325ix Rear Differential Rebuild DIY

[Motorsport1207]

Ok, So before I disassembled this diff I tested it like a clutch pack diff, holding input flange and using a torque wrench to see the point it start to rotate. I measured 39 ft / lb torque. I presume this is good as this would be the similar result that AWD_30 observed. Sent from my iPhone using Tapatalk

[AWD_E30]

Yep Nando is right. My center diff viscous coupler testing has shown there is actually a speed vs. Temp relationship (think 3D surface plot) that results in a different torques. In my case I was able to compare the bad diff vs good diff out of the car by turning left/right output flanges but this was not very scientific. My bad one was completely dead... No life left. No guarantee if the coupler was weak or on it's way out by using this method.

[nando]

you can bench test it but not like a clutch pack diff. There's not a breakaway torque, the locking torque increases with the speed of rotation, which takes a special testing method to measure.

technically the VC can lock nearly 100%, of course there is a limit to the actual torque it can hold without overheating.

[Motorsport1207]

Hi, Thanks for this info, can this be bench tested similar to the standard LSD diffs where you lock up the pinion flange in a vice and use a torque wrench to turn the axel output shaft flanges and determine the breakaway torque (BT). So for a M20 at 168 HP 25% lock up would yield a BT of 42 ft lbs I presume this can be applied to the IX viscous coupling diff and they also would have the 25 % lock up Thanks Ted Sent from my iPhone using Tapatalk

[AWD_E30]

I found my rear viscous coupler was bad was by jacking up the rear of the car, placing the car in gear (manual) or park (auto), and trying to turn one wheel forward by hand. If the viscous coupler is bad the other tire will spin in the opposite direction pretty easily. If the coupler is good the other tire will spin in opposite direction but with considerable force.

Side note: Jacking up only one rear tire will test rear and center coupler if the car is in neutral. This is not ideal because it's hard to tell which coupler is providing resistance. I accidentally did this when I bought my car and found out later the center diff was good but rear was bad. Good luck!

[Motorsport1207]

Hey, reviving this post. Diving into rebuild my 4.10 ix diff. One question I have how do you know the viscous unit is good and not worn? Do you do a breakaway torque test? What value is good vs bad Thanks Ted Sent from my iPhone using Tapatalk

[The Dark Side of Will]

Well don't reuse them now...

[nando]

They are torque angle.

100nm +/- 10nm
50 degrees +/- 5 deg

https://tis.bmwcats.com/doc1037037/

[AndrewBird]

Nm would make more sense looking at this chart:

https://www.boltdepot.com/fastener-information/bolts/Metric-Recommended-Torque.aspx

[nando]

sure, but I've never seen a TTY bolt on a BMW that wasn't torque + angle.

[The Dark Side of Will]

Sounds like they are. 140 ftlbs is a VERY HIGH for an M12 bolt, even 12.9.

Are we sure that spec isn't 140 N-m?

TTY bolts are typically spec'd with torque + angle, but don't have to be.

[nando]

are they TTY?

if not, I wouldn't hesitate to re-use them.

[peter69]

With everything clean we can bolt the crown gear on. Because the crown gear is a slight interference fit to the carrier just install 4 old bolts and use an impact alternating bolts until the gear is fully seated on the carrier. Then you can juice up all of the new bolts with Loctite and hand tighten them, BMW does spec out to replace these. The crown gear bolts are torqued to 140 ft-lbs. I did one pass at 100 ft-lbs then a final pass at 140 ft-lbs.

The P/N of the bolts is 33 12 1 211 593 but they are no longer avaible since 2013.
Where have you bought yours?

[ttrousdell]

thanks for taking the time to write this up. much appreciated

[The Red Baron]

Awesome you posted this. Basically made me feel better i didnt overthink when i had done mine. Great stuff!