Clunking sounds from rear - 2000 GT

My 99 auto with 104K on the clock has never had this symptom, so IMO it is not particular to our cars and is only particular either to 5spd's or people that beat up their cars because they have a 5spd. Any/all of you having this problem ever dump the clutch in first at 4000+ rpms? My buddies 5 speed had problems with his 5spd when it was real cold and when it was real hot out.

Maybe it is only with manual trans...maybe you could not duplicate the sound because of the extra weight (you and him). I just discovered how to duplicate my sound without driving the car. Whil keeping car in gear, I was checking the tightness of my lugs. When I crank down on the front wheels, the car rolls forward slightly. When I reduce pressure the car will settle backwards and clank. Its like there is something in the tranny allowing movement or busted U-joints or slop in the aftermarket gears. I just got my poly trans mount in, but now I dont think that is what is causing the noises and thumps. Keep posting untill someone figures this out!!

I had a problem with the back thunking and it was a loose shock mount. Probably doesn't apply to you guys but just thought I would mention it.

Same here, i also have this problem. (80k)I'm no mechanic by no means but after watching horse power TV or something else (don't laugh) they were talking about the drive shaft. Something along the lines in removing the joints and putting in new shims. The old was pressed in and the only way out was to torch it so the rubber melted out. Now the new were pressed in the shimmied in. What stuck with me that they said a clunk sound and low vibrations.If the drive shaft is bent or the joints worn it will cause all of what we are experiencing. It happens to me when i engage first gear from neutral. No shop can determine this unless they specialize in drive lines.

I have the same problem as everyone else. I took it to the local Mustang guru (who also happens to own a transmission shop) and he said the noise is a normal thing. He said to think of it like this, at any given time there may be 15 different gears engaged in the transmission and they might all be in spec. But when you start to add up all the backlash that's when the noise happens.

The cars with auto trans aren't going to make the noise because the gears are engaged thus no backlash, thus no noise.

When you change your rear end fluid with Royal Purple read the instructions it says not to add friction modifier because it is already part of the formula.

i was having the same problem on my 01 gt. i was checking under the rear part of the car and found the rubber bushings that hold the exhaust pipe off their seat. i readjusted them and secured them w a little of RTV. problem solved.

My vote is 100% for the differential fluid + friction modifier solution.

Ford had a TSB about this garbage a few years ago. I took my still-new car that only had 15k miles on it in complaining about EXACTLY what you're describing.

The monkeys changed the differential fluid and added friction modifier.

Fast forward three years and the problem comes back. I decide the do the job again and lo and behold, I find that when I crack the differential cover off, only HALF OF A QUART came out of my rear end. There should be like 1.75 quarts in there, i believe. Check your manual.

I filled her back up with the proper amount of fluid, using Royal Purple MaxGear 75w140 and a bottle of Ford's friction modifier.... its like a 3 ounce white bottle.

I haven't had any problems since then, but if you do decide to do the job yourself, may I recommend that you remove the rear sway bar in order to make accessing the differential cover easier? I had an unpleasant experience doing my differential due to the sway bar being in the way. And it was raining

Good luck, PM me for any help I can give.

Now you just made me nervous...I had a Ford tech replace my pinion seal...Something else to look at I guess. I just got my new poly trans mount in...let you know if I get any different results.