4th gear shifting issue

[Benrad]

So I filled transmission. Less than 3 quarts went in. When I was down there I saw that I had drained from what looks like the front diff and there looks like a drain also on the transmission. Both 24 mm. Did I drain from the wrong plug? Do I just wait for fluid to settle to shoot for the last quart? Thanks.

[Benrad]

And yes I had the 19mm backed out.

[dlb]

It's been a while since I did this but IIRC, I drained from all three just to make sure I get as much of the old fluid out as possible. Sorry, I feel like one of us should have caught that and mentioned it earlier.

The good news here is that if you got 1.5 quarts out initially and it only took 3 quarts now, that means it probably had about 2.5 quarts in it. That's obviously low but probably not low enough to kill it. I would drain all of the oil out now from all three drains, and refill it with all new gear oil. I would go the synthetic route myself but as mentioned earlier in this thread, this is very much a matter of personal preference.

Good luck.

[Petros]

This statement is just plain false. I'm running a full-synthetic Redline MT-90 GL-4 gear oil in my transmission and it is NOT "too slippery." It certainly shifts better than when I had replaced the original fluid with generic, off-the-shelf conventional gear oil.

well good for you. Your statement is untrue and without support. It would be better if you asked why I would say that, rather than making an untrue statement: I and other members of this forum have different experience with 100 percent synthetic gear lube.

Perhaps 100 percent syn works on a new transmission, but both myself and long time member SynthDesign tried 100percent synthetic in our Tercel4wd with the manual 5 spd trans, and both of us got gear clashing when shifting, also on mine, it started leaking out of the seals. it was like the syncros suddenly were worn out and doing nothing, I had to double clutch to get it to shift smoothly.

the syncro work by friction as the next gear engages, if you reduce the friction by using a slippery gear oil, they will not function the same way. Lubrication engineering is like anything else, Toyota designed this transmission in the late 1970s to work with the common gear oil available at the time. With new syncros and seals, the trans may perform acceptably, but not as the engineers intended, and once worn, it will perform less than acceptably. I do know a fair amount about lubrication engineering, we had to review all the lubricants used in the factory Nissan race cars I helped design and build in the late seventies and early eighties when Nissan had a racing program. We were taking an engine with a stock 180 hp, and a 6800 rpm red line, to about 900 hp and a 11,000 rpm red line. all the lubricants had to be changed (the bearing clearances as well) for the more severe usage, and we worked with the factory engineers for guidance and also did our own reseach to determined what worked best, sometimes by trial and error.

And my own Tercel4wd trans has about 400,000 miles on it, I have replaced some of the seals, but it has never been rebuilt (not even opened up). By many trial and error, guided by some knowledge of lubricants, I find it runs happiest with 2 quarts regular gear oil (per the FSM), one quart of synthetic to reduce friction, and one quart of ATF, that improves the worn syncro performance, and the detergent action keeps it free of sludge. I have tired 100 percent sythetic, as stated, it leaked out the seals, and the syncros stopped working, I have tried 100 percent conventional gear lube, and it worked okay except when cold it was very difficult to get it to shift without double clutching it. the combo I have now works well for the age and wear on the current trans.

Others may find what I have learned useful.

[The Professor]

Petros, let's start off with a few questions about your specific situation:

What brand of 100% synthetic gear oil did you use? What was the weight? How long ago was this fluid change performed? Were your transmission seals new when you tried the synthetic lube, or did they already have 200k+ miles on them? The leaks also seem to be isolated to your transmission alone, and did not occour in SynthDesign's transmission. Were you two using the exact same fluid? You mentioned that you replaced SOME of the seals, but not all of them? Were the seals you replaced leaking? Did the leaking go away when you changed back to the cocktail of fluids?

IMHO as a vehicle design engineer with experience in Field Service, there are just too many variables in this equation for me to be willing to place the blame on ALL SYNTHETIC fluids. Based on your comments, I would say your transmission has sustained extreme wear to the syncros and that your experience cannot really be compared to that of the average member.

Your work with Nissan nearly a half century ago is noteworthy and I would be equally proud if it were my experience, but lubrication technology has also improved over the last 45 years. Same conversation we had about engine design and fuel formulation in another thread.

Let's take a look at your complaints about synthetic oil and compare it to the MT90 lubricant from Redline:

•75W90 GL-4 gear oil (similar to SAE 5W40/10W40 engine oil viscosity)
•Popular in Nissan, Mazda, Mitsubishi, VW/Audi, Lotus Elise/Exige, Toyota, Mendeola transmissions and Atlas transfer cases for Off Road

"The syncro work by friction as the next gear engages, if you reduce the friction by using a slippery gear oil, they will not function the same way."
•Offers quicker shifts, perfect synchronizer coefficient of friction
•Safe for brass synchros, as it lacks the reactive sulfurs found in most GL-5 oils that cause damage
•High performance gear protection and longer synchro life

"Both myself and long time member SynthDesign tried 100percent synthetic in our Tercel4wd with the manual 5 spd trans, and both of us got gear clashing when shifting"
•Eliminates notchy shifting, even when cold
•Recommended for GL-1, GL-3 and GL-4 applications, as well as where most special synchromesh fluids are specified

Based on how you describe your transmission and how poorly it shifts, this lockdown might be the perfect opportunity to replace your transmission with a low mileage alternate, and crack open the 400k+ mile transmission for an inspection and a refresh.

Not everyone is limping a 400k+ mile transmission to the grave. Some of us want to preserve the life our transmissions still have. Until you're ready to try a synthetic fluid that is, LITERALLY, designed for our transmissions, I think the Petros' Cocktail should be reserved for transmissions that are on their last legs, and NOT be the base recommendation for EVERY Tercel.

[Petros]

What brand of 100% synthetic gear oil did you use? What was the weight? How long ago was this fluid change performed?

75W90 MTF Gear Lube, Royal Purple synthetic, both synth and I used the same gear oil. I do not recall, perhaps 5-6 years ago.

Were your transmission seals new when you tried the synthetic lube, or did they already have 200k+ miles on them? The leaks also seem to be isolated to your transmission alone, and did not occour in SynthDesign's transmission.

I had replace the cv axle seals, and the rear seal. the shift lever seal was original, as was the input shaft seal. Synth had the same leaking issues, his trans had fewer miles than mine. I have since replaced the shift lever seal.

You mentioned that you replaced SOME of the seals, but not all of them? Were the seals you replaced leaking? Did the leaking go away when you changed back to the cocktail of fluids?

See above for seals. I had switched to 50/50 Royal Purple MTF and GL-5 75W90 gear lube, and it stopped leaking, and the poor syncro performance disappeared. Synth also tried the 50/50 mix and was impressed with the improvement in shifting, and his leaks stopped as I recall. I have with the most recent gear oil change, used my current mix to further improve the syncro performance (2 qt gear oil, 1 qt ATF, 1qt MTF) and to economize the gear oil change some. No leaks, no other whine or gear noises. runs smooth.

Based on your comments, I would say your transmission has sustained extreme wear to the syncros and that your experience cannot really be compared to that of the average member.

I do not know about "extreme" wear, with regular gear oil it shifts fine except when it is very cold (well below freezing) until the gear oil warms up. that does not take long, but I can imagine that 90 wt gear oil is pretty thick and sluggish when is it 18 degree F and I first drive off.

Your work with Nissan nearly a half century ago is noteworthy and I would be equally proud if it were my experience, but lubrication technology has also improved over the last 45 years.

not quite, it was about 34 years ago, they ended their racing program in about '92. but the issue is, that has not changed, the Tercel trans was designed in 1977-1978 for the gear lubes that were available back than, not for modern synthetics.

"Both myself and long time member SynthDesign tried 100percent synthetic in our Tercel4wd with the manual 5 spd trans, and both of us got gear clashing when shifting"
•Eliminates notchy shifting, even when cold
•Recommended for GL-1, GL-3 and GL-4 applications, as well as where most special synchromesh fluids are specified

Are you describing a product that is designed for use in a transmission designed 40 plus years ago? If so, I am not familiar with the product you describe. It may indeed be an improvement over the Royal Purple MTF, but it seems unlikely that a company would create a modern formulation for an obsolete transmission design. there would not be a very large market for that I suspect.

Based on how you describe your transmission and how poorly it shifts, this lockdown might be the perfect opportunity to replace your transmission with a low mileage alternate, and crack open the 400k+ mile transmission for an inspection and a refresh.

why should I replace it? it works perfectly well in all modes, all gears and all speeds. it runs and shifts quietly, the only issue is the first and second sycro is worn. But even with regular gear oil in it, it still shifts perfectly well if you dont rush it, no gear crunches, it is just oddly very slow to go into first and second gear when just staring out when it is below freezing. I would not pull it apart for that. especially since my gear oil mix makes it work acceptably well. I got too many other projects to mess with than to change out a working transmission. besides, I am not locked down, my work as a professinal engineer is considered essential. I am as busy as ever.

Not everyone is limping a 400k+ mile transmission to the grave. Some of us want to preserve the life our transmissions still have. Until you're ready to try a synthetic fluid that is, LITERALLY, designed for our transmissions, I think the Petros' Cocktail should be reserved for transmissions that are on their last legs, and NOT be the base recommendation for EVERY Tercel.

it is not "limping", it works perfectly well. I would not hesitate to drive it to Florida and back. I really doubt it is on its "last legs", I have owned perhaps 12 or 14 tercels, and driven and worked on many others, I know what a bad transmission sounds and feels like.

you say there are synthetics designed for use in our transmissions, perhaps so, but I have not tried it, I have not seen it. it must be something newer on the market than when I tried the Royal Purple. it is costly lube, and my formulations works well and is less costly to use. I just as soon keep changing the trans lube every 30,000 miles to clean out any build up and sludge, and to provide fresh lubricant, to make it last as long as possible. I have met people that have put 500,000 miles on their Tercel4wd trans, no reason to replace it when it is not necessary, changing the oil on time will make it last longer.

My experience, and Synth's experience, with the Royal Purple MTF, was identical, and changing to a 50/50 mix solved the problems, and saved money too. No reason for you to degenerate what I found works. you are free to do something different, not going to insist what you are talking about it false. it just seems to me, as I recall, the reason the synthetic oils reduce friction is they use a thinner weight oil, but cause the film strength is higher and does not need the thicker oil layer. if it is thinner, it seems more likely to leak out the seals more often than using a thicker formulation.