I have a vibration that has been slowly building that I need some help finding. It occurs the most when driving around 40 and up with a light load. It feels like it's coming from the rear, at least I don't feel it in the steering wheel at all. I've also noticed if I let off the gas, I'll feel if for a couple seconds and then it goes away and everything is smooth.

Not sure if this is related, but I've noticed a couple times that the tranny couldn't decide which gear it wanted to be. This has only happened a couple times over the last couple months.

Tires have been rotated and balanced twice since this has started - no difference. I pull a couple qts of tranny juice from the stick 2 times a year and replace the filter every other year. Fluid looks and smells good. Rear end was rebuilt about a year ago, and was fine for 5-6 months before this vibration started. I did add some friction modifier a while back because the limited slip was being a lil to limiting. I can't remember how close that was to the start of the vibration, but it did fix the catching when accelerating through a turn.

'00 5.4 ext. cab. 4r70

Any ideas?

 

I had a similar issue on my 02. When I replaced my shocks, it seemed to go away.
How old are your shocks?

If you have a 4x4, when was the last time you changed the transfer case fluid?

On another truck of mine (chevy), the rear transmission bushing wore out. I had to remove the tailshaft housing and replace the bushing and seal.

Just a couple of things to think about.

 

I have an 04 fxr 5.4 and it has been in the shop 3 times for the rear end. The last 2 times was for viberations in the rear end taking off or while towing my camper. They had to replace the pumpkin. Then I was back in 1000 miles later for same feeling. This time it was the drive shaft where it goes into the tranfer case. dunno what yours is but thats what mine was

 

Thanks guys,

The shocks aren't all that old, so I should be ok there. I didn't mention it in the first post, but it feels like a rotational vibration.

How did you know the rear tranny bushing was bad? Did the drive shaft have some play in it?

I hate to admit it, but it's been a good while since I have changed the transfer case fluid. Whether that's the problem or not, thanks... I need to change that.

 

Something else to check is U-joints. That can give a vibration like you describe.

 

Well... changed the transfer case fluid. Can't say it helped the vibration any, but it was prolly good to get done regardless.

I changed out the u-joints today. I also greased up the output shaft before reinstalling the drive shaft. The vibration is much better, but not quite gone completely. One thing I noticed, is some of the tranny fluid i put in the transfer case was on the output shaft and it was slowly dripping from the opening where the drive shaft goes in. Should there have been any of this fluid in there? I have no idea what's going on inside there, but it seems like if I need to keep grease on the output shaft there shouldn't be any other fluid in there.

 

make sure your E brake is completely releasing itself inside the rotor/drum in the rear. It might be on just slightly, or not releasing all the way back.
-Patrick

 

How about tire balance? That was my problem once and that cured it.

 

The e-brake has been pretty much useless for about a year. I don't know if I messed something up pounding the rear disks off last year or what, but I haven't been able to dial it back in since then.

I've balanced all 4 tires twice now, and haven't noticed a difference either time.

Changing the U-joints and greasing the output shaft helped a lot, but there is still a lil bit of a vibration left. I'm thinking of slapping a lil more grease on the output shaft and see what that does. Maybe the glob I put on didn't spread out enough.

 

You could put the rear axle on heavy duty jack stands (on cement) and run it at 40 mph in 2 wheel drive. If it vibrates take off tires, put lug nuts back on and see. Be careful and don't aim it at the garage door Both rear wheels off the ground.