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Nuts & Bolts: Detroit Slippage

Posted in How To: Tech Qa on February 1, 2019
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I have a Detroit Locker that has been in the rear 9-inch of my Ford F-150 for about 20 years now. Lately it feels like it will randomly unlock one side while I’m just driving straight down the road. At times it’s pretty violent, with the truck wanting to change lanes. I’ve had a couple of close calls, and at this point the truck is borderline undrivable. Do Detroit Lockers wear out, or is there something else wrong?
Kelly S.
Via nuts@4wor.com

Like any moving part, an Eaton Detroit Locker can wear out over time. That said, we can’t say we’ve ever seen one that’s simply worn out due to age and mileage. We took your question to differential guru Chris Durham at Chris Durham Motorsports (cdmracing.com) and he had a couple of suggestions before you shell out the money for a new locker.

First and foremost, open up the locker and see if there’s anything broken or obviously wrong. Detroit carriers are a two-piece design and can be split by removing the retaining bolts opposite the ring gear. Be careful when splitting the case because the internal components are spring-loaded and can fly apart. It’s not enough pressure to really hurt anyone, but it’s enough to send parts flying. Use a press, a vise, or a buddy to maintain pressure on the case while you remove the bolts so it can be separated in a controlled fashion.

Once the case is split, make careful note of how things go together. In the middle of the locker is the clutch assembly, and you should examine all of the clutch components closely. Check the teeth for rounded edges and also closely inspect the disengagement cam, which is the piece in the inner and center portion of the clutch assembly. This is the piece that will often break from the shock load of a broken axleshaft. If there is something mechanically wrong with the locker, it should be pretty obvious.

If it all checks out, then most likely the preload springs are simply worn and need replacing. These springs control the amount of preload on the clutch assembly, and when they lose their tension or are too soft for the application, they can cause the clutch to disengage when it shouldn’t and create the problems you describe. These springs are often color-coded, so note any color you see. Also make a note of any numbers that are present on the case itself, as that can help them determine the spring needed as well as the age of the locker. A really good drivetrain shop can source replacement springs for you as well as other internal parts, but if you strike out locally then contact Eaton directly and Eaton should be able to steer you in the right direction.

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