Catastrophic failure of Rear diff and repair DIY

[ard]

The fluid looks pretty clean, not like it has been grinding away for 20k miles then triggering this failure.....

[wsmeyer]

Originally Posted by ard

The fluid looks pretty clean, not like it has been grinding away for 20k miles then triggering this failure.....

I thought the same. The amount that drained out seemed reasonable as well considering there was also a hole in the side so I don't think it was low on oil or that the oil had broken down.

[wsmeyer]

After a lot of calling and emailing I found one local to me with 81k miles for $750 delivered to my house. I would have liked to find a lower mileage one but it was VERY clean inside and the oil was still clear so I'm happy.

[dadysev]

Originally Posted by wsmeyer

After a lot of calling and emailing I found one local to me with 81k miles for $750 delivered to my house. I would have liked to find a lower mileage one but it was VERY clean inside and the oil was still clear so I'm happy.

Hello, just had the same happen to be on got a used diff and I'm about to do the same repair.
What did you seal back the diff with? silicone?

[wsmeyer]

Originally Posted by dadysev

Hello, just had the same happen to be on got a used diff and I'm about to do the same repair.
What did you seal back the diff with? silicone?

I just used your basic black (oil resistant) gasket seal. In my experience virtually any quality sealant will work if you properly clean the surfaces. The oil is on the thick side, is not under pressure, and the diff housing is extremely rigid and won't flex at all - this would not typically be prone to leaking.

[dadysev]

Originally Posted by wsmeyer

I just used your basic black (oil resistant) gasket seal. In my experience virtually any quality sealant will work if you properly clean the surfaces. The oil is on the thick side, is not under pressure, and the diff housing is extremely rigid and won't flex at all.

Thanks! last question. When you loosened the 50mm nut did you just use the tension on the trani to counter the 50 mm nut or did you grab the big 12 point flange? i know all the manuals say not to but the diff is garbage at this point anyway.

[wsmeyer]

Originally Posted by dadysev

Thanks! last question. When you loosened the 50mm nut did you just use the tension on the trani to counter the 50 mm nut or did you grab the big 12 point flange? i know all the manuals say not to but the diff is garbage at this point anyway.

That sounds like one of those things written in as "best practice".
Seriously, the engine generates 350 lb-ft of torque, how could I or any normal person damage it with hand tools?

[wsmeyer]

Now for the repair. It's pretty straightforward but two things you need to be aware of.

A. the diff weighs about 60 pounds
B. The bolt that holds the driveshaft onto the diff is 50mm in diameter and is glued on. I'd guess it takes around 200ft/lbs of torque to turn it and it never gets easier until it is off!

If you think you are up for the challenge here's what you need to do.

Basically:
Raise the car.
Gain enough play in the axles to pull the axles out the side of the diff.
Separate the driveshaft from the diff
Remove diff
reverse process to install

YOU MUST REPLACE THE DRIVE SHAFT NUT.
BMW part number 26117567770



1. Break the lug nuts loose on both rear wheels
Get your torque wrench out and put it on the drivers seat (Old school way of making sure you don't forget to tighten them).

2. GET THE CAR UP ON JACK STANDS
Most commonly done by jacking up the rear by the differential. Just double check that the housing isn't cracked from the failure.

3. Remove both rear wheels
Mostly just to give you some extra room.

4. Deflate the air springs
Technically you only need to do one side but releasing the other will raise the suspension up giving you some extra room.

Two choices.
A. In INPA it's under Chassis >> 1-axle Air Suspension (the lower one is rear).
F6 / Activate
F2 Actuators
Then hit F1, F2, and F3 and you'll hear the air releasing.
B. On the passenger side of the car, under the car below the front door, remove that long plastic cover. Behind it is the valve block with the red and blue air lines going into it from the springs. Loosen the 10mm brass nut on each line until you hear the air coming out.

5. Unhook the left rear bowden cable.
This is the cable going to the electronic parking brake actuator.

5a. In the back, in the storage area, grab that red plastic tool. Then remove the cover inside the left rear corner. In the corner there is a silver cable end sticking up. Use the tool to pull this up and you'll feel the it release the latch holding the left and right bowden cables together.

5b. Underneath the car, above the rear swaybar you'll see the actuator module. (Pic1). Remove the plastic collar that holds the cable onto the actuator and pull the cable out.

6. Remove the speed sensor
Drivers side, #25 in pic2. Tape it or tuck it somewhere it won't get yanked.

7. Remove the brake caliper
Two 7mm hex nuts under a plastic cap on the inside.
Zip tie it up so it's out of the way and NOT hanging by the brake line.

8. REMOVE THE ENTIRE DRIVER SIDE AXLE / WHEEL ASSEMBLY
Remove the 3 nuts on the ball joints and bolt I circled in pic2.
It's going to take some muscle but once you remove bolt 7 in pic2 you can rock the bottom of the assembly out and then to the right to remove the left upper arm, then left to remove the right. The entire assembly now comes right out.

9. REMOVE THE DRIVESHAFT NUT
This is BY FAR the hardest part of the entire process. See the 4 pics below for reference. There's a lip on the 16 sided pinion nut that holds it to the diff, and then it threads onto the driveshaft holding the two together.

That blue stuff on the threads is not loctite. It is some sort of JB-Weld like epoxy somehow applied in two layers. When you install it the two mix together and locks it in place. The notes in the service manual say that once you start threading it onto the driveshaft you have 5 minutes to torque it to 55 ft/lbs. Keep that in mind and be ready to complete it;

- Check you have enough room to turn your giant 50mm wrench, I had to shorten mine 4 inches.

- The jaws of your wrench need to be 15mm or thinner. I had to grind mine.

After struggling in the tight space a bit I went another route. I used a die grinder to cut the lip off the 16 sided pinion bolt on the diff. I used that same red plastic tool to manually put the car in neutral then cut a bit, rotate crankshaft by hand, cut a bit.... that got me to pic 3 with the diff and driveshaft separated but the nut still on the driveshaft.

10. REMOVE DIFFERENTIAL
Support it with a floor jack then remove the 2 bolts in the front and one in the back. Lower the jack a little then it will slide back and to the left until the axle and driveshaft come out and then it's free.

11. FINISH REMOVING DRIVESHAFT NUT
Pull the red tool out to put it back in Park, get your 50mm wrench and muscle it, it is standard right hand thread. It's a PAIN IN THE ASS but at least now you have plenty of room

12. INSTALL NEW DIFFERENTIAL
Pretty much just the reverse but a few pointers.

With the new diff on the jack, slide the driveshaft into the diff first and turn the nut 1/2 turn or so but be careful not to get to the start of the glue.

You can then rock it to the drivers side and slide it back to the right and onto the passenger side axle. Then lift up and bolt in place.

To re-install the parking brake cable. Pull that cable in the back up about an inch and then clamp it with locking needle nose or something to hold it there. Place the threaded rod at the end of the cable into the actuator and then use the square part to turn it 5 or so turns counterclockwise. Then release the cable and it will be easy to thread the plastic collar back on.

13. DRINK A LOT OF WELL DESERVED BEERS

That's all I can think of. If something doesn't make sense let me know and I'll do my best to edit it and make it more clear.

[ard]

Well done! Excellent trainee too.

[blue dragon]

nicely done. I'm subscribing to this thead, even though this is one of the tasks I'd probably send to my indy