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How does a Dana/Spicer Powr-Lok Work?

Putting the Tink back in Tink

You might remember—or you might not—that "Tink" is the nickname for my 1946 CJ-2a. I've shown you some of the adventures Tink and I have had together and also shown you what needed to happen to get Tink into running and driving shape all on fourwheeler.com.

When you put an old Jeep like this together with mostly used parts, you have to have some help. Whether that's a local Jeep resto and parts house, or a friend (or friends) with a similar affliction, it's a near must. Why? Although new reproduction parts are widely available, some things just aren't.

Take for example Tink's front axle. It's the stock Dana 25 that had an open differential. And while that is adequate, it's not ideal, and our buddy Mike knows that. He just happened to have a usable Dana/Spicer Powr-Lok Limited Slip for a Dana 25. That Powr-Lok is what helped me break, or "tink" Tink's front at the annual Tiera Del Sol Desert Safari here.

We call Mike a friend, but he's more than that; he's a brother and a family member, so when we showed interest in this Powr-Lok, it was as good as ours. And of course, Mike wouldn't take any money for it. We took it and will do whatever we can to repay Mikes selflessness, and in the end, the differential is pretty righteous—if you can find one.

What is a Powr-Lok?

We've heard about Powr-Loks for a few years, and what we were told sure sounded good. In a lighter 4x4 like a Jeep, the Powr-Lok acts like a limited slip, which is great, but it gets better. As part of the design, the tale goes, you can tap the brakes on said lighter 4x4 and the Powr-Lok will "actuate" and lock up much like a locker.

Now it might only lock for a second or two, but that is often all you need to grapple a bit further up the trail. It does this with a combination of friction surfaces and a unique cross-pin design that causes the side gears of the differential to load the friction surfaces until the diff does what it does and behaves like a locker. If you are like us, that sounds great, but a visual aid helps cement the form and function. Here are a bunch of photos and a video of Mike and tech editor Simons going through this Powr-Lok for a Dana 25, which is unfortunately no longer available. It is somewhat specific to the Dana 60/70 Powr-Loc, but this online manual gives all kinds of info on re-building these differentials.

Powr-Lok parts are available for Dana 25, Dana 27, Dana 30, Dana 44 (19 and 30 spline), Dana 60, Dana 70 (still available as new parts), and some Chrysler axles (like the 8 3/4). There are two splits and part numbers for each, as in 3.92:1 and up (slow, numerically higher, series 4) and up vs 3.73:1 and down (fast, numerically lower, series 3). Ebay is your friend for carriers, unless you need a new one for Dana 60/70, then Summit Racing is your friend. And Herm The Overdrive Guy has new and used parts for 25, 27, 30, and 44. Also if you want new and locking action Motive Gear has Lock-Right for Dana 25s (PN 2110-LR) and many other axles.