My friend has a 2004 f150 4x4 that I am considering buying. It has a shudder in the rear end when starting into a turn from a stop. I have seen a few threads about this issue and see that it could possibly be fixed by adding some friction modifier; however, he has had the truck for several years and said he had the clutch pack replaced 2-3 years ago by the dealer and said it improved for a few months before starting back up again. How would this affect the thinking on this issue?

 

I once did see a 8.8 axle almost seem like a spool.....the rear end grease...HAD...friction modifier in it. You would go around a corner and skip the tire....bought the friction mod fluid.....within 3 turns it went smooth....IMOP....its not a myth.

 

Friction modifier will cause crazy symptoms if left out

 

for 8 bucks, I would try adding modifier in there. Worst case, youre out 8 bucks vs 1500 for a rear end.

 

Friction modifier fixed the rear end grumble on slow corners in my wife's 02 Explorer. I recommend using the Motorcraft friction modifier but that's just my recommendation.

 

This is true, change the fluid and add proper modifier.

 

I just bought a 2005 f150 5.4 4x4 with 125k and it runs great, but it shudders a little only when turning from a dead stop. Can I just add some friction modifier to the rear diff without flushing it?

 

IMO, it'd be a good idea to crack the can open.
It'll give you a good idea as to the condition of the rear end. Maybe it was flooded before or water got in. Maybe the gears are tearing themselves apart. I would open it and see. It's pretty easy, just time consuming. Just get some black RTV and make sure to clean both mating surfaces very well. Also clean out the part of the cover that comes off. Are you sure it's the rear-end shuddering? The power steering systems on these trucks is quite weak at regular idle.

 

I used this stuff (alone), website says
"Contains special additives to reduce chattering in limited-slip differentials"

https://www.valvoline.com/our-produc...hetic-gear-oil

LSD works great and I only get a quiet "wah-wah-wah-wah" sound when turning at slow speed in a parking lot.

 

thanks, but I don't have the time or space/tools to do that. I'm 90% sure it's the rear end.