2004 Grand Marquis Transmission problem

I recently took my 04 Marquis on a 650 mile trip. The second half of the trip I heard a clunk sound while the tranny was downshifting from 4 to 3. The car has 161,000 on it and I'm not sure if it has ever had a tranny flush. Will the flush fix this problem or will I be investing in a new transmission? Any feedback would be appreciated.

It well could have been road debris that happened exactly at that moment. But it wouldn't hurt to change the filter and fluid, which should be done according to your maintenance schedule. If it happens again on a different road, then I would worry about a problem.

i'm sorry I wasn't clear. It clunked every time it switched from 4 to 3. Approximately 7 hours into a 12 hour trip.

I had a 1989 Olds 'Sword' auto tranny that had over 230 thousands on it.

On a road trip...it started to occasionally skip-pause for about 2 seconds causing
a 'thump'. It would continue for the balance of the trip (>300 miles). My wife & I would
try to time and distance each time it would occur....

Upon arrival @the destination....borrowed the son-n-law's vehicle ramps and did the
Flush-N-Fill w/some Reslone Tranny 'slick-stick' stuff.

The return trip was event-less...!

However...about another 15 thousand miles later...the same old 'thump' came back
for a while...2 to 3 months...

After checking the Fluids...which were in fine level and color...Never felt the 'thump' again
before retiring the 'Sword' with more than 255 thousands miles...

Summary: Try the Flush-N-Fill...it's not much of an expense...fairly short time period to perform

As a backup...take it to a Tranny shop...get their thot's....!!!