I have a 2006 F150 Lariat Supercrew that I brought brand new off the lot 9 years ago. I only have 72K miles on it, and it never gave me a lick of trouble just like all my previous Fords that was until recently.

The biggest most irritating issue is that when I'm at a dead stop and I take off turning either right or left from a stop sign my truck feels like the rear end is slipping and it kind of "stutters" the truck. Once I'm done the turn it's OK. A former co-worker of mine has the same issue with his '06 F150 Supercrew, but he has 340K miles on his. I'm just shocked and little disgusted because the truck isn't used too often and never anything that casual driving. Any clues on what this issue could be? Some times its a heavy shaking and other times its mild, but its always there and it's needs to be fixed, but I don't know where to start.

Secondly, my truck bucks sometimes when accelerating from a dead stop. Not when switching gears but during a normal take off it'll buck before it switches gears. The odd thing is that if I gun it then it won't buck, but it's another issue that has developed lately. I didn't know if this was related to my rear end issue or not, but hopefully someone out there has experienced the same issue(s) and can possibly tell me what it is so it can be fixed.

Also recently I noticed I had to hammer it to move past someone and the truck started misfiring. If I gradually increase speed it'll run fine, but if I hammer it then it'll misfire then smooth out. I was thinking this might be a clogged injector rather than a tune up. Am I right?

Thanks for listening.

 

Your rear end issue is related to your clutch packs. Easiest fix is to top of the diff. with friction modifier. That normally takes care of the problem. At 72K, if you haven't had the diff. fluid changed, go ahead and do that. I recommend Royal Purple with the modifier already in it. I always add an additional 7 ounces of friction modifier.

As for your engine bucking. Sounds like COP's to me.

Good luck.

 

Thanks for the heads up about the rear end. I just watched a You Tube video on that last night, and it seems easy enough. Do you know off hand how much rear end oil I need?

What's a COP? I've never heard that term before.

Thanks for replying, because I'm at my wits end.

 

COP= "Coil on Plug" Probably wouldn't hurt to do the plugs while you're at it.

 

If you have a limited slip differential in the rear of your truck, it probably has a service interval on the fluid change. Make sure you get limited slip rated oil and also add the Ford LS additive. When I had LS in the past I would change it every two years or 30,000 miles.

 

I went ahead and got under my truck today to replace the rear end oil, and when I went to check the fill plug to make sure I can remove if before I start the job I noticed this:






I see it's been leaking, and slinging oil onto my fuel tank. This may be a stupid question, but do you think this is the source of my problem? I stuck my finger in the fill hole, and I didn't feel anything so I added some oil just to see how low it was, and it only took a little bit before it started overflowing. So now I'm really at a loss. Any idea of what I should do? Thanks for listening.

 

Your pinion seal is "done". Have it replaced by someone that is qualified to do so. Improper torque of the pinion nut will cause noise and premature wear of the ring gear.

 

No, the leak has nothing to do with the limited-slip differential chattering on turns. You may as well let somebody do both jobs now that you have found the pinion seal leak.

 

Rear gears can't slip, what you feel is simply best described as "clutch chatter" as the limited slip clutch discs slip along against each other in a no load situation. Loading them (hit gas WOT) will lock them, but spin the inside rear wheel on those turns which wears tires.

When new, they have new lube with new additive, and they slip "smoothly" so you don't feel it. The lube and additive prevents their wearing out. Yours has 72,000 mile old gear lube and friction additive so they "chatter" like finger nails on a chalk board without the screech.

First thing I'd do is check my gear lube level in there.
If really low, I'd R&R that pinion seal.
If not much low, then I'd just use my hand evacuation pump and pull the fluid out until I couldn't get more out, then put in friction modifier additive and top it up to fill plug with recommended gear lube for now and monitor it.
I say that's what I'd do as your seal leak evidence looks like long time fine seepage to me but it might look different first hand and up close in person.

Something else that may explain it is a factory overfill. In 2013 "Wife Unit" spied what turned out to be a '08 Mustang GT 5 spd with very low miles she (and I) liked. We took a drive in it, I looked it over, and saw that it was a well maintained car .... and while I did give it a good looking over, I never put it up on a lift. I get it home and first oil change after a short drive I find a couple drops of gear lube hanging under the rear center on the snout. I then removed the fill plug to check rear lube, it started coming out the fill hole so it had more than enough and there was a short "woosh" sound. It too had some on the chassis and floor pan.

I could not change the seal then that day so I watched it and every so often would back it up on ramps to check and it was always full, but still there'd be drops hanging. I could wipe the drops off (wrag with 2+2) and it'd stay dry until next drive. No leaks just moving car short distances, only after drives long enough to heat it up.

So I pulled the axle vent (in the cap is a short weak spring with disc valve that opens after a slight pressure build up but stays closed otherwise like if in a "creek car wash", etc .... but on the Mustang the "rattle cap" as I call it was crimped on tight enough that there was not much "rattle" room so I thought maybe the spring was just "preloaded" more than was healthy.) ... and I fabbed a fitting for a hose and ran the hose up to a loop on frame and then back downwards into a frame member and no spring loaded vent.

This is how my '77 rear axle vent is, it just goes way higher in a 4x4 to top of hose and ever since when I am under there changing oil or whatever, no more drops of gear lube and stuff stays clean. The "loop" is really just a high "U" turn to create and air lock against water. I have a seal for it and if ever I see any signs of seepage again and there's no stoppage in that hose, I'll replace it then.

 

Good detective work on that diff vent. Most people don't even know there is one. I used to have a Cherokee and both front and rear vents were right there on the firewall when you raise the hood.