Ok guys my truck started having a weird vibration about 2 months ago and I'm still trying to figure out what's causing it. At 40 and then again at 60 the whole truck starts vibrating or shaking slightly. But then if I speed up or slow down it goes away.

So far I've checked:
tie rods
U joints
Looked for bubbles on the tires

I'm gonna get the tire balance checked next weekend. And I'm gonna change the fluid in the diff. Any other ideas on how to narrow down what's causing this?

Dave

 

It's usually tires if you rule out the obvious stuff as you have done.
I just had the exact same thing happen.
No obvious signs.

 

Carrier bearings do wierd things when their rubbers fail.

 

Yeah I am with you on this William.. My Carrier Bearing rubber failed, and it felt like it was going to shake the truck apart. It also needed a bit of shimming to get the proper shaft alignment too! Double check those U-joints too!

 

Oh one other thing check the bearings for excess play!

 

By carrier bearing im assuming u mean for a 2 piece driveshaft? cuz i only have a single piece.

And what other bearings were u talking about?

 

That's right you have that stubby little truck The carrier bearing is on the two piece drive shafts. another thing to check is your transmission Mounts, if the rubber has failed, it will cause the alignment of the drive shaft to be off a bit. If it is a tire issue it is most likely a front tire, as most rears out of balance are rarely ever felt unless they are severely out of balance. just start by eliminating the easy ones first... then go from there... I had a vibration I couldn't pinpoint, and after changing U-joints recently it disappeared Although they didn't seem bad , one of them was starting to fail... I only felt it above 65 mph..

 

I agree that it is usually tires.

But if that doesn't fix it, check the driveline again. You cannot really check U-joints without removing the driveline. And sometimes the balance just goes sour for no apparent reason. That is when you take the whole shaft to a driveline shop and have it rebuilt and balanced.

You might be able to tell a problem with tires from a problem with running gear. If you can feel anything in the steering wheel, it is probably something in the front end, including front tires. If you feel it in the seat of your pants and the soles of your feet, it is probably running gear. But admittedly, often you just cannot tell by feel.

 

Ok I got the balance checked yesterday and it seems to have done the trick. Both tires were off by .75 ounces according to the guy. Not sure how much of an effect that could have had. Still gonna lube the u joints and check the fluid in the axle.

Speaking of which does anyone have any tricks for draining a ford 9"? There's no drain plug and no removable cover and I would like to be able to change the fluid without removing the third member

 

You need a suction gun. You can get one at any auto parts store. Stick the tube in the fill hole and suck as much fluid out as you can. Then refill.

If you got this service done at most lube shops, that is how they would do it, even if you had a removeable cover.

 

Ok that works. Now I just gotta hope for enough clearance behind the fill plug with the fuel cell being behind the axle

 

Shouldn't be a problem. This will be a flexible hose. I believe you can use the same tool to fill the unit that you used to suck it out. Not sure, because I've always dropped the cover. But I've seen the tool in the store. Cheap plastic thingie.

 

I think I might actually have one in the garage. I'll check in a bit. I have another project to wrap up before I lube the joints and change the fluid

 

Greased the U-joints and the steering today so we will see if the vibration is totally gone when i drive up to SB in a couple hours. Unfortunately spring break is over and spring quarter is about to begin