My 1990 420sel has started making a grinding like noise when I put it in reverse and start backing up. It shifts fine and goes into reverse with no problems, but when I start going backwards, it makes the noise. I have listened with the windows up and with them down and it seems to be noticable only with the windows up. It may have been there all along, but I don't remember hearing it before now. the car has 143k on it. I have also had a waterpump put on about 8k ago and have noticed some loss of antifreeze and I feel I hear a noise similar to the noise when the last waterpump was going out. Is it possible that the noise is the waterpump going out again and my thinking is that the noise would be there drive and reverse. It is not possible that it is the waterpump again? The sound in reverse almost sounds like you holding a piece of plastic against a fan and letting it hit. any help in diagnosing this problem with my confusing description is greatly appreciated.

That is a sign that the reverse clutches are WORN out. The noise that you are hearing is the piston for reverse hitting against the 3rd gear clutch drum. VERY common failure! DON'T wait or you will need a complete overhaul.

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