I have an S4 LSD with 3.9 gears and a Open 4.10 diff. I want to combine the two. is there a preferred direction, i.e. swap gears into LSD case or move LSD into 4.10 center section. Hope this made sense

 

So you are wanting a 4.1 LSD? If so I'll just swap the 3.9 LSD straight across with ya. If not, I'm assuming you can probably just swap the 4.1 ring onto the LSD and use the 4.1 pinion.

 

I was wanting the gear mesh pattern to be the best possible. installing the 4.10 ring and pinion on the LSD diff. Simplest would be, leave the pinion in the open diff case and move the LSD with the swapped 4.10 ring gear into that case.
Only gear set ups I've done were Dana 44 in Jeeps. The Dana axles had a pinion depth stamped on them, so the pinion shims stayed with that set up. Alot of shimming involved, pain in the ***.

 

Yes. Easiest is to not press out the pinion (swap LSD over to the 4:10 gears and case). The mazda stuff is 3rd members style like the toyota 4x4 stuff. Except the FC is a really crazy long pinion design with 4 different pinion bearings. It is a pain to disassemble and reassemble. So just check pinion depth and if it's decent, set back lash and let r' buck....

 

Well, if you ever feel like selling that 3.9 ring and pinion. I've been looking for a set for a while.

 

The easiest way to do it is remove the diff intact/complete and swap in a complete diff that has the LSD and ratio you want. don't have to open the case if there is no need, probably cheaper than doing ring an pinion job.

 

he won't need to swap the R+P if he leaves the empty cases alone without taking out the pinion. just swapping the LSD carrier into the correct ratio case and putting the ring gear onto it.

can't put the LSD guts into an open diff carrier, so that's out and only really leaves one rather simple option.

 

Thanks, Be haven LSD fun soon ( can't believe these cars were sold with out LSD. after driving the 85 SE for a while, then taking the 86 Base out , just not the same.)

 

If you are changing the differential you need to at least check pinion depth and you will have to adjust backlash. There are often differences between different diffs that will change these. Plus be sure to bring the carrier bearings AND their races over to the 4:10 diff case.

 

Will do, hope I don't have to change pinion depth, backlash is easy on a Dana axle. Bens post about multi pinion bearing sound no fun.

 

Contrary to other posts below, you need to swap the entire matched R&P set. The 3.9 R&P set has 43/11 teeth for R&P, respectively. The 4.1 R&P set has 41/10 teeth for R&P, respectively. Use the same pinion spacers for the pinion gear that you are using. The S4 LSD differential housings had a slightly larger oil capacity, but you can use either housing. The S5 VLSD housing is same as S5 open housing. I put an S4 LSD with 4.3 gear set into my 90 GXL using the S5 housing. Make sure you have the proper tools (i.e., micrometer, dial indicator and torque wrench) before you start the job.