[LimpBimmer]

Hi all
I'm in the middle of changing a very noisy diff on my e90, but can't for the life of me get the prop shaft to come off the diff.
Am I missing a trick here? All 4 of the bolts are out, and I assumed that as I lowered the diff down that would force the prop shaft off.... Obviously I was wrong!

Help please! I really need this car running again tonight! 🙈😫🧐

[e90yyc]

How this prop shaft connect to that diff? I’m struggling to see whether it’s a circular flange? (On my car it’s a flex disc so different.)

If I’m seeing it right, it looks pretty rusted together. You might need some heat and a thinner prybar to get between the two. Be careful not to mar the surface and do NOT use heat if your prop shaft has a centering bush, as this will contain rubber and possibly plastic too. I’d also suggest not trying to drop the diff any further until you can separate the two. Your idea of dropping the diff to separate the two ought to have worked, but you don’t want to put too much stress on the prop shaft u-joint either.

On my setup, there’s also a centering bush attached to the driveshaft that needs to actually come straight out of diff flange, so if you have something similar (can’t tell from pic) definitely raise the diff back up and work at separating them on a level plane.

Hope that helps. I don’t really have any hot tips for getting them apart. My post also assumes it’s a circular flange on circular flange, so if it’s something else let me know and I’ll think of what might be different.

Be careful because you can damage things if they’re at too extreme an angle.

[LimpBimmer]

Thanks e90yyc
As best as I can tell there's no centering bush, though not sure if it's hidden.
I've taken a picture of the replacement diff, and another of the prop shaft on the car. Hope this gives enough info

[e90yyc]

Okay thanks that makes it clearer.

Honestly, the two are rusted together. Even with my giubo setup it still took some effort to pop it free, and there was just a little bit of oxidation.

It’s probably going to be a bitch to get free even with heat. If you’re just planning to bin the old diff, try using a torch on diff flange and then smoke the ever-living christ out of it with your hammer (hitting face of diff flange and avoiding any part of propshaft). Use good judgement obviously—I’m not suggesting you go Captain Caveman on it.

Before you do any of this, raise the diff up so the shaft isn’t at such an extreme angle. You don’t want any shock from your hammer to damage the u-joint. Ideally you shouldn’t need to bludgeon it to death.

[infinite_creations25]

Originally Posted by LimpBimmer

Hi all
I'm in the middle of changing a very noisy diff on my e90, but can't for the life of me get the prop shaft to come off the diff.
Am I missing a trick here? All 4 of the bolts are out, and I assumed that as I lowered the diff down that would force the prop shaft off.... Obviously I was wrong!

Help please! I really need this car running again tonight! 🙈😫🧐

I can’t offer you any advice but could you describe the kind of noise you were getting with your old diff? Was it a high pitch whine/howl at certain speeds?

[LimpBimmer]

Originally Posted by infinite_creations25

could you describe the kind of noise you were getting with your old diff? Was it a high pitch whine/howl at certain speeds?

It's noisy at all speeds. Sounds like a hair drier on steroids!
It's by far the dominant noise in the car at any speed.
The nose changes as you apply / release throttle, but is always there.

[jsunma]

Yeah, I'm going to concur that that's just rust. What have you used so far as rust-busting preparations?

Here in the Northeast US, we get rust like that...and I'd soak the whole thing down with PB Blaster (which you may not have over there), whack it a few times with a hammer (vibration seems to improve the action of most rust-dissolving preparations) and then let sit for a little longer. Then try separating again. I may also use heat...either a heat gun or a propane torch (I'm guessing you have nothing more powerful). Then whack it again.

Shirley a trip to your local autoparts store will turn up something that's good for blasting rust.

[e90yyc]

Can you get a prybar in here and use diff flange as fulcrum point?

I don’t think that should be an issue. A little marring on the propshaft there shouldn’t be a problem.

[LimpBimmer]

Thanks for the suggestions jsunma , e90yyc

So far I've soaked it repeatedly in penetrating oil and blasted with a propane torch for far longer than could ever be safe, considering it's proximity to the fuel tank ����

I've left it for the night now and returned home. I'll go back tomorrow with a crow bar and a lump hammer.

Last ditch plan, if all else fails, is to remove the driveshaft completely (assuming it's not rusted at the transmission end), and take an angle grinder to the diff. The vibration from that should help, and if nothing else it'll leave a much smaller more manageable section to hammer off the prop shaft

[F31B48]

Originally Posted by LimpBimmer

Thanks for the suggestions jsunma , e90yyc

So far I've soaked it repeatedly in penetrating oil and blasted with a propane torch for far longer than could ever be safe, considering it's proximity to the fuel tank

I would suggest refitting the diff back onto the 3 mounts first before using a pry bar. It will be very difficult to get any sort of leverage with the diff not mounted and flopping around on the ground.

Also, i don't want to freak you out or anything but there are rubber seals on the universal joint cups. If you have heated that universal joint those seals may now be damaged and will not keep the water out and grease in. That could be an issue with the salty roads over there. How hot did you get it?

[LimpBimmer]

Finally!
Spray - lump hammer - blow torch - pry bar - Spray - lump hammer - blow torch - pry bar.... Repeat for 4 hours.... It's free!
Looks like the big sticking point was the prop shaft flange on the left hand side, though the rest weren't helping.

[e90yyc]

Nice work. That thing was welded on there.

[E92_William]

Well now when you put it back together make sure to coat some of that area with a thin layer of any seize so it doesn't happen again if your "new" diff takes a dump

[LimpBimmer]

Originally Posted by E92_William

Well now when you put it back together make sure to coat some of that area with a thin layer of any seize so it doesn't happen again if your "new" diff takes a dump

Sage advice! I put a thin layer of moly grease on the driveshaft flange.

[LimpBimmer]

I'll wrap this post up with a few lessons learned, just in case anyone else has the same problems.....

1. Release the prop shaft first, before the driveshafts and the diff itself
2. The handbrake cables get in the way. Not much you can do about it, though releasing them from the little "J-clips" helps a little
3. Undoing and refitting the prop shaft and driveshaft fixings is easier with 2 people - one person under the car, and the other in the car on the brake / gear shift / handbrake. It didn't save much time, but it does save having to get up from under the car every time you need a new angle on the prop / driveshafts
4. I'm not convinced the heat really helped releasing the stuck prop shaft. I suspect that was mostly the penetrating oil, hammering and pry bar. It does need some significant brute force.
5. Be careful undoing the diff fixings. It's heavy and you don't want it rolling onto your head or trapping a hand. Use a trolley jack or transmission jack to support it
6. It goes without saying, wear safety glasses working under the car. There's a lot of rust and dirt falls down
7. A thin layer of moly grease at the prop shaft flange should prevent any future rusting issues. Be careful not to get the grease into the threaded joint.
8. Use new fixings when you refit the prop and driveshafts
9. An 18mm ratchet spanner (for the two front diff fixings) will probably save you an hour, assuming you've not got the car on a lift and using power tools

[M-technik-3]

Old threads but my driveshaft is the same way crazy how secure it gets. Hoping it breaks free soon.

Edit: Ended up beating it with 3 pound sledge and rotate it and did the same.