mwiegert

I have a 1990 Audi 100 (200,000 miles) with a 3-speed auto transmission. It recently all of a sudden started to "whine". I checked the differential fluid and it was low, so I filled it up and changed the ATF also. The whine is still there. Any ideas??

4N 4RING

If is whining only when you accelerate (in all gears), but goes away when you release the acceleration, then is the differential.
Nothing to do, it is becoming worse; you should plan for a replacement. Eventually, replace completly the fluid, this would delay its death.
I hope I am wrong, but I had similar disease

mwiegert

Thank you. That is exactly what is happening. Only whines upon acceleration. Any idea how expensive it is to replace the differential?

Maini

Mine does only when the CD or radio is turned on... I think it is just some interference... and you may not have to worry too much about it... but do get an opinion of the dealer...

4N 4RING

These are my tribulations in fixing the differential whining noise. Read it if you are in trouble, otherwise it might be boring.
My old Audi 80 3 speed had the same problem; I went to the dealer, they drove the car and told me is the transmission, but they only replace (they do not fix it); the cost of a rebuilt transmission (in Germany) is $3500. I went to Aamco, left the car, the manager called and said the liquid was low, but they have cannot give me a diagnostic without disassembling the transmission. I asked about the maximum cost I would expect, I was told to be $1200-1400, I said OK. I was called next day and informed about the problem: the differential has to be replaced, that is minimum $1000 + the transmission rebuilt (because of the stress from the differential), another $1400, total $2600!! Until than, the word DIFFERENTIAL was never pronounced. I asked why did it make noise, I was told the liquid dried and the differential was running dry. A legitimate transmission repair shop would have told me all this before even disassembling. (I am not a transmission specialist, but now I know about the cause of the whining noise and I would suggest to the client about the possibility of a faulty differential, but this would drive out the clients because they have the information they need to take the correct decision). I said I will shop for a used transmission + diff., they said they WILL NOT install if I bring one, but they might look for a used one for me. I said OK, they found one for $1600 (transmission/diff and installation, they did not want to trell me the price of the used transmssion), I said OK again, but they backed up, because it did not match. I was proposed to pay $2200 for rebuilt differential (by another shop) and they will rebuild and install the transmission. I said NO, told them to reinstall everything back; they did it and I paid around $500 for it. As a matter of fact, when I took the car THE COOLING FLUID WAS MISSING: if I had not popped up the hood, I would have melted the engine!
After that I bought a brand spanking new transmission with differential for $700 (a guy who's fader passed away and hew was selling his stuff). I went to Cottman for installing for $270; big mistake: they do not like new stuff because they do not make money. I should have backed up when they DOUBTED about the transmission being new: it was still in the cradle, with the stickers in German. They installed the transmission, I went to take the car but it did not engage in any gear: the shift linkage was not installed. I came the next day, the manager gave me the car and ADDED more oil because it was too low: he did not know the oil has to be at the dot not at the twist. Anyhow, I got the car and I drove it gently. After one week I noticed a weak WHINING NOISE; my family told me I am nuts. I hoped I am. I pumped out the differential fluid to find it with a black MAGNETIC SLUDGE and small shinny metal chips. I replaced it. I flushed the transmission fluid to find out it is clear, but with small magnetic pieces in the filter. I replace it, too. The noise did not go away, but it was steady. I replaced the differential fluid two more times and the transmission fluid three more times in one month to make sure I flushed the crap out. I am certain they put metal chips in both transmission and diff., because the transmission gears are not magnetic (after one year I was still finding small metal chips, but this time they were not magnetic anymore because they were coming from the gears), it is extremely improbable to have differential and transmission grinding (these are different fluids), and all this in the first week, while driving softly!
I replaced the fluids almost every month and I managed to make 30 kmi since (two years).
Conclusions: ask a lot before allowing anybody to disable your car; they make money by crippling and after that squeezing you.
If you have little doubts about the person, do not go ahead.
Do not trust anybody unless is your brother, he loves German cars more than the fatherland and you can blackmail him.

@dri@n100s

I'm having the same rattling noise when accelerating... How do you change the differential and transmission fluid? I'm hoping transmission is not crippled yet, I started hearing this noise yesterday. I had just replaced the oil filter and an O2 sensor, I was hoping maybe I dropped a screw under the hood. What kinds of fluids will I need to get, is there something better fit for a 93 Audi 100s? Any help would be appreciated.

4N 4RING

For differential you have to have the car leveled, so I put the front wheels on ramps and I lifted the rear at the same level with a hydraulic jack. I used a 17 mm HEX (L-shaped), but my transmission was new. You might need a hex for a ½ inch drive. The differential has only a screw on the driver side (no bottom plug to empty) so I used a peristaltic pump to pump out the fluid. You have to insert the hose (1/8'') down to the bottom of the case and to pump. After that, I pumped the new liquid inside until it dripped out.
For transmission, I put on ramps only the front wheels. With a pipe wrench I unscrewed the side pipe going in the transmission pan (the pipe accommodating the transmission dipstick). Thus, you drain the fluid out. After that, unscrew the four screws holding the pan (use a socket, I do not remember the size, it might be 13 mm). Separate the pan, careful not to spill on you the remaining liquid. Unscrew the filter holder to take the filter out and to clean it; use engine cleaner and let it dry. Same procedure with the pan, take the gasket off and clean between the gasket and pan. You might have a new gasket ready, just in case (I did not need it for the old transmission, is not going to be burnt, but you never know). Reinstall the filter, the pan, the side pipe and refill with fresh liquid.
I do not have pictures of the job, sorry.
If you do not have peristaltic pump, use a big seringe type pump; I have something similar (a hand all-glass-piston-seringe 250 mL), I might mail to you.

@dri@n100s

Thanks a lot for your reply; since I really like this car, I decided not to mess with the differential yet. I did change the transmission fluid, it was pretty clean, and the tiny magnet at the bottom of the pan wasn't really loaded. I'm definetely not sure I have the right level of fluid. It's not spilling out, and it's not giving me an error, and there's no dipstick. I think i took out about 4 1/4 liters of fluid, and that's how much I put in. Maybe a little more.
This should really not be on a car to car basis, how much transmission fluid did you put in?

Thanks again.

4N 4RING

4 L, the mark is the DOT. Differential is easier, I can ship you a manual pump (you keep it).

@dri@n100s

I'm in deeper trouble than I thought. I really appreciate your help, but I think I'm going to take it to a shop soon. Changed the ATF, as I said, but now I'm not getting any power, it takes me really long to get to 35 mph. And on the highway it won't go faster than 60 mph, if i step on it harder it will shift to a lower gear. Would a wrong ATF level cause this, do you think? The ratlling is more accute, and it whines when I press the gas pedal more. I checked every little duct for vacuum leaks, didn't find anything unplugged.