Transmission issue?
 

Ok there's 2 issues being described but I don't think they are both transmission related.

First one is quite simple to describe, sometimes while I'm stopped the truck will want to surge forward (usually it keeps surging until I go). It's not a large surge. This doesn't happen all that often and happens with a cold engine and a warmed up engine.

Second issue is the one I'm thinking is going to cost me more money than I have, especially if I have to wait to fix it and it gets worse.

From a 0mph start there is a thud (or clunk) when the truck first starts rolling. If I am super light on the go pedal it doesn't happen. It also occurs during stops and the severity of the thud depends on the gentleness of the stop. The stopping thud doesn't happen until the truck is stopped.

I'm not familiar with transmissions and haven't worked on one. I don't have a level place to work on it, so I will most likely have to take it in.

Im not gonna venture a guess on the surge, but the clunk you are having sounds like it could be driveshaft or rear end related. A bad u-joint will cause the same symptoms and so will a bad pinion bearing. Jack the rear end up and put truck in neutral. See how much you can turn the driveshaft before the axles start to move, if it is very much at all then you have too much backlash between pinion and ring gear and most likely it will be pinion bearing gone bad. Hope this helps

I read your reply earlier today while lurking and while I was out going to and from the shelter I realized that it was indeed coming from the rear end. I'll have to get some jack stands and find a flat spot and test the drive shaft.

What about dry slip-joint splines in the rear driveshaft, particularly since it occurs at take-off, and right when coming to a stop?

I'm with Torky2. Best to remove either end of driveshaft (mark it for balance) then clean and lube the splines with special lube from Ford. After breaking several wrenches I jacked up the frame and jack stands were set. Slipped back one end of the slip joint boot and applied gun grease liberally.
Klunk gone.

For u joints, you can roll under with it on the ground and get a firm grasp on the drive line. Then shake it like you are strangling someone. If it moves excessively then you will probably need u joints too.

Oh goody I've never pulled a drive shaft before :D Guess that will have to wait until Fri or Sat since Mon-Thur is booked time wise.

Pfft, pulling a driveline is easier than pulling your tires off. There are 8 bolts, possibly looking like this:
http://i1180.photobucket.com/albums/...s/IMAG0075.jpg

If that's the cast you may want to get some Grade 8 hex head bolts that are the same thread pitch. In my own experience these 12 point OEM ones wouldn't not stay in no matter how hard I torqued them. Some Grade 8's and a touch of threadlocker and they haven't made a sound since.

That's the other thing to check while you're down there are these bolts. Your u joints might be ok but these bolts can make it sound like they are bad.

i believe everyone has you on the right path as well. for me it was the slip shaft that needed to be packed.

now for the surge its possible your brakes may not be holding you properly once stopped. also wouldnt hurt to have the tranny fluid and filter replaced for good measure.

What size tires are you running?

You know, I wonder if the clutch disks in the C-6 could cause this kind of issue? I've never had an issue with the slip shaft (that's in the middle of the drive shaft right?) but my clutch disks were totally shot not allowing my tranny to shift out of 1st or downshift, and it wouldn't go into reverse without insane amounts of RPMage.

Anyways, just a thought.

Oh she shifts just fine up, down, and backwards :) So let's just say (haven't checked yet) that the rear u joint is bad, should I replace all of them or just the one that is bad.

With regards to the brakes not holding, I don't think that's it. I had them checked the fronts have 75% and the rears have about 70% and it stops very well (almost totaled one of those new smart shoe boxes today when she pulled out in front of me with only about two car lengths between us in a 45mph zone).

If you replace 1 bad joint, you want to do all of them. Who knows what the others are looking like since that one joint was bad. Never hurts to have new ones right?

that rear driveshaft can be a pain to rebuild, i recommend taking it to a shop and letting them mess with it. you will be glad you did.

I would pull codes, is the motor surging when your sitting at a stop? the truck shouldnt move when your stopped so something is not right

kemical ... no codes (other than a HG02 lean sensor due to a vacuum leak somewhere) and the surge is very unpredictable. I haven't experienced it in a couple of days.

I'm not sure I can afford to take it to the shop to get it done :D I'll know more Sat after I actually get around to taking a good look.

Vacuum leaks make a huge difference. Even a pin head size hole is bad. May I suggest going ahead and replacing all the plastic hoses with rubber?

https://www.ford-trucks.com/forums/1...uum-lines.html