so i have been having some serious problems with my truck grinding when i would go to second gear. i put redline mtl/mt90 mix in it about 5 weeks ago. drained it tonight after about 3000 miles on it. it was blacker than any engine oil i have ever seen. i put the stock trans fluid in it. pretty much cleared up what i thought was a syncro being broke. it still grinds a bit, but improving the more i drive it. if you are having nv5600 grind problems, i would definatly look at the fluid in there and see if u have the same result i did. almost $70 bucks for oil that trashed itself in less than 2 months. i am a firm believer now that the stock oil is all that should be put in these. . i think redline is going to hear about this also, cause it was starting to cause what could have been very expensive syncro problems. has anyone else had trouble with the redline oils??

 

the mixture of redline 90 wt is not rated for the yellow metal in the syncros of the nv5600 it is a GL4 rating and the MTL is a GL5 IIRC. I have been told by redline as well as tranny shops not to mix any 90wt or any other thickness oil into my nv5600's it will burn the sycros up.

 

i just put amsoil syncromesh in today and on the front it said it was 5w-30. how it last. my stock fliud had 90k miles and still looked good and smelled ok. same with the differentials, smelled ok and looked fine.

 

i am finding all this out now. i was reading on here before i put that mix in there, and people were saying to put a 50/50 mix of mtl/mt90 in there, if it was really hot outside. i live in yuma az... about 130 degrees in the summer. what are the chances that syncro will come back to life with the stock fluid. it feels like its a lot better than it was before

 

Yep the 5600 takes a 5w 30 type oil with additives for the synchros. If the 5600 is like the old Getrag the 90 weight might have additives that react with the metal in the sychros.