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Testing Lunchbox Lockers - Differential Upgrades

1956 Jeep Cj 5 Wheeling
Verne Simons
| Senior Editor, Jp
Posted August 9, 2013

Front Or Rear?

Someone once said, “To be or not to be: that is the question.” We don’t know about that or what that question really means. It seems to us that one day around the age of three, we just were. Do you remember making that decision? ’Cause we don’t. Oh well, since we currently be…er, are…or whatever, we will stay as is for now and quit contemplating that obtuse question. Instead, since we are addicted to Jeeps and Jeep building, we decided to ask a different question: front or rear? That is, which differential to lock if you could only lock one? This may seem like an easy question to answer, but it’s not…necessarily. Why? Well, because your opinion on the answer to this question is probably the opposite of someone else who knows what they are talking about. What to do? Well, we decided to test this using our ’56 CJ-5 as a test mule. That way we could very unscientifically resolve this life-long question…or not.

To figure out the answer to this question, or at least provide ourselves with a venue to discuss the pros and cons of each, we contacted West Coast Differentials for a Powertrax Lock-Right for the Jeep’s Dana 30 front axle and No-Slip from Powertrax for the CJ’s Chrysler 8.25 rear axle. Once we had these traction-adding devices in hand, known commonly as lunchbox lockers, we installed one in our driveway, ran a trail, removed that locker, installed the other again in our driveway, then ran the same trail. What happened? Which worked better? Well, you are gonna have to follow along to see what happened and what we found.

Just to be clear, we are running these lunchbox lockers because of their affordability and ease of installation. We would not recommend using them to lock a 760X U-joint-wearing Dana 30 or a 29-spline Chrysler 8.25 with tires over 33s. The strain on the stock axleshafts and differential carrier would certainly end in failure. Even with 33s or smaller tires, we know that we may break axle parts. That’s the cost of having lockers!

Easy Decision Time
There are some situations where making the decision on where to put the locker is pretty easy. Generally, if you have a ’84-or-newer Jeep with a Dana 35 rear axle, you are playing with fire by adding a locker to it. In that case, we’d almost certainly put the locker up front first—unless you are gonna run 30-inch tires or less, in which case we might consider locking the Dana 35. With us, 99 times out of 100 we’ll tell you to avoid spending money on your Dana 35. Instead, save it for an axle upgrade.


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The other time that making the decision of where to run a locker is easy is with any Jeep with a Rear Dana 44 with once-piece flanged axles. This axle is gonna be stronger and more reliable than the Dana 30 or 27 that would have accompanied it from the factory. Another instance in which we would opt for rear locker first is in Moab. Why? Well, all that driving on high traction slickrock in 4WD is gonna be hard on your Jeep’s steering, U-joints, axleshafts—heck, basically the whole front end of your Jeep.

Step By Step

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  • We started this crazy test by tossing a Powertrax No-Slip (PN 92-0382-2905, $467.00) from West Coast Differentials in the 29-spline Chrysler 8.25 axle in the rear of our restomod ’56 CJ-5. Why the rear first, you ask? The 4.10 rear has an easily removable cross pin, while the ring gear of the high-pinion Dana 30 front axle prevents removal of the cross pin. That means you have to pull the bearing caps, remove the differential from the axle, and then remove the ring gear from the differential in order to get the cross pin and differential side gears out to install the Lock-Right locker. We decided we only wanted to mess with the front diff once, so we would install the rear locker and then pull it. Or so we thought.

  • Installation of the Powertrax No-Slip went seamlessly. We used some heavy grease to hold all the little springs in place during assembly. After testing the rear locker by itself, we found removing the No-Slip wasn’t nearly as seamless. We will talk more about that later.

  • Having a locker in the back of our old CJ made it very capable off-road. We could now go almost anywhere we aimed the Jeep. We headed down a small trail in a wash that flexes out suspension and causes a tire or two to head skyward. The little trail also has some steep rocky climbs that allowed us to load the rear axle with most of the weight of the Jeep.

  • The No-Slip locker did make the occasional clunking and banging as the locker un-locked and locked. They do that. The added traction is well worth dealing with the noise and shimmy that come from the locker. We also noticed off-road that the locked rearend was pushing straight despite how we tried to steer the Jeep. This effect is worsened when the Jeep has most of its weight on the rear axle like during climbs or on high-traction surfaces. Also, stress on the rear axle is pretty high as you are driving the Jeep on the road, as both rear tires are gonna want to turn at the same speed.

  • The Powertrax No-Slip reuses the factory 8.25 C-clips, which are ever so slightly larger than the window machined into the Active Slotted Spacer (that’s part of the locker). It’s just small enough that the C-clip will pass through the window with a little force, but won’t for love nor money come back out. Unbeknownst to us, grinding a little of material off the C-clip so that it would easily pass through the window in the Slotted Spacer would have saved us hours of work lying on our backs under a Jeep. Finally, we had to drill the C-clip out of the locker. It sucked.

  • A B A We recommend test fitting the C-clip in the Slotted Spacer before installation. If it does not easily slip through the window, grind down the edges (arrows A) of the C-clip a touch. We also notched the back of the C-clip with a triangular file (arrow B) so that we could more easily orient the C-clip for removal of the locker in the future in case we break an axleshaft or need to service our wheel bearings or seals.

  • Once we got the Powertrax No-Slip out of the rear axle we pulled the front differential and installed the Powertrax Lock-Right from West Coast Differentials in our Jeep’s high-pinion Dana 30 with 4.10 gears (PN 2210, $310.00). Installation was simple other than messing with pulling the front carrier and having to remove the ring gear. That’s a bit of a pain, but it’s still easier than installing a full-carrier locker, which would require shimming to adjust the backlash and ring gear pattern. Again, we used that thick grease to help hold parts in place during installation.

  • On the plus side, with a front locker it’s generally easier to crawl the front tires up on an obstacle. In most cases, once the front tires are up on an obstacle, you can use a bit of momentum to bump the rear tires up in the rare situation when the rear tires are not pretty firmly planted with most of the vehicle’s weight. Also, strain on the axle while driving on-road is less because the front axle is not engaged and the locker will just ratchet, making a little noise as you go around turns.

  • On the downside, front axles have U-joints and they generally don’t like the stress of a locker. Add in the lack of a rear locker and the front axle ends up doing lots of hard work. This can result in U-joint or axleshaft failure. Also, on descents the front axle wants to go straight, which can be a problem trying to go down a slope at an angle. If you have to back up all of a sudden, you are in danger of snapping a front axle because all of the weight of the vehicle is now on one U-joint. Add in any kind of a bind, and bam! This is also a good time to start watching your axleshaft U-joints spinning caps, stretched axle ears, and so forth. Lockers are not easy on parts!

Arguments for or Against
Most of the arguments that we have heard for one end of your Jeep versus another can be easily countered. For example, Jack might say that on a steep climb most of the vehicle’s weight is on the rear axle, so a rear locker would be better. Bob could argue that because more of the weight is on the rear, the rear tires are more firmly planted and less likely to spin even without a locker. In that case, Bob could use basically the same reasoning as Jack to say a front locker is better. The truth of the matter is that depending on the situation you find yourself in, having one end locked versus the other may be beneficial to you. On some obstacles your Jeep may benefit more from a front locker, some from a rear. Basically you are set until you get to the next obstacle on the trail, or even a different line on the same obstacle, where the opposite may be true.

Step By Step

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Lock Both!
So what is best? Well, honestly, having both axles locked is the best, and chances are once you’ve got one end locked up you are gonna want the other one locked! Our little CJ on narrow tires with two lockers will go places few would imagine it could. So the correct answer is if you want a locker and think it might help your Jeep do better off-road, buy one based on which of the two axles in your Jeep is strongest. Then start saving for the next locker and some upgraded parts, like one-piece shafts, chromoly shafts, chromoly U-joints, a bigger axle….Oh boy, here we go again!

Step By Step

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West Coast Differentials
Rancho Cordova, CA 95742