Yeah most of the time there is only a single bump when starting off but I've had a few that shuddered. You see a lot after 18 years at the dealer. It would be worth it to pull the slip yoke apart and clean out the old grease and apply new. The old grease could be gummy after the years. The only things applied in the trans in 1st gear is the forward clutch and the low one-way. I suppose the one way could be chattering but have never seen that. You can rule it out by shifting to manual 1st to apply the low/reverse band and see if it shudders. If it still does then the one way is not the cause. The forward clutches could be glazed but I would think it would show up in 1-3 since its applied in those ranges. How is the forward engagement when shifted to drive? Does it engage quickly and smoothly or does it take a few seconds to engage? Once the clutch is applied they usually dont slip unless its burnt then you would be able to smell it in the fluid.

 

There is a theory of not shocking the trans with all new fluid all at once , some feel the 4.-5 quarts at a time makes good sense . Plus down the road you need to do it again without some fancy equipment . Your truck -your call .Ford leans to not changing the filter -does that make any sense especially if you tow? Mine is orig at 225k mi. I have the dorman drain pan . I pull a 7k payload .

 

Yeah, I've heard that theory. I don't buy it at all. Not even a tiny bit.

I also lean towards not changing the filter. It isn't needed. If there is enough junk in the filter that it needs to be changed, the trans has already failed. This filter isn't very fine and does not clog until the trans self destruct. It doesn't hurt to change the filter, but it doesn't help, either.

 

Thanks guys, now I've got some stuff to check out. Not today but next week. I'll report back to let everyone know what I find.

 

This is crazy. It's gotten warmer here in Michigan over the last week or so and the shudder has gotten considerably better. It's still there if I turn the corner and accelerate but it has completely disappeared if I am accelerating in a straight line. I drove over 100 miles today so the truck was certainly up to temp. I'm starting to think it is the slip joint as when I manually pulled the trans into 1st gear and took off around a corner the shudder was still there but not nearly as bad. I'll have a little time tomorrow so I'll try giving the slip joint another shot of grease. Weird people trucks. I'll keep this thread updated over the next week or so.

 

That is textbook limited slip clutch chatter symptoms. Are you sure its not limited slip??
It's definitely not the transmission. Either slip yoke or LS clutches. Maybe a U-joint.

 

When I was at the Ford dealer the other day and they ran my VIN they told me it didn't have a limited slip. I also changed the rear end fluid a few months ago and didn't see a clutch pack. It's possible it's u-joints but there is no clunk when I put it gear and like I said it's gotten better lately. The only thing I've done is grease the slip joint over the winter. I'm thinking that the grease I put in it is finally getting distributed. I'm going to give it some more grease in the next couple of days to see if I can get rid of it completely. I also tried putting in low gear manually as suggested above and the shudder did not go away. Again, I'll let everyone know what goes on.

 

I would pull the driveshaft out and take it apart at the slip yoke then clean the splines and apply the TSB grease I linked above. Make sure you mark it first so it goes back together the same way so it stays balanced. You can also check the u-joints while its out. A joint can be bad and not have a clunk. The rear axle has two tags on the cover with the ratio and part info. The tag on the passenger side is for the ratio and ring gear size. If its limited slip it will say 3 L 55 for 3:55 gears and non limited wont have the L.

 

There's also the theory of never changing the fluid. Most of us have heard someone say that once you change the fluid, your transmission will fail. Although I can't imagine how contaminated fluid, 100% or at any percentage, can be better than fresh fluid. I've always thought that automatic transmission fluid should be checked regularly and changed as needed.

 

I agree 100%.

 

I said I would report back my results and I am. The first thing I tried was 3 pumps of grease from a grease gun in the slip joint. It seemed to help but did not cure the problem. About a month later I put 12 pumps of grease in the slip joint and it seems to have eliminated the problem. The upshot is that a very low speed shudder is probably not the transmission but is most likely lack of lubrication in the slip joint in the drive shaft. Thanks to everyone for their help.

 

I lied in the above post, I didn't mean to, but the grease on the slip joint did not cure the problem, but some friction modifier in the rear end did. The door tag and the Ford dealer VIN check both said I didn't have a posi, but adding the friction modifier did. The upshot is don't necessarily believe the door tag on a used truck and if you have my symptoms from about spend the few bucks and put the additive in your rear end. Sorry for the confusion.