M 56 trans fluid puzzle

[JimBee]

I recently replaced the outer passenger side axle boot. When I pulled the old axle seal at the transmission quite a bit of fluid—maybe 4 or 5 oz leaked out. After reassembly, I assumed I'd need to top up the level. When I removed the (upper) filler plug, quite a bit of fluid leaked out. I wasn't ready with a container so it flowed onto some corrigated I had under the area so I'm not sure how much leaked, but it seemed to keep seeping out. So between the open seal leakage and what seeped out of the filler port there was maybe half pint lost. Plus the seal I replaced seemed to be leaking a bit so there was more fluid loss there. The car has been sitting for a couple of weeks on level ground. Today I checked the level to see if maybe fluid had to make its way into an internal reservoir, and it's topped up.

After all that leakage I don't understand how it can be topped up. I also don't understand, if it is at the normal full level, how so much extra fluid could be added. When it's full, any more just flows out. Last time I added some would have been at least several years ago when I replaced the drivers side boot. It would have been properly topped up then.

I poked a piece of straw into the level to make sure I wasn't looking at a bubble. The real fluid level is what's visible. Of course, I wouldn't want to run it with low trans fluid.

Am I missing something?

[erikv11]

Either (a) it was overfilled before or (b) it's actually low right now.

I didn't understand your explanation - have you driven it since all the spills? If not, why don't you think it can accommodate more fluid?

I don't have experience with the manual boxes. But with an auto box I know I can put the car on stands, pull the bottom plug and drain the pan, then refill with exactly 3.5 quarts. If you have some simple drain and fill experience to go by you then can get the level close and take it for a drive before finalizing it.

[Cookeh]

Manual takes 2.2 quarts of fluid, if the car is completely level. I've never managed to get more than 2.1 quarts in, but then I've also never owned a level driveway. Its almost impossible to overfill a manual trans unless you've only jacked one side up to a considerable height, so I don't believe that was the problem.

If you've lost an half a pint then you've lost an eighth of your total capacity. This is not inconsiderable and should be noticeable, fluid should slowly be seeping out of the fill plug if it is at the correct level.

If you're at all concerned about the fluid level, this seems like a perfect opportunity to do a drain and fill. That will ensure you have the correct level, and fresh fluid has no downsides.

[abscate]

Most manuals are splash lubricated so a bit low on fluid isn’t too critical. Try to find a level place and top off. I’m guessing you probably slightly overfilled last time if it’s level now.

[JimBee]

Why I'm puzzling about this is it is topped up—even after losing all that I described When I bought this car 12 years ago I drained and filled with Amsoil ATF, drove it for maybe 1,000 miles, drained and refilled again with Amsoil ATF. It still looks clean. I'll drive gently around the neighborhood and check it again. If the level is still visible right at the lower edge of the filler port well, that's where it's supposed to be.

One thought occurs to me. The only time I've had this car in to a shop for a repair was a year and half ago and I don't remember what the repair was. But it's possible if they had it on the lift some extra fluid was pumped in and the plug quickly replaced to prevent it from flowing back out. Who knows!

BTW: When I bought the car, the transmission had a slight but noticeable whine in first gear when decelerating. the original fluid was kind of muddy looking, so needed to be gone. With the Amsoil the whine soon went away and has never returned and shifting has always been smooth when under way, though it can be a bit resistant getting into reverse or first gear when it's cold.