heat marks on stub axle?

[bimmerboy]

i had my axle nuts impact wrenched off by a local mechanic, he said there are some heat marks on the stub near where the nut seats, didnt know if it was serious or not. i looked and sure enough, a little discoloration, thats not on the other. i may have heated with a torch when i tried to get it off. but cant remember, what should i check for if this is something to take into consideration?

Thanks

[jerry]

i've seen the same discoloration on a few of my stub axles. clean your bearings up and check them for discoloration. if they are dull grey that is consistent with overheating. that would explain the discoloration. alternatively, it's possible you or a PO merely heated them up to remove the hub.

i don't believe these are heat treated, but i could be wrong.

maybe it's time to do a hardness test on one? i'll bring one to work and check. watch this space for update.

as for being worried about the blue tint, i'm not.

[TobyB]

I've seen the same,

on stubs that were otherwise fine.

If they're set up right and kept tight,

they'll be OK. If they have wear, they might not...

hth,

t

[jerry]

i just got back from testing the hardness on the stub axle.

i'm pleased to report that it is indeed a hardened steel.

The hardness values were in the range of 48-49 Rockwell C (HRc).

this is typical of a quenched and tempered steel. I would expect higher numbers for a carburized steel.

i was unable to test in the vicinity of the blue tint without sectioning this part (it is scrap (due to spline wear) and i would have no objections to cutting it up, it's just a time/effort issue now).

anyhow, this particular part has the blue tint at two locations

a) inboard of the threads adjacent to the outward edge of the splines

the fillet just inboard where the dust cover seats against

looking at location (, there's no logical reason why that should have turned blue 'in-service'. Therefore, i'm suspecting the discoloration occurred during machining operation at the factory.

if anyone has had a stub axle fracture, and care to describe the location of the fracture, please post and add to the collective knowledge-base.

[peteinjp]

Isn't it most likely that ht eblue marks are the result of teh heat treatment. The shaft itself could be treated with a flame whilst the threads and flange are not thus leaving blue marks at the edge of the flame.

[jerry]

Isn't it most likely that ht eblue marks are the result of teh heat treatment. The shaft itself could be treated with a flame whilst the threads and flange are not thus leaving blue marks at the edge of the flame.

yes, i think you may be right. darn me for not taking a reading on the flange surface to know conclusively.

i was thinking these were loaded into a furnace whole, but selectively hardening them would provide both hardness where needed and ductility elsewhere. i was suspecting they were finish machined after hardening, but that would be extra tool wear or slower grinding process. i have seen tool burns from too fast a feed rate, but i think your comments are on the mark.

[peteinjp]

Thanks for taking the time to check the hardness. Interesting toknow this kind of stuff. I just bought a set from COOP's group buy second hand but I've been wondering if a new factory set might be just as good.

[TobyB]

I've NEVER had a fracture, and I don't exactly treat them very well...

What happens is that the hub/spline interface starts to fret. The splines on the stub are a terrible fit to the hub, with very little metal in actual contact, so as soon as it starts moving, things wear very quickly. That wears the compression points for the sleeve and hub, and in no time the nut's loose.

THEN you're in real trouble!

Worse, then you take it to a mechanic, who puts in new bearings with the old worn sleeve and splines, and the bearings fail right about the same time it loosens up again, since the shortened sleeve isn't the right dimension for the trailing arm any more.

Amusingly, the sleeve failure point on all (6?8?) that I've seen is 0.2mm- they're ALL worn the same amount. Probably right about where the bearings just can't take it any more!

wow, look at me ranting. Just had to do one on Jenn's car last night, and embarassingly, it's something I did 8 years ago and missed the wear, too.

t

[bimmerboy]

(nt)