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RWD rear end vibration

I have a 2004 f150 RWD with only 40k miles on it that I just bought 6 months ago. I also has a posi rear end. I had to immediately put new tires on it as the originals were weathered badly. Soon afterwards, I began feeling a very slight vibration that I almost thought was my imagination. It only occurs when accelerating from a stand still and turning. The vibration has become more distinguishable since and seems to be getting worse though it could be my paranoia. A friend recommended that I change the rear differential fluid. He’s a mechanic. I’m far from it, so he did for me as a favor. He said everything looked tip top in the differential but the vibration continues. Any thoughts? Could this be bad tires?

It could very well be bad tires. Possibly one is defective or has become unbalanced from a lost wheel weight. You might try rotating the tires front to back to see if the vibration follows. If it does, have tires from the vibrating end re-balanced. Have them checked before the tech takes off the weights so you know for sure if a wheel was out of balance. If they are in balance, the is a machine that can test road force variation (usually at luxury car dealerships or tire stores that service high-end cars) to determine if the force variation is causing a vibration.

If the vibration stays at the rear, that is the place to look for a failing driveshaft U-joint or driveshaft center bearing support. Since your friend said the differential is OK, I will rule out pinion bearings. If it is pinion bearings, the vibration (and some noise) will get much worse fairly quickly.

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Thanks for the input mustangman. Much appreciated

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Technical service bulletins (TSBs) are published by vehicle manufacturers to help their technicians diagnose and remedy certain recurring complaints with specific vehicles. They often help mechanics figure out tough to figure out situations.

Download 2 TSBs that could possibly shine some light on this. Have a look at them, or better yet, have your mechanic friend have a look and see if he thinks either is a possibility.

One TSB is for low speed driveline vibration (Ford TSB # 06-4-4) and the other highway speed driveline vibration (Ford TSB # 07-10-9).

The low speed bulletin is for F-150s with Limited Slip.

The high speed bulletin is more a front-end vibration.

Good day,

Because you feel the vibration on acceleration, it is likely this is NOT tires. A tire vibration would be there pretty much all the time. It’s probably a U joint.

Try rotating the tires front to rear. The vibration should move. If it doesn’t, it isn’t tires.

Since you just purchased the tires I would just go back to the dealer and have them balanced again. It would be nice to know where the vibration comes from, front or rear. If you have the time and energy you could switch the fronts to the back and see if you can narrow down what makes the vibration.

My guess is either tires or a U-joint. Granted, the truck has low miles but the grease in the U-joints is about 14 years old.

For what it’s worth, I recently bought a set of tires for my Lincoln. The car vibrated very slightly. I took it back and had them rebalanced. It still vibrated slightly.

So I grudgingly took the tires off at home and balanced them all on my antique bubble balancer. All 4 showed to be off a bit and the issue is now resolved in a very low tech manner.
I’m not saying that you should go hunting for someone with a bubble balancer; only that it worked and has worked in the past for me.

It’s not that the bubble balancer is more effective/accurate than the balancer the shop used

It’s that you had the patience to do the job correctly

I’ve mentioned on this website, several times already, that there are a LOT of guys that THINK they know how to balance rims properly. But I watch them, and I drive the vehicles afterwards. And they’re doing it all wrong. There are many reasons why they’re doing it wrong, but the end result is the same


Thanks guys. Took it in to have the tires balanced and rotated but to no avail. Did a little looking around and sounds like that round of f150’s are famous for clutch packs wearing out quick. Sometimes as early as 20k miles. Also found that the differential additive my buddy put in often takes many miles to work it’s way in to stop the chattering. Sometimes up to 400 miles. Soooo, I’ll keep driving and see if it can do its magic. Right now I’ve put 200 miles on it since the fluid was replaced. I’ll keep this up to date.

I had that on my Ford truck (much older than yours, ford 9 incher rear limited slip) and I replaced the differential clutch packs, which helped. Didn’t entirely solve it tho. Actually the problem I was having then wasn’t a vibration, but a clunk when accelerating. With only 40K miles, I’d tend to discount the clutch packs as the problem on your f150. Posters above offer some good suggestions. I’d focus on these

  • Prop shaft center carrier bearing may need adjusting or replacing (if used)
  • Any play in any of the prop shaft u-joints, replace the u-joint, very common cause of vibrations
  • Replace diff fluid and when re-filling, make sure to add the special ford stuff they spec for your diff & correct amount
  • This is what I actually guess is the cause, if you have a two piece prop shaft, splined in between: That joint may need a proper lube with synthetic grease. Take a look here. Best of luck.

Did you read that Ford Clutch Pack TSB (link) I posted a couple of days ago (above) ?

I have a hard timing understand how diff clutch packs would cause a vibrations just going straight down the road. They don’t do anything when going straight, only when turning. And if the friction surface wore out, I wouldn’t guess that would cause a driveline vibration, the symptom for that would be it no longer worked as a limited slip or posi-track rear end. But it would still work as a normal differential. I guess a vibration might occur if the clutch packs completely disintegrated tho, and shards of metal were strewn around inside the third member’s bearings and gears.

That could be limited-slip differential chatter, tires would vibrate a slow speeds. An experienced technician should be able to recognize limited-slip chatter.