Physical clunk from somewhere on driveline
Hi all, as of recent I've been experiencing a strange clunk with my car. This only happens going highway speeds, and most noticeably around 65mph. What happens is that if I'm coasting down the road and press the gas, I can feel a fairly strong clunk as if something is physically moving. Once the clunk happens the car accelerates normally, but it definitely feels like a delay in power delivery. This only seems to happen in overdrive. If I hit the gas hard enough to force it to drop down to second (of which I rarely do - I usually just turn off O/D to kick down to third) it doesn't clunk.
I have yet to check the driveshaft U-joints, but I do plan on doing so when I get around to doing the transmission fluid soon (of which is bright red but smells a bit burnt - it was last changed a bit over 20k miles from the PO but that was back in 2007) and differential oil. The car is currently almost stock, the only thing that would affect driving would be the Marty tune I have installed, although I can't recall if it did the clunking prior. I've tested the engine mounts too and they appear to be in fairly good shape given its age and low miles (43k). The transmission is not J-Modded (yet)
A buddy of mine has a 2002 Grand Marquis LSE and he seems to experience the same issue as I do - perhaps it is related to the age of our vehicles since they're within a year of age. Fingers crossed it isn't related to the transmission.
If I have time I may try and get a video for y'all to better describe my issue.
Thanks.
2003 300B Mercury Marauder
Built 01/22/03
Purchased 01/29/20
68,xxx miles
July 12, 2023 - 68,203 Miles - RIP original engine
October 31, 2023 - Rebuilt engine installed
Modifications/Stuff I have done on the car:
Engine:
rebuilt stock; slightly overbore. Original 68k mile heads, new OEM Ford performance timing kit, Terminator Cobra Oil Pump, Billet Steel oil pump gears, ARP head studs, main cap studs, and side bolts. The latter ARP stuff for future endeavors.
Transmission:
Thor 2800-3000 Stall Converter
Suspension:
ADTR Front + Rear Sway Bars
Metco Billet Watts Link
Metco Billet Rear Control Arms
Cosmetic:
1998-2003 Amber tail lamp conversion - Painted and smoked to near-OEM spec.
HID Projector Headlamp Retrofit
OEM Mercury Mountaineer Hitch Cover
Front in-channel rain guards
Other Stuff:
4-pin trailer harness
Class III Tow Hitch
Cadillac 4-note horns
Hayden 679 Transmission Cooler
Obligatory Marty Tune