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Old 10-02-2018, 09:17 PM   #1
tmontague
 
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Manual Transmission Fluid Woes

I decided to throw this post up to gather all the info I have researched and experienced in regards to the proper type of fluid to run in a Toyota manual transmission with a clutch type LSD

Spend time researching the question online and you will not find a solid answer. You'll read a few musing here and there but nothing that gives you any confidence in what type of fluid to run. It should be noted that the 100% proper fluid to run is the fluid that the manufacturer of your LSD recommends. Typically this is their branded fluid such as Cusco or Kaaz fluid.

When I first started using my the trans with the LSD (Tom's old trans) I used Cusco fluid that Tom sent with it. This is a non synthetic 75w85 and it makes the LSD very quiet and the shifts were smooth - happy syncro's, happy LSD. The obvious question is why didn't I just stay with the Cusco fluid?

The Cusco fluid is $27 CAD a liter and add an extra $10-20 on that for shipping, so about $75 per trans fluid change. This is a non synthetic fluid so with heavy track days I would have to change it every couple track sessions which adds up quickly.

Even with all of that, the main issue is that I cannot find the fluid locally but it has to come from Japan. I prefer to use a fluid that I can go out and grab in a pinch if I need to. I also would rather use a synthetic fluid that I can trust in high temp track use. I had previously run Amsoil MTG in my open diff trans as well as Redline MT-90. I found the MT-90 to work well but was a bit notchy especially in the cold weather. The MTG was smoother for me so I always ran that.

I tried it in my LSD trans and within a few days the clutches started banging, or basically grabbing and letting go violently. I previously called Amsoil and they said that there isn't a reason the fluid shouldn't work but that they couldn't confirm for sure if it was compatible. I went out and purchased some CRC friction modifier and added it in one ounce at a time every few days. The plan was to add a little bit until most of the diff chatter went away. Add too much and the LSD can become an open diff.

I got the diff to quiet down after adding about 4.5 ounces or so of the friction modifier. Then I started noticing a grind shifting into 3rd if I I did a quick shift. Then the odd time in first at stop lights. Then a lot of grinding at the track - I did notice the odd 3rd gear grind before at the track during a hard left turn but this was almost continuous. Turns out that adding friction modifier makes the fluid more slippery so the clutches slip but the side effect is the syncros don't have the friction they need to work properly.

I had some extra MTG in my shed so I drained the MTG with friction modifier from the trans and mixed it with the new MTG and refilled the trans. 99% of the syncro grinding went away. However I wasn't satisfied that the MTG was the correct fluid to run and was on a mission to find a suitable fluid. I asked Ron what he/his racing friends recommended and he said Redline fluid. I didn't want to go and spend $40 on fluid if it was going to cause the same issue so I did some more reading. A few people had luck running MT-90 mixed with MTL fluid. Others stated they preferred the lower viscosity of the MT-85 with less notchy shifts than the mt-90. A shop close to me sells Redline fluids so I figured I'd give the mt-85 a go

It's been a couple days and about 70 km of driving and so far I'm impressed. I have not added any friction modifier to the trans fluid yet and I'm waiting to see if I need to. If I do it will only be 1-1.5 ounces. The diff does chatter a bit
especially in the morning during a cold start but it is not a violent banging and is much more tolerable. Sort of a noise you would expect from a clutch type diff but not as silent as the Cusco fluid. I have not had a single syncro grind yet since I swapped fluids.

FWIW others online mentioned that they found success mixing 1 quart of the manufacturers fluid and 1 quart of a synthetic M/T fluid. This is a pretty good way to keep the imported fluid lasting longer. If the mt-85 I'm currently using starts having issues then I will end up going half and half with Cusco fluid.

It's possible that I didn't wait long enough before I added more fiction modifier but typically it was at least 90-150km of driving before I'd add another ounce. It is also possible that the 90 weight fluid isn't thin enough for the clutch plates to properly slip which is probably why Cusco goes with a 75w85 vs the Toyota spec'd 75w90. This is also possibly why the mt-85 by Redline worked better than the Amsoil MTG.

I'll post back if I have any issues but so far I am happy with the mt-85 with no modifier added. It should be able to handle track use with no issue since it is a proper grade IV synthetic fluid and ti should also cold shift well. It's about $19 per quart here in Canada so not cheap but easy to get and no shipping charges.

Hope this helps someone else in the future who's looking for a transaxle fluid with a clutch type diff
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Old 10-04-2018, 07:53 PM   #2
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short update - the diff chatter has actually seemed to smooth out quite a bit w/ the MT-85. Only noticed one very brief grind going into 3rd and this was on a very hard and fast shift and the grind was very mild compared to before. So far so good, I am going to stick with the MT-85 for now and I'll have to see how it is next track season. If I still notice gear grinds at the track then I'll mix in a quart of the Cusco fluid.
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Old 10-06-2018, 10:01 AM   #3
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Thought about amsoil severe gear? I used to run that in my XRS and liked it
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Old 10-07-2018, 10:30 AM   #4
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I've never used any severe gear before as I've always stick to mtf type versus a gear oil. Although I came across it on other forums of people using it with some luck.
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Old 10-08-2018, 09:12 AM   #5
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It was back when I drag raced my XRS...never let me down
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