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Rear Hub/Axle Collar nut failure on e36?!?!


faisduvtt
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Calling on all e36/e46 teams for advice.  We're ran at Lemons Barber Race this weekend - had a blast but had two identical failures, 1 that ended our Saturday run and 1 that ended Sunday.

Both Left and Right wheels broke off.  We believe hub failure but can't determine root cause necessarily because of the catastrophic failure and subsequent damage.  

Wondering if teams have experience hub failure or axle collar nut failure (we did visually inspect prior to race and the nuts on both sides were dimpled in. We had also installed the hubs as replacements, everything torqued correctly.  Newest one was about 3 years old.  Both have been through about 6-8 Lemons/Chump races.  Never had failures like this before.  Both lower control arms, trailing arms, half shafts had all been replaced so nothing "old and crusty" under there.

 

Any ideas?  Also open to suggestions on how to reinforce, strengthen, and any pre-race prep or checklist teams go through for their suspension as they prep their e36. 

Thanks!

 

Tom Butler, Raleigh, NC
B&W Racing, 1994 BMW 325i Cat in the Hat Theme

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Any chance it was a loose bolt that caused the caliper to jam inside the wheel? I've seen that before, can be very destructive.

 

Never seen a failed rear hub (lots of bearings, but not a single hub), seems very odd to happen on the 6th or 8th race. 

Edited by ABR-Glen
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Not a BMW guy but reading your post I can offer some thoughts, if both hubs were about the same age race wise I would make note of that and start a routine repair/replacement.

Next when you set your axle nuts and dipple them into the keyway get a paint stick, red or yellow and paint a line across the nut, end of axle to hub flange. In pit stops you can

quickly see it the nut has backed off or moved. We have had them loosen on our Miata.

 

If the wheel completely came off are you saying the hub broke? Lug bolt failure could also be an issue. Pictures of what was left might help also.

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1 hour ago, TimS said:

New sway bar bushings, removed damaged old clutch slave line. Prepped trans added a vent hose to the trans. Swapped output flange and guibo. Best thing To happen was Huggy texted to tell me my engine was done and he was coming through Charlotte this week on his way to Road Atlanta and could drop it by my house. Next weekend should be fun. Thanks Chris. 

 

Uh.  WAT????

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@E. Tyler Pedersen car had the axle nuts loose at Sebring this year.  I went out in practice and could feel some instability in the rear end.

 

I brought the car in and the wheels had a bit of wobble to them.  We got lucky and were able to just retorque the nuts and send it.  

 

I can see that destroying a bearing quickly and leading to this failure!

Edited by wvumtnbkr
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3 hours ago, wvumtnbkr said:

@E. Tyler Pedersen car had the axle nuts loose at Sebring this year.  I went out in practice and could feel some instability in the rear end.

 

I brought the car in and the wheels had a bit of wobble to them.  We got lucky and were able to just retorque the nuts and send it.  

 

I can see that destroying a bearing quickly and leading to this failure!

 

 

Puts a heck of a lot of stress on the axle tip. I have seen that cause a failure on a few vehicles for sure.

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Teams - first thanks for all your replies!  Pictures attached here to show more detail of damage.

 

Here are answers to the questions and recommendations that have come out in thread.

  • Lug bolts are fine - they stayed intact on wheel as rotor fell apart.
  • We're going to start a replacement of hubs after 5 races to be proactive.
  • I like the idea of the paint stick across nut and dimple to see if it has moved or backed off.
  • I can confirm we torqued to spec, 184ft lbs on both sides.
  • Axles seemed fine and were new-ish, 3-4 races.  End of spines now slightly damaged due to hub failure.
  • Good idea to check the three rear differential bushings hold the differential to the subframe. That might have caused some slop in the rear causing undue stress to the sides.

hub_failure.jpg

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  • Technical Advisory Committee

What does the broken hub look like?

 

Are you sure your torque wrench is accurate?

 

Where did the axle nut go?

 

Are you missing a washer?

 

Are you using the lock ring on the nut?

Edited by Huggy
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The only way the hub fails like that is if the axle nut comes off....where the hell is the axle nut.  Am I seeing things or does it look like part of the place you stake the nut has gone away? (I know you said part of it was damaged).  Something happened with the nut, either it backed itself off for reasons unknown or the metal on the tip but I wouldn't call this a hub failure.

 

800585_x800.webp

 

PSA: Please replace the rear rubber brake line.

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Axle nut and hub flew off in the "accident" - see exciting video here:  

 

So - no way to see hub or nut as they flew off are are track debris we didn't get back.

 

Our "best" guess is nut failure - it backed off and/or failed which released everything and caused the failure.  

We have accurate torque wrench and torqued to spec as well as correctly staked in the nut.  

We've been running for 12 years - never had this type of failure...

 

Actions we're taking are to paint stripe nut&hub so we can visually inspect each pit stop and catch if an issue.

Replace proactively.

Appreciate the PSA on the brake lines - it's on our list to do :)

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  • Technical Advisory Committee

I'll echo it is likely a nut torque issue.

 

Small potential if bearing went that it allowed for the axle nut to loosen up and disappear.

Or somehow stretch in the axle itself.

Or threads on nut failed/stretched.

Or the corner wasn't fully assembled.

 

Those nuts take a ton of torque, and shouldn't just come undone.  

 

When rebuilding, make sure bearing is full installed, hub is pressed in completely, axle fully seats and confirm your torque numbers with a second, known good torque wrench.

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Elaborating on the above, if for any reason there was stretch or give after tightening, a paint may not give warning as the nut never moves even though torque is reduced because some sort of "settling"

 

It would be best to hit this on a pre-race checklist while the torque wrench is out., perhaps add 10ftlbs to the spec.

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My general rule is to exceed torque specs everywhere except head studs and flywheel bolts and tapered bearings and crush sleeve bearings (diff).
When I changed the e30 rear wheel bearings before Indy I hit the nuts with 5 ugga duggas @100psi, then I put a 2.5’ breaker bar on it and stood on the end (375 ft-lbs), then hit it with the impact again. (My impact is having issues, probably doesn’t exceed 250 ft-lbs anymore). You really can’t get those nuts too tight (unless something breaks or strips). 

Edited by enginerd
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my best guess is that the nut was torqued while the half shaft was not fully seated or the nut was reused.  I have a hard time thinking it couldn't be installation with both failing.

 

I won't use anything but oem half shafts, repacked and installed with a new nut.  I've heard of nothing but problems with remanufactured / aftermarket ones.

Edited by theblue
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  • Technical Advisory Committee
4 hours ago, faisduvtt said:

Teams - first thanks for all your replies!  Pictures attached here to show more detail of damage.

 

Here are answers to the questions and recommendations that have come out in thread.

  • Lug bolts are fine - they stayed intact on wheel as rotor fell apart.
  •  

 

 

 

how about a pic of what was still attached to the wheel?

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38 minutes ago, theblue said:

 

I won't use anything but oem half shafts, repacked and installed with a new nut.  I've heard of nothing but problems with remanufactured / aftermarket ones.

 

Same.  Good OE reman's or good used factory units.  The "new" ones are all coming out of China, and have questionable strength.  Seen too many try to shake themselves to pieces even at highway speeds, or had the tip shear off due to the weak area where the threaded tip meets the splines.

Edited by SonsOfIrony
I can has proofread?
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2 hours ago, enginerd said:

My general rule is to exceed torque specs everywhere except head studs and flywheel bolts and tapered bearings and crush sleeve bearings (diff).
When I changed the e30 rear wheel bearings before Indy I hit the nuts with 5 ugga duggas @100psi, then I put a 2.5’ breaker bar on it and stood on the end (375 ft-lbs), then hit it with the impact again. (My impact is having issues, probably doesn’t exceed 250 ft-lbs anymore). You really can’t get those nuts too tight (unless something breaks or strips). 

I wouldn't do that.

We started doing that on our VW because the nuts came loose all the time.

Instead of the nuts coming loose, we started snapping off the end of the axles, right behind the threads.

Now we red loctite and double nut the hubs.  They still come loose, just not as often but with zero axle failures.

 

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By what has been said I would agree it was not a nut failure but the one turning the nut. Not trying to make that sound bad but I toss the impact wrench on axle nuts and set

them with my impact then set the dimple and paint the line. Even on our Miata's one can come loose at times and it is easy to catch in a pit stop. If you see it has moved you

just hit it again with the impact. 

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