1999 TJ re-gear to 4.56

Turboloft said:

So even a Eaton E-locker sold with Nitro axles that are chromoly are no dice? That's interesting to me...

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that is how I understand it. Unless it somehow also converts the bearing to one that does not ride on the axle shaft, 4140 or 4340 chromoly is a no-go. That is not to say that the molybdenum 1541 axles aren't plenty strong.

lumberjacklloyd said:

Eaton used to sell the coil magnet, spider gears, locking ring all as rebuild or part kits. They did not sell many and finally phased them out. Users either had no issues or the carrier was toast at the time of rebuild.

My locking ring showed wear on the teeth that engage side gear after 50k miles. The side gear dogs and engagement channel in the carrier were near perfect, so they sent out a locking ring from their engineering facility for free via 2 day.

I really can’t complain. The only thing they don’t like is cold 85w-140.

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In response to reliability, there was no issue that made me open it up. I had it out for regear and wanted to see how it looked inside. I do think this wear happen when I activated the locker with the rear wheels off the ground and held a wheel. It made the ratchet sound of teeth engagement that it never makes in normal use. So, I won’t do that again. I can appreciate by design that the locking ring is the sacrificial part of the mechanism. The carrier grooves were still completely smooth to the finger and side gear was flawless. Spider gear wear looked great.

I ran the stock 4.10s in my 5-speed 2004 Rubicon with 33s for 20 years before carefully choosing 4.56s a couple years ago. I also accept the tradeoff in advantages and disadvantages 4.88s offer. They aren't low enough to fully optimize 4th gear for a pass, but they're shorter than I'd want to spend 4-6 hours driving 75mph+. In my car I don't mind spending hours at 3200rpm, but it redlines at 7250 and has a very different personality. I would honestly say there were 2 advantages to the 4.10 gearing with the 5-speed. The reality is there is a range of reasonable differential ratios that can work and each has tradeoffs.

You are choosing what rpm at a given speed you want to be at on this power curve in all 5 speeds in your transmission, with emphasis on 5th gear.


When I switched to 4.56 and installed 1.7 roller rockers I was able to do 60mph through the climb up to ~12,000 feet at Eisenhower tunnel in 4th gear, which was a major win. I couldn't hold the 50mph speed limit before. I don't think either would have done it on their own, but the combo worked. For me 4.56 with the 5 speed provides a good balance up to the 80-85mph speeds on the interstate in UT and WY and enough gearing in CO where we are down on power due to the altitude. The roller rockers helped the engine breath better as the rpm climbs extending the usefulness of 3rd gear.

As for the gears, I'd also recommend Revolution for the R&P with the REM finish if you don't want to deal with the break-in prcoeedure, ECGS/Yukon for the shim pack and Spicer seals from Denny's Driveshafts. As Timken are a mix of India and US mfg now, I don't have a strong opinion between those and the Japanese offering.