Odd change in behavior - 4R100
 

I have a 4R100 in my 7.3L Excursion. Recently I've noticed that it doesn't stay in gear when I have my foot off the throttle unless I'm in OD. It will lock up and stay in OD coming down a hill with my RV but as soon as it slows down enough to come out of OD, it stays at idle and I get no engine braking power. No combination of gearshift position or OD switch changes this behavior and I'm pretty sure this is new.

I have a PHP tuner, but I've set it back to '00' - factory programming - and get the same results.

Other than this, it shifts and drives fine - even with the RV which weighs about 8k#.

Edit: So it looks like the coast clutch has failed. I wonder how long I'll be able to drive it around before it blows up.

I've seen them drive for years with a failed coast clutch.

I would probably drive it around like this indefinitely, if it weren't for the fact that it's downright scary coming down even small hills when towing. I'm on the brakes constantly and I worry that if I go down too big of a hill, really bad *** is going to happen when I get to the bottom.

Well at least I have time to shop around.

I just put a new 6.0 cooler on this about a year and a half ago. I changed the fluid in it almost a year ago. Is it necessary to buy a new cooler for it, given that the trans hasn't actually failed and filled the cooler with debris? I also have an external filter on it, which I plan to replace with a screw-on filter when I get the new transmission in.