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Nuts & Bolts: Leaky Axle

Posted in How To: Tech Qa on March 15, 2019
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I have a 1997 Ford F-250 4x4. We put new solid-axle Dana 60s in it front and back with 4.10 gears. The rear axle is a full-floater, and the axle seal keeps failing. They’ll hold for about a week and then go out. We’ve tried everything and run out of ideas. Do you have any tricks to get them to seal up?

Bryan A.

It can be tricky to get full-floating axleshafts to seal to the wheel hubs. We assume the seal between the shaft and the hub is what you’re talking about, and not the seal between the wheel hub and the spindle. The latter issue is usually due to a groove on the sealing surface of the spindle, which is there to allow gear oil to seep beyond the seal and/or waster wheel bearings.

There are several things to getting a full-floating axleshaft to seal. First, the sealing surfaces must be 100 percent clean and dry with no oil anywhere, even the bolt holes. This can be a challenge when the seal has been leaking. Jack up the leaky side a few inches so the oil runs downhill, away from the sealing surfaces. Hose everything down with brake cleaner, and use compressed air to blow out all the bolt holes. Often (but not always) there are metal or plastic gaskets from the factory, so make sure they’re in good shape or obtain replacements if they’re not. Use a quality RTV or silicone sealant Use new lock washers if present. Add some red Loctite, and torque the bolts to spec in a crisscross pattern like you would do for wheel lugs. If possible, leave the end jacked up for a while so the sealant has a chance to set up. Run the truck around the block a few times, then recheck the torque on the axleshaft bolts.

If you’ve done all of that and it’s still leaking, something could be out of true. Make sure the wheel hub bearings are tight and the wheel hub isn’t wobbling. Take a wide, flat file and dress the sealing surfaces of both the wheel hub and the axleshaft to ensure that they’re flat. It might be worth checking to see if the axleshaft is bent. If both sides are leaking persistently, it’s possible that the housing could be bent. Many of the leaking axleshafts we’ve had are due to the bolts perpetually loosening up, particularly if the axle has a spool or is welded. Sometimes this can be solved by swapping the bolts for studs and nuts with aggressive lock washers, and we’ve even seen people safety-wire them.

One of these things or a combination of a few of them should get your axle to stay sealed up, or at least lead you to the cause of why the seals are failing.

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