So I have searched here after reading an article on CF about fluid to use in the NV5600. Some say Pennzoil, Amsoil, OEM..etc. First off, is the Syncromesh transission fliud made for the GM brand the same stuff reccomended for this tranny? From what I can read I think it is, just makes a fella question it when GM sells for less then half of what Dodge dealers want. I have also read the theory of adding the limited slip (1 bottle) to the tranny when doing an oil change to it. Has anyone in here been doing it to theirs? I think i'm going to do a fluid change on mine and not sure what to put in it. I can't get the Pennzoil or Amsoil here in Canada where I live so it's gonig to be dealership oil or maybe the GM fluid if it is in fact the same and the limited slip oil if it's a good idea

Can't understand putting LS in the NV5600,thats for clutch type disks in a diff. GM did use the NV5600 in thier trucks also,so yes that is the same fluid,I would add 1 extra quart over the recommened just to help with lubricating the rear bearings,also I would change every 60-75k.

Appreciate the input. I know you have alot of experiance with the 5600. Just looking for anything that makes something better or last longer.

I finally tracked down some Pennzoil fluid and changed my fluid today. Added 6 quarts, and also took the PTO cover off to have a peak and wipe the bottom out, but once I took it off I saw there's no room to even get a rag down in there to wipe it out. The gears stick out there and take up pretty much any room it has . Surprised the fluid I took out didn't look that bad.

I use Royal Purple SynchroMax in the 5600, SyncroMesh in the 4500. Redline MTL is recommended, too. http://forum.mopar1973man.com/threads/5768-Nv-4500?p=53132#post53132

SyncroMax is designed for manual trans trucks that take ATF, but it does list the NV5600 as an application? Seems odd, it must be a syncromesh of sorts. My dad has it in his G56, so well see how it does. Syncromesh is specifically not for the NV4500, but for the NV5600 (among others). I can't find a Royal Purple Syncromesh, so which are you using? Royal Purple lists Max Gear 75w-90 as their fluid to run in a NV4500. It needs a 85w-90 GL4. I am running Amsoil MTF Syncromesh in my NV5600, all of 9 qts with my fast coolers.

John, I'm gonna have to check.. I may have them backwards..

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I mis-typed.. It is SynchroMax in the 5600, and Max Gear in the 4500...

My bad; I'll correct the above post..

The chrysler fluid for the 4500 is a 75w85. I also used rp synchromax in my 5600 with no ill effects.

Anyone here have experiance using LS addative? Mine like to grind going into reverse but if you select and forward gear first then reverse it slips right in. No other shifting problems at all.

Mine has been doing that since i bought it with 110k roughly 160k on it now with no problems -Jordan-

How often are you guys changing the fluid in your tranny's? I have the 6 speed and have no idea how old the fluid is in the box, so prolly is time.Thx,FT

I'm doing it at 50K mile intervals.

Not sure what part of Canada your in but AMSOIL is available just about everywhere here in Alberta.I have run AMSOIL MTF since almost day one on my truck, it's got over 255,000 miles on it now and it shifts better now than when new.The biggest key to longevity is the 6 quart (liter) overfill and you have that covered. Pulling the PTO cover is a good thing to wipe it out also. It's tight but can be done, the other thing for next time is to jack the rear end up as high as you can get it, you'll be surprised how much oil is still in there when it all bleeds out the PTO hole.Jeff

i am former chrysler tech, i did study and research about the fluid for NV5600, i knew the chrysler keep said use the Mopar fluids for the specific transmission.. i had to use mopar fluid as for NV5600 only as i can get good price for it as i has friend who still work for chrysler (the chrysler was almost hire me but Ford shop hired me first as they wanted me)... the problem is i had seen few customers had brought in the diesel truck that has transmission noise or shifting problems. i did always asked for what kind of oil and when did they changed the fluid?? some of owners had never changed it for 150K or more, other owner did not follow the owner manual's fluid specific as just pour the thick gear oil like between 80W-90 to 75W-140 which it is not good.. most of time it has sync teeth go bad and gears has chipped, etc.. i had make two quote as rebuild it or swap it for reman one, most of owners rather go for reman as better warranty and cheap labor as just swapped it... but i do inspect the clutch system to make sure it is good or time for replacement... one guy had me to fixed the nv5600 at work as he had pulled it out and brought it in to my work for me to inspect and repair it... it was a bearing noise because he did not changed the fluid as he had stopped it when it made a noise first place not keeping driving until it get failure...also it is good idea to keep the fluid level same as fill hole on transmission but if you want overfill to keep lube the rear bearing, that is ok but be careful as i do see some of customer who brought the truck in for transmission oil leak, as transmission rear output seal got old and leaking the fluid out...

I have Royal Purple Synchromax and a bottle of the Mopar LS additive in my NV5600 for about 25,000 miles now, and so far so good. It seemed to help my 2-3 shifts when cold. I definitely hesitated when I was pouring the LS additive in, but no complaints and shifts good. I don't know if it is good or bad for the internals, but definitely feels better than the previous - which I believe was the Penzoil synchromesh.