Hey Guys,

My KR Screw has the same symptoms you guys have described and I've done a little testing to better understand what's going on here. The transmission refered to in this chart is a 4R70W unit in my '01 KR 5.4L Screw.


From the table, you can see that a 2-3 shift can occur at as little as 16 to 20 MPH. In other words, you can find yourself in third gear at as little as 16 to 20 MPH and it takes just a tap on the accelerator to make it jump down into second. I'm not sure how this particular transmission works yet but I will after I do some more research. I used to be a transmission rebuilder years ago and I've built many racing automatics so I'm not new to dealing with issues like this one, just new to the 4R70W unit and the electronic shift point aspect.

From what I can tell, the problem with the clunk is somewhat normal to this transmission but don't get me wrong, I don't like it and I think that something can be done to eleviate it but I don't know what exactly.

Years ago, when automatics would shift from 1-2, it swithced from a first gear clutch pack to a band. From 2-3 it switched from the band to the high range clutch pack. With this unit, I'm not sure if it has a band or are all the ranges controlled by individual clutch packs. Armed with that information, it may start to fall into place as to why it clunks from 3-2 when accelerating but not from 2-1 or from 4-3, only from 3-2. Transistioning from one range to another happens in milliseconds, granted possibly hundreds or even thousands of them, but that's a fraction of a second.

If the transition from one range to another is not handled just right, then all sorts of mechanical slack might have to be taken up or accounted for. If this transmission is fully programable as some might suggest, then it seems that the Super Chip very well could eleviate this issue and thus so could Ford.

I'm not sure I've done anything here except muddy up the water but I think, at least in my mind, that this issue is not serious but just annoying.

I've got another issue with my truck that falls into a similar catagory but I was reluctant to start a thread thinking it's already been handled. The issue is when I start from a stop, a good many times there seems to be a sort of slippage but almost more like the differential is slipping just a bit. I suspect that the limited slip differential is actually slipping upon acceleration.

Anyone else have this problem? I guess when they say limited slip, they didn't say it wouldn't slip at all but just when it needed to prevent something from breaking. Any comments or thoughts?

DaveMan

 

DAVEMAN wrote:
I've got another issue with my truck that falls into a similar catagory but I was reluctant to start a thread thinking it's already been handled. The issue is when I start from a stop, a good many times there seems to be a sort of slippage but almost more like the differential is slipping just a bit. I suspect that the limited slip differential is actually slipping upon acceleration.

Anyone else have this problem? I guess when they say limited slip, they didn't say it wouldn't slip at all but just when it needed to prevent something from breaking. Any comments or thoughts?


DAVEMAN,

I also have the same second issue. I don't believe it's associated with the Limited Slip, because unfortunately, I don't have LS. When starting from a stop, it seems as though it's shuddering a little bit. My dealership says that it is all normal, of course. Bull!!

Thanks for all your hard work concerning the Tranny Thunk. Any new info is great.

Tom

 

Hey T21,

I'm not sure it's not in the differential in my truck but I will say that I didn't rule out the leaf spring shackles or the whole differential moving just a bit. I really don't think it's the transmission though, I think it's somewhere from the drive shaft to the rear wheels and that could be a good many things.

One thing else might be the rear axle is loose where the U-Bolts attach the it to the springs or it might be the leaf springs shifting themselves. I don't know for sure 'cause it's hard as hell to see anything while you're trying to drive it hard. One of those little digital eyeball cameras mounted under the truck with a recorder running would surely show up just what the hell is moving or shifting under acceleration from a stop.

DaveMan

 

Mine thunks (although I'd call it more of a cha-chunk), yours thunks, they all thunks. It's a truck and heavy duty things make noises when the work. If you don't want thunks, buy a Jaguar.

I think it must be in the drive line too...that's just how it "feels" to me, plus turning makes it more likely to happen which suggests maybe something happening in the LS.....or more likely something triggered in the rest of the driveline by whats going on in the rear end.

You know I'm just trying to stir you up a little right Daveman?

 

Hey Logical,

Long time no hollar at, hey?

I'm cool, I figured you out a while ago. As long as I don't **** you off, I usually can get away with most playing around on this board. However I don't think I've ever pissed you off, yet! Yo, if your tranny goes cha Chunk, then maybe that's some of the gear teeth breaking off! Or maybe that's the muffler bearings getting out of syncronization with the thermonuclear sensing bobbet check valve, that sheit is serious and needs to be looked at by your local dealer immediately or danger could fall upon you or your truck.

Hey man, lets figure this damn take-off issue out. I'm almost positive it's in the differential but can't put my finger on the exact cause. I was thinking about removing the drive shaft and attaching a torque wrench to the yoke of the differential and detemining how much torque is required to make the clutches in the diff slip. Armed with this knowledge, we should be able to estimate how much torque is required to take off from a light with a certain amount of acceleration and determine if the slippage torque is being reached at take-off.

Anyway, what are your thoughts on this theory?

DaveMan

 

Well you guys certainly have been helpful. After purchasing my first brand new vehicle, 2002 Supercrew, I noticed the driveline "thunk" as well. Wondering what to do led me here. After reading through the posts I saw that alot of the information was geared towards the 1999-2000 models. Has anyone found a useful fix for the 2002?

Thanks, Nick

 

OK, I'm having some thoughts on the tranny clunk issue. I am by no means a tranny expert or an expert on anything else for that matter but here goes.
Is this really a tranny issue? Now I mean a real hardware tranny issue. It just seems to me that the tranny is not shifting into a lower gear early enough and when you get back on the gas at about 18 mph it downshifts and you get the clunk. Should it not be down shifting by itself at this speed? Mine only does is around 18-20 mph. I can't tell if it's the 2-1 down shift or the 3-2 downshift. This tranny (4R70W) seems to shift kinda weird anyway. Should I be in third at 20 mph? I mean 1-2 at about 8-12 mph. Just seems kinda early to me. I know this is to help gas milage but still seesm kinda early.
Ok, well I guess my real question is, is this just a computer problem? Would reprogramming the computer not solve this? Some people have said the dealer reflashed the computer and it seemed to solve to issue. Does anyone have any other thoughts on this or am I just way off base on this? I am open to any ideas positive or negative.
I'm taking my truck to the dealer tomorrow to talk about this.

 

T21,

I had that thunk too when I first got my 2001. It went away after a few hundred miles.

I attributed that to the computer "learning" my driving style.

Hey FallScrew,

Can you find out what TSB your dealer applied?

John

 

Anyone have any success with a fix? I read in this month's Truck Trend magazine a reader wrote in asking about the same question. Basically the magazine's tech guy said it is either A. Normal for the F150 or B. The planetary whatchamacallit.

Not much help...

 

I had the same issue since my truck was new. I told the dealer and they said they would inspect the entire driveline system. Well, they had my truck for 2 days and still did not get a chance to look at it. I got a free oil change cert and said I will take my truck and figure I would have them address it some other time. As always when dealing with a dealership I figured I would have to bring it back 4-5 times before the real issue is addressed.

After this I began making MOD's to my truck. I added a chip which changed the shift patterns, rev limiter, fuel/air mix and timing. Well, to my amazement after the install the problem went away. I beleive the more aggressive shift pattern cured the problem.

Not sure what the problem was but the chip mod fixed it.

:

 

I've got a 2002 Screw 4x4 5.4L .... and the wonderful tranny clunk. Seems to happen in the downshift as described earlier. Became more obvious after the about 7000 miles, but may have been there all along.

Has anyone had the dealer fix this successfully? Sounds like the TSB is not the answer?

Thanks,
Greg

 

Not sure if this is the solution, before I moved from VA to UT I had the dealer inspect my Tranny concerning the THUNK. They said the same thing, “normal operation”. After insisting, they did a computer diagnostic and completed some reprogramming. The Thunk has disappeared; it’s now been 5,000 miles and has not returned.

 

I have read a few post that suggest a computer upgrade will fix this. I rarley have the think problem with my superchip.

If thats all it is then wouldn't that be a fairly inexpensive fix for Ford to put out a recal on?

 

my truck thunks but it is usually only noticeable right when i take my foot off the brake at say a stop sign or stoplight. the dealership hasn't been successful in getting rid of it yet. first they tried lubing the slip yoke and that worked for a week. then they put a new yoke/driveshaft on the truck and that worked for about two weeks. now i'm back to square one...but at least it doesn't thunk as bad as it did a couple months ago.

 

I too have this annoying clunk in the transmission. I have brought it back to the dealer 4 times so far. First time they found a broken bolt. That didn't work. Then they fixed the spring in the transmission that someone talked about earlier. That didn't work. Then they said my sway bar was off center. Fixed that and that didn't work. They really have no clue what is going on. I am going to bring it back and tell them to reprogram the chip or replace it.

Has anyone had any luck with getting this fixed besides the chip? Has anyone called FORD and if so what did they say.

Glad I found this bulletin board. I thought I was the only one having this problem. Also have the problem of shifting out of 1st gear too quickly and the shuttering when taking off. Sucks!!!!

db_9