observations on my first t4 transmission disassembly

[dlb]

Since I got my latest tercel, it has occasionally had some problems shifting. The problem is weird: every now and then, I wouldn't be able to get the shifter far enough to the left to get it into 1st or 2nd. Other times I wouldn't be able to get it far enough to the right to get into 5th or reverse. Other times it wouldn't want to go forward into third, other times it wouldn't go down far enough to get into 4th. It was inconsistent and only occasionally happened initially, and would go away after one affected shift, so the first several times it happened I figured I had shifted poorly or something. But several weeks ago it stayed like this for about five minutes, so I couldn't use 5th or reverse for that time. I want to be clear that it didn't appear to be a synchro issue, as I couldn't even get the shifter near the affected gears, and there was never any issue with crunching or grinding into gears. Actually the vast majority of the time each gear was very easy to get into, it seems like the synchros were in really good shape, but something was amiss.

I drained the gear oil and found it was really dark, like used engine oil dark. I was surprised at this because I had replaced the gear oil just several months ago, and the previous owner had done the same just a few months before that. I removed and disassembled the trans using some of xirdneh/robert walker's videos on youtube but didn't find anything obviously damaged inside. However I didn't go so far as to remove all the gears and synchros, maybe if I had gone all the way I would have found something but I had been hoping for an easy-ish fix (Robert had mentioned that perhaps one of the bolts securing the shift forks was loose but no luck there). I had a good trans in my parts car so at this point I decided I would just swap them.

When I drained the gear oil for the trans in the parts car, its oil was still clear and golden despite being over a year old and seeing more use than the gear oil in the bad transmission. So I'm guessing that the consistently dark, dirty oil in the bad trans is a clue as to what the problem is in there. The two previous owners of that car were neglectful, and the trans had several leaks, so it's very possible it was run low but I'm not sure how that would have made the gear oil so dirty that it stays dirty even after two flush and refills.

Anyway, I noticed a few other things that were interesting to me so I wanted to share them here. One is cracking in the case of the diff.

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I showed these pics to Robert and he said it was normal. Lo and behold, when I separated my good trans from its diff, Rob was right -- it was the same! Weird.

The other interesting thing was the breather on top of the trans. I'd never seen it before and wondered where it was located. It's at the top of the case, just above the input shaft. On one of my transmissions, the cap for the breather was loose like it should be. But on the other trans it was stuck and plugged with crap so I loosened it and tried to keep the crud from falling into the trans. Once I separated the trans and diff though, I saw that some of the crud had fallen in. See pic, red circle is the breather, blue circle is rusty crud that fell into the trans. I cleaned it out of course, and thought I'd mention it here in case it's helpful to anyone one day.

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[SirFoxx]

If the oil is getting dark quickly, you have a bearing thats getting hot and scorching the oil. you need to find the bad bearing and replace it asap before it nukes the trans.

[dlb]

If the oil is getting dark quickly, you have a bearing thats getting hot and scorching the oil. you need to find the bad bearing and replace it asap before it nukes the trans.

Interesting! I have already reassembled the dirty oil trans but if I ever need it in the future, I will remember this and find the bad bearing. Thanks Keegan.

[Nordical25]

Looks interesting. And good that you have some spare parts for those transmissions. I have never opened myself a transmission but who knows when that day will come. These pictures and Roberts video will be helpful for sure in that case.

[Mogordo]

Hey dlb, Thanks for letting us know what you found.
And thanks to Sirfoxx for the tip about what can cause gear oil to get dark quickly. That is something I am going to keep in mind.