Strange Advice About Manual Tranny?

wgarrjr · wgarrjr's Garage

My indy BMW shop guy (a Certified Master Tech) who has given me great service at a reasonable price, and good DIY advice, recently advised me NOT to change the fluid in my 1997 328iC manual tranny. He said as long as it is full, leave it alone because new fluid in an old tranny (148K miles) is very likely to cause slippage and other problems. I asked what to do if it is low, and he said it was OK to top it off, but that he doubted it was low since he had not observed a leak around it. I have heard about synchro problems with old trannys and high viscosity fluid. It sounds kind of reasonable not to change it if there are no problems, but it also seems a little strange not to replace the old, dirty, fluid. The previous owner changed the fluid regularly according to schedule. I know my shop guy is not trying to drum up tranny business, and he said he would change it if I wanted him to, but he would definitely NOT recommend it. I was going to do this as a DIY, and use the fluid recommended in the Owner's Manual and the tranny label. Has anybody else gotten this advise? Is it accurate? Which is the "worse of two evils - contaminated/old fluid, or possible slippage? Has anybody had problems after changing their fluid on an older car?

Wayne 962 · Wayne 962's Garage

Yes, this is a question that is asked often. The fear comes from stories of people who have changed their fluid, and then experienced problems. So, it does happen. If the fluid has been changed fairly recently (within the past 60,000 miles), then maybe I would just leave it alone for now. But check the levels and indeed top it off...

-Wayne

Manolito · 11-06-2011, 07:24 AM

I think that if there are problems associated with changing fluid, it is likely due to mixing incompatible fluids or putting in the wrong fluids. I have caused some manual transmission problems in my 45 years of driving, but it was due to putting synthetic gear oil in a manual tranny that was intended to use conventional ATF. I killed two trannys that way before I learned not to put fluid in a tranny that was more viscous than the manufacturer recommended. The Toyota I was able to rebuild inexpensively, but the Volvo tranny was a boat anchor.

This thread reminds me. My '97 328 with a manual tranny has 275k on it and I have not changed the transmission fluid since 175k. Better add that to my to-do list.

Rrrockhound · Rrrockhound's Garage

I've never heard this advice for a manual before. It doesn't make sense that changing the fluid on a manual would cause slipping because the gears are always meshing. One of the first things I do when I buy an old car is change the gear oil, and I've never had problems doing so.

Jared at Pelican Parts · 11-07-2011, 07:17 AM

Uh, whats slipping in a manual gearbox? There shouldnt be any problems provided you use the reccomended fluid and change it at the correct interval.

wgarrjr · wgarrjr's Garage

Thanks, guys! That whole slippage in a manual gearbox thing had me scratching my head too. That's why I thought it was "strange advice". I appreciate the feedback. Maybe I'd better ask to see his "Certificate"...

Manolito · 11-11-2011, 07:14 AM

There is a part in a manual tranny that 'slips' in a controlled manner, it is the synchros. They don't work properly with the wrong fluid.

richardlw · 11-13-2011, 01:44 PM

He is way off base. contaminants get into the tranny through the breather, the oil degrades, etc. It has a limited life.

There is nothing to slip except synchronizers, and that only if you put GL5 oil in, add more additives, or use an oil too thick.

That is an old wives tale about automatic transmissions. But it is still wrong there, but based on the fact that if you go way too long on ATF, especially the cheap stuff, the new oil has to clean up the mess from before, but you fix that with two oil changes, a week or two apart.