'99 F-150 4.6 4X4 Lariat.

It's getting worse every day. At first I thought it was my tires, but have since realized it is not. I get a shuttle that feels like rumble strips on a take off, but mostly only when I am turning right or left. It does not seem to happen if I take off straight ahead. If it is, I don't feel it. It does seem to be worse starting uphill and to the right. I also notice a tight feeling when turning hard like pulling into a parking space left or backing up. While backing up I almost feel a grind feeling like it is stuck in 4 wheel drive or something bound up. I had a buddy watch my front axels as I inched up and they are turning, but I am not sure if they are supposed to be turning all the time even in 2 wheel drive? Should they always turn even in 2 wheel drive on '99 ?

Help

 

The limited slip clutches in the rear axle are probably chattering. You do have a locking rear axle, right? If so, there's a couple things you can do.

The official fix is to replace the clutch packs with revised clutches. The fix I'd recommend before going into the differential would be to add a bottle of friction modifier to the differential and drive it for a few days before doing anything else. In addition, if it's been a while (say, 100K+ miles) since the differential has been serviced, even though it may take the high dollar synthetic 75W140 fluid, it wouldn't hurt to change the fluid and add friction modifier. Either would be easier and cheaper than replacing the clutch packs, and either just may fix your problem.

 

Not sure on the locking part, but what you say makes perfect sense to me. I will give it a try. I'll let you know how it works out.

Thanks a ton.

 

The tag on your rear diff will have the ratio on it, either 3.55 or 3.73. If it's limited slip, it'll say 3L55 or 3L73.

 

Hey Quintin,
Thanks for the help so far. I am a little confused. Will I have the clutch packs in a locking rear axle or a limited slip differential rear axel "or" are they the same thing with different names?
I want to be sure before I put the friction modifier in. Also is that all I ask for at the parts place (friction modifier)?
thanks again,
Hal

 

Generally speaking, "locking" and "limited slip" terms are used interchangably. Different manufacturers have different ways of providing limited slip, but Ford uses spring loaded clutch packs.

And yup, all you need to ask for is friction modifier, comes in a little bottle, smells like skunk oil. Unbolting the ABS sensor and dumping it in through there is the easiest way to get it into the axle.

 

thanks, I'l get a bottle this week and give it a try.