2.73 to 2.56 conversion?

[erasedhammer]

What is required to change a 2.73 differential to a 2.56 geared one?

Can I throw the ring and pinion of a 2.56 in it and be fine or do I need more?

 

[Havok]

technically thats all you need. Im curious how the hubs would hold up with all the extra torque

 

[erasedhammer]

technically thats all you need. Im curious how the hubs would hold up with all the extra torque

Technically? Do 2.56 diffs have any other different parts compared to the 2.73? I assumed they were identical?
Extra torque from the turbo engine?
Or...?

 

[86humv]

2.56 will only give you slightly less RPM's.
They were in the early trucks.
Hmmwv's had 2.56, 2.73, and 3.08.

 

[erasedhammer]

2.56 will only give you slightly less RPM's.
They were in the early trucks.
Hmmwv's had 2.56, 2.73, and 3.08.

Thats the reason I'm looking into the diff regearing.

Since I will be swaping in a turbo I thought I wouldn't miss the torque off road and get a little more reduction in rpms for highway cruising.

 

[HETvet]

Honestly, it's not much of a gear difference I doubt you would notice. You need a 4 speed trans with an O/D and a lock up converter.

 

[erasedhammer]

Honestly, it's not much of a gear difference I doubt you would notice. You need a 4 speed trans with an O/D and a lock up converter.

I already have a 4l80.
That conversion have a ~800 rpm reduction.
2.56 gears would give me a 200 rpm reduction from what I've heard. 1/4 of the rpm drop for about a 1/12th of the cost, worth it for me, personally.

200 rpm reduction is the difference between 55 and 60, and auditory-wise its noticeable.

 

[Skrilex]

I don't know about hmmwv diffs but if they are as normal as a regular the best you can find for a swap cost to have someone else do it is about $1600 for both. There's a lot that goes into a properly setup gear set and it takes a lot of time and care. I'm sure you knew that but just wanted to make sure because if you spent that much on your trans then I need to rule out that trans!

 

[erasedhammer]

I don't know about hmmwv diffs but if they are as normal as a regular the best you can find for a swap cost to have someone else do it is about $1600 for both. There's a lot that goes into a properly setup gear set and it takes a lot of time and care. I'm sure you knew that but just wanted to make sure because if you spent that much on your trans then I need to rule out that trans!

I thought changing the ratio was just installing new ring and pinion gears? What special things need to be done that would be worth $1600 of work. That sounds like a rip off personally.
I spent $2500 on my 4l80 conversion.

 

[erasedhammer]

The reason I am skeptical is because I have torn about geared hubs before on a whim and it's a really simple thing to do. Only precision part is shimming a cover plate.

 

[Skrilex]

Anyway as usual YMMV but the process is tough enough (x2) that most shops will recommend new bearings too so that's why the cost gets up there quick.

If if you do have a shop do it for you I'd suggest not using a 4wd shop but rather find the local big semi truck service shops and see if they will do it for you. That will assure it's done right because those guys need gears to last millions of miles. Also if you bring them the complete carriers it will cut down on some costs.

 

[Skrilex]

Weird my last response didn't show up yet until moderator approves. So stay tuned lol.
Also can someone confirm if the diffs on these are removeavle as a complete carrier or must they be setup in axle?

 

[erasedhammer]

Weird my last response didn't show up yet until moderator approves. So stay tuned lol.
Also can someone confirm if the diffs on these are removeavle as a complete carrier or must they be setup in axle?

Humvees are independent suspension, diff bolts to the frame. Disconnect the half shafts, driveshaft and the supports for the diff. Drop the thing out.
I think I'll remove the diff and dissasemble it for my local shop then they can do the precision work and I'll reinstall it.
Probably much cheaper and easier for everyone.

 

[ken]

What year did they change to 2.73?

 

[Skrilex]

I wonder if there are people who would want to trade complete diffs with you for their 2.56? That would be the easiest and most cost effective for sure.

 

[98G]

Seems like a lot of work for 6.5% difference in top speed, or a 6.5% difference in rpm at a given speed.

What am I missing?

Edit - when I posted this i didn't see the 4 or 5 posts towards the bottom of the first page. I don't know if I missed them, or if somehow they weren't displayed.

My gear calculator says the difference is 55 to 58mph. All this for 3mph?

 

[patracy]

If you're interested in 2.56 diffs, I can help. Much easier to drop the entire unit instead of bothering with a gear change.

 

[Action]

Also, there is a special tool for the humvee called a diff spreader. It bolts to the case and pushes the sides slightly to allow the assembly inside to come out. Wouldn't you also need a shim kit and precision instruments for measuring tolerances when you put it back together?

 

[HETvet]

I don't know, but you don't have to have shims. Axles like the Ford 9 inch have have internal threaded washers that you screw in or out to make the adjustments you need. In order to have a gear set that actually lasts, you must make sure your pinion depth is correct, gear back lash is with in spec., have correct contact pattern between the ring gear teeth and pinion gear teeth, poroper pinion bearing preload, proper side bearing preload, proper turning torque of the pinion and each axle (if a limited slip equipped carrier is used), just to name a few. Tools needed are; torque wrench, bar type torque wrench, dial-indicator with magnetic base, gear paint. Typically it takes about 30-45 minutes to get all that right; so long as it's not a shim type diff. And the person doing the work actually knows what they are doing.

 

[Rmtaunton]

It's a model 20 rear end


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