I have a 2000 F-150 with 5.4L and 4R70W transmission and well under 100k miles. At WOT from a dead stop. 1-2 shift seems to slip into neutral and the RPM flares up for a short period(approx .250-.050 sec) then goes into gear firmly. This only occurs at WOT. Anything less then WOT and it doesn't happen. All other shift points are quick and firm. Below WOT even 1-2 shift is quick and firm. It's been doing this for over a year with no change, better or worse. I cant say I take it easy on my truck either, I drive it like it's stolen. I installed a TransGo shift kit few months back and noticed no improvement on my issue. I didn't have the good foresight to buy a new 1-2 accumulator(steel one with molded rubber seals) but I didn't see anything wrong with the exsisting aluminum one either. The seals appeared to be in good shape and I don't recall any scaring inside the accumulator piston housing. I did replace the upper and lower springs in the 1-2 accumulator for firmer shifting. I didn't find any material in the old fluid beyond what might be expected and the old fluid didn't look or smell burnt.

Anybody have any thoughts on this?

 

Your 2000 definitely shouldn't have had the aluminum accumulator pistons in it unless someone installed them after the fact. Those were discontinued either in the 96 or 97 model year.

I suspect that you are having a problem with the intermediate one way clutch. Either that or something is sticking in the valve body.

Darrin

 

I'm probably mistaken about the aluminum piston. When I installed the shift kit I inspected the valve body. I didn't find anything wrong and there was very little or no foreign material in the valve body that might cause something to malfunction.

You are probably right about the intermediate one-way clutch.

If it is the intermediate one-way clutch that is failing, would it make sense that the condition hasn't gotten worse in over a year and it doesn't happen on a WOT 3-2 downshift? I'm pretty certain it's only occurring when the RPM reaches above a certain point. Sometimes if I go to WOT from a rolling start, 2-1 down and then 1-2 up, it doesn't occur. I think it doesn't occur because the RPM's don't rise high enough on WOT from a rolling start.

Also, how long do you think it might be until the clutch fails completely?

98 and up 4R70W trannies have a mechanical diode intermediate one-way clutch and from what I hear are suppose to be almost bulletproof.....well that's just my luck.....LOL

John

 

Actually, I have seen a bunch of issues with the mechanical diode one way clutches. I have one in the shop right now that is nearly broken in half. Usually what happens is the snap ring that holds it to the reverse drum comes partially off and causes erratic operation.

How long will it last? Lord only knows. Particularly when we are only guessing about what is wrong.

Darrin