Whats so tough about swapping differential input flanges?

[DanDombrowski]

I've been slowly rebuilding the rear end in my 525i over the last few weeks. I finally got my old 3.23 open differntial pulled today, only to find that the input flanges are different , I was expecting them to be the same.

The side flanges look the same. So whats the big deal in swapping the input flanges?

I read Jeff's writeup on his diff rebuild, and mabye I'm stupid and/or exhausted, but I didn't see you address the preload on the input flange in there. From the Bentley, it looks like all you have to do is unbolt the old flange, pull the flange off (I have a puller if necessary) install the new flange, and torque the nut down to the specified torque (Bentley says M20 is 137 ft lbs, nothing about M50 in this one).

Anything Im missing? I'll post pictures tomorrow mabye, I got a million things to do now.

[gale]

Your right, it's easy. Getting the preload set right is where it gets iffy. I torqued mine to 100 ft-lbs with Loctite since that's all the higher my torque wrench goes to, & then hit it with one quick short burst with my 1/2" drive impact wrench. How does one get that stupid little flimsy stamped sheet metal retainer to stay put? It bends all to crap when trying to stake it in place. I finally took it out & straightened it & smeared some heavy grease on it & called it good.

[DanDombrowski]

Here's the new 3.73 LSD flange:



Heres the 3.23 open. I could have sworn I had a better shot of the front flange, but I guess this is it. I'll go look again.

Found it!

[DanDombrowski]

Don,

You definitely get half the credit for this whole project! I dunno that I can say I'd have been able to get through this without your help.

Anyway, I think I can tackle the input flange swap now, my torque wrench is of the 250lbft variety. I haven't gotten to the sheet metal retainer part yet, but Im sure I'll have a bit of difficulty with it, sounds like.

Is there anything difficult about setting the torque to 140lbft with the torque wrench?

[gale]

Nice pic's! Dunno that I deserve any credit if I didn't turn a wrench on it, but thanks anyway. Certainly no more than 140 ft-lbs. I'm thinking since it's a crush ring that gets compressed at the factory for setting the preload, that the tighter it gets, the more it pulls the pinion away from the ring gear, thus making the fit looser/sloppier, and it's when the fit is loose that they tend to go south after awhile. On the other hand, you want to make sure it turns freely by hand. If they're too tight they can be trouble.

My 3.91 felt really loose after I swapped hubs when it was dry. When I filled it with fluid, it felt perfect and that was over 3 years & 15k miles of hard driving, so I think I'm out of the woods, knock on wood. Wipe as much of the old grease as you can out of the CV joint on the end of the driveshaft & pack it with new grease when you put it together. Make sure the convoluted gasket is in place or it will sling it all out.

[DanDombrowski]

I found a better picture for each of the flanges that should be a good shot top down.

[632 Regal]

preload is paramount, I dont know exactly how many inch lbs these should be so I used my experience with rear ends. If you just torque the sucker down...that sounds spooky to me.

[Rigmaster]

I believe you are supposed to use a new crush ring- that's pretty much the whole point, they "crush" once properly torqued so they are one use only.

It's not that hard to do, but you have to do it properly or risk diff whine and possibly damage to the diff if you really screw it up.

I think the probably the hardest part is holding the side flanges still while you torque the input nut. Not that hard to just drill a couple of holes in some angle iron and use them on the side flanges.

Bret.

[Blitzkrieg Bob]

New crush ring and seal is the least you should do.

Jeff, didn't your previous rearend fail cause someone monkied the flange down?

[winfred]

id torque it less then spec to avoid moving anything around, if it's supposed to be 137# id hit it with a shot of locktight and 100-110#