom in shows no galling on the thrust shoulder. That is a key difference.
On yours, in order to gall steel in the pattern you have this points to the bearing race rotating. If you use a 10X loop or other magnifier you can see the score lines. They should be radial. If they are radial, the bearing was spinning. If the score lines are not radial, more jagged all over the place, then this points to maybe an impact loading smash which I'm not really thinking that's the case, it's more a radial gall.
That galling is the problem and I think you see that as I do. So the question is, where is the gall coming from?
The laws of friction do not have surface area in the equation at all. Force and the surface material coefficient of friction are the 2 variables that have to change. Not surface area.
Once that thought is realized, how did the gall happen?
The bearing bore, it is dead on center tolerance within 4 decimal places or is it sitting on the large end of the tolerance?
The shaft OD, it is dead on center tolerance within 4 decimal places or is it sitting on the small end of the tolerance?
You will need a mic to get that close, a caliper has more chances of error in it which I'm sure you know.
That would be my first place to look. It would not shock me in the least the shaft is ground small or the bearing race too big. Once the bearing starts spinning on the shaft under load, its all over and it's going to gall something. Yes, this is not an interference fit as it has to slide on, but the fit has to be right or the bearing will spin.
The other part of the equation is the coefficient of friction of the 2 steels changed. That is a lot harder to check. Hardness could be off or the steel itself. I would put this steel factor lower in odds of the issue, odds are much higher there is a bearing fit issue.
Again I agree the shaft shoulder is small, but that small shoulder is not changing the friction holding the bearing from spinning.
Hope this helps
John
