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biggman100

1994 Dakota strange vibration, especially at lower speed.

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Hi guys. On my 1994 dakota 3.9 5 speed, it recently developed the oddest vibration, but, only in the rear, and, is worse at lower speeds, such as 20MPH or less. The vibration is so bad, that with my 4x8 utility trailer, it actually made the trailer slide side to side while moving. I have had the wheels checked, as well as swapped tires around, with no change, so, the other day, i decided to lift the back completely off the ground, and, noticed that with it in gear, engine off, i can rotate either wheel, and they seem to spin fairly freely. I always thought that at least one wheel, most likely the right rear, since that is the first one to lose traction and spin in mud, wouldnt turn unless the transmission was in neutral, but they both do. I pulled the cover from the rear axle, and dont see any metal shaving, the ring and pinion look good, gear oil didnt smell bad, so i am beyond at a loss on this one.

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biggman100...If the wheels turn independently or one rotates rearward while the other goes forward, you have an open differential.  If both wheels spin together in the same direction (turning forward), you have a limited slip differential.

Friction plate Chrysler limited slip axles (Spicer Trac-Lok) require friction modifier to keep the plates from sticking together.  The friction modifier breaks down or often gets left out during fluid changes.  If the plates do stick together, you can have very unusual handling on hard surfaces and otherwise.  Usually, this is accompanied by jerkiness upon turning, especially tightly.  Rear axle only in 2WD mode, the vehicle will torque steer if the plates stick.

Determine whether you have Trac-Lok limited slip that requires friction modifier.  If you do, Mopar and others offer the friction modifier.  On our Liberty, which we bought new in 2002, the OE friction modifier broke down around 30K miles.  I added the usual amount required during a fresh fill, mixed with gear lube.  The notchy handling and jerkiness disappeared.

Moses

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Moses, it is an open diff, and, as much as it pains me to say it, this is one time i wasn't thinking, and overlooked something important. Both rear wheels were off the ground, and, as i turned one one way, the other would turn the opposite direction, as they are supposed to. Today, after rethinking it, i jacked up one side, left the other side on the ground, and the wheel wouldn't turn unless it is in neutral, with the same result when i checked the other side, just as it is supposed to. However, i may have solved this one. I wont know for a few days though. As i was messing with some other stuff on it, i happened to notice that the right rear brake drum is missing a chunk about 2 inches long, maybe a quarter inch wide, at the edge of the brake drum where it rides over the backing plate (what i call the inside edge). I think the reason i didn't catch it before is that the missing piece of the drum was pointing towards the ground, and, since i wasn't thinking it could be related to a brake drum, never once looked at them as i was rotating and messing with the wheels and tires. I took both brake drums off, and found that the one is so rotted along the back edge (the edge closest to the inside of the axle), that i could actually break small pieces off with very light pressure, so, before i go any further with it, i am going to replace the drums, and see if that fixes the issue. It may not be for a few weeks though, as i have another vehicle that has been sitting that needs some road time to determine all its bugs and issues before winter, and, as that has been sitting without moving for almost 5 months now, and needs to be figured out by late august at the latest, i'm going to be driving that daily for at least the next month.

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I finally got back to this, and even after replacing the rear drums, still didn't fix the issue. However, thanks to my youngest, the issue has now been resolved. One day, while we were outside, i went to get something out of the truck, and, she says, daddy, that tire looks funny. I happen to look to see what she was looking at, and, sure enough, the front tire had not only a bulge in it, but very obvious signs of a broken belt, since the tread pattern didn't go straight anymore (I have taught my children from a young age little things to look for on vehicles, hoping that, as they become drivers, those are things they will remember, tires being one of the things i taught them about, lights are another. Since my brothers shop does tires, i use the bad ones he replaces as training tools). All this time, since i never once felt a vibration in the steering wheel, i concentrated on the rear end of the truck. However, the wheel she was looking at was the left front, so, the lesson i learned is, don't ever assume anything, since you could just be wrong. After the way this summer has been, i have had many D'UH moments, but, this one by far is my biggest one. One bit of clarification here though, when i said i swapped tires around, what i actually did is replaced one rear tire with the spare, then, when the vibration didn't go away, swapped the other rear tire with the spare. I was so convinced it was something in the rear, i never thought to even look at the front.

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It's often easy to overlook the easiest or most obvious...We're supposed to start with basics and not borrow the big troubles!

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Moses, i know, but, sometimes, i tend to overlook the obvious. I think it is a flaw that develops over time if you do something enough times.

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