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Slight shudder on take off with light to moderate acceleration

18K views 14 replies 8 participants last post by  Soledad 
#1 ·
Sorry for the newb post but I've been noticing a slight shudder from the rear of the truck when taking off from a dead stop. I haven't really stomped on it yet so it's always been during light to moderate acceleration. I'm pretty sure if I take off in a straight line there's no shudder but I want to test that a few more times to be 100% sure. However, I'm absolutely sure that when I make a left or right turn it definitely does it.

The truck was purchased used last week and is an '06 XLT/FX4 SuperCab longbed with 91k miles on it so far and is bone stock and no tunes (yet). I checked and it has a two piece driveshaft. If I were to guess I would think it's the rear diff (3.73 LS (axle code 3L)) since it always seems to happen when making a turn and accelerating. If it's the center bearing causing the shudder then I'm not sure I understand how it could cause that. I guess once it warms up outside again I'll get out there under it and see if those drive shafts have any play in them.

I was going to change out the rear diff oil to see if that helps but wasn't sure if I should add a friction modifier to it or not. Does the LS diffs in these trucks require a friction modifier? My old '97 Dakota required it just not sure if the F350 with LS does.

What's funny is that I test drove a used F250 and two other used F350's and they all had that rear shudder. I must have subconsciously ignored it when I test drove my '06 because I was so smitten with it. :D
 
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#7 ·
So, last weekend I found that there was some play in my slip joint. With the tires in the air and the transmission in neutral I could rock the two pieces about maybe an 1/8" of less. So I took it apart and lubed it up good. Put it all back together and tried to rock them again and couldn't do it. It was solid now.

I took it out for a long test drive and no joy. I'm still getting some bad shudder.

Next on the list is to drain and refill the rear LS axle. If that doesn't do it then I'll cut some spacers to space the center bearing. If that doesn't stop the shudder then, well, I'm not sure what else to try other than maybe finding a GoPro and seeing exactly what my axle is doing.
 
#3 ·
Two piece driveline, the rubber donut carrier in the middle, that's your shudder. I've had 4 superduties. On number 1 & 2 I played with shims and delt with the problem for years. On truck 3 & 4 I went with custom drivelines on day one. A one piece rear fixes all. Unless your lifted it shouldn't be an issue. Got lift I assume?
 
#4 ·
Actually no lift what so ever. She's bone stock. Well other than how ever much the FX4 feature lifts it. Hmm....does it being an FX4 mean it's lifted slightly? I do want to lift it eventually (about 4").
 
#6 ·
Thanks for the help! I'll get under there when it gets warmer out and lube it up and check to see if it has any play.
 
#8 ·
Ok, I wanted to update this because I'm really, really surprised.

Soooo, I had greased up the slip-joint on the driveshaft and changed out the gear oil and friction modifier in the rear axle. But, it didn't change anything. And I never did make some spacers for the center bearing. I've been driving it for the past couple of thousand miles and just dealing with the rear-end shudder which never got progressively better or worse.

Fast forward to Sept-15 where I installed Matt's SRL tune on my truck and have been having fun with it. For the past few days I've noticed I have zero shudder now no matter how hard I try to get it to do it when making a hard right or left turn from a complete stop. And this high frequency vibration that I would get at about 70mph is gone too.

I think it might have been the tune that did the trick and here's why I say that; Someone had mentioned that it might be a rusted u-joint causing the problem. I had no clanking, no clunking, no play or slop, no nothing like that when shifting from R to D and when testing the driveshaft with the truck in neutral. There was no big outward indication that a u-joint was bad. But, when I first installed the SRL tune the truck was shifting pretty hard and I think it was that hard shifting that maybe free'd up a potentially rusted u-joint. It's my best guess. Or, looking at a worse case scenario, there is a problem with the trans and the increased shift pressures are masking the problem. Going back to the stock tune should show whether that is true or not and I plan on doing this soon so I can update my SCT and try out his 8K Tow Tune.

What do ya think?
 
#13 ·
Did you happen to check the rubber bushing that surrounds the center bearing. Lubing up a torn center bearing will not do much good for the rubber part supporting the bearing as it spins. Once it has sheared, you will get the shudder you describe.
 
#9 ·
I had similar shutter that you described. Only when I turned from a stop or entering a slow turn and accelerating. I know you said you already changed your rear dif fluid, and it didn't seem to help. Just adding my experience. I researched a lot, and seems the consensus was to replace rear dif fluid with royal purple with friction modifier already added. I did that, and it didn't relieve the shutter at first, but slowly it went away (1-2 months), as if it needed time to soak in real good?? I dunno, but its totally gone now. I have not added any tunes or done anything with drive shaft, u joints, and such.
 
#11 ·
I guess it could be that the friction modifier took a few thousand miles to finally work itself in. And I'm damn glad the shudder is gone.
 
#12 ·
Pull the driveshaft and check the joints for tighness. I had the exact same thing and it turned out to be the rear u joint was junk. No play in the joint, it was the opposite. It was real tight pivoting in one direction and caused the shudder. At least check them before you break one out on the road.
 
#14 ·
It can be a few things, if it happens going around corners my first assumption would be that the clutches in the limited slip carrier are sticking as they do, mine did this when I bought it, I assumed thats what it was, changed the fluid and it helped a little, but really went away after I added the banks tuner stuff to it, which has since been swapped for SCT. Anyway my theory at the time was that the extra power of the tune both taking off in a straight line, or around corners was enough to easily push past the clutches grabbing, or it could have been ringing donuts as I finished off my stock tires lol. Either way I've seen this in mustangs and trucks alike where the extra power will help either push through the diff clutches or if anything, as time goes by more of the fluid is worked into the clutches helping to eliminate grabbing as well.

If its more of a clunk or thud, I'd suspect the center carrier bearing on the driveshaft, there's a rubber bushing that others have mentioned...ask to see one at a dealer then go wobble hours around under your truck and see how much more slop yours has in it. This, and checking for bad/worn u joints needs to be done with the truck in neutral, otherwise with it in park theres almost always tension on the driveline as the truck rocks up against the parking pawl in the trans. Just make sure the truck doesnt run you over, I saw a guy at a freakin dealer F up really bad lol. He was under the truck with it in neutral, drivers door open, rockin the driveshaft back and fourth, and I guess the bay was slopped or something or he was really rockin the driveshaft, because the truck started to roll, and it pinned the truck door up against the garage bay's wall, messed up the door and the hinge and all, but better than rolling out to the parking lot hahaha.

The splines on the slip joint will wear too, if there's any noticeable rocking move meant of the splines, again in neutral, then they'd be suspect too...but that and the center support bearing on the driveshaft would make that noise going straight and around corners.

As long as its not in the drive line, you could out a Detroit in it and be done with it if the problem persists with the diff clutches. That's next on my list as soon as rranny is back together.
 
#15 ·
Yeah, I had checked the rubber in the center carrier bearing and although it definitely doesn't look new, I can maybe move the rubber about 1/8" or less when moving the drive-shaft. It's not sloppy at all. And I had greased the slip-joint on the drive shaft because I was actually able to get the two pieces to move individually and produce a very small clunk although I never heard anything while changing gears or driving.

Oddly, I was able to get the truck to shudder in reverse too. Not when backing up straight but when backing up in a hard left or right direction. And it didn't matter what speed I backed up either (crawling or normal).

But now the shudder is gone. My plan is to get all new u-joints and the center carrier bearing replaced but I'm just not sure exactly how much that would cost (I won't be able to do the labor myself).
 
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