1997 BMW M3 Third Gear Grind

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M3997
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I own a 97 M3 w/ manual tranny w/ 42000 miles. When the car is cold it grinds on 3rd gear. I was told to change the tranny fluid and it requires an ATF (automatic transmission fluid) oil. To my old experience, I had an Accord 5 speed (Honda) that grinds the same as my BMW. When I check the tranny fluid, the previous owner had red fluid in it and assumed that it was ATF, I change it to gear oil and behold the problem is gone. With this history, I opt for synthetic gear oil instead of its original ATF. Now the there is a little grind on 2nd and not the 3rd, but when giving a little gas before shifting it goes in right away or in normal driving condition.

But my main problem is when driving a little aggressively. When downshifting from 4th to 3rd in a hi rpm, it wont engage and grind totally or when rolling in neutral and engaging in 3rd.
Apr 3, 2007 at 7:03 AM
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2CARPRO JACK
  • ✓Experienced Mechanic
  • 11,533 POSTS
That is because you are using the wrong oil. The engineers that design the trannies know what fluid is correct for the application. If you must, mix about 1 qt of mototr oil in the ATF you put in it
Apr 4, 2007 at 12:57 AM
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M3997
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In other car forums for BMW, a lot have complain about this sticky, grinding, clutching noise in their manual gears even w/ less milage, Is it true that Auto manufacturer using copper syncro instead of steel, cause this problems. And is there a part to replace it w/ steel for BMWs.
Apr 4, 2007 at 3:19 AM

Suggested Repair

Drain the gear oil and refill with the manufacturer-specified ATF. If a slight modification is desired, the expert suggested mixing about 1 quart of motor oil into the ATF. Do not use gear oil in this transmission.

Conversation Summary

The owner of a 1997 BMW M3 manual reports third-gear grinding when cold and failure to engage third on high-rpm downshifts or from neutral during aggressive driving. After replacing the previous red fluid with synthetic gear oil, based on a past Honda Accord, second gear now grinds slightly instead of third. The expert said the wrong fluid is being used and recommended the specified ATF, optionally mixed with about 1 quart of motor oil. A follow-up about copper versus steel synchros was not answered.

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