Differentials and Wheel Bearings Tip

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Class A Motorhome Cartoon
This tip is courtesy of Jim Foreman

Let’s talk about rear ends. No, not those in tight jeans we like to admire but that big thing with four tires that holds up the back end of your RV. This comes from several years ago when I spent about $1500 to get the rear end on my Winnebago Minnie Winnie rebuilt. Just as we got to Clinton, Oklahoma headed west on I-40 I heard this screeching and grinding sound coming from the rear axle. I pulled into a Dodge dealer because that was the chassis under my rig. It didn’t take long for the mechanic to announce that the left wheel bearings on the rear end had failed. He also told me the closest place to get it repaired was a shop in Oklahoma City that did nothing but truck rear ends. After a couple phone calls, I was told that if I brought the whole rear axle to them the next morning, they could have me out by quitting time.

The dealer loaned me the shop truck to take it to the shop a hundred miles away. I was parked in front of their door when the opened the next morning. As he lifted the rear end assembly out of the pickup with a fork lift, he asked which side. I told him the left side and his reply was, “That figures.”

I went to a restaurant a block away where I had breakfast, drank coffee and read the newspaper until almost noon. He was washing his hands getting ready for noon when I returned so I offered to buy his lunch. While we were eating I asked him about his remark about the bad bearings being on the left side. He told me that 90% of all rear end failures on RVs were on the left. Then he explained why.

The wheel bearings on a rear end with a full floating axle are lubricated by rear end grease. Since the oil level is a couple inches lower than the end of the housing, oil has to migrates out along the axle shaft as it turns and into the bearings. RV owners are so concerned about keeping the refrigerator level that they avoid parking anywhere except where it’s level. Also, there is a crown on all roads to make rain drain away which keeps the right rear wheels an inch lower than the left. Also, any time they pull off the road, it’s almost always to the right where it leans even more to the right. This constant tilt to the right is just enough to keep oil from migrating out along the axle shaft and none of it ever gets to the bearings. They finally run dry and lock up.

Trucks and pickups are commonly parked leaning one way or the other and oil is always flowing out to the bearings so it’s not a problem for them. When a rear wheel bearing goes bad, it starts spinning the inside race on the extension of the rear end housing which destroys it. Part of the repair was to cut the end off the housing and weld a new one back on. This and replacing all the gears and bearings brought his bill to just under $1500 where a new one would have cost over $2500. Those were 1990s prices so are probably a lot higher now.

One should drive their motorhome to someplace where the right rear wheels are at least six inches higher than the left ones, let it set for a couple minutes and then tilt it the other way. A good time to do this is each time you change the engine oil. It can save you a very expensive repair. Mine had 30,000 miles on it when that happened which the mechanic was about the usual time when it happened.

Visit Jim Foreman’s website


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