Swapping gears in the dif?

[euroZ06]

Hello,

So i bought the car a little while ago, and it came with a spare dif (3.23 open), currently car has 3.91 with posi. With 3.91's my rpm's are very hight on the highway, so id rather have 3.23 gears, but i want to keep posi. I was told i can just swap in the gears...? Can anyone advise if that's possible, and if so how would i do it? What parts would i need?

Car is 73, 4spd manual and a 440.

Thanks

[1974dodgecharger]

just swap out the posi out of the 3.91 and put in the 3.23 gearing its a little housing simple....just mark your diff so you know how much how much to turn your end diff rings down with your spanner wrench....

[fy469rtse]

He wants to keep posi,
centre will need to come out , you really need some one experienced rebuilding ,
posi out of centre , pinion and crown gear swapped, pinion depth to be reset,
You do need a hand full special tools , I think if it was me I would be installing new carrier min bearings, new bearings needed for pinion, a varied range of shims will be need to set pinion depth,
A decent torque wrench, inch pound torque wrench for pre load setting,
Read your factory manual a few times and post back if it makes sense , and you think you could do it

[HPP]

He has two complete pigs, one sure grip 3:91, one peg leg 3:23. You can swap the carriers without removing the gears from the case. Simply remove the bearing caps and adjusters from both pigs, and pull the carrier and ring gears out. Swap carriers to appropriate ring gear, reinstall and adjust bearings per FSM specs. Only special tool required beyond regular hand tools might be a spanner wrench. Also, be advised the ring gear bolts are left hand thread.

However,  OP, since you also asked if you can swap a sway bar in the driveway, I'd be somewhat suspect of your mechanical ability on something as critical as carrier bearing set up and your tool collection is somewhat suspect. This type of change will require jacks and jack stands.

[fy469rtse]

You still have to swap pinion gear , ? Different ratios , gear sets have to stay matched
Pinion matched to ring gear,
HPP is right, you need the right tools,
Even when I have done them , have had to borrow tools from a friend, and I have a lot of tools ,
And I remember first couple  close to right but lucky I had a knowledgable friend to correct what I didn't get right ,
Not for the novice

[HPP]

In my scenario the ring and pinions are staying matched. I'm only proposing swapping the ring gear carriers, not the entire assembly. The pinion stays in the case.

I'm not saying take the sure grip with a 3:91 ring gear and put it in the case with the 3:23 pinion. That won't work. I'm saying take the assembly with the sure grip and 3:91 ring gear out, do the same with the 3:23 open, remove the ring gears from the carriers, put the 3:23 ring gear on the sure grip carrier, then re-install the 3:23 ring gear with sure grip carrier into the case with the 3:23 pinion. Repeat with the 3:91 on the peg leg carrier and re-install with the 3:91 pinion and case.

[euroZ06]

In my scenario the ring and pinions are staying matched. I'm only proposing swapping the ring gear carriers, not the entire assembly. The pinion stays in the case.

I'm not saying take the sure grip with a 3:91 ring gear and put it in the case with the 3:23 pinion. That won't work. I'm saying take the assembly with the sure grip and 3:91 ring gear out, do the same with the 3:23 open, remove the ring gears from the carriers, put the 3:23 ring gear on the sure grip carrier, then re-install the 3:23 ring gear with sure grip carrier into the case with the 3:23 pinion. Repeat with the 3:91 on the peg leg carrier and re-install with the 3:91 pinion and case.

I am not planning on doing this myself, and have teo options. One local shop that has some older cars sitting. There, and the owner himself has a nice old mustang. He told me they never done this on a charger, so they dodnt know the details of what all need to be done (they specialize more in chevy's). My second option is this older guy thag hangs out with a buddy of mine and helps him rebuild his 73. He has his private garage, and was able to put my buddy's transmission together... In general seems knowledgeble about mopars (has a built challeneger dragster in his garage). Anyway, i just wanted to get some other opinions from people before i let that gent work on it (with all due respect to him, i just want to be safe).

About two months ago i had another shop try and just swap in the 3.23 gears as is, but they couldnt. They said the diff was too short or too long (cant remember). They try to find that one piece that connects the diff and thhe driveshaft (i forgot the name of it, but it's like a 4 point cross), and they said it would need to be a weird size and the cant find one. So they eneded up putting 3.91 back in the car (one of the biggest money wastes! Paid those assholes $300, and they didnt even check if it would work!).

[71charger_fan]

Where are you located. I have a 3.23 sure grip I took out of my Charger to replace with a 3.55 sure grip from Dr. Diff. Too heavy to ship, but if you're within a few hours of Western Maryland, it might be worth the drive.