Revolution Gear and Axle Swap – Is there a Difference?

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Words by JD Keating

Photos Brad Morris @Dads_That_Wheel

We have a distinct advantage of having two well-built and nearly identical Jeep JL’s to compare against one another, which sometimes takes the confusing guesswork out of installing and running aftermarket parts. 

Is a re-gear worth the investment and more importantly, can you notice a difference? 

We recently upgraded our factory 33” BFG tires with two sets of 40 x 13.5 x 17 Cooper Discoverer STT Pro’s, mated to the incredible 850 RE Torqueflite 8-speed Chrysler transmission, making the drive on the highway and the trail very impressive. 

While a bit of lag difference was inevitable with such a huge tire change, we could still smoke the tires off our Jeeps if we wanted to. Merging into traffic is never an issue, and once recalibrated, there really isn’t a lot of difference – other than the loss of the overdrive 8th gear. 

But let’s take a step back a bit. The 2018-and-up redefined Jeep JL is available with a redesigned 8-speed transmission. Intended to improve fuel economy, this new tranny boasts direct-drive in 6th and overdrive in both 7th and 8th.  This means that, in essence, your transmission is actually optimized in 6th gear. From a pure wear and tear standpoint, the transmission is not working any harder with 40’s on stock Rubicon 4.10 gears. 

Technically speaking, a re-gear is not entirely necessary. So then, why do it and what does it change? We reached out to Revolution Gear and Axle to find out. We asked for the largest gear change (that they also recommended) capable of withstanding the abuse of 40” tires. 

With that in mind, a shiny new set of 5.38’s arrived on our doorstep and we were in business. The cool thing about Revolution Gears is the REM coating they offer. A slick post-production application, REM coating is designed to eliminate the break in period that’s typically required when installing new gear sets. 

What’s more, Revolution’s REM coating doesn’t require an immediate gear oil change, but we swapped ours anyway, just to see. With our new and potentially stronger 5.38 gears installed by the fine folks at Rock Spyder Motorsports in Markham, ON, we hit the trails to put them to the test. 

Our immediate reaction was that daily driving is now much smoother with the higher gears. For instance, 1st gear doesn’t hold on as long, making for smoother shifts under less engine load and the transmission temperature increased just one-degree, which is negligible. The take away here is that the transmission is not over-worked running in 6th gear (ie: direct drive) all day. Suffice to say our re-gear so far has simply proved that running stock 4.10’s and 40’s is not putting any increased strain on our transmission. 

What about fuel mileage? This is everyone’s first question. Does re-gearing your axles magically improve fuel consumption when driving what is essentially a breadbox on 40” tires? The answer is it didn’t improve drastically enough to justify the added cost of a gear swap. 

However, there was a minor improvement in fuel mileage when travelling long distances. But there are so many other variables (like speed, wind, driving style, drafting, elevation, incline, decline, etc.) that we would not recommend re-gearing for the sole purpose of gaining improved fuel mileage. In fact, engine RPM with 4.10’s in 6th is the same as 5.38’s in 8th gear.

So what does a re-gear net? Installing 5.38 gears into a Rubicon Jeep JL provides a slower crawl ratio, which means having more control over the rocks and bumps when running in 4-Lo. More control also equals less breakage. For this factor alone, assuming you are taking your jeep through some pretty serious terrain, a re-gear is a worthwhile improvement. 

For our purposes, re-gearing was a no brainer (and something we should have done sooner) since our rock crawl-ready Jeeps are also our daily drivers and we barely noticed any change except for a drastic decrease in speed while crawling on the trails. The improved control is completely worth it in our opinion. 

We have encountered more shift hunting with the new 5.38’s, which is not really an immediate concern but it’s worth mentioning. Aftermarket gear sets have also been known to produce an audibly louder whine, typically due to a lesser quality product than OEM. The set of 5.38’s from Revolution Gear and Axle don’t make this sound.

In the end, we are pleased to say that the Revolution Gear and Axle gears we installed are high quality parts. There is no increased concern about breakage with a higher gear set. 

Trust us. We’ve put them through the test.