Differences between manual transmission fluids
 

I've heard a lot of talk about Honda MTF, Amsoil MTF, Redline MTF, and GM Synchromesh but has anyone tried some of these back to back? I'm wondering which transmission fluids have the most effect on syncho feel and life.


I ask because my newly aquired 2010 Sport with 165k miles has some pretty chunky shifting and I'm 99% sure it's just worn out synchros.
I changed the trans fluid in my miata with the same issue to some Ford fluid the miata forums recommend and it vastly improved the shifting feel to the point where it almost felt brand new.

I believe my trans has Honda MTF in it right now and I just want to hear from some people that have tried other fluids and how the fluids compared to each other.

Ive only used honda and redline on this. Honda was way to thin to me by comparison, the other is buttery but takes a while to heat up. If its cold by you id go with honda and maybe cut in some thicker stuff with a single drain to test it out. Synchro n redline will help cover up the servos. Redline is my jam.

You're saying GM Synchromesh and redline combo? Which redline fluid would you reccomend? They make about 89462 different kinds. Thanks.

Redline calls it MTL like they wanna be different. I meant doing a single drain and refill as opposed to 4 which is a full change. With the single change add in just redline, or synchromesh if they say its compatible with all mtfs. Redline says it can blend. I'd do a full tranny change if its your first one. Several people on this forum have recommended a full change every 30k, but this can be supplemented by doing a single drain and refill at 7k miles, along with an oil change.
i judge it by shift feel, and 7k for a partial suits me just fine running all redline here in southern california.
if you're in a cold climate I would recommend sticking with honda with 1/4 of the total capacity being redline. If you want thicker after trying that you could add redline again at the next refill, and keep doing that until shift feel is fine. the redline just takes a while to heat and get smooth.
the fluid I added in for a really thick blend just to try it is redline's light weight shockproff gear oil whose purpose is use in wet sump systems. It looks like smurf blood and should only be added in a small amount, like 1/8th total capacity, if you choose to try it. Its not intended for our transmissions because of thickness, hence the small amount, also its super smoothness doesnt last quite as long, but if your wear is significant you might find it promising. Its a popular cocktsil among the mitsubishi crowd. I cant recall if redline themselves actually started making it that way.

I'm using Amsoil Manual Synchromesh Transmission Fluid in my GE8 and it feels great.

You're using pure Amsoil Manual Synchromesh?

If by "pure" you mean ONLY Amsoil Manual Synchromesh in my transmission, then yes.

DO NOT USE SHOCKPROOF/or lightweight Shockproof, It is for Dog ring boxes or transmissions with race style steel synchro's NOT regular transmissions,
I did it once accidentally and I ended up pulling the trans to get all the synchro's and bushings replaced.. It basically corroded them..

Make sure whatever you put in is the same GL rating as what comes out unless you've got really solid data that its safe, there are 3 different "blends" of gear oil and if you use the wrong one the synchro's won't like it,, neither will some bushings in the transmission.

Redlines customer service number can tell you which product matches the Honda spec.
Same with Amsoil.

You;re going to have to think this one through carefully. I've seen Amsoil recommended on this site people seem to like it.

FWIW, Honda is very clear they recommend Honda fluids only on: AT, MT, Differential. Much more flexible on engine oil and coolant IMO.

You haven't got a BMW or NSX here and I'd just go with Honda. Throw a weighted shift knob on it for better feel. But you know, there are options beyond that too.

Itll take a while
 

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i'm going to run a UOA on my redline MTL. My service interval is a single drain and refill ~ every 7k miles. Should be comparable to anyone who does theirs at 30k. My car currently has 67k miles on it. I'd rather not draw out the process, so if someone has a similar service interval using modern honda mtl we can compare results via UOA to determine equivalency. If someone has been running a different fluid from those two, feel free to do the same. They mail out (at least) the first test kit for free. The analysis will likely have a fee.