Rebuilding BMW/ZF 188mm Limited Slip (25% -> 40% lock)
Posted: Wed Jan 09, 2013 9:49 am
This is real simple. For my turbo car I rebuilt one going from 25% to 60% lock by machining and fitting 4 clutches/dog plates in place of 2. For my daily driver '95 525i I decided to fit an LSD diff and rebuilt it for 3 clutches/dog plates which will result in a more calm 40% lock up. 60% is nice in the turbo car but tight radius turns result in tire chatter since the axles are so locked.
'93 3.23 LSD Differential by Jon Kensy, on Flickr
Old clutches were in good shape:
IMG_0055.jpg by Jon Kensy, on Flickr
Replacement clutch set:
BimmerDiffs.com 3-Disc Upgrade by Jon Kensy, on Flickr
You just remove the end plates and then remove the ring gear/LSD carrier. You make sure that your carrier depth is ~96.8mm and your LSD cover plate is about 14.0x mm inset. Then, just swap out a spacer plate and old clutch/dog plates with new. ZF used a spacer in the diff that can be removed and is the exact same thickness as an additional clutch/dog plate. So, going from 2 clutch to 3 clutch is easy. 2 clutch to 4 clutch required machining down the carrier cover by the stack thickness difference, still not hard, though.
Old parts out:
3.23:1 LSD 40% Lock-up Setup by Jon Kensy, on Flickr
Measuring backlash:
3.23:1 LSD 40% Lock-up Setup by Jon Kensy, on Flickr
Spec is 0.06 - 0.014mm (0.0023 - 0.0055"). Mine measures in at 0.0041", well within spec.
Measuring backlash:
[vimeo]56961733[/vimeo]
'93 3.23 LSD Differential by Jon Kensy, on Flickr
Old clutches were in good shape:
IMG_0055.jpg by Jon Kensy, on Flickr
Replacement clutch set:
BimmerDiffs.com 3-Disc Upgrade by Jon Kensy, on Flickr
You just remove the end plates and then remove the ring gear/LSD carrier. You make sure that your carrier depth is ~96.8mm and your LSD cover plate is about 14.0x mm inset. Then, just swap out a spacer plate and old clutch/dog plates with new. ZF used a spacer in the diff that can be removed and is the exact same thickness as an additional clutch/dog plate. So, going from 2 clutch to 3 clutch is easy. 2 clutch to 4 clutch required machining down the carrier cover by the stack thickness difference, still not hard, though.
Old parts out:
3.23:1 LSD 40% Lock-up Setup by Jon Kensy, on Flickr
Measuring backlash:
3.23:1 LSD 40% Lock-up Setup by Jon Kensy, on Flickr
Spec is 0.06 - 0.014mm (0.0023 - 0.0055"). Mine measures in at 0.0041", well within spec.
Measuring backlash:
[vimeo]56961733[/vimeo]