This morning, on my way to work I had my back glass slid open and while at hwy speeds I heard my differential whirling. I know that it wasn't my tires, in fact, I have pizza cutter tires on it. what could be wrong? I checked the fluid and its full.

another prblem I had was it was shifting too high and then acting like it wouldn't downshift therefore causing the truck to bogg down, could these two problems be related to each other?

Its on a 89 f150 4x4.

 

Have you checked for slack at the rear shafts for bearing wear?? I assume this is a automatic- if so check for vacuum leaks from intake to transmission module. I also had a undetermined sound, I thought it was the drive shaft but turned out to be a wheel bearing on the rear passenger side, had to replace.

 

I don't know how to check for that but I don't htink it would be a barring in the wheel because it only whirls when I have the gas pedal depressed. When I let off its not even a spit second and the sound is gone. But when I give it a little gas its back again.

 

Possibly could be the ring and pinion/bearings in the pumpkin. You would have to get both tires off the ground to where you can turn the shafts and see if thier is any slak at the wheels and then check where the drive shaft mounts, of corse dropping the shaft from the rear would give you better feeling for slack/play in the pinion bearings. And also this will let you turn the everything without anydrag from the transmission. OR you could get both tires off the ground by way of jackstands/cynder blocks something strong enough to hold the weight, scotch the front tires in both directions FIRST, then start and put in drive and find out where the sounds are accually comming from, just have someone else help you if you do this cus you need a little drag on the rear wheels so the other person applys enough pressure on the brakes to act like its going down the road. If you do this just long enough to figure out where the sounds are comming from it wont hurt yer brakes at all. I've done this to figure out a few drive line problems.

On a personal note, A week ago I replaced the rear in the truck that I fixed the wheel bearing on, the pinion bearings where bad and vibrating the truck bad, couldn't figure it out till I done the mention above. Steve

 

If it is whirling like you say:goes away when your foot is off the gas, louder at higher speeds -- it is the bearings in the rear end as mentioned in the previous post.

I can confirm this because I had the exact same symptoms and I had them replaced and the whirling was gone.

 

are these baearings in the rear end pretty simple to change?

 

bearings in the rear end or the one on the drive train going into the rear end or pumpkin?

 

Where you wheel mounts, thats the wheel bearing. And it can be hard or easy, depends on yourself. The hardest part is if the bearing retaining ring will come off for you without having to cut it off, like I had to with a cutting torch. Easiest part is putting it back together, all in all. took me a few-2hrs to 2 1/2 because you have to take the brake shoes and all the hardware out to get to the shaft's mounting bolts/nuts.