leaking rear differential

[ingramlee]

My rear diff appears to be leaking from the front of the unit. I am almost sure its the input seal. The fluid is traveling straight to the back of the diff.The output shafts have no fluid on them. how difficult is it to replace the input seal? THX

Edited February 23, 2019 by ingramlee
mispelling

[TobyB]

Not too bad IF you pay close attention.  There is a crush sleeve in the diff, so you 

have to replace the nut on the flange to almost exactly where it was before,

or the pinion bearings fail.  However, if you go back to EXACTLY where it was,

the nut sometimes doesn't have enough tension on it to keep the flange tight.

So you may end up 1/128th of a turn farther, and hope the bearings were on the loose side.

 

The 2002 instructions say to change the crush sleeve every time.  The 320 instructions

say you can get away with re- establishing the nut position.  It's effectively the same diff,

(heh) so it oughta work...

 

t

 

[ray_]

My front diff is dry.

 

Where do I add the lube to check for leaking?

 

[Ian]

My diff leaks also.  I just figured it was BMWs method of rust-proofing the undercarriage.

Edited February 24, 2019 by Ian

[Buckeye]

instruction how to replace pinion seal without needing for replacing crush sleeve is covered by BMW SERVICE INFORMATION document dated Sept. 1971

Instruction is covered on pages 49&50

Technical Customer Service Part 7 683 to 710.pdf

 

[Bentworker]

The excerpt from that service information seems to match up with best practice I have seen on other crush sleeve type preload setups.  Measuring threads, "clocking" or marking the pinion nut and other black magic methods are not as good as the "before & after preload" method described in that link that Buckeye posted.

 

Only catch is you need a quality beam or dial type torque wrench that reads down in the dirt (1-30 inch pounds is about right).  Doing this without a proper torque wrench is a total crap shoot.  

 

In a nutshell, before you touch a thing, disconnect the cv's and prop shaft, get the inch pound dial type torque wrench on the pinion nut and turn it.  Note the amount of force it takes for continue rotation (not break-free torque).  Write that down somewhere and then go to town replacing the seal.  Before you go nuts tightening the pinion nut take a chill pill and do the following.  

1) Make sure you don't end with a leak on the splines….clean-clean-clean, and use some sort of product like the "Right Stuff" sparingly on them.  

2) With a healthy dose of thread locker on the pinion nut lightly snug the nut, then measure force to turn the pinion.  If it is below what you noted before you started tighten the pinion a small amount (like 1/16 of a turn), then check the rotational force again with the torque wrench.  Repeat until you have increased the preload a small amount over what it was before you replaced the seal…. That example in the service information was about 3 cmkp higher (about 7.5 inch pounds) after seal replacement.  Personally that seems a little much.  I'm more of a 2-4 inch pound kind of guy.

 

If you overshoot there is no going back.  You must remove the seal, the front pinion bearing and replace the crush sleeve… then try try again.

 

Going too loose or too tight on bearing preload is a recipe for calamity.  Read noisy rear end at best, total thermonuclear failure at worse.

 

 

[TobyB]

Quote

 If it is below what you noted before you started tighten the pinion a small amount (like 1/16 of a turn)

you mean, like, 1/242nd.  The 'joy' of a diff with pre- bedded bearings is that the difference between 

4 in/lbs and 40 ft- lbs really is less than 1/16th of a turn.

 

From a 'how it works' standpoint, you need enough preload to offset maximum torque

down the driveshaft (120 ft/lbs x 3.94 (or whatever 1st gear is) plus whatever inertia a clutch dump can generate)

but no more.  And that's really something like 5 in/lbs.  NOT INCLUDING whatever drag the seal puts on it.

 

Practically speaking, reclocking (but noting seal drag before you get to any bearing preload) plus making sure

it has about 4-6 in-lbs rotational is about right.  WITH diff oil, nothing else.

And really hard to measure accurately.

 

I do it by feel.

 

Loose can be worse than tight.  Or not.  Depending.  

 

t

is about to tell Ray where to go.

Edited February 25, 2019 by TobyB

[TobyB]

12 hours ago, ray_ said:

My front diff is dry.

 

Where do I add the lube to check for leaking?

 

YOU, my son, have just earned the job of putting the chains on my now- two- wheel- drive pickup.

 

In the mud.  And slush.

 

That the horses have left behind.

 

t

thinks Ford's ttb front end was a really  bad idea.

But it still needed fluid, he guesses.

Based on personal experience.

Edited February 25, 2019 by TobyB

[PaulTWinterton]

12 hours ago, TobyB said:

the difference between 

4 in/lbs and 40 ft- lbs really is less than 1/16th of a turn.

 

This is where I take it to a specialist for resealing.  I looked at the service manual and there were enough "whats?" to convince me that if I made a mistake I'd kick myself before and after removing the diff AGAIN... to get it to a pro to do it right.

 

The output shaft seals and o-rings are straight forward to remove and replace but that pinion seal is beyond my comfort zone.

Edited February 25, 2019 by PaulTWinterton

[ray_]

8 hours ago, TobyB said:

YOU, my son, have just earned the job of putting the chains on my now- two- wheel- drive pickup.

 

In the mud.  And slush.

 

That the horses have left behind.

 

t

thinks Ford's ttb front end was a really  bad idea.

But it still needed fluid, he guesses.

Based on personal experience.

Just bring it by! Sunny and warm here today. Was 88 Friday. Eeek.

 

?

[71bmr02]

Not the kind of info i wanted to read.  I was in the process of changing out diffs 391 back to 364 and during cleaning i pulled on the input shaft and noticed it pulled out approx 1/4 inch.   hmmmm, not good thinks i so i  checked another diff and no free play.  i removed the keeper from the pionion nut and discovered i could tighten the pinion nut by hand. Question is am i screwed so i now have to replace the crush sleeve because i have no reference point for the pinion nut original location.

[PaulTWinterton]

Without experience, knowledge or the correct tools I'd make some calls to drivetrain specialists to find a shop that can reseal your diff at a reasonable price.

You could look at the shop manual (in the history section) to determine if you are capable of doing it yourself. 

[71bmr02]

Thanks, I am at a complete loss when it comes to rebuilding/setting up diffs.  I know a couple of shops that may be able to set it up.  I did read the shop manual but am sure this job is way out of my comfort zone.  thought there may some quick fix much like retorqueing wheel bearings but that was just wishful thinking.

 

Thanks

 

fwiw, I've got a 320i parts car i could pull the 364 from but it's cold and  wet and  i'm not as young as i used to be but  that may be my final option