Author Topic: Auto Locker Functionality Explained by John Zentmyer (Lock-Right inventor)  (Read 2777 times)

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Being a Toyota guy, I think it’s really cool that the first L.A. Locker was for the Toyota 8” differential. Can you provide any additional information about why that became a problem that led to the name being changed to Lock-Right?

You previously said that because a selectable locker is a spool (when locked) it can put significant torsional strain on the axle shafts when turning on rock.  You also said that until there’s no torsion in either axle shaft the locker won’t disengage. This is all makes sense to me, but can you explain how things are different, or the same, with an automatic locker?  My experience in Moab with automatic lockers (Detroit Locker in the rear and Aussie Locker in the front) has been that my drivetrain will get bound up to the point of effectively locking my steering wheel and I simply cannot turn.  My automatic locking differentials have to be locked in these situations and I cannot imagine a scenario where what I experience could result in less stress overall compared to having selectable lockers that could be disengaged a large majority of the time. Are my automatic lockers not disengaging because there isn’t enough backlash available in those situations?


Of all the timing that could have happened--just yesterday I found a slide dated 1989 that is probably the only photo in existence of the L.A. Locker at a show. This particular one was for the Suzuki Samurai (now L-R model 1510), but the first L.A. Locker (now L-R) for a one-piece differential case was model 1610 for the Toyota 8-inch (the Samurai has a two-piece case). I chose the name “L.A. Locker” because “L.A.” seemed more up-and-coming, while “Detroit” seemed more like the past. The Detroit people took exception to my choice because it supposedly was too close to their name, and they even claimed that they had a lock (pun intended) on the term “locker,” which I promptly disproved and shut them down on that score. My attorney said that it would be an easy win, but even so, fighting that battle would have taken more resources than I had at the time, so I changed the name. I’ll put this in print for the first time--the person who came up with the name “Lock-Right” was a guy named Richard Denny, who was a machinist at the shop where the L.A. Locker was being made. I thought it was a pretty good name and so I used it, and the rest is history. He went to that great machine shop in the sky more than 20 years ago, but many thanks, Richard.

The answer to the difficulty in steering question is that when two tires are connected together with a solid shaft they are both turning at the same rate (duh!). That is why with a selectable locker locked there has to be some “give” at the ground or something will break because the tires are rotating at different rates while the vehicle is turning. If you’re turning in a sandy parking lot with a selectable locker engaged, there will be a constant “hiss” as the tires slip on the sand. If you’re locked and turning on solid rock (why is your locker engaged?), both tires are effectively glued to the ground but are being forced to turn at different rates, which creates tremendous stress in the axle shafts until one tire slips (if it can). This condition also produces noticeable understeer in a turn because both tires want to go in the same direction and they are trying to force the front end to also go in their same direction.

This condition of binding up when turning on rock also occurs in a vehicle with two automatic lockers, except that instead of binding up side-to-side the axles will bind up front-to-back, which, of course, includes the steering. When turning on solid rock, both outside tires over-run and are not part of the equation. Both inside tires are providing power to the ground, but they are also directly connected to each other by the axle shafts, drive gears, drive shafts and transfer case. The turning radii of the tires are not the same (the back tire doesn’t follow the same path as the front tire), so with both tires rotating at different rates a lot of torsion will build up in these front-to-back driveline components. Eventually the friction in the moving parts will be enough to stop the vehicle (or break something). This is called “driveline windup” and was mentioned in my early L-R instruction manuals as being something to watch out for. When this binding up happens, the steering knuckle on the bound-up side can’t move either, which is why you couldn’t steer. In extreme situations the only solution is to jack up one wheel on the inside of the turn and watch it go “sproing!” to relieve the driveline tension. You can’t undo a hub or put the transfer case in 2WD because they won’t release due to the friction. About the only other solution is to either back up and slowly turn in the opposite direction or goose it and try to get a tire to slip. Although I haven’t needed to try this, it would seem that if you put a piece of smooth material in front of one of the tires and drive onto it that this would reduce bite at the ground enough to let the tire slip and relieve the tension. Vehicles with two selectable lockers locked will experience the worst of both worlds because they will bind up both side-to-side AND front-to-back, which means that the driver really needs to be observant about the terrain under his vehicle.

In this same turning scenario with open differentials you’ll get the same result, although it will take longer because the differential gears are also rotating so that the driveline torsion builds up more slowly. I’ll guarantee you that if you are in 4WD with open differentials on solid rock and driving in a circle that you’ll also get driveline windup, and either you’ll stop moving or something will slip or something will break. That’s why rule no. 1 with a 4WD vehicle is that you don’t drive in 4WD on pavement (and shouldn’t on solid rock either). Since driveline windup occurs more slowly in 4WD with open differentials, with a selectable locker the problem of torsion buildup in 4WD will occur less often IF the driver pays attention to his surroundings and turns it off when not needed(or selects 2WD).

Sorry if this got a little long, but I am glad that I could add my information to that of the other experts out there who are probably even more familiar than I am with the subjects I’ve covered. Just for my street creds-—I got my first 4WD vehicle in 1964 (back when I was really young), which was a WWII Ford GPW into which (for some unknown reason) I put a Studebaker flathead 6 engine. Yes, it did fit! Later on I had a ’48 CJ-2A to which I added a Warn overdrive. I’ve also owned a 1941 WWII Dodge 1/2-ton 4x4 panel truck and a 1942 WWII Dodge 3/4-ton 4x4 WC54 ambulance, to which I added a MoPar 360 V-8, an NP-435, a 2-speed 6x6 transfer case and 9-5/8 third members. This latter vehicle is the one for which I invented the All-Trac automatic locking differential in 1985, which then led to the L.A. Locker (later the L-R) in 1989 and eventually much later to the Torq-Locker ( In 1993 I brought in two other people and formed PowerTrax, but three years later there was a hostile takeover and I left the company but stayed close to lockers. My last article was in the March, 2000 issue of Four Wheeler and is still on the internet ( My present ride is a 1992 Dodge W250 3/4-ton 4x4 pickup with a Cummins first gen diesel engine and a 1-ton drivetrain. It has a Spicer 60 in the front end with a prototype TorqLocker and a Spicer 70 in the rear with a production L-R, and a gear-driven transfer case. Of course, it’s a stick (so were all my others). For those of you familiar with what’s out west, I have a photo taken in 2015 of my dog and me and the Dodge and the sign at the top of Imogene Pass at 13,114 feet, between Telluride and Ouray, Colorado (my wife took the picture and really enjoyed getting high with me on that trip).

Hope my info helps. Happy four wheeling!
« Last Edit: Dec 31, 2016, 02:24:04 PM by blackdiamond »
1989 4Runner: Dual Ultimate (Inchworm front & Marlin 4.70 rear), Marlin Twin Stick, 1200-lb clutch, 4.88 R&P, Aussie Front, Detroit rear, 30-spline Longs, Long hub gears, ARP hub and knuckle studs & 35x12.50 Cooper STT PRO tires.  Marlin rear bumper & sliders.  FROR front bumper.  SAS with Alcan springs & Rancho 9000XL shocks.  Budbuilt Bolt-on traction bar.  Custom Interior Cage by Those Guys Rod and Customs.

Moab Tested & Rubicon Approved


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