1st gear rattle

Hi all,
greetings from Munich, Germany. I imported my 2008 Mustang GT Convertible from NY two years ago and enjoy cruising around the alps. (Yes, gas prices of almost $8/gallon do hurt).
It's a high mileage car (214k miles) and had a tranny swap 80k miles ago, before my ownership.

Last year it started developing transmission noise, which I now want to diagnose and subsequently fix. Since it's a pretty uncommon car here, it's hard to find someone that knows about the car and its issues.

So maybe you have some experience and can help me point in the right direction:

In 1st gear, under light load, the transmission rattles and clutters. Once in 2nd gear and up, as well as in neutral, there's nothing. There are no driveability issues, I even did 120mph on the autobahn last night without any issues.
There's no leakage, no excessive heat, no warning lights on the dash.
Last year I checked transmission fluid and made sure it's on the right level (and found Mercon V to put in!).

So what do you think the issue may be?

Does it stop rattling if you hold the gearshift lever?


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At a stop and idle - does it rattle? Push the clutch pedal in, does the rattle stop? If so it is most likely the throw out bearing going bad. It could also be excessive play with the transmission input shaft which would require a transmission rebuild to replace the bearing's. Could also be a failing pilot bearing. Or the clutch going bad. If you're lucky it's just the shifter linkage that is wearing out. There are plastic bushings in the linkage. Those obviously don't last forever.

Regardless, a closer inspection is necessary to properly diagnose and that would require dropping the transmission to inspect everything I just mentioned. At 214k miles, it could be anything that has reached the end of it's lifecycle.

Hi @WJBertrand and @rocky61201 thanks for the quick response.

I failed to mention that my car is an automatic. Only automatic gear shifter - solid, no rattling, and of course no clutch pedal.

I am hoping to be able to fix without getting a new trans in, getting one is the issue!

Oh and @rocky61201 good to see someone with even more miles than my pony!

Noise in just one gear would point to an issue internal to that gear. Without hearing the noise, its difficult to say.
Unfortunately, I agree with pull and disassemble to inspect.
They all rattle a bit in neutral while stopped, but should not rattle in gear and moving.
Internally, it is just a manual trans, nothing special. A reputable shop should be able to handle the work. Parts, thats a different story.

Are you sure it's the trans and not just a cat heat shield that broke a spot weld and is vibrating at just the right harmonic?

No worries, I read MERCON V and assumed it was a TR-3650. Good luck with diagnosing your problem.