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Originally Posted by DOCTORBILL
Reading around about Geo Metro manual Transmission fluid, I get
the feeling that this is a controversial topic.
It looks like it is a toss-up between GM Sychromesh and Redline MT-90.
Any fervent opinions from the early 90's Geo Metro owners ?
Mine is a '93 with 3 cyl 5 speed manual.
It shifts nicely, downshifts nicely and I am wondering if I should
change the fluid as I bought it used and GOD ONLY KNOWS if or
when the fluid was changed.
Maybe 'If it ain't broke, don't fix it' applies here since some folks
seem to aquire transmission problems after changing their fluid....
DoctorBill
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Use what the manual recommends.
Now here is the part where I ruffle the feathers of REDLINE fanatics...
dont do it! Lets think this through logically.
First off most users who are having shifting issues - clunking, slow engagement, grinding - already have problems with their synchros. They report and improvement.
If you live in a cold climate and find shifting issues when cold. They report an improvement.
Well the one with cold shifting issues could go to a lighter gear oil in the winter. The others with already fuddy sychros...well they are just buying time with redline.
Synchros work by friction, so essentially one could say they are a cone brake. When you shift the synchro is pushed against the gear whick quickly spins it to synchronized speed and then the shift collar engages the gear. When the syncros wear or have been treated with teflon additive, they lose the ability to quickly spin the gear up to speed before the collar tries to engage the gear. Mismatched speeds = grind.
So how does Redline "Improve" worn/contaminated synchro cones? It does it by increasing friction. In other words its a light oil and the parts rub against each other more instead of a thick oil film that seperates them like standard gear oil offers.
So in short.. sure it will improve shifting, but expect to replace synchros in the near future due to the increased wear. Dont take my word for it, I can point you to many people that swear REDLINE hosed their transmissions. (I disagree, I think that their transmissions were needing service anyway.)
For me, I use clean, fresh, standard gear oil. Heavier in warmer climates, lighter in colder. (Mine is stubborn when its cold; I drive one block in 1st gear and its all ready to go.)
FWIW,
Blake