I need to do a quick update on this ... I'm completely buried at work but this is important so I wanted to squeeze it in ...
After running standard (non synthetic) GL4 gear oil in the Mitsu M/T for a year without any major incidents, I had the tech swap it back to the Amsoil full synthetic the first week of April - so almost exactly two months ago. It took about a week and a half and about 700 miles before all the same issues started showing up. Problems downshifting, eventually popping out of second gear under compression load, cranky shifting like the clutch wasn't disengaging entirely, cranky shifting like the syncros weren't lining up correctly, etc. Same story, different day.
The tech and I went back through everything we could possibly conceive of down to and including the 3.5L engine swap that was done several years ago. Back through the ENTIRE clutch system, including bleeding it several times in several different ways, readjusting the clutch master and pedal, etc. The tech found an 'oops' that the previous tech did when he as doing the engine swap where the slave cylinder wasn't bolting in correctly and fixed that. It helped slightly but wasn't the smoking gun. Flushed, blead, adjusted, re-flushed, re-blead, etc. about a dozen times. Every time we did something that seemed to help, within a day it was back to where we started.
That left me back at the fluids I was using. The standard gear oil did ok but it wasn't perfect; the manual transmission still had issues shifting. One thing it did not have was the weird syncro behavior like the gears weren't lining up during the shift. That led me to think it might be a 'weight' issue so when I switched back to the Amsoil I used the heaviest GL4 oil they had. Which did absolutely nothing to solve any of the issues.
When the transmission started popping out of 2nd again, I decided to chuck the whole synthetic in the manual transmission thing altogether. This spring I've had zero time to futz with this and I need my truck on the road and reliable and my patience was running a bit thin by this time. One more time I went back to researching - this time for a good - maybe heavier - standard gear oil.
In the process of poking around the major manufacturers of gear oil, I stumbled on a blurb on RedLine's site about one of their extreme 'race only' gear oils warning about using it in 'street' vehicles and noting all the problems that could occur with 'some' manual transmission. The paragraph was pretty specific and described every one of my issues exactly. The problem with using this specific gear oil is that it actually works TOO well and that's what causes the transmission issues. That was useful information but obviously didn't supply a solution.
At this point I still didn't really care, I was still looking for standard gear oil, and I was out of time and needed something RIGHT NOW. I stumbled on a RedLine product that looked like it wouldn't actually be worse, did some surfing through the Mitsu boards and found that was what most of the 3G guys were using, found a case cheap and called it a day. I did note that RedLine recommended it in most Japanese manual transmissions. What I did NOT note was that it was full synthetic - until the box arrived. Duh.
Unfortunately that was 2 days before I had it scheduled for service and that left me with no time to find a replacement. Screw it. In it goes. Can't actually be worse.
That was about a week and 350 miles ago. Its back to shifting normally. No more popping out of 2nd gear. Shifting through the gears feels normal now. Doesn't feel like the clutch isn't completely disengaged half the time. And strangely the transmission is much MUCH quieter than 'usual'. The V5MT1 is never silent but with the Amsoil its sounded like there was no gear oil in it at all. Its also silent and glass smooth now on the street. Its actually behaving better now than it did with standard gear oil.
MT-90 75W90 GL-4 Gear OilI don't have any idea what this would do in a Sport M/T that hasn't been rebuilt. I ran Amsoil for 6-7 years in the stock transmission without incident. I don't know if there was a change in the chemistry of if the non-OEM parts used to rebuild our transmissions now are different or both. At this point I would not recommend Amsoil for the V5MT1. It takes about 18 months for the transmission to eat itself and while the rebuild isn't terribly expensive (the last rebuild cost $600), removal and install is a PITA and takes about 10 hours.
What I absolutely know is that my M/T is a LOT happier with the RedLine and unless something crops up, that's what I'll stick with for the manual transmission. If things go well through the fall, I'll put the same thing in my stock (little) '97 OEM transmssion and see how that goes.
Note: I didn't get to see this, but the tech remarked that the gear oil was 'unusually dark' when he drained it last week. No unusual metal flakes or shavings or anything on the magnet, just unusually dark for fluid that was only in for two months.
Edward
