Early Honda LSDs

Don Foreman

New member
I saw someone on Facebook mentioning running a welded diff, vs an open diff in an 84-87 HP Civic . Just sharing some info. I have a 78 civic. My car came with a 84-87 Mugen diff and an early SB1 Mugen diff made for the 78 civic. They both are interchangeable in the 70s SB1 box same spline, same ring gear holes, etc. The difference is you swap the ring gear from one side to the other when you change diff style but that's it. Since Mugen diffs are so rare, that bit doesn't help much but... Mfactory makes a new helical gear lsd for the SB1 civic. Not sure if they swap the same way in the later box, but I have one if someone needs measurements or Mfactory may send a better drawing. https://www.teammfactory.com/mfactory/h ... -TRS-05SB1 Anyway just putting the info out there incase someone wants to do some measuring. Mfactory made the design for a vendor I know about ten years ago with a preorder of 25 diffs then after that everyone is able to order them one at a time. So if someone is real particular about an exact match, they may do the same for the 3rd gen civic as the insides and the splines would be the same anyway. Here is a picture of the 84-87 Mugen diff compared to the Honda SB1 factory diff. You can see the bearings and OAL are the same. Just the location of the ring gear flange changes. Also early Mugen lsd take a special bolt, that's NLA. If you have one that the clutches aren't trashed on, try Subaru part 800610740, I think you will be pleased.
This is the Mugen bolt next to the Subaru part. The Mugen bolts are very soft and tend to come to people with rounded corners that just get worse with time. The stock Honda bolts are too short and you don't want to use those as they can pull threads out of the diff. The Subaru parts work well. I also have photocopied papers on how to adjust the Mugen diffs for more or less slip but they are VERY faded. Most clutch packs are so worn, you set it at full stiff an hope for the best. If someone wants them let me know and I can send them your way. Adam Malley went to a Helical diff instead of a Mugen 20 years ago, even back then the Mugen clutch packs were hard to find as they haven't been made new since the late 80s.