I need to ditch the 3.90 in favor of a 4.10 or higher. I can get a rear diff off a '86 SE for really cheap. Can I pull the 4.10 ring and pinion and put it in my S5 rear diff? Considering neither one has LSD?

 

Why not just install the '86 rear into the S5 as is, without pulling the ring & pinion? The R&P's are the same size, not teeth.

 

I don't want to have to remove the whole diff. You can change the gears with the diff still attached. Also the flange on my S5 rear diff has been modified because I'm using a TII trans and shaft. Also would a S4 TII rear diff and shafts bolt right in? So the S4 R&P won't work?

 

Geeze what does it take to get answers to legit questions. Maybe I should of called it "Should I get this spoiler?" so people would look.

 

^^its a technical question, about something not too many ppl know. its not like you're asking a show question.

 

Then whats the point of this place.

 

I am not sure this will help but the gear sets are together so it your 3.9 pinion is modified to fit a T II drive shaft then you need to modify the 4.11 pinion too. I don't see how you can switch all that parts with the diff. housing still in the car. NA rear end housings are all the same so you can swap gear sets or diff. unit around all you want, the ring gear and pinion gear with the same ration has to stay together but can be moved to another housing or go with open or limited slip diff. unit.

 

The flange is whats modified for the TII shaft. I'm pretty sure the ring and pinion can be swapped with the housing still in the car. Are S4 and S5 mounts the same for the rear diff?