Help! 1999 high speed rear end issue

[Indytona675]

Hi all I just bought a 1999 127k miles. On the highway at 50mpha or higher I will get a terrible rubbing type noise and heavy drag. The back end will wobble shaking the whole truck. As I pull over and slow im pretty sure the rear tires are locking up one side then the other. At about 30mph it will go back to normal. I have gotten a small shudder coming to a stop and when just starring to move again a couple times. When on the highway and it starts to act up I feel nothing in the break pedal and putting it in neutral clues not change it at all. Im wondering about LS issue. Im going to pull rear diff cover to inspect then fill with proper fluid + LS additive.
Anyone on here have any ideas? Im guessing rear is shot and im screwed. The small lot I got it off of took it to Goodyear and they replaced both front cv axels torsos on passenger side, idler arm, and sway bar links. Didn't fix it cause its in back. Dealer wont do more. Its up to me. I do 99% my own work and have worked as full mechanic in the past but I have little experience with ls.

 

[K5rnt]

Rear driveline could be outta time. Had that problem on my f150 one time changed the u joints and when I put the shaft back in I bolted the flang back to the rear end 90% out. Made the whole truck shake like hell.

 

[Indytona675]

Most likely the rear drive shaft. Im as certain as I can be without having a lift. Couldn't find a matching drive shaft at the junk yard. It was my cheapest option. They were all to short. I guess I have the long expedition. Now im looking at u-joints and balance. I changed the diff fluid. Everything looked ok in the rear end. Im about out of cash after buying the thing so hopefully it wont cost to much.

 

[K5rnt]

Is the truck 4wd?

 

[K5rnt]

Never mind I see where you had the front cv shafts changed. Check your tire sizes. The 99 up 1st gens are awd if you tires are bigger in the front than the rear the computer thinks the rear tires are slipping as they are spinning faster. Your awd is probably engaging.
There are 2 ways to fix this problem

1: buy new tires

2: brown wire mod

 

[K5rnt]

Pull fuse 104 under the hood. That is the fuse for the transfer case. Pull it and see if the problem goes away.

 

[Indytona675]

K5rnt you are my HERO!
Pulled fuse 104 and no more issue! Tires are a little uneven front to back. I will plug it in again when I get tires. You just saved me some $$$ Than you Thank you Thank you!

 

[K5rnt]

You can also do the "brown wire mod". That will disable the awd system completely but still allow you to have 4hi and 4lo.