Ive got a 1998 Expedition with a 2WD 4R70W (it has the 4.6L engine) in it. It works great when cold (first cranked) but after driving for awhile at stops it seems to go almost into neutral at idle, give it just a little but of gas though (raising it maybe only 100rpms) it will pop into first and go. Giving it a moderate bit of throttle from a stop results into it slamming into first gear. All the other gears seem to work perfectly fine. Another thing is that when this happens the transmission sort of senses it and raises line pressure (that my guess anyway) resulting into a very hard 1-2 shift. The odd ball part is putting it into Manual 1st (or second) it wont fall out of gear at idle! Ive parked the car to avoid major damage as I cannot afford a rebuild. Ive changed the fluid and filter but still have the same problem. Help figuring this out would really be appreciated! Only other issue ive noticed is sometimes theres late engagement from a 4-2 shift down (such as stomping it to pass someone). But this isnt repeatable, pretty random when it happens as most of the time the 4-2 kick down is fine. Trans has crazy mileage on it and im not sure if its even been rebuilt, dash says 375k on it, and yes you read that right lol. I have a 2004 F150 with the 4R75W that I can "borrow" parts from if absolutely need be but id rather try to avoid that.

 

Manual and Drive 1st and 2nd gears utilize different clutch combinations, thats why you have different symptoms when in D or M

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Hate to be the bearer of bad news, but more than likely you're looking at rebuilding the transmission at this point

 

But at the same time, you could pull your valve body, check for possible a busted c clip on the 1-2 accumulator piston, the accumulator piston itself, and check the valve body for a torn or pinched valve body gasket or within the valve body itself. But I do find the chart very informative

 

What I ment by slip was the drop out of gear at a stop. Give a little bit of gas and its firmly in gear though? I can floor it at that point with no slipping occurring? Just trying to explore all options and explain the symptoms the best I can before I do anything else. Dont want to pull it apart, clean everything and replace some burned clutches just to have the same problem :/ as ive read of a couple of people doing just that. Ive been doing some research and of a few with the same issue only one ended fixing the issue by letting his dealership look at it when the dude that he had rebuild his trans couldnt figure it out. Ended up being the internal wiring harness in his trans, would be nice if mine was that simple! So any information posted is helpful! Thanks for the speedy reply!

 

Unfortunately that's probably going to be internal. More than likely a seal in the forward clutch or one of the check ***** in the drum. Since it drops out, I'm betting on a lip seal issue. Here's why.

I'm almost positive it isn't electrical. The forward clutch won't drop out lake that due to an electrical issue on this transmission except in one instance that isn't going to cause your symptoms. To do so, both shift solenoids would have to be shorted on and you would be in 4th gear. In that instance, giving it gas isn't going to bring it back and it isn't going to drop out where you can free rev it.

On this transmission, having the gear selector in any position other than park, neutral or reverse is going to engage the forward clutch. The forward clutch stays engaged in first through third and then when the call for overdrive is made through applying shift solenoid 1 while shift solenoid 2 is applied, the forward clutch is disengaged. Then, on a downshift out of overdrive when shift solenoid 1 is turned off again, the forward clutch is brought back on.

Knowing how it works combined with your symptoms leads you to the forward clutch is having trouble =engaging and staying engaged at lower line pressures.

So, what would cause that? Most likely a seal has some damage to it that is letting too much fluid pass while it's trying to seal, but then once it does it will hold as long as there is enough pressure. Or, a check ball is hanging in it's bore until there is enough pressure to overcome whatever resistance is holding it up.

Then, the dropout. Why would a check ball without a return spring that is being pushed against a seat by fluid pressure unseat once it has seated as long as it has any pressure? It probably won't, so that's most likely out.

So, a forward clutch seal. Probably a damaged lip seal on the forward clutch piston.

At least that's my thought process.

D

 

Thanks for the explanation! I know what to look for now when I tackle this thing. Going to pull it apart sometime in the future (never disassembled any automatic transmission but ive been doing a lot or research and watching multiple youtube vids) Any good manuals out there for these transmissions? Also would Manual 2nd apply this piston? Because Manual 2nd does not slip either at idle? Or does it work differently from Drive Second like Manual 1st does compared to Drive 1st

 

Both first and second work differently in manual positions. Which is exactly why I tell people NOT to shift manually on performance applications with high power unless you have a dedicated manual valve body. The gears might have more holding power, but the shifts take longer.

D

 

The Forward clutch in this transmission does most of the work in 1st thru 3rd. Once you put the shifter in D, the forward clutch applies and stays applied in 1st, 2nd and 3rd. It only releases in 4th/OD.

In manual 1 and manual 2 all you are doing is forcing the low/reverse band to apply.

Darrin is correct, your Forward clutch is failing and the transmission will require a rebuild or replacement to fix it.

 

Ive been driving it around just making to to pop it into Manual 2nd (I found a chart that claims the low reverse band isnt applied in manual 2nd, but the overdrive band is along with forward clutch, google "clutch band application chart 4r70w" its the first one to pop up) at a stop. Changed the fluid and have been driving it the 2 past days since the fluid change, even towed a loaded car hauler trailer today (had a 03 infiniti g35 sedan on it) through the city. All with 2nd gear starts without an issue, no burning of fluid, used scanxl pro to keep check on tranny temps, highest it ever got was 165F. Doesnt shift hard into any gears. Drive 1st is my only problem gear :/ so the forward clutch pack SEEMS fine (not saying its not burned some) if 2nd and 3rd both use it. (2nd gear starts on a hill at WOT to get going happened a few times too, then some spinning tires as a result of turning around in a ditch.. so it got a decent thrashing) I did do something a little out there though when I did the fluid changed. I threw in 4 bottles of lucas stop slip in place of about roughly 3 quarts of mercV (mainly to see if it maybe just maybe will swell that supposedly bad seal) and every once in awhile I pop it into drive at a stop, it has stopped falling out of gear and doesnt change half as harshly from D 1st to D 2nd now either but still changes hard the very few times I tried D from a stop. Im going to keep driving it just with Manual 2nd starts (I pop it into drive around 35mph at 2.5K rpm so it will shift into 3rd and so on. When stopping I pop it into Manual 2nd once ive come to almost a complete dead stop or rolling less that maybe 2mph) and see what happens, if its pukes it pukes but so far so good. Ive read some horror stories about the lucas stop slip finishing the tranny off but eh if its screwed its screwed, worth a shot. Before the fluid and lucas additive all other gears were unaffected just like now. Will post if any new problems come up or 1st gear begins to work better than it is atm for anyone interested. Almost at 376K (about 30 miles shy of it) now put a good number of miles on it the past 2 days. One time while driving, I got on it and it did a kickdown to Drive 1st on a hill (oops) which seemed to slip a little and then banged into 2nd. Incase any of this doesnt sound believable I shall be posting some youtube videos tomorrow while driving it. Not sure if linking here is allowed even though its related to a problem im having. Because from what ive read and yall have said other gears should slip too if its on the same clutch pack I did hop on the interstate and do a 2nd-3rd change which it did so fine, ill be on the interstate tomorrow aswell so should be able to get a clip of that. Maybe the youtube videos will clear things up if my explanations are too confusing (and long like this one) I know it will probably have to be rebuilt I would just like everyone to see the problem as first hand as possible. So just trying to put some info out there of the problem instead of worrying so much about fixing it now.