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  1. #1
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    Post 335i and 135i Differential FAQ (No LSD, really?)

    Shortly after the N54 powered 335i and 135i were released, enthusiasts and tuners wanted to ‘fix’ the lack of limited slip differential. Making easy and abundant power was simple with the twin turbo inline 6, but putting it to the ground was not.

    Enter the infamous final drive. Open, LSD, welded, bolted, large body, small body, 3.08, 3.46 etc etc. We will try to make sense of everything with this blog entry.

    Open vs. LSD:
    The 335i and 135i were not offered with a limited slip differential. Yes, BMW sold a twin turbo, 6MT sporty car without a LSD. No factory option, nothing. So, owners had to rely on the aftermarket for a solution. Initially the solution was pretty simply, till BMW switched things up on us.

    Open:
    Click here to enlarge
    LSD – limited slip differential:
    Click here to enlarge

    Welded vs. Bolted:
    Very early 6MT equipped cars had a traditional ‘bolted’ setup where the ring gear was bolted to the gear carrier. Shortly after, the engineers in Munich decided to weld, not bolt the ring gear to the gear carrier. Well, that complicates matters a bit!

    Welded:
    Click here to enlarge

    Bolted: (we are using a bolted aftermarket diff for illustration purposes)
    Click here to enlarge


    Master Reference Chart:
    Click here to enlarge

    Does your car have a welded or bolted differential??
    See chart above. As you can see, the majority of 335i and 135i owners are blessed with the welded differential. This makes adding a LSD a bit challenging, as the ring gear must be separated from the carrier carefully to ensure it can be re-used. Very few shops can do this properly and consistently, but we pioneered the what we think is the best way of performing this operation.
    This is how we do it.




    Large or small differential?
    There are 2 differential (housing or ‘pumpkin’) sizes. The table above shows which cars have which size. So, a Quaife ATB limited slip unit designed for the 6MT large housing will not work in your 2009 335i automatic. Fortunately, Quaife and Wavetrac have solutions for both the large and small differentials. Here are some pics so you can see the dramatic difference:

    Click here to enlarge

    Click here to enlarge

    Click here to enlarge

    Click here to enlarge

    Click here to enlarge

    Gear Ratios:
    See chart above. All 6MT cars were equipped with 3.08 final drive ratios. Automatic cars had 3.46 ratios. Note: we have built a few 3.46 differentials for 6MT cars and the owners were thrilled. They were willing to sacrifice top speed for an incredible power band around town :-) Lastly, DCT equipped cars have 2.56 and diesel cars have 2.81 final drive ratios.

    Conclusion:
    When you modify your N54 or N55 powered E9X or E8X, a proper differential is an essential modification if you want to put all of that power to the ground. While it is quite confusing, I hope this entry makes it a bit easier to understand.

    Click here to see how a 335i 135i VAC Performance Built Differential is made!

    Click here to buy a 335i 135i VAC Performance Built Differential!
    Last edited by Mike@VAC; 04-09-2013 at 12:44 PM.

  2. #2
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    Nice post! I will rep it when I can.

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    good info to have, repped
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    Click here to enlarge

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    Great stuff, now i know a little more about what you guys did for me. Should answer a lot of questions from people like myself.

    LSD was one of the best mods i did to the car, made it much more fun to drive and easier to put the power to the ground

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    I appreciate this thread, very informative. Good stuff!

    What's dripping from the car with the LSD installed? is that the A/C or something?

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    Good info Click here to enlarge

    Does the large vs small housing have any impact on performance/reliability?

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    Same question i asked over e90post, i'll ask again, why when doing a burnout my car leaves two marks when DSC completely off and not one as shown above in first pic. I dont have LSD.

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    Click here to enlarge Originally Posted by Bash Click here to enlarge
    Same question i asked over e90post, i'll ask again, why when doing a burnout my car leaves two marks when DSC completely off and not one as shown above in first pic. I dont have LSD.
    You are not the first owner of the car and are lucky?
    Click here to enlarge
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    Click here to enlarge Originally Posted by Bash Click here to enlarge
    Same question i asked over e90post, i'll ask again, why when doing a burnout my car leaves two marks when DSC completely off and not one as shown above in first pic. I dont have LSD.
    Need someone to confirm this, but I believe if you get traction with both wheels, then the torque is split relatively equally between them. It's only when you have worn your tires down some, are on not-so-smooth/perfect terrain, on wet roads, snow, ice, etc that the LSD make a difference. If both your tires have exactly the same wear and the road beneath them provide exactly the same amount of traction, then I believe they should both spin equally... that's the only way I could explain it.

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    Sticky'd.

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    Click here to enlarge Originally Posted by skim7x Click here to enlarge
    Need someone to confirm this, but I believe if you get traction with both wheels, then the torque is split relatively equally between them. It's only when you have worn your tires down some, are on not-so-smooth/perfect terrain, on wet roads, snow, ice, etc that the LSD make a difference. If both your tires have exactly the same wear and the road beneath them provide exactly the same amount of traction, then I believe they should both spin equally... that's the only way I could explain it.
    Sounds reasonable, i think the difference between the LSD and our open diffs is when one wheel looses traction the car applies more power to that wheel causing even more wheelspin, with an LSD its the opposite or power is generated to the wheel with best traction. As far as i have learnt.

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    Easyest way to be sure you do have a LSD is put it on an open car bridge and turn one rear wheel.
    If the opposite rear wheel turns in the other direction you have a LSD.

    If both rear wheels have the same traction you will get 2 spinning wheels. However, if one wheel has a different load, as in while cornering, the wheel with less load will get the most engine power, spin and you will lose your drive. That will be your cornering inner rear wheel.
    With a LSD the opposite happens, i.e. the wheel with the most grip will get the power provided ergo you will come out of corners much faster.
    There are two theories to arguing with women. Neither one works

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    just got my wavetrac and love it.

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    Didn't BMW introduce an "e-diff" through traction control from '08+?

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    Click here to enlarge Originally Posted by gary88 Click here to enlarge
    Didn't BMW introduce an "e-diff" through traction control from '08+?
    That's not really an LSD though it's just traction control.

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    I bought an OS Giken Performance Built diff from VAC. Nothing but the best. Flawless product, no issues. Buy from these guys.

  17. #17
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    Click here to enlarge Originally Posted by gary88 Click here to enlarge
    Didn't BMW introduce an "e-diff" through traction control from '08+?
    No dif: take a corner with too much throttle, inner wheel spins, no drive
    E-dif, same situation, inner wheel gets brake applied so no spinning inner wheel, still no drive
    true dif, drive goes to the wheel with the most grip i.e. the outer wheel which has the grip, so drive out of a corner. Overdrive it and the rear breaks out.
    There are two theories to arguing with women. Neither one works

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    Click here to enlarge Originally Posted by DavidV Click here to enlarge
    E-dif, same situation, inner wheel gets brake applied so no spinning inner wheel, still no drive
    With the brake getting applied to the slipping wheel, more power will get transferred to the wheel with traction than if the brake was not applied. So it is limiting slip and biasing torque to the wheel with traction, just no where near as effectively as an LSD.

    Both wheels see the same torque with an open diff. The disadvantage is this torque is limited by the wheel with the least traction. By applying the brake, the torque at each axle shaft is a sum of the torque required to make the slipping wheel slip plus the torque required to overcome the friction of the brake being applied on the slipping side. The important thing here is both axles see the same torque, but it is higher than the torque of just the slipping wheel, for instance, if DSC and DTC were off with an open diff.

    With an LSD and DTC on (DSC off, naturally, it is for pussies), the biasing of the LSD is enhanced. The torque seen by the wheel with traction is a sum of the torque required to make the slipping wheel slip plus the torque required to overcome the friction of the brake being applied on the slipping side. That sum is then multiplied by the bias ratio of the LSD. This is the torque seen by the wheel with traction. This is why an LSD is bad ass, and why you should use DTC even with an LSD, provided it is not limiting engine output.

  19. #19
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    Click here to enlarge Originally Posted by ajm8127 Click here to enlarge
    more power will get transferred to the wheel with traction than if the brake was not applied
    No noticable difference.
    In the differential there is no mechanism that transfers more power to the wheel where no brake is applied, so that just won't happen.
    It receives the same torque, as you yourself explain.
    Click here to enlarge Originally Posted by ajm8127 Click here to enlarge
    Both wheels see the same torque with an open diff
    The difference with a LSD is night and day.
    There are two theories to arguing with women. Neither one works

  20. #20
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    I do have to correct myself a little.
    As the inner wheel gets the brake applied the outer rear wheel will become the wheel with the least resistance and thus gets more power.
    However, the moment the car detects any slip on the outer wheel the engine power will be cut off, thus creating a very annoying power gap when trying to accelerate out of a corner. You will get out of a corner with a LSD in all cases.
    There are two theories to arguing with women. Neither one works

  21. #21
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    Click here to enlarge Originally Posted by DavidV Click here to enlarge
    In the differential there is no mechanism that transfers more power to the wheel where no brake is applied, so that just won't happen.
    It receives the same torque, as you yourself explain.

    The difference with a LSD is night and day.
    The mechanism that increases the torque to the wheel with traction is the DTC system. As the brake is applied to the slipping wheel, the torque required to spin that wheel will increase over that which was needed to spin the wheel without the brake. That is, the torque required to spin the slipping wheel is less than the torque required to spin the wheel plus the torque required to overcome the friction of the brake. Because both axles see the same torque, this is how torque is increased to the wheel with traction.

    Don't get me wrong, it is not a replacement for an LSD.

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    @Mike@VAC , your reference chart seems to show that AT 335I's from Aug '06 to Aug '07 have a bolted diff, so do the Sep '07 and beyond, with the difference only being the pumpkin size. However on the wavetrac site, it seems to show that from 03/07 to 09/07, you will need the same install kit as any other welded vehicles. Why is that?: http://www.wavetrac.net/application_bmw335.htm

    Layman question: Will the open diff from a 3.46 fit in a 3.08 diff vehicle? I was wondering if my open diff can be used again by someone else who has a manual for quicker low end acceleration.

    Thanks

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    what about 535 6MT? Is it the same?
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    Click here to enlarge Originally Posted by Turkeybaster115 Click here to enlarge
    Layman question: Will the open diff from a 3.46 fit in a 3.08 diff vehicle? I was wondering if my open diff can be used again by someone else who has a manual for quicker low end acceleration.
    The Final Drive Ratios can be swapped from 6AT to 6MT or vice versa. For example, Shiv's personal car has a 6AT's 3.46 Final Drive for increased acceleration (1/4 mile) purposes.
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  25. #25
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    You have to replace the ring gear and the pinion when changing final drive ratios.

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