Hi guys
got a 2005 F150 FX4 and I just replaced the whole rear end. It works great but when I switch to 4x4 it starts shaking like crazy on the road , cannot even drive it. It is almost like the rear is braking while the front is pulling. Now I just said that I replaced the whole rear end, I made sure I got the same gear ratio as in specs and what it was before . I was just wondering before I take the transfer case off and put another one in , maybe somebody can give me some ideas about what could cause this.

Crazy thing is even after I take it off 4x4 into 2HI it still acts up a little bit, after like 5 minutes is gone back to normal in rear wheel drive.
So far I tried removing the front drive shaft and it looks fine no bents or anything.

again I really appreciate any input .
Thanks
Al

 

it really sounds like you have the wrong gear ratio in that diff.

 

My thoughts exactly.

 

id have to say X3 on the wroung ratio

 

That happened to me, I did the same change and the rear end was with 3.05 and the front was 3.55... so I think you need to double check the gear ratio

 

Well

Based on what you guys said I went back to whomever sold me the axle shaft and I was told to take it back to them because it is a positive traction problem.

What exactly is that.

 

Posi-Trac is GM's term for a limited slip differential. Ford calls it's version Traction-Lock or just plain Limited Slip. It basically delivers some power to both wheels as opposed to a standard "open" differential that only sends power to one wheel - usually the one with the least traction.

I would say your problem is NOT a LS issue since it only happens when you engage 4 wheel drive. The limited slip comes into play automatically and only when you need it. Sounds like you bought this bad boy from an idiot.

 

As a little explanation, here's what's most likely going on. Let's say your truck came from the factory with a 3.55 gear ratio rear end. That would mean that it also has a 3.55 ratio ring and pinion in the front axle. So, for every 3.55 times the drive shaft (shafts in 4x4) spin, the wheel spins once.

Let's say your idiot sold you a 3.08 ratio rear axle. That would be fine as long as you were in 2 wheel drive. As soon as you drop it into 4x4, the driveshafts (front and rear) are spinning at the exact same rate. But, one axle is trying to spin the tires 3.55 times for every driveshaft revolution and the other is trying to spin 3.08 times. So, one axle is fighting the other. That's not a limited slip issue.

 

First thanks for your input

Well I took the part back and they are supposed to open the dif and check make sure that it's got the right gears for me.
I'll let you know what they say.
Again thanks for the input

 

Also sounds to me like incorrect gear ratio. Good luck with it, hope they do you right and get it fixed.

 

al78,
this problem can also be caused if you didn't mark the correct possition on the drive shaft when you removed it. A drive shaft out of position will produce terrible vibrations making you think it is dragging the break. The drive shafts on trucks must be balanced and they come from the factory with the optimum position with relation to the rear end gear spline. If the truck isn't releasing the back breaks you will notice a burning smell and there can be no mistake, you should also have a ABS warning light if this is the case. Also, are you sure this is a rear end problem and not an engine malfunction? My buddy had a 98 F150 XLT and when the coil pack started to go it felt like the transmission was going to fall out at anytime. The truck jerked and shook as you drove until a certian speed. Let me know how it goes.......

 

Hi guys

Thanks for all the advice everybody, it was an incorect gear ratio.
I got this axle from Michigan Truck Parts, they were very fair to admit that it might have been a mistake so I had to take it down and they exchanged it with the one that has the right gear ratio,

the only problem I had with this company, I gave them the axle full of syntethic oil, it cost me $20 a quart and they gave it back empty, they did offer me regular ear oil though but I went and bought syntethic again, that's the way to go

I put the new axle up and it works good this time, BUT, there is a but
in 4x4 hi when I turn the wheels all the way left or right somethig doesn't fell right, again, like a wheel, in the front is breaking. Mabe I broke something in the front, because not knowing about the problem with the 4x4, I went on the sand dunes with the truck. I had traction but there was a strange sound from the front just like 2 metals banging.

 

Not saying you dont have a problem there.... But its never a good idea to turn the wheels all the way one way or the other in 4wd

 

Go down to the '04-'08 forum and do a search for IWE problems. TNF150 has posted up some pdf files on trobleshooting the Ford 4x4 system. They should help you find and fix whatever problems you might have.