Gettin' Geared Up: 3.5 to 4.56 info needed

[bentendo]

I'm about to try opening an already thoroughly opened can of worms:

What all do I need to consider going from stock 3.5 gears? My truck is a 72 Bronco with a freshly rebuilt Explorer 5.0, NV3550, 32" BFGs. I'd like to go with 4.56 matching set front and rear. Here's what I have so far:

– My rear is, according the VIN, a 3.5 factory limited slip, 28 spline with original axles. Should I take this opportunity to either rebuild my LSD or go ahead and update to a 31 spline locker with new axles? I'm looking at this Dana 4.56 set:

https://www.rockauto.com/en/moreinfo.php?pk=4956591&cc=1105490&jsn=1326

– For the Dana 44, I'll need to get thick cut 4.56 gears to be able to utilize my stock open carrier which can only go up to 3.73 standard cut. Is this correct? Looking at this gear set:

https://www.rockauto.com/en/moreinfo.php?pk=11385761&cc=1105490&jsn=1323

– I replaced my barely-hanging-in-there front axles a while back with a set of high-strength axles from Tom's thinking I'd alter gears later. These should be sufficient to handle the 4.56 gears up front, yes?

https://www.tomsbroncoparts.com/pro...erminator-dual-heat-treated-chromoly-full-set

Final thought: there's a diff rebuilder in town that will do both front and rear, parts and labor, for $1,800. Would I be time and money ahead to let an expert handle this? I've read the 9" is pretty straightforward but that the D44 is tricky.

As usual, thanks all!

 

[Broncobowsher]

A new front open carrier is something like $50 the last I got one. If you are really going for an open front diff, just get the new carrier.

For the rear, 31 spline is a good upgrade. Added gearing is added torque on the shafts.

The front axle upgrade is an odd choice. You are planning on keeping an open front diff. Looks like you only have 32" tires. The factory shafts are generally pretty good, it is only the little U-joint that is weak. But with an open diff there isn't that much load. Generally the only way to pop that U-joint with an open diff is an airborn spinning tire landing while on the throttle. But if you are in that situation you probably should have something besides an open differential in the front. Looks like an odd mix of parts with high end shafts on an open diff with fairly small tires.

 

[okie4570]

The 44 is only tricky imo because you can't pull it out and lay it on the bench to set it up like the 9". There's so many youtubes out there on how to rebuild axles now, that really it just comes down to budget, and if you want to buy specialty tools for a one time mod. I actually kind of enjoy the whole regearing procedure, but I've also got access to a shop with a lift. I've done several broncos and jeeps. I suppose if I were laying on the floor, I might have a different outlook lol. If think you'll ever want lockers, do it while you're changing gears.

 

[Timmy390]

With the D44 you need setup bearings........

Both require bearings to be pressed on/off so a shop press is needed. Calipers are needed as well as a dial indicator and magnetic base. Rubber mallet, torque wrench and a vise is handy.

As far as the work goes you need an understanding on how Diff's are setup. The 9 has side adjusters but the 44 has shims to put in and pull out. The 44 also has shims under the pinion bearing races that set depth where the 9 has the shims between the case and pinion support. There are some great written instructions for both out there.

I did my front and rear on the Bronco. 9 was a few hours....the 44 was all day......lol

For the 9, I wouldn't go with a clutch style LS. Get an Eaton True Trac and be done with clutches and oil additives forever. They're super strong where as the stock LS is weak. While doing the 9 get a solid spacer/crush sleeve eliminator. WORTH IT when you go to change a pinion seal leak. Upgraded axles in the rear is always a good idea....

Tim

 

[Broncobowsher]

Skip any clutch style limited slip, worst of both worlds.