Clutch suddenly won't fully engage

[Earendil]

I'm driving along in 3rd gear at normal speeds when I make an easy shift to 4th. The car revs high and I think "I missed the gear". I try again, and the same thing happens but this time I can feel it catch before it breaks loose. I proceed to nurse it a few more miles, but anything past 1/16 throttle breaks it loose.
Of note:
Clutch pedal feels normal
Shifter feels normal
All gears are selectable and do in fact change the gear ratio
I have fluid in the reservoir
Clutch is only a year old, and was very strong just before it went out.

So where do I look first, and what are the chances this gets even worse? I'm going to try and nurse it a few miles home tonight after traffic dies down, hopefully it'll be okay.
But I'm baffled. Google searches show lots of brokens trans, shafts, and diffs, but that cant be it. I know a half dozen things that'll keep it from DISengaging, but to keep it from engaging fully? Shattered clutch disc? Rear seal blow out violently and sprayed oil over anything? Nothing was dramatically dripping by the time I parked it on the side if the road.

Anyway, if I make it home to iffy I'll report what I find. I guess if nothing stands out I pull the trans...god I hate doing that...

[E30_Pare]

glazed it?

[e30austin]

Look under the car for signs of anything leaking. What kind of clutch did you put in?

[Earendil]

Look under the car for signs of anything leaking. What kind of clutch did you put in?

OEM Sachs. Resurfaced flywheel. All new everything within 24 inches of the disc as well. As I've had more time to think about it, I'm feeling like oil or something must have hit the clutch. If the clutch had shattered or was in any way fubared I'd think I'd either hear something odd, or the clutch wouldn't depress the same as it always does. I mean, I'm getting solid push back. If the disc were jamming I would get a different feel in the pedal, no?

[accident]

I had this happen in my first E30. The slave cylinder piston seals shit the bed and it pissed fluid into my bell housing. Pedal felt slightly spongy, but not enough that most people would notice. Had to replace my clutch disc and have my flywheel resurfaced. The flywheel was lots of pretty colors because I couldn't afford to fix it for 2 months and it glazed something fierce lol

[Earendil]

I had this happen in my first E30. The slave cylinder piston seals shit the bed and it pissed fluid into my bell housing. Pedal felt slightly spongy, but not enough that most people would notice. Had to replace my clutch disc and have my flywheel resurfaced. The flywheel was lots of pretty colors because I couldn't afford to fix it for 2 months and it glazed something fierce lol

Maybe my slave just got a little excited and let out a little squirt? I can hold my clutch pedal against the floor for a few minutes and not lose pressure, and then have it come back as usual. The engage point, while weak, is in the exact same spot it was prior to the incident. And I can most definitely disengage the clutch still.

I was able to get it home last night, but it was exactly like driving on ice, except that I could hold corners like a demon. This promoted some interesting (but mostly legal) driving as I tried to make it up hills. I was thwarted by one red like that made me back up into a more level parking spot so that I could start again. Time to clear out the garage...

[Earendil]

I put the car up on blocks in the garage and went to work pulling it apart. I was expecting things to be covered in either engine and/or tranny oil, and found nothing of worth. In fact after pulling the bellhousing-half-cover-thingy I found the flywheel and the inside of the bell housing perfectly dry.

Rewind 48 hours:
I did a thought experiment wherein I tried to think what besides the clutch it could possibly be. The car shifts, it has some bite, maybe 10%, and all pedals felt normal. No missing fluids. I thought "what happens if an LSD goes bad?" And my immediate response was it would turn to an open diff. A diff can't possibly act like this....I was wrong.

Present day:
At one point I moved my lights around and I saw it, my drivers side axle was completely separated from the diff. I need to investigate the damage, but that's the answer to the question. It felt like a 10% clutch because it was the LSD clutches taking everything, with one wheel basically free-wheelin.

This also answers the question "what could go wrong if I try to drive it home?". At the point when the shaft fell out I had likely done no damage to the LSD clutches. Continuing to drive it might have burned out my newly refreshed LSD :(

[accident]

Ouch.

[Earendil]

I feel in my own defense I should state that the diff has seen 3 track days and a hill climb event, along with around 3000 miles of public roads. I've inspected the underside of the car, especially the diff, since the diff was reinstalled. It never showed signs of loosening up, or made any noise. The last event, the hill climb, was on a rather hot day and was followed by a 300 mile drive home. I guess they all spun loose at that time.

I also inspected the 6 bolts and the threads feel okay and the bolts aren't broken. This has me somewhat puzzled because I would have expected the axle to rip the last bolt or two out. The threads may not actually be okay, but they aren't stripped.

The passenger side axle is still properly torqued.

Parting shot: this is all I could think of when I was typing this.

[Wanganstyle]

Blue loctite is your friend here

Also new bmw external torx screws seem to handle vibrations better than the original 8mm allen heads. E36/46 use these

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[Earendil]

Blue loctite is your friend here

Also new bmw external torx screws seem to handle vibrations better than the original 8mm allen heads. E36/46 use these

Oh really? I might have to invest in a set of those.

Last night I removed the bolts and cleaned them up. No visible damage to threads. I then checked them by hand threading them into each hole on the diff. Everything went smooth, so I reinstalled with blue loctite and a torque wrench.

The lack of damage to the threads on the bolts and the diff has me somewhat baffled. That would mean that all the bolts came loose at the exact same time, otherwise I'd expect for a bolt to be ripped in two or the threads on one or two of them to be torn up.

[Wanganstyle]

Oh really? I might have to invest in a set of those.

Last night I removed the bolts and cleaned them up. No visible damage to threads. I then checked them by hand threading them into each hole on the diff. Everything went smooth, so I reinstalled with blue loctite and a torque wrench.

The lack of damage to the threads on the bolts and the diff has me somewhat baffled. That would mean that all the bolts came loose at the exact same time, otherwise I'd expect for a bolt to be ripped in two or the threads on one or two of them to be torn up.

The left side rear cv is more stressed by vibrations; our built chassis enduro car likes to shake them free.

My street e30 with a welded diff also shook loose the left axel screws on the freeway; was hilarious to drive home 1 wheel drive (right only).

Thankfully a welded is much better attached to a solo tire than anything else

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