TeamSwift

Is this MT-90 recommended by the manufacturer as an alternative? Im gonna be changing my gear oil soon to try and stretch my tranny's life over the winter and i want to try something new, but still within the manufacturer's specs....so does this redline MT-90 fall under that catagory?

Redline isn't officially recommended by Suzuki the way GM Synchromesh is, but many people have had positive results with it. The very fact that it mentions that it contains friction modifiers for synchro operation would make me very comfortable with using it.

OK here's my story. i've had 2 '98 fireflies - 1.0 5-speed both. we'll call them "old" car and "new" car.

here's the short version: the viscosity of the tranny oil that came from the factory is much lower (thinner) than 75/90 that the owner's manal says is OK. i put in 75/90 synthetic and it caused shifting problems which i solved by going back to a lower viscosity oil (GM Synchromesh).

here's the long version of how i figured it out:

thinking i was being nice to the "old" '98 car, i changed the tranny fluid when i got it (at 142,000 kms) to synthetic 75/90 gear oil, following the specification in the owner's manual.

i started to experience crunching into 2nd gear shifting up or down. to avoid the crunch, i had to shift slowly at lower RPM, or double clutch. i thought maybe the synchros were just wearing out - it didn't occur to me that the owners manual could be wrong.

then i bought a "new" very low mileage '98 firefly that had been sitting for several years. again, thinking i would be nice, i was going to change tranny fluid, again using the recommended synthetic 75/90.

but before i poured the fresh stuff in the "new" car i decided to compare the viscosities of the ORIGINAL fluid (which i had just drained out) to the fresh 75/90 synthetic. i did this by pouring a measured amount thru a cotton filter.

result: the original tranny fluid (i am certain it's original, from the factory) poured down in 2 minutes. the synthetic 75/90 took 8 minutes! for the same amount at the same temperature. i repeated this several times.

so, following the advice in this and similar threads, i went to the GM dealer and got some Synchromesh manual transmission fluid (bottle says "part synthetic). did the pour test, and it poured down in just under 2 minutes. which tells me that's the stuff to use, based on viscosity.

i haven't sold my "old" firefly yet, so i drained the 70/90 from it and filled it up with the original fluid that i had just drained from the "new" car. result: the old car shifts fine again. no more crunchies.

this tells me the problems people have been having aren't related to whether the fluid is synthetic or not, but because of wrong viscosities.

GM's original oil (and Synchromesh replacement oil) is dramatically less viscous than 75/90. exactly how much i can't say: the bottle of Synchromesh doesn't have a viscosity rating anywhere on it. bizarre.

doesn't matter. it works. no more crunchies.

and a final note: my experience with the "old" firefly running 75/90 was in summer temperatures. now that it's getting colder, i'm sure the problem would have gotten even worse. also, now that i'm selling the "old" car, it's good to know that a prospective buyer is not going to experience shifting problems on a test drive. peace of mind for me - makes it much easier to sell.