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In the early 1970s, real muscle cars were fading away, and average Americans were becoming more concerned with a plush ride than with high performance. In the 1973 model year, General Motors decided to start using the Gov-Lock in trucks, in an effort to eliminate chatter associated with conventional spring preload clutch type positractions limited slip differentials. This was the one of the few solutions available using 1970’s technology. Thus, for GM trucks produced after 1972, the only traction-enhancing option was the Gov-Lock (produced by Eaton). These governor actuated units provide a locking differential without chatter. Great for the average truck owner, but not for those who really use their trucks off-road. Often referred to as a “time bomb” or “Timex Posi”. These locking differentials work fairly well for occasional use when traction is of small concern, but not when power transfer and traction are the main goal.
The Gov-Lock can fail in any number of ways, and often does. Usually, the case will break in half, but sometimes small internal parts will break. I have no intention of defending them except to say that the Gov-Locks used in 3/4 & 1 ton trucks hold up fairly well due to their sheer size, and especially well when compared to the smaller designs. For readers looking for something stronger, Yukon makes redesigned units that are worth showing off. The Yukon Dura Grip is not actually a “new” design so much as a vast improvement on the old design. The basis for these new units is the heavy-duty positraction that was originally produced for big block GM muscle cars in the 60s and early 70s.
Dura Grips now come with composite clutches that are more durable than their steel counterparts.
New units also use stronger spider gears produced with Net Form Forging technology. These stronger spider gears look very different compared to standard cut gears. They are made from 8620 steel to increase strength and durability. Net Form Forged gears perform at least 20% better than standard cut gears in both impact testing, and testing for fatigue under heavy loading.
In addition to the other improvements, Yukon has improved the case designs. The original 12-bolt truck positraction was very similar to the passenger car design but was not nearly as strong as it’s passenger car counterpart. The new 12-bolt truck cases are about three times stronger than the original ones used in the early 1970s, and all Yukon Dura Grip cases are now made of nodular cast iron with increased material thickness in critical areas. The new 10-bolt cases now have larger bearing journals that increase the case strength and use bearings with more rollers than stock.
Overall, the new Dura Grips are superior to the admired and sought after original OEM GM positraction. By using 90’s technology, Yukon has built a stronger, harder working positraction that does not chatter.
Yukon has developed Dura Grip limited slip differentials for:
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