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Differential Rebuild - (Aceandrew?)

engine and drivetrain

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13 replies to this topic

#1 Tommy

Tommy Garage View Garage

Posted 05 August 2013 - 08:46 PM

I'm doing my first full differential rebuild using AceAndrews' instructions. I'm using e30 lsd unit which is a bit different + e21 case and e30 3,91:1 pinion and ring.

 

One question about instructions. Is the following really correct that the pinion should rotate easier when the nut is tightened? I can understand that the crush sleeve could do that but first you would think the opposite.

 

"The factory manual calls for 25ft/lbs. of rotating torque. As you tighten the Pinion Shaft Nut down you'll feel quite a bit of resistance from the crush sleeve, be sure to stop frequently to rotate the flange/pinion by hand. With every twist the pinion should spin easier. Repeat this process until you hit the 25ft/lb mark continually (that is to say the pinion doesn't loosen as you twist) the final feel is similar to putting a finger in molasses (thick but smooth). With the nut torqued down, tap in your new lock-plate (it will be tight but it will expand into the relief slot on the flange [if you don't bend it in half])."

 

Another question - is this conversion correct? I don't have a clue about imperial torque units.

 

"25 pound foot = 33.9 newton meter"

 

AceAndrew - Thank you for your great article! It really helps a first-timer.

 

    Tommy

 


Racing is Life - everything before and after is just waiting!

#2 Preyupy

Preyupy

Posted 05 August 2013 - 09:02 PM

I don't have my book in front of me but I'm sure 25 ft/lbs is too tight. I believe the correct number is listed in INCH/Lbs. check the repair manual before you over tighten the crush sleeve. I may be wrong, it has been a few months since I did my last '02 diff but I'm sure it should be much less than that. TYPO MAYBE?
1970 1602 (purchased 12/1974)
1974 2002 Turbo
1988 M5

#3 Tommy

Tommy Garage View Garage

Posted 05 August 2013 - 09:32 PM

I was thinking same. That's why I had doubts about the conversion.

 

  Tommy


Racing is Life - everything before and after is just waiting!

#4 tjones02

tjones02 Garage View Garage

Posted 06 August 2013 - 06:39 AM

25in/lbs sounds correct as I recall being taught 2ft/lbs of rotational torque of the pinion 15 years ago when a builder taught me. Might be good to look it up in a BMW blue binder repair manual though...

Edited by tjones02, 06 August 2013 - 06:39 AM.

Tom Jones

Works at Casey MotorSports in Petaluma CA
66 BMW16oo stored, 67 1600-2 lifelong project, 2 more 67-8 1600s, 66 1800A F/Sale, 86 528e 5sp 466k, 86 528eA Rosee's
Mom&Dad's, 65 1800TiSA, 70 2800, 72 2002Tii 2760007 orig owners, 03 325iT, 12 328iT


#5 tjones02

tjones02 Garage View Garage

Posted 06 August 2013 - 07:13 AM

Images from the '02 blue binder... "Ncm (cmkp) 320+-30 (32+-3) with seal installed". That's with a rotational torque meter though; not with a normal click type torque wrench... There's also a fine difference between breakaway torque and rotating torque with breakaway being larger. The factory procedure calls for rotational torque...

null_zpsae9efeac.jpg

This one has a good image of the rotational torque meter:
null_zps366e2d7e.jpg

HTH

Tom Jones

Works at Casey MotorSports in Petaluma CA
66 BMW16oo stored, 67 1600-2 lifelong project, 2 more 67-8 1600s, 66 1800A F/Sale, 86 528e 5sp 466k, 86 528eA Rosee's
Mom&Dad's, 65 1800TiSA, 70 2800, 72 2002Tii 2760007 orig owners, 03 325iT, 12 328iT


#6 mlytle

mlytle Garage View Garage

Posted 06 August 2013 - 07:22 AM

25ftlbs is not correct.  i believe i posted that in andrews thread.

 

25inlbs is too much also....based on using a bar type tq wrench to check the rotational tq.   3-6inlbs was more like it.   i went through several crush rings finding this out building a diff with the parts you are using.  i ended up tq'ing by feel...just like a wheel bearing, which this basically is.  once the "big crush" is over and it gets easier, just keep adding a little until most all the slop is out of the bearing.  if you go to far you will feel it starting to bind up.

 

buy several crush rings. you WILL need them.

 

how did you arrive at the correct thickness for the pinion spacer shim ring?


Edited by mlytle, 06 August 2013 - 07:33 AM.

marshall
75 M2 - build thread
http://www.bmw2002fa...les-m2-madness/

a 75, but it contains parts of a 71, 73, 73 tii, 74, and 76, and an 88 M3 thrown in for sport.


#7 AceAndrew

AceAndrew

Posted 06 August 2013 - 08:24 AM

Wow, you guys are on the ball.  11pm thread started, and by 9:30am we've got plenty of good responses.

 

I am wrong about the 25 ft/lbs with the conversion, as it's in in/lbs (though I did refer to it as rotational torque as Tom's expounded on).  As Marshall pointed out this is largely done by feel and is hard to quantify in text (although he's done a much better job than I).  That's why I did try and describe what it felt like.
 

After each turn (or half turn) I'd take off the wrench and turn the pinion by hand, after a couple turns it does get smoother, and once you feel what Marshall's described (after the big crush and as the bearing slop is being removed) that's when you measure the rotating torque.  The reason I say that is because If you try and take the measurement prior to the crush washer .... "crushing".... you'll think it's tight enough.


Edited by AceAndrew, 06 August 2013 - 08:30 AM.

  • radio9phs likes this

#8 Tommy

Tommy Garage View Garage

Posted 06 August 2013 - 08:25 AM

I actually just found my pdf of the "blue binder" which says about 3Nm. That would convert to 25 inlbs but Marshall says even that is too much? 3..5inlbs = 0.3...0,5Nm which is close to nothing! I'm leaning towards finger touch...

 

I plan to use the pinion spacer that was installed with the pinion. Then I will check the tooth contact with paste and hope with fingers crossed that it looks good. I could measure the backlash also but the finger feel probably is enough.

 

Differential and gearbox are the only parts that I haven't taken apart and rebuilt in my cars so it's about time. I have installed lsd in the diff of the racer and that was successful.

 

  Tommy


Racing is Life - everything before and after is just waiting!

#9 Tommy

Tommy Garage View Garage

Posted 06 August 2013 - 08:38 AM

It's 7:30 pm here - I was waiting for whole day :)

 

I got you now Ace. I'm pretty confident that I'll get it sorted but I'll order few of the crush washers.

 

I'm not in rush with this. I think the lsd has been opened about 8 years. Every once in a while I've been fitting it together with -02/e21 parts. It's originally with 3,23:1 gears so it doesn't fit straight together with 3,91. I need to make 7mm thick spacer under the ring and it's also a bit tight to fit in the case. I think I can make it work :) Let's see. Those lsd's are not that easily available here so I'm working with what I have. Thanks guys for your help!

 

  Tommy


Racing is Life - everything before and after is just waiting!

#10 Preyupy

Preyupy

Posted 06 August 2013 - 09:03 AM

Yes, the correct spec is 300+/- 30 Ncp which converts to 3+/- .03 NM = 26.3-26.8 INCH/Pounds or 2.19-2.23 FT/LBs
1970 1602 (purchased 12/1974)
1974 2002 Turbo
1988 M5

#11 mlytle

mlytle Garage View Garage

Posted 06 August 2013 - 11:09 AM

although that is the correct book tq, by the time i got to 25inlbs of rotational tq, the pinion was almost completely bound up.  after two "test" crushes and finding the rotational tq on the other 4 diffs i had sitting in my shop (one fresh rebuild from aardvark) were in the under 5inlbs range, i just used the wheel bearing technique.  :)   diff has not blown up yet after two hard track weekends..... B)


marshall
75 M2 - build thread
http://www.bmw2002fa...les-m2-madness/

a 75, but it contains parts of a 71, 73, 73 tii, 74, and 76, and an 88 M3 thrown in for sport.


#12 AceAndrew

AceAndrew

Posted 06 August 2013 - 11:23 AM

although that is the correct book tq, by the time i got to 25inlbs of rotational tq, the pinion was almost completely bound up.  after two "test" crushes and finding the rotational tq on the other 4 diffs i had sitting in my shop (one fresh rebuild from aardvark) were in the under 5inlbs range, i just used the wheel bearing technique.  :)   diff has not blown up yet after two hard track weekends..... B)

 

 

One other thing to note, The pinion loosens considerably once it's been run on the car.  This is why after break in you're only running 5in/lbs range.  If aadvark's fresh diff came that loose I would just be careful long term.  I don't think Dave is doing his own rebuilds, but I'd ask if they're test ran or something similar.



#13 jimk

jimk

Posted 06 August 2013 - 12:02 PM

If the pinion were torqued to 25ft-lbs, it would last about 5 minutes and would be as blue as a baby's butt.  How about some reality here.  I presume these are NEW bearings and races.   Cause if they are being reused, then it's too late but the runniing torque is supposed to be measured before it is taken apart and duplicated upon reassembly.  Roller bearings only go thru run-in once.  Try it twice and chaulk it up to disaster and/or practice cause there will be a second opportunity to argue whether the torque is ft-lbs or inch-lbs.


Keep your hands out of your pockets. Things are getting twisted. It is painful to straighten them out.

#14 TobyB

TobyB
  • LocationSeattle

Posted 06 August 2013 - 03:46 PM

Jim, I don't recall baby butts getting particularly blue... do you use machinist's bluing for that, or just sharpie?  >grin<

 

Rotating the pinion assembly never gets 'easier'.  It just gets less and less 'wiggly' until, all of a sudden, it becomes slop- free.

If you're lucky, you snuck up on it and it's not suddenly 'grindingly tight'

 

Now here's the hard part- you have to get it just a little bit 'stiff'.  25 in- lbs sounds too high, from experience- it needs to be stiff

enough that it never comes loose, but never so tight that it gets notchy.  And you may NOT back up!  For some reason, I have 13 in-lbs

stuck in my head from the E21 manual, but I don't have an inch- lb torque wrench, so I never got a number.  And it's one of those

'soft' torques that you can use a beam wrench on, but probably not a clicker.

 

What DOES get easier is tightening the pinion nut- as the collar crushes, you'll notice that your biceps are merely

burning, not popping out and screaming and running around the shop like little boy- children who want popsicles. (use an Ahnold the Govahnator accent here)

 

The 'little bit stiff' is pretty subjective.  If you've set up a lot of tapered roller bearings, it's pretty easy- just like you stop turning the

bolt just before it gets easier to turn (and the head pops off) you stop tightening while it's still 'smooth,' just before it goes 'bindy'.

Actually, you could probably go just a little bit bindy, because:

 

I recheck them after running them for a weekend or 3.  3 out of 4 loosened, but stayed in the 'slightly bit stiff' category that you want,

and one got 'too free' and needed another few degrees of tightness.  And that was really tricky, because getting that nut to

turn a few degrees without overshooting it is a REAL bear.  I've only overshot a couple, but dang, it's really a matter of just

a few degrees from 'click- click' to 'welded solid'.  And 'click- click' will not only die a premature death, they'll give you hell for

getting rid of driveline vibes...

 

Also, get 3 or 4 seals- I've probably destroyed twice as many E21 seals as crush sleeves- and I can't even exactly tell you why...

...oh, and that oil slinger ring, too, if your pinion has the provision for it.  And it's still available.  Which I suspect it isn't, given how

hard it was to find 6 years or so back....  (yes, I've left them off, too)

 

My two cents.

 

t


"Believe me, these things don't just fit by themselves."
-Martin





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