1 Topic by Dave (edited by Dave 2017-09-14 03:11 PM)

  • Dave
  • Dave
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  • From: PGH PA
  • Registered: 2009-10-09
  • Posts: 993

Topic: Looking for soild info on medium case (188mm) bmw differential

Ive been looking for info on changing ring gears and this is what I found.  3.07 and numerically lower numbers are all interchangeable and 315 and numerically higher gears are all interchangeable.  From what I read, you can cross this threshold by adding or removing shims.(between the ring rear and the carrier)  What I am trying to do is go from a 346 down to a 279, does anyone know if this would require adding or removing said shims??

Thank you, Dave

It Ain't My Fault

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  • From: Brookfield, WI
  • Registered: 2009-12-15
  • Posts: 222

Re: Looking for soild info on medium case (188mm) bmw differential

The ring gear stays the same diameter and the pinion changes size.  So going 346 to 279 means the pinion gets bigger.  This requires the ring gear to get thinner, or remove shims.  Don't know about BMW stuff, but a ring and pinion is usually a matched set.  Shims are used to set bearing preload and backlash.

If it doesn't have 2 doors, 3 pedals, and 5 lug nuts per wheel - It isn't a real race car
  • Dave
  • Dave
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  • From: PGH PA
  • Registered: 2009-10-09
  • Posts: 993

Re: Looking for soild info on medium case (188mm) bmw differential

Anarchyjet wrote:

The ring gear stays the same diameter and the pinion changes size.  So going 346 to 279 means the pinion gets bigger.  This requires the ring gear to get thinner, or remove shims.  Don't know about BMW stuff, but a ring and pinion is usually a matched set.  Shims are used to set bearing preload and backlash.

The shims I am referring to is between the ring gear and case, I understand the process of setting up a differential, thanks anyway.

It Ain't My Fault

Dave's Website

  • From: Antioch
  • Registered: 2012-09-20
  • Posts: 51

Re: Looking for soild info on medium case (188mm) bmw differential

the shims on the medium case are to align the ring gear with the pinion.  Different ratios require different carriers.....Or sometimes shims are installed  between ring gear and the carrier it is bolted to....

  • From: Staunton, VA
  • Registered: 2012-05-16
  • Posts: 606

Re: Looking for soild info on medium case (188mm) bmw differential

Are you dead set on a 2.79? You can get a 2.93 with factory LSD.