Mixing in Syncomesh, and Friction Modified?

[AuburnRyan]

Nissan 240sx with turbo motor and 5 spd Transmission. Nice day driver and some weekend track excursions.

Last year (8kmi ago) the transmission was the smoothest I've felt and had no issues on some generic gl-4 fliud. Drained and put in some GL-4 Amsoil MTL, with negligible effect.

The transmission has gradually become nothchy and now even the aftermarket shifter needs to be "fiddled with" to get into gear. Feels like the gate has closed into first sometimes - like things aren't lined up. This may be an issue in itself...it dosn't grind synchros or anything...

However I was considering changing the fluid again (2.5 liters) by either:
1. Mixing the MTL and 1 qt symchromesh
2. Mixing some MT90 and 1 qt synchromesh

Good or bad Idea? I know Synchromesh it thinner hence the 1 SM/1.5 gl-4 mix.

So the rave was Synchromesh, but no everyone screams Synchromesh FRICTION MODIFIED - what gives? I suppose some additives....but which do I want?



Think the first order is to inspect the shifter that started to act up, and repace if necessary, but I thought the new fluid mix may help?

Thanks in advance. Opinions Welcomed

 

[AuburnRyan]

Sorry for the typos above.

OEM spec is 75w-90 GL4

 

[Pablo]

You used MTG, correct?

As you state, you need to assure your notchy issue is viscosity related. MT's don't usually need much FM, or rather depending on the method of synchro and shifter action, too much FM's can cause issues. I doubt "Synchromesh" (GM?) has too much FM's.

I actually have no issues with custom blending MT lubes. You could replace one qt of MTG with MTF for a slightly lower viscosity, if this is your problem. I run a MTG/MTF blend in my Volvo 5 speed and it shifts great.

 

[AuburnRyan]

Correct- my mistake - Amsoil MTG was used.

Thanks!

 

[unDummy]

Synchromesh is too thin. You'll sacrifice transmission longevity for shift quality.

Depending on the mileage of the transmission, it could just need a rebuild.

And, I find that the 2nd drain/refill with a fluid is usually better then the 1st. It could be that too much old fluid was left behind or that the new fluid did some cleaning. Feel free to just change the fluid with MTG again.

Since Nissan switched a bunch of transmissions to 75w85 fluid for the sake of better shift quality, you can mix the Redline MTL/MT90 or Amsoil MTF/MTG. Stick with same brand when mixing.

 

[MolaKule]

All Manual Transmission Fluids (MTF) fluids, including "Synchromesh" are friction modified so as to provide the proper synchro engagement. This is done using a special chemical compound called a "friction modifier," which allows exact shearing of the fluid in the synchro assembly to allow smooth engagement.

If you use Amsoil manual transmission fluids in a Nissan, use 1/3 Amsoil MTF with 2/3 Amsoil MTG or 100% MTG.

Synchromesh fluid by itself is too thin for proper operation and design of the Nissan transmission.