Changing LSD from 3.70 to 3.90 ratio
Submitted by QMAN
Remove stub axles by removing the two bolts from inside of axle.
Then drain and remove rear cover.
Check for excessive metal or other chunks.
Remove the side bearing caps and mark them(left and right).
Keep them with the rear end they came from.
You will need to reuse the 3.90 side caps with the 3.90 ring gear.
Next remove the diff unit by rotating and pulling towards you.
You will see 10 bolts(I think) You can get these apart using a wrench and a breaker bar if you do not have a vice.
Remove the 3.70 RG and set it aside. Repeat the procedure for the 3.90 diff.
Take the 3.90 RG and place it on the LSD unit.
This where it can get tricky.
I have run into this a couple of times.
The bolts may be a little bigger or a little smaller than the holes in the diff.
If they are the ones that are a little bit smaller you will be ok.
If they are a little bigger then you will need to open the holes a little bit.
If needed do this now. Clean unit again.
Now you can start to assemble the "NEW" unit.
Be sure to use the "Loc-tite" of your choice,
I used the blue stuff.
Get these as tight as you can and all will be good.
After you have the diff unit removed from the 3.90 case wipe it out.
Then place a rag or the like and cover the pinion gear and bearing.
Look at the two empty cases and compare both and you will see where it is ground down to accommodate the LSD.
You need to replicate this cut-out in the 3.90 case.
After you think you have removed enough material do a test fit.
Now wipe it out again and use some brake clean to make sure you have all debris out.
Use brake clean because it will evaporate. Now install the unit.
Now would be a great time to replace the side seals.
Also make sure to reinstall the rubber pieces that go over the axle stubs.
Make sure that you use the side caps that match the ring gear.
Very important as this will maintain your gear mesh.
If it isn't the right set you run the risk of getting noise and mismatch.
Install the bolts in the side caps and then install the rear cover.
Take out the top "fill" plug. I run Kendall limited slip gear oil.
Fill to recommended levels and then install it in the car.
Go drive and enjoy the new "traction" advantage.
See ya', Ken
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