Should Manual Transmission Oil Be Changed?

[JohnGunn]

Since Ford doesn't recommend changing manual transmission oil, the assumption is that it is unnecessary to do so.

My past experience has suggested to me that even worse than "unnecessary" it may be harmful.

When I replaced the original fluid in my 1990 Festiva 5-speed it came out gray and cloudy. I was certain it would shift smoother after the change. It didn't. In fact, the shifting had a harsh quality that was absent when the original dirty looking fluid was running in it. I tried other brands of ATF before going to gear oil, but it was never as smooth as it had been before I changed it.

I replaced the fluid in my Aspire 20 days and 600 miles ago. At first I thought it was maybe a bit smoother, but yesterday I noticed I was shifting it just as I had learned to shift my Festiva, slowly with a slight pause in the middle to allow time for the synchronizers to work. I don't remember having to do that before I changed the fluid.

Here is what I fear is happening. ATF has an additive that keeps particles suspend so that they can circulate through the filter and be trapped there. There is no filter in a manual transmission so keeping particles in suspension is the worst possible thing to do. Particles should be allowed to settle down and stay there.

That is what eventually happens as the additives in the factory fill of ATF loose their effectiveness. When the transmission is new there are few particles to be dispersed and by the time they reach numbers to become harmful the dispersant additive has lost its effectiveness. At that point there is nothing better in that transmission that the original ATF with its exhausted package of additives.

I'm posting this in hopes that some of you will be able to tell me that I am wrong. That the slower shifting of my Aspire is just in my imagination and that it will not get worse as time passes.

I originally thought this first change would act as a flush before adding some Mobil 1 synthetic, but now I'm thinking its additive package would be even more destructive to my poor 5-speed.

Particularly helpful would be reports from people who have looked inside old 5-speeds. Do they normally have a sediment at the bottom which might be harmful if released by fresh ATF to flow through the gears?

Also, I would like to hear if anyone else has noticed poorer performance after adding fresh fluid. In particular, has anyone ever used Mobil 1 ATF in a 5-speed and noticed any improvement?

Can anyone tell me if gear oil has dispersants added to keep particles suspended?

Would there be any way for me to flush my transmission so thoroughly that there would be no particles left to disperse?

[FestYboy]

FYI, there is no filter in a manual trans (usually EVER).

[Damkid]

There's typically magnets inside the trans that'll catch any possible shavings

[georgeb]

Part of the reason to change the oil is to drain the sediment. There shouldn't be any in the replacement oil. You can change it more frequently if you suspect contamination. Also you can get the oil analyzed.

[kellen302]

^But only ferrous shavings, not aluminum or Brass

[angrygocart]

I bought my festiva with 85000 miles. The 5 speed trans was noisy and it looked like it had the origional gear oil in it from when it was new. Put ATF in and the noise was louder, sounded like a bearing going bad. Put gear oil in it and change it occasionally.

[NicholasJackson]

I like to.

Everything breaks down over time. Better safe than sorry.

Make her happy too.

And by her i mean the car.

[nitrofarm]

Yes it should be changed. Its the most neglected fluid in many a car. Just work at a Tranny shop if you doubt me.

[JohnGunn]

FYI, there is no filter in a manual trans (usually EVER).

Thanks for responding. I don't know if motorcycles count in this discussion, but I've read that they often use the same oil and filter for both engine and transmission.

Seems like a more honest solution to the problem than to just to say nothing about changing fluid and leaving it up to the ignorant owner to decide whether he will or not, and how often.

Nothing lasts forever. They, clearly, were just hoping the car wouldn't last long enough for this problem to surface; and, for most owners, it didn't.

[JohnGunn]

There's typically magnets inside the trans that'll catch any possible shavings

I think I read about this somewhere. Is it also true of the Festiva/Aspire transmissions?

[JohnGunn]

Part of the reason to change the oil is to drain the sediment. There shouldn't be any in the replacement oil. You can change it more frequently if you suspect contamination. Also you can get the oil analyzed.

Thanks for this comment, georgeb. I've decided to work at getting the transmission cleaned out by changing fluid about once a week and at that time pouring the removed oil back through the transmission several times, after, each time, running it over a strong magnet and decanting to leave any sediment in the drain pan.

I suspect some damage has already been done, but I figure this is the best I can do at this time. I wish I had saved the original fluid. Then I could filter and decant that and put it back in the transmission to prove or disprove my theory.

I've never had an oil sample analyzed, but the reports I've seen on the Internet don't make much sense to me. Getting the analysis is one thing. Analyzing it is yet another.

[JohnGunn]

I bought my festiva with 85000 miles. The 5 speed trans was noisy and it looked like it had the origional gear oil in it from when it was new. Put ATF in and the noise was louder, sounded like a bearing going bad. Put gear oil in it and change it occasionally.

Good to know I'm not the only one who discovered that gear oil will work perfectly well in our transmissions. I used it for 17 years in my Festiva with no further deterioration in performance. It didn't undo the damage done to the synchronizers, but, at least, it didn't get worse in those 17 years.

I was getting 42 MPG (city/highway) for much of that time. I would guess it might have been better had I been able to use ATF, but 42 was still pretty good.

[JohnGunn]

Yes it should be changed. Its the most neglected fluid in many a car. Just work at a Tranny shop if you doubt me.

Thanks for the comment, which I assume to be based on your own experience.

Since you've seen the effect of this neglect, do you think it dishonest of Ford to sweep the whole issue under the table and refuse to make a recommendation for change intervals?

There must have been some pretty heated discussions before coming to that conclusion.

[denguy]

I worked at a Ford transmission plant for 30 years. Every auto trans got a donut shaped ceramic magnet in the pan. The engineers said the fluid should last forever [no drain plug] but some will evaporate and will need to be replaced. The filter is oversized and will not encounter that much contamination. Trans fluid doesn't face products of combustion like motor oil does.

http://www.freerepublic.com/focus/f-chat/2713202/posts

[JohnGunn]

One thing about draining the original fluid that I failed to mention may have some value.

I allowed the fluid to drain until all dripping stopped. Just to see what would happen, I screwed the drain plug back in without cleaning the hole threads. It was not a pleasant experience. There was so much grit in the threads that I stopped before I had gone one turn. After cleaning the threads with a round brush, it went in without problem. But that told me there was very likely more of that grit just a couple of millimeters above, covering the bottom of the case.

That led me to come up with the idea of pouring old fluid back through the transmission several times after, each time, running it over a strong magnet and decanting it to leave any sediment in the drain pan.

I've marked a plastic water jug at the 2.6 quart level and, after decanting the old oil into it, I plan to add enough fresh oil to bring the level up to that mark before pouring it back through the transmission. Doing that until there is no grit in the threads, the magnet is clean, and there is no sediment left in the bottom of the drain pan. Then, filling it with clean fluid and doing it all over again in a week.

After 17 years of poor shifting, I am willing to fight to save what is left of this pretty low mileage transmission. I suspect this would not be happening if Ford had only had the courage to admit the problem and specify a 15,000 or 20,000, or 30,000 mile change interval.