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Broken Diff or CV?

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    Broken Diff or CV?

    A few weeks go, my 3.73 lsd started making some gnarly clunking while going through low speed corners/driving around in a parking lot. Pretty much any low speed parking lot-like corners. Eventually it got so bad that it seemed like the diff would start to bind and almost wanted to spin a wheel. Based on the symptoms, I removed and opened up the diff, and sure enough, I found a good amount of metal pieces and broken teeth. Based on the shape of the teeth I was able to determine what gear must have been damaged, I’ll make a link to real oem in a comment to this post.

    Anyways, I just got a ‘good’ 3.25 lsd from an automatic 5 series, and was promised that the diff was in good condition, and that it had been run in an e30 and traded out for a 3.46. So I swapped in the 3.25 last weekend, and after taking it around the block a few times and up the freeway to put it through a heat cycle, I started getting some noises from the rear end that sounded very similar to the noises my 3.73 started to make.

    So far, I have done the following-

    Removed caliper and discs from rear hub to check play in wheel bearings- there is none.
    Removed parking brake assembly from passenger side (noise seems to come from this side) no change.
    Checked axles for play- no play at all (at least using my hands to pull on it), only normal axial (in & out) play in CV’s.

    I’m starting to think I was sold a broken diff. Is there anything I can do to absolutely confirm the diff is or is not the issue? While on jack stands, clutches seemed to breakaway smoothly (rotating tires in opposite directions), and the dull grinding/clunking noise seems to be less dependent on turning than it was when my 3.73 broke.

    As of now, all I can think of to try other than throwing parts at the car, is to jack up the rear, remove caliper and discs (leaving just the hub) and start the motor in 1st to get the rear end spinning on jack stands, and listen to everything with a stethoscope. That and/or just drive the car until the noise gets worse and is easier to determine where it’s coming from- obviously not an optimal choice.

    Any insight and suggestions are welcomed, let me know if I should explain something more clearly

    Did you take the cover off the new diff and inspect before installing? did you change the oil in the new diff? and if so have you drained it out and had a look for shiny metal bits?


      The diff was shipped to me so the fluid was already drained, I removed the cover and there was still a bit of fluid inside, I didn’t notice any metallic material even through the fluid was filthy. Visually I couldn’t see anything wrong with the ring gear or what I could see looking into lsd unit.

      the teeth I found in the oil of my 3.73 that went out seemed to be from the inside of #11 on this diagram ^ , where the lsd unit engages with the output shaft.

      On the 3.25 I got, it came with e30 output shafts already installed. One was backed out a bit when I received the diff, and I was able to pull it the rest of the way out relatively easy, and slid it back in and tapped it a few times with the malet. There was no apparent damage on the output shaft that came out.

      when installing the 3.25, I filled it with fresh 45-70 gear oil that came with lsd additive. I forget the brand but will check and report back.


        Originally posted by NotJesus View Post
        when installing the 3.25, I filled it with fresh 45-70 gear oil that came with lsd additive. I forget the brand but will check and report back.
        You should be using 75W-90 for a street driven car that isn't autocrossed or tracked. Start there.
        Originally posted by kronus
        would be in depending on tip slant and tube size


          My mistake on the oil, I looked at the bottle and the gear oil I used was 75-90 Valvoline with limited slip additive. I'm going to disconnect the axles and listen to the diff with a stethoscope while spinning it tomorrow.


            It's not hard to disassemble a LSD and replace parts...