2003 Transmission clonk in overdrive downshift to 3.... Going up a grade... Pretty good bang! If I push overdrive button.. no bangs, runs perfect

[doztwo]

2003 Transmission clonk in overdrive downshift to 3.... Going up a grade... Pretty good bang! If I push overdrive button.. no bangs, runs perfect... Over 200000 miles
Bought this Expedition with 80000 miles 10 years ago.. this problem has been since the beginning for me.. tow a car trailer once in awhile... It's my snow monster truck up north.... Runs great except for the bang! I've been waiting for the transmission to blow up any day,, but it keeps on going , I just disengage the overdrive button when I'm going to climb a hill and no problem.. I'm new on the forum, hopefully someone has some insights.. thanks!

 

[whtbronco]

I'm not sure, but it sounds kind of like 4th gear is partially engaged, stuck. Have you scanned it, there may be a code from the trans associated with this. Some scanners can show you what the trans is commanded to do and what it is actually doing.

 

[SafariGoneWrong]

Your problem got me thinking so I watched a 4R70 teardown on YouTube. I've torn apart my Bronco's C6 3-speed 3 times over the last 11 years so am somewhat familiar with the Ford way. Overdrive is actuated with a band versus a clutch in the 4R70 (I wasn’t aware of that until yesterday). I’d say it’s a question for a knowledgeable transmission technician. Funny, there’s actually an anti-clunk spring that wedges between the case and direct drum shell but doubtful it has anything to do with what you’re feeling.

 

[doztwo]

Thanks for your replies! No codes..
I'm driving around North Carolina for a couple months, relatively level area... Transmission runs flawlessly.. bang .. clunk.. happens going up steep incline.. 100 thousand Miles been doing this.. thought it would blow up by now but keeps on going, oil is not burnt... Couple years ago I added Lucas transmission fix.. thinking I should replace filter and oil but I'm very hesitant.. I push button to disengage overdrive and no clunk or bang... Last year I pulled a overweight car carrier 1600 miles back and forth.. just careful to disengage overdrive...

 

[terr5178]

Check you u joints on the drive shafts. Mine did the same then some time later the clunk turned into a shake then I changed front shaft u joint and later rear shaft u joint and it was good for another 80k till the frame rotted away and wheels fell in