strtbobber

2008 F-150 with 5.4 engine.

Once in a while, when turning a corner from nearly a dead stop, the diff makes a shudder sound/feeling. It's also happened when pulling my boat. Best way I can think of describing it is, it feels and sounds like when you have a full posi rear end and you make a u-turn. That sort of "one tire spinning, one tire not spinning" sound and feeling.

The whole drive train is quiet on the highway.

I have had the diff oil and additive changed. We are leaving on about a 2000 mile trip in three weeks. I'd like to know if I should feel ok heading out on this trip, or do I need to have this thing looked at? Any advice is appreciated! Thank you!

04 Lucho

I have the same problem, it's in the differential. Do you have limit slip? If so did you put the friction modifier. Mines comes and goes, after a long trip it will go away for a while.

strtbobber

Not sure if I have limited slip or posi. How can I determine which I have?

And, yes they put the friction modifier in. I called it "additive" in my original post.

So, are you telling me that going on the long trip should be fine, in your opinion?

Nocturnal1

Several Methods:

1) Info on Vehicle Sticker (on the door jam of your truck) & confirm with tag on differential cover (Axle Tag)

http://www.fordf150.net/howto/decode.php

2) VIN code lookup http://www.etis.ford.com/vehicleRegS...214FE.fcvas502


You can conduct an internet search for "Ford or F-150 axle codes" or "Ford or F-150 vehicle sticker" if you require more info.

Rick's 06

Sounds like you've got a limited slip if the additive was included with the lube change. Look it up for sure and then you'll know. You didn't mention how many miles are on the truck. If you've got a lot of miles it's always possible your clutch packs are on their way out which means you'll need some service at some point to replace them. If I were you, I'd add a little more friction modifier to see if that helps with the shudder. I tried royal purple gear oil and didn't add the FM and I had the shudder. After I added some FM my shudder went away. Like many have said, even if the lube says it's included, you still need to add more.

strtbobber

Thank you for the valuable info!
Yeah, sorry I should have mentioned the miles. It has about 145,00kms or 90,000 miles.

Is it a major/expensive job to get the clutch packs replaced?

How much FM modifier should I add? And do I need to remove an equal amount of oil from the diff first?

PerryB

Most likely you'll have to replace the clutch packs in the diff. to make the problem go away. Thats what I had to do.

Millinex

Mine does the exact same thing with my 3.73 LS. You can try changing the oil and adding 8oz-16oz of friction modifier (I've heard both numbers), in case there just wasn't enough, or you can look at doing the clutch packs. They aren't very expensive or complex to do from the looks of it.

I took mine 1400 miles to Oregon, and then 1400 miles back, and it gave me zero problems. Every once and a while it's kinda annoying, but it certainly didn't ever worry me.

strtbobber

Well, that makes me feel better. Mine is 3.55 LS. I think I'll put a bit more FM in the diff and relax on our trip. Thanks for the reply!!

Toshbar

I changed my fluid with Valvoline synthetic, which said it already had FM in it. Still got the shudder. Added 6 oz of FM and all is well. Jacked up the driver side of the truck so I could add the fluid.