Have you ever had your axles crossed up on a Dairy Queen speed bump and had to listen to the laughs as your wheels spun due to the open differentials? Did you ever wish you could have a locking differential like those curb-hopping high school drug dealers in their jacked-up supertrucks? Well, your wish is about to come true.

There are many types of locking differentials available. Some are for hard-core trail riding, with poor street manners. Others have better manners but still have some quirks in handling. One very unpleasant aspect of any locker or limited slip differential is the tendency to slide sideways in slippery, off-camber situations. This is where the manually controlled lockers like the ARB or Ox-Locker shine, as they can be shut off when needed for street driving and off-camber situations. But have you priced one of those babies lately? If you can convince your wife why you should buy one, stop reading now. Maybe you can solve world hunger while you're at it. Otherwise, consider the Vern-O-Lock.

The Vern-O-Lock is not for everybody. I have received a lot of queries about folks interested in their own Vern-O-Lock. I designed it around my limited machining capabilities. If you had to pay for the machine work, that would add up quickly. In that case, I'd recommend purchasing a proven commercially made locker versus my experimental design.

It would only work on a rear axle full-floater conversion. The heart of the Vern-O-Lock is an extra-long axleshaft that is free to float lengthwise within its splines. The inner splined section is extra long and can engage the opposite side gear inside the differential. The other axleshaft stays put. A cable actuated shift fork and collar arrangement moves the sliding axleshaft to control this locking action.

Since building my Vern-O-Lock, I've learned the concept is not exactly new. Jack McNamara of Australia produced a locker with a sliding axleshaft many years ago, although it was not remotely actuated. I've never seen one, so do not know all of the internal details. (A big thanks to John Young for sharing the link.)

Here is a close up comparing the two shafts, showing how the one shaft has extra long splines. The end of the grooves follow the radius of the cutter and must extend into the necked down section. However, the side gear will engage only the full diameter due to the effective length of the splines:

This shows how the long splines extend inboard from that axleshaft's side gear. I have chosen to use the driver's side shaft, but the passenger side shaft would have worked, too. Note the gap, showing how the shaft is not engaged with the opposite side gear, resulting in a normal, open differential The fixed axleshaft on the right is recessed in the side gear, just like in the stock configuration:

Now the axleshaft has been shifted inwards, and has engaged the opposite side gear by 3/8". From my meager calculations, this engagement should provide adequate strength. If nothing else, it looks about right and is not much less than the side gear depth used by the factory in the Powr-Lok. Both axleshafts are locked together Although not shown, the outboard splines are 3/8" longer allowing the axle to shift inside the Warn hub. No snap ring is used on that hub:

Here is a view inside the differential carrier. The ring gear and bearing caps are not installed. This view shows it unlocked. The special shaft for the spider gears, explained later, is not yet installed for clarity:

Since the axleshaft extends where the stock pinion shaft (aka cross-shaft) would be installed, two stub shafts were used to hold the spider gears. This may have provided adequate strength, but I wanted to keep the inner free ends as steady as possible. A stabilizing ring, machined from a large nut, supports the inner ends of the stub shafts. The stub shafts are hardened Allen-head shoulder bolts with the heads turned down to fit snugly in the differential carrier. The shaft bores are not identical in the carrier, so the stub shafts are sized accordingly. The stub shafts are threaded into the sides of the nut in the middle. The critical surfaces of the nut have been machined for a proper fit:

Here is an exploded view of that shaft assembly. The stock shaft is to the side for comparison. The flat sections on the side of the stock shaft are for better lubrication inside the spider gears. I did not duplicate this feature in case I ever had to retorque the stub shafts. Note the lockpin hole in the stock shaft. The hole for the lock pin will not be drilled in the stub shaft until final installation:

Here is the stub shaft assembly installed in the differential carrier. None of the gears touch the nut. If you look closely, the sliding axleshaft is visible in the gap on the left side. The sliding axleshaft is retracted from the righthand side gear so the differential is unlocked:

One of the stub shafts is locked to the carrier by the lockpin used for the stock shaft. In addition to Loctite on the threads, the other stub shaft is peened in place so it doesn't back out:

The shifting mechanism will need to move the long-side axleshaft to control the locking action. This picture shows the pair of collars and roller thrust washers fitted in the middle of the axleshaft. The collars are an interference fit installed by heating the collars and freezing the axleshaft. A pair of shallow dimples are drilled in the axleshaft and a setscrew makes sure neither collar works loose. Note the spherical rod bearing which forms the pivot point for the shift fork. Unlike a transmission shift fork, this one pivots instead of sliding back and forth along a rod. The inner diameter of the shift fork clears the outside of the axleshaft:

Here is an exploded view of the roller thrust bearings. The wave spring washer is used to add a slight amount of preload so that the roller bearings are never flopping around. Two races and a roller bearing form a thrust bearing assembly, one on each side of the shift fork. Only one wave spring washer was needed:

This split image shows how the control cable moves the axleshaft in or out. The blue line down the middle is a reference showing the pivot point formed by the spherical rod bearing. The yellow reference lines at each end show how the axleshaft has moved while the pivot point is stationary:

This picture shows the hollow block which will be bolted to the backside of the axlehousing. Note the recess in the housing which will hold the outer race of the spherical bearing, forming the pivot point. The control cable will move the shift fork to the free position, while a compression spring will move the fork to the engaged position when the cable is released:

This picture shows the block with the fork. The fork will be inside the axletube when installed. Note the odd profile of the block (it is laying on its back in this picture) where it will bolt to the backside of the axletube. A short extension housing contains the compression spring. A setscrew on either side of the block is used to fine tune the travel:

On the aft side of the axle tube, a hole was carefully drilled and deburred for the shift lever. The outer race of the spherical bearing does not fit in the hole but is sandwiched against the outside of the axle tube by the mounting block. Note the four bolt holes, none of which extend into the axle tube:

Here the mounting block is bolted on the aft side of the axle tube. The block fits above the leaf spring and is well protected. The block is sealed against the axle tube to retain the gear lube. Note how the brake line dips down to clear the control cable:

This view is from the outboard side. The profile of the block against the upper and lower spring perches is more evident. Note the plug installed after the control cable is connected to the shift lever inside. A clamp on top of the block secures the brake line:

This view, between the front seats, shows the shift lever in the up position. The cable is relaxed and the axleshafts are locked together. This handle is a swap meet mystery parking brake lever that was shortened, with mounting feet welded underneath:

Here the handle is down, pulling on the cable to unlock the differential. The cable passes through a small hole in the vertical lip aft of the seats:

With the Vern-O-Lock installed, it was time for some testing and debugging. A slight turning maneuver lets the splines line up, and if the handle is raised the spring pushes the axleshaft to the locked position with a satisfying clunk. Like a kid with a new toy, I grinned from ear to ear as the tires chirped going around corners.

With just a few minutes of on-vehicle testing, I managed to break the original control cable. When pushing the control lever down, I was able to put too much pressure and overwhelmed the cable. The resistance was caused by the torque load on the engaged splines, preventing the axleshaft from shifting outwards. This was not a huge setback, as I was expecting this resistance.

A post mortem exam of the failed cable showed the threaded ends were not very securely swaged, much to my relief. The flexible cable was only inserted into the rigid ends by approximately one half inch. I built up new custom cable ends, with the length of the swaged area doubled for increased strength. Knowing that the original pre-fabricated cable was not very securely built made me feel better, meaning the force I had imposed was not excessive.

With that repaired, more playing, er testing, was in order. The secret to smooth shifting is to have the vehicle rolling in a gentle S-turn, but with the clutch pedal depressed to relieve pressure on the axleshaft splines. If stuck immobile, it can be engaged by gently spinning the tractionless wheel. I played, I mean tested, with the four locking hubs. With the Powr-Lok in the front axle, I could unlock any three of the four hubs and still drive. All I need is one wheel making contact with the ground and I'm all set. No Dairy Queen speed bump will stop me now!