Hey all, any advice or direction you can give on tis would be greatly appreciated. I'm sure it is something I will have to take to the shop, just want an idea of what may be wrong first and how much I should expect it to cost.

bought a 2007 king ranch 5.4L 4wd with 150k miles a couple months ago. Last few weeks I've been noticing a loud.... clang I guess would describe it (sounds and feels like hitting a metal handrail with a piece of rebar). This happens when cruising along in 4th gear (overdrive) and pressing the accelerator lightly. The transmission tries to downshift into 3rd, there's a loud clang and vibration through the truck along with a hesitation for a sec or two (like the truck went to neutral), then everything is normal and it accelerates. The lower the speed, the louder the noise. if I'm between 40-50 and try to lightly accelerate, my wife is looking around for a car I just hit because the metal clang noise is so loud. If I'm going around 60 or higher, it sounds and feels almost like hitting a couple of grooves on the edge of the highway.

I'm assuming it is something wrong with the overdrive unit. this only happens on downshift from 4th to 3rd. but for all I know it might be valve body, transfer case, differential, etc. just wondering if anyone here has had or knows of something similar.

 

Does the CEL light flash at all on the dash when this happens? It might be only for a split second.

 

Great question. I have not noticed it but have not been looking directly at the dash when it happens, usually just gritting my teeth hoping the trans doesn't fall out. on my way home today I'll do it again and watch the dash to see if it blinks.

Also, when I bought it from the dealership, they had changed the fluid and currently fluid is at perfect level and very clean.

 

Almost sounds to me like you are experiencing misfires under load, until the trans downshifts, then once it downshifts and the revs come up it smooths out?

 

That's what I was thinking. The telltale would be the misfire cel flash.

 

Just did it again on the interstate, no cel flash on the dash. just the noise and vibration through the truck

 

A bit of a stretch since it doesn't do it from a dead stop, but maybe slip yoke grease? I'm just thinking of the least expensive options first.

 

Thanks. definitely worth checking, I appreciate the feedback.
and yeah, doesn't do it from a stop, it only happens when downshifting from 4th to 3rd, and then it is only if I have been cruising at a steady speed for at least a minute or so. if I get up speed, let off the accelerator, feel it shift into 4th, then slightly accelerate right after - it will downshift without any issue. but if I am going a steady speed (with or without cruise) while in 4th and try to slightly accelerate - it does the noise and vibration every time.

I'll check the yoke grease this weekend and bring it to a shop if that didn't do it. I know it's a weird kinda off-the-wall issue, this is just my first truck and I was hoping someone here would have had experience with something similar and they could say "ohh this is the issue"

 

Someone here might know the answer. I'd let this post soak a bit more.

 

I would still say to look into misfires as there have been many many people that come onto this forum asking about a shuddering transmission in overdrive from 45-50 mph and it's usually a new set of spark plugs and cleaning the cop contacts does the trick.
it could be other things if course but that's what I would look for first.
I think if you have or ask for a shop to scan it during your condition looking at data for misfires or mode 6 data and you see misfire count increase during this condition that would confirm it.
Or if you don't know the history of the vehicle you might just want to start with a new set of plugs...

Edit: here is just one of the many previous threads read the first post:
https://www.f150forum.com/f4/5-4-tri...8/#post5921207