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LSD Breakaway Torque Test [pics]

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    LSD Breakaway Torque Test [pics]

    I finally dug out the 4.10 LSD I have laying around and did a proper breakaway torque test per the instructions all over the place. What I can't figure out is if my implementation is focked, or if this LSD just has new/hardly used clutches.


    Here is the top down view.



    The input shaft is held in place, and one output on the [picture view] right is held in place. I will then put a torque wrench to the left side and keep upping the torque on my wrench until it slips instead of my torque wrench clicking.



    Another angle.



    So, the torque wrench is going to apply a twisting action to the socket, and the socket to the vice grips. Because the socket is off center towards the wrench, my guess would be that when the wrench experiences 90 ft/lbs, that the center is actually experiencing more (an even longer arm). But perhaps my thinking is off. I am rather tired.

    Help? Isn't 90 ft/lbs high, even for a new low milage LSD?


    And for anyone interested in the components used in that MacGyver scenerio, here they are.

    -------------------------------------------------
    1989 - E30 - M20B25 - Manual. Approx 300,000+ miles - Track Rat & Weekend Fun
    2000 - E46 - M52TUB28 - Manual. Approx 130,000 miles - [not so] Daily Driver

    sigpic

    I'm looking for a Lachssilber Passenger Fender and Hood. PM if you have one or both to sell!

    #2
    The off center application of torque is going to raise the breakaway point. Knowing the distance from the center of the nut to the center of flange you could calculate the error.

    The factory spec is 65ft-lbs and if you are getting 90ft-lbs you have a very good set of clutches in that differential.
    The car makes it possible, but the driver makes it happen.
    Jim Levie, Huntsville, AL

    Comment


      #3
      Originally posted by jlevie View Post
      The off center application of torque is going to raise the breakaway point. Knowing the distance from the center of the nut to the center of flange you could calculate the error.

      The factory spec is 65ft-lbs and if you are getting 90ft-lbs you have a very good set of clutches in that differential.
      So, it turns out that something is wrong with my test. I put the 4.10 in my car and the very first hard corner I took felt weird. Another hard corner, and I was able to feel the back end break loose under application of power. Totally not what the 3.73 LSD felt like.

      I took it home and jacked one of the rear wheels off the ground, leaving the other rear solidly pressed into the ground. I then started the car and slowly let out the clutch, thinking that the LSD should deliver at least some power to the grounded wheel, and cause the car to try and move. Nothing at all, I was able to fully releasing the clutch in first, and have the raised wheel just spin there.

      So, does that mean this diff is no longer an LSD? And if it isn't, how did I go so wrong with my test? Any ideas?
      -------------------------------------------------
      1989 - E30 - M20B25 - Manual. Approx 300,000+ miles - Track Rat & Weekend Fun
      2000 - E46 - M52TUB28 - Manual. Approx 130,000 miles - [not so] Daily Driver

      sigpic

      I'm looking for a Lachssilber Passenger Fender and Hood. PM if you have one or both to sell!

      Comment


        #4
        With the diff in the car, jack up the left rear corner and use a torque wrench on the axle nut. Apply the torque clockwise.
        The car makes it possible, but the driver makes it happen.
        Jim Levie, Huntsville, AL

        Comment


          #5
          Originally posted by jlevie View Post
          With the diff in the car, jack up the left rear corner and use a torque wrench on the axle nut. Apply the torque clockwise.
          And with a similar principle as when it's out of the car, have the input shaft "locked" in place be engaging first gear?

          I'll give this a shot.
          -------------------------------------------------
          1989 - E30 - M20B25 - Manual. Approx 300,000+ miles - Track Rat & Weekend Fun
          2000 - E46 - M52TUB28 - Manual. Approx 130,000 miles - [not so] Daily Driver

          sigpic

          I'm looking for a Lachssilber Passenger Fender and Hood. PM if you have one or both to sell!

          Comment


            #6
            The transmission must be in neutral. And obviously the parking brake must be off.

            I just noticed that you had the diff input shaft restrained when you tested the diff out of the car and that is wrong.
            The car makes it possible, but the driver makes it happen.
            Jim Levie, Huntsville, AL

            Comment


              #7
              Originally posted by jlevie View Post

              I just noticed that you had the diff input shaft restrained when you tested the diff out of the car and that is wrong.

              Yes, that is wrong. You only want the the 2 outputs involved.


              EDIT: What is the diff out of? Is it possible it is a non-clutch type LSD say from an ix?
              Lorin


              Originally posted by slammin.e28
              The M30 is God's engine.

              Comment


                #8
                Originally posted by jlevie View Post
                The transmission must be in neutral. And obviously the parking brake must be off.

                I just noticed that you had the diff input shaft restrained when you tested the diff out of the car and that is wrong.
                Seriously? Damn. I was taking my advice from this other thread I started, where they state that the input shaft must also be locked in place.

                The guy seemed to know what he was talking about. See post #5.


                Originally posted by LJ851 View Post
                Yes, that is wrong. You only want the the 2 outputs involved.


                EDIT: What is the diff out of? Is it possible it is a non-clutch type LSD say from an ix?
                No, it's not out of an IX. The guy is a rather prominent forum member here (8000+ posts) so I sorta trusted him. Perhaps he delivered the wrong diff to me. In any case, that'll teach me to trust sellers!

                The guy that sold it to me said he pulled it himself out of the car, tested it, and was going to put it in one of his own cars before plans changed. He had been sitting on it for a year before deciding to sell it.

                I'll try the torque test in the car. But I know for a fact that when it was out of the car, I was able to spin each output flange independently with my hands :roll:

                Thanks guys. I'll let you know how it goes.
                -------------------------------------------------
                1989 - E30 - M20B25 - Manual. Approx 300,000+ miles - Track Rat & Weekend Fun
                2000 - E46 - M52TUB28 - Manual. Approx 130,000 miles - [not so] Daily Driver

                sigpic

                I'm looking for a Lachssilber Passenger Fender and Hood. PM if you have one or both to sell!

                Comment


                  #9
                  Originally posted by Earendil View Post

                  I'll try the torque test in the car. But I know for the fact that when it was out of the car, I was able to spin each output flange independently with my hands :roll:
                  Hmmmm.. That doesn't sound good. What does the tag on the diff say?
                  Lorin


                  Originally posted by slammin.e28
                  The M30 is God's engine.

                  Comment


                    #10
                    Originally posted by LJ851 View Post
                    Hmmmm.. That doesn't sound good. What does the tag on the diff say?
                    Tag says 4.10S. Also, it spins like an LSD (same direction). It's just easy to overcome the rather notchy resistance I feel with it. My 3.73S when I took it out of the car seemed rock solid between each output shaft.

                    I'm thinking this diff is seriously toast...
                    -------------------------------------------------
                    1989 - E30 - M20B25 - Manual. Approx 300,000+ miles - Track Rat & Weekend Fun
                    2000 - E46 - M52TUB28 - Manual. Approx 130,000 miles - [not so] Daily Driver

                    sigpic

                    I'm looking for a Lachssilber Passenger Fender and Hood. PM if you have one or both to sell!

                    Comment


                      #11
                      Does it sound funny when you turn really tight, like full lock circles?
                      Lorin


                      Originally posted by slammin.e28
                      The M30 is God's engine.

                      Comment


                        #12
                        Originally posted by LJ851 View Post
                        Does it sound funny when you turn really tight, like full lock circles?
                        Not at all. And with the interior torn out (I can look back from the drivers seat and see my spare tire) I would notice a difference. The only thing I notice while driving is what feels like one tire breaking loose.

                        Okay, well there is a clunk when I go into reverse suddenly too. I'm hoping that is just one side of the diff not being completely tight ;)
                        Checking that tonight when I get off work.
                        -------------------------------------------------
                        1989 - E30 - M20B25 - Manual. Approx 300,000+ miles - Track Rat & Weekend Fun
                        2000 - E46 - M52TUB28 - Manual. Approx 130,000 miles - [not so] Daily Driver

                        sigpic

                        I'm looking for a Lachssilber Passenger Fender and Hood. PM if you have one or both to sell!

                        Comment


                          #13
                          If you can turn them opposite by hand, it needs a rebuild.

                          To test, you need the input open like jlevie said or you are just meshing the gears themselves and not testing the limited slip.
                          john@m20guru.com
                          Links:
                          Transaction feedback: Here, here and here. Thanks :D

                          Comment


                            #14
                            how much breakaway is too much for a street driven vehicle?

                            Got a spare 188 diff here with 3 clutches and standard 2mm dog ear plates (i.e. the thick shim was replaced with clutch and dog ear plate of same combined thickness) that seems to be 105 ftlb which seems excessive

                            the old unit when stock was 40 ftlb so seems like too much of an increase given changes made or maybe because the clutches are fresh ?

                            EDIT: with only 2 new clutches and the 4mm shim it was 70ft-lb breakway i.e. this is 100% stock setup
                            Last edited by digger; 01-05-2022, 12:31 AM.
                            89 E30 325is Lachs Silber - currently M20B31, M20B33 in the works, stroked to the hilt...

                            new build thread http://www.r3vlimited.com/board/showthread.php?t=317505

                            Comment


                              #15
                              Sounds good to me! Let me pm you my shipping address!

                              heh

                              I've noticed that when spanky- fresh, you get nice numbers like what
                              you're seeing for 2 plates, but after a track day
                              and an oil change, it drops by at least 25%.
                              I've never tried the 3- clutch setup, but
                              those numbers seem like the very high end of 'yeah, that'll wear smooth pretty quickly'-

                              me, I'd try it. But then, anything short of a spool and I'm in.

                              t
                              curious, too.
                              now, sometimes I just mess with people. It's more entertaining that way. george graves

                              Comment

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