My NV5600...how much I hate it!

[steved]

I hate this trans... it shifts poorly, it eats fluid, it is a PITA to change fluid... but at least it is supposedly stout?



Just got done replacing the fluid in the NV5600 last night... got almost 20k out of the Redline MTL/MT-90 blend, which is by far the longest I've gotten out of any fill of synchromesh-type fluid. Starting about two weeks ago, shifting started to drastically fall off... almost impossible to hit 2nd in the morning... had to baby every shift in order to not get a little bump (gear clash). It was mainly 2nd that was the problem... but there was no normal shifting of the trans (it was bad enough I almost got rear-ended by a Stratus... the pause between shifts isn't something the other drivers are anticipating). Not to mention the fact the trans was starting to run warm... it was heating up quicker, and a little higher than it should normally do. A UOA last year of another synchromesh indicated the fluid shears in this trans... that causes my increased shifting difficulty.



Ordered 7 quarts of MTL from Summit Racing on Monday, got it last night. The bottles of MTL now read that it is a synchromesh fluid... which is new. Decided that since it was winter, I'd just use straight MTL, and leave the MTL/MT-90 blend for summer.



Did a quickie drain and fill, didn't pull the side covers (this leaves around 0. 75 quarts of old fluid in my trans). The fluid drained absolutely clear and red, just like when I installed it. And the magnet was completely clean. Refilled with straight MTL (short what was still in the trans) and got around 6. 5 quarts in the trans (it has Fast Coolers). This was the first time I actually didn't end up wearing half my fluid change...



Take off this AM... I can hit 2nd fine, but now its cranky going into 3rd... Overall it does shift better... and it rolls a ton easier (I feel this might be where some of my mileage has been lost as of late).



I'm starting to drive it like a 3-speed... 2-4-6 shifts instead of the typical row through the gears. This doesn't seem to lug the engine at all and no clutch slipping is needed, and is a lot easier on the flats to gain speed... it is one of those things, there are only certain places you can get away with it, you got to know when...



Its hard to believe, but I've actually change the fluid in this trans more than I have changed the oil in the engine...



steved

 

[TWilkening]

My 93 W250 gasser has an NV4500 in it, and it is hard to shift when cold sometimes. If it's real cold what I do is put the transfer case in neutral and put the transmission in 4th. This seems to help quite a bit.

 

[steved]

My 93 W250 gasser has an NV4500 in it, and it is hard to shift when cold sometimes. If it's real cold what I do is put the transfer case in neutral and put the transmission in 4th. This seems to help quite a bit.

My dad's 99 has an NV4500... if only my NV5600 would shift as sweet as it does! You'd have to drive both transmissions to see how much difference there is between the NV5600 and NV4500 shifting characteristics. I can drive his NV4500 all day long without one bit of synchronizer complaint... can't say that about my NV5600...



I really can't let the truck sit and idle without the neighbors complaining... I remember someone else stating they let the trans warm up in 6th with the tcase in neutral as well... I just can't do that where I live...



We found that running Pennzoil Synthetic 75w90 gear oil makes that NV4500 trans shift like butter, if you look to change fluids... FWIW. Dad currently has over 150k on Pennzoil... gets about 50k per fill before shifting gets sticky.



steved

 

[roperteacher]

Steved, I have heard that a G-56 bolts directly to an NV5600 ??? You might consider the upgrade as the new G-56's have a higher gear ratio

 

[betterthanstock]

Steve, before you yank that nv5600 out of there, may I suggest to you to drain out 2-3 quarts of whatever oil you got, and replace with ATF type F. Type F was made for brass clutches, exactly like our synchros, and is thinner than the synchromesh, so unless you tow very heavy, I would give it a try.



Keep in mind, the G56 uses ATF.



http://www.atra.com/consumers/bulletins/cb-110.pdf

 

[steved]

Steve, before you yank that nv5600 out of there, may I suggest to you to drain out 2-3 quarts of whatever oil you got, and replace with ATF type F. Type F was made for brass clutches, exactly like our synchros, and is thinner than the synchromesh, so unless you tow very heavy, I would give it a try.



Keep in mind, the G56 uses ATF.



http://www.atra.com/consumers/bulletins/cb-110.pdf

See, that's just it... my NV5600 seems to react better to a slightly thicker fluid... in the realm of synchromesh fluids; RP synchromax is the thinnest, Redline MTL is the thickest, and Amsoil MTF is in the middle. My trans literally refuses to shift with straight RP synchromax, even on fresh fluid... it does best on MTL with a couple quarts of MT-90.



I think this is the reason my trans starts shifting badly after a few miles... the fluid shears, becoming thinner, and that causes my increased shift effort. I would wonder if the trans would even shift with a really thin fluid? I might try it once this fluid is getting some miles, but I'd hate to ruin $65 in trans fluid that I just put in...



And again, the best mix I've had to date is 7 qts of MTL (a 70w80 "gear" oil, or 5w30 motor oil) with 2 qts of MT-90 (a 75w90 "gear" oil). I use "gear" oil loosely as it is actually a manual trans fluid, and not really a gear oil.



steved

 

[RVTRKN]

Steved, I have heard that a G-56 bolts directly to an NV5600 ??? You might consider the upgrade as the new G-56's have a higher gear ratio

Although it has differences from first thru sixth than the NV5600, the latest version, is the same in sixth, @ 2050 RPM at 70 MPH (NV5600) to 2050 RPM at 70 MPH (G56) with 3:73 gears



steved: my NV5600 has 50K on the trany and I have never changed the fluid due to maintenance not required yet per the manual and if cold it is a MTF to shift but I have never had the issues you describe and maybe you have a problem with it. Overall I like the NV5600 but it is a stiff trany and has a lot of posts in the past on this subject as well, but I've learned to live with it. The G56 is smoother and I prefer it over the NV5600, but having to drive them both, even on the same day, can cause some strange shifting in the first mile or two. I would look into a tear down of the trany and look at the sycronizers or any other problems, and if you find early signs of wear, fix it before you scramble the trany completely. These are very expensive and hard to find a properly rebuilt one.



How many total miles do you have on the Clutch and Trans? I didn't see it in your post except for the current fluid miles.

 

[steved]

How many total miles do you have on the Clutch and Trans? I didn't see it in your post except for the current fluid miles.

Roughly 146k on everything... clutch still has a lot of pedal, I should make 200k before it needs replaced. Fluid has been changed at least every 20k since 50k... the first 50k I just put up with it, but now I change the fluid when it gets difficult to shift. Some fluids have lasted less than 10k per fill...



The trans has acted this way since it was new... I have never seen any indication there is a physical problem with the mechanicals of the transmission. Fluid always drains clean/clear, very little if anything on the magnets. And it runs cool for the most part. I can run a rag around inside the case and it never finds any sludge or solids in the bottom.



I would almost say it is either from my driving habits (a lot of city traffic, therefore a lot of shifting) or the nature of the 6spd/4. 10 combination (sit at a higher cruise RPM than with 3. 55s/3. 73s). Something is causing the fluid to fail early...



It is actually weird to be able to see the fluid die the way it does... it will work well for most of its life, then it will literally fail (start declining in shifting performance) in under 2k miles. I have no doubt the fluid is still in excellent condition (as far as protection), and that the additive package is just used up. It is very apparent when it starts to happen... I knew it was starting soon after I got the injectors done, then it just went downhill really quick... just like it does every other time. The temperature starts creeping up... not hot, just enough that you see a slight increase in temps over new fluid... and the shifting quality drops right off...



I just find it funny that some guys have 100k on factory fluid and claim to have no issues... and I can't get past 20k without changing fluid!



steved

 

[05mxdiesel]

Either you've had synchro problems since new or your patience is just short with your trans. When cold mine is a bear, but once driven 20 miles or so, everything is peachy smooth with mine. I am on my second fill of amsoil, change at 30k miles. The factory fill did wear out before the 15k when I changed it, so I understand your synptoms of that.

 

[05mxdiesel]

I just find it funny that some guys have 100k on factory fluid and claim to have no issues... and I can't get past 20k without changing fluid!



steved

Some people just don't notice differances as easy as some.

 

[Gary - K7GLD]

Some people just don't notice differances as easy as some.

I really don't think it's that, as much as relatively wide variations in build tolerances with the 5600 - the variations in owner experiences with the 5600 on this board alone would fill a book! It's a good solid transmission, beefy and all, but even the best ones seem to display a small "catch" between some gears - my own would do that slightly when cold from 2nd to 3rd, and from 3rd to 4th.



Tried a couple of supposedly better lubes, but for my specific 5600, the OEM stuff was head and shoulders better. The most effective improvement from mine, was when I recently added about an ounce of the differential friction modifier to the transmission - all "catching" is now gone, and if anything, it shifts better cold than when warmed up - but absolutely NO issues either way. .



Luck of the draw, I guess! :-laf

 

[MMeier]

Steve, post up here if you try the ATF add. I'm getting ready to service mine in the next few weeks with Torco RTF... (Racing Trans Fluid) and see what happens. Crap had better work, at $15/ qt!! #@$%! Might add fast coolers, don't know yet.

 

[steved]

Some people just don't notice differances as easy as some.

This is hard to NOT notice... when you can't catch a gear WITHOUT getting tooth-to-tooth contact, its more than annoying. It gets worse with mileage (ie wear on the oil)...



Amsoil didn't last as long as the Redline MTL... it shifted nice in the beginning, but quickly fell off. In 10k, it was as bad as this Red Line fill with 20k on it...



steved

 

[steved]

I really don't think it's that, as much as relatively wide variations in build tolerances with the 5600 - the variations in owner experiences with the 5600 on this board alone would fill a book! It's a good solid transmission, beefy and all, but even the best ones seem to display a small "catch" between some gears - my own would do that slightly when cold from 2nd to 3rd, and from 3rd to 4th.



Tried a couple of supposedly better lubes, but for my specific 5600, the OEM stuff was head and shoulders better. The most effective improvement from mine, was when I recently added about an ounce of the differential friction modifier to the transmission - all "catching" is now gone, and if anything, it shifts better cold than when warmed up - but absolutely NO issues either way. .



Luck of the draw, I guess! :-laf

Agreed, I feel it is "loose" quality control more than an actual problem... every NV5600 is unique. I can tell you that the very first NV5600 I drove (a 99 3500 IIRC) was smooth as glass shifting, a whole different animal than this one I'm currently living with.



I have tried straight fluids, fluids plus LSD modifiers, fluids plus Lucas transmission additive, and fluids plus LubeGuard gear supplement. I've used Pennzoil Synchromesh, Royal Purple Synchromax, Red Line MTL, Amsoil MTF, a blend of RP Synchromax and MaxGear, and a blend of Red Line MTL and MT-90. Nothing has given a substantial improvement, nor has any worked as well as my Red Line MTL/MT-90 blend...



steved

 

[steved]

Steve, post up here if you try the ATF add. I'm getting ready to service mine in the next few weeks with Torco RTF... (Racing Trans Fluid) and see what happens. Crap had better work, at $15/ qt!! #@$%! Might add fast coolers, don't know yet.

It will be a while before I experiment with the ATF, but I doubt making things thinner will work in this trans base on my experiences...



I think I might actually look at one of three synchromesh fluids... BG makes one, Torco makes one, and GM has a "friction modified" synchromesh (in addition to their "normal" synchromesh). I like the idea of using synthetics for the protection, but they can't be protecting to good on gear clashes...



I have heard good results with the Torco fluid... but its hard to find!



steved

 

[Cattletrkr]

Have you tried sticking with a particular fluid even after it "fails" early. Change the fluid to the same fluid. I've read here that sometimes it takes a while for a trans to get used to a particular fluid... if that makes any sense.

I've never had any bad results with any fluid.

In my '01 with the NV5600 I never changed the fluid until after 100K. I was young and foolish I guess. I changed it to Mobil manual tranmission fluid, a straight 50w oil. It is meant to be used in OTR class 8 type transmission, not synchromeshed ones. I didn't know that at the time. I ran that for 30K+ right up until I sold it. Didn't know it was "wrong" until I did a little more checking before I did my first change in the '04. 5. Couldn't tell any difference in shifting or anything. Not even at -10*F.

Crap had better work, at $15/ qt!! #@$%!

I checked 3 dealers around here, they all have the same price on the factory fluid and they're the ONLY place to get it. $15. 83/qt + tax.

 

[steved]

Have you tried sticking with a particular fluid even after it "fails" early. Change the fluid to the same fluid. I've read here that sometimes it takes a while for a trans to get used to a particular fluid... if that makes any sense.



I've never had any bad results with any fluid.



In my '01 with the NV5600 I never changed the fluid until after 100K. I was young and foolish I guess. I changed it to Mobil manual tranmission fluid, a straight 50w oil. It is meant to be used in OTR class 8 type transmission, not synchromeshed ones. I didn't know that at the time. I ran that for 30K+ right up until I sold it. Didn't know it was "wrong" until I did a little more checking before I did my first change in the '04. 5. Couldn't tell any difference in shifting or anything. Not even at -10*F.





I checked 3 dealers around here, they all have the same price on the factory fluid and they're the ONLY place to get it. $15. 83/qt + tax.

Back to back Pennzoil Synchromesh... back to back Red Line MTL, back to back RP Synchromax, back to back Red Line MTL/MT-90. I know exactly what you're saying... even replacing the worn fluid with the same fluid (only fresh), it takes over 100 miles to get the full effect of the new fluid.



The straight RP synchromax performed the worst, only lasting for around 1k miles before getting weird...



You might want to check at a GM dealer... they have the synchromesh cheaper than you can get Pennzoil synchromesh... the "friction modified" stuff is more expensive.



steved

 

[steved]

And when you say "straight 50-weight oil", do you mean 50-weight motor oil or 50 weight gear oil????

Considering a synchromesh is the equivalent of an 5w30 motor oil or a 70w80-ish weight gear oil, the 50-weight would have simply been thinner (like an ATF, possibly like a RP Synchromax)...

steved

 

[Cattletrkr]

You might want to check at a GM dealer... they have the synchromesh cheaper than you can get Pennzoil synchromesh... the "friction modified" stuff is more expensive.

I was told by an oil distributor the Texaco 1874 MTX isn't available anywhere other than DC. That was the brand/# on a sticker on my '01's NV5600.

And when you say "straight 50-weight oil", do you mean 50-weight motor oil or 50 weight gear oil????

50w manual transmission fluid, whatever that means. I've always thought a 50w is a 50w regardless of its intend use.

 

[Cattletrkr]

Considering a synchromesh is the equivalent of an 5w30 motor oil or a 70w80-ish weight gear oil, the 50-weight would have simply been thinner (like an ATF, possibly like a RP Synchromax)...

I don't know exactly what the 50w is, but I know your comparison is not even remotely close. The 50w is much much thicker than a 5w-30 motor oil. I'm getting a little deja vu here. I think we've had this conversation before.