NV5600 strength - upgrades req'd???

["Mad Max"]

Folks,



From everything I have read about the NV5600 6-speed, it is good to go right out of the box and does not require any special voodoo to have it hold up to 'normal' driving and towing. I consider normal to be around 250 hp/580 tq, pulling 15-20,000 lbs gross, including truck. So, typical modified 12v CTD truck pulling a decent sized camper trailer.



As I am getting ready to do the mods to my 1st gen I want to install a NV5600, Dana 80 rear, D60 front, 29-spline 205 t-case, and my uses will be as described above, occasionally pulling more trailer weight and possibly cranking over 300 hp in the future. I already have the Danas and t-case, and I'm in parts-aquisition mode for the transmission.



Can anyone out there think of any reason why a nv5600 won't hold up to any of this?



Secondly, does it matter where the transmission is purchased, meaning is one from a bone yard just as good as one from a big-league transmission supplier? Any thoughts on mileage and things to look for?



Many thanks,

- M2

 

[GCroyle]

MM



I am not a transmission expert, OK?



My time with the NV5600, I would look at these points.



Input shaft, pilot bearing load bearing surface, pitted/worn/size.

Input shaft up/down play. I don't know how much is allowed, but if it is loose, then that would indicate bearing wear, compare to a newer low mileage transmission, better yet, hope a transmission pro chimes in here.

Pull both PTO side plates after draining the oil. look down inside and at the gears, go fishing with a magnet around in the lowest sump area of the case, see how much comes up. Look at the drained oil for water contamination.

The shift tower comes off easily, look inside for wear, gear condition. Try putting it in each gear and turn the input by hand, would a damaged gear be noticeable? If you had the PTO plates off, you could select each gear, turn and get a look at the visible gear surfaces. Release bearing guide tube, surface condition, this controls the clean free slide of the release bearing. Pivot ballstud, these can wear, we snapped one off trying to replace it, use patience and caution. It took a while to drill the old one out. Front surface of the aluminum case, look for big divots, and threaded holes, pay close attention to the hols for the alignment sleeves. When you install, make sure you have both of these in place, or you will tear up the clutch disc.



Re-read my opening statement.

 

[getblown5.9]

Nv5600 behind a 250hp 12v would get awesome mileage and be strong as can be. not to mention would give great towing gear choices for the mountains etc.

They say nv5600 is bullet proof but they can be broken if driven like a sports car behind a 500hp cummins. Noticed some broken main shafts in 600+hp sled pullers lately also, but as for daily drivers/tow rigs the only failures i have heard of are bearings due to insufficient fluid in the case.

On that note, I have a 5600 for sale that needs a 6 gear set put in it since the brass/carbon synchro ring broke. I've been kicking it around the garage and haven't fixed it yet.

 

[Gary - K7GLD]

The NV-5600 is a stout transmission, no doubt about it - just be aware that the Overdrive, like most overdrives, is intended primarily for use in lighter load situations. The engine may well feel strong towing a load up a hill in OD, but the OD shaft bearings and some other parts, will NOT like the stress of being used in operations they were not intended for!



I tow an RV at the 14-15k GCW, and DO use OD out on the flats and in minor grades - but shift into direct when grades are longer and in the 6% and greater range.



Good luck with an excellent transmission choice.

 

[PVanderlugt]

Why not use a G56 ?? since it is a Dc designed and build tranmission, maybe it will be produced longer than the nv5600 was. Havent heard anything bad about it. Looks like there are now 2 "models" available with 2 different sets of gear ratio's

 

[Gary - K7GLD]

Why not use a G56 ?? since it is a Dc designed and build tranmission, maybe it will be produced longer than the nv5600 was. Havent heard anything bad about it. Looks like there are now 2 "models" available with 2 different sets of gear ratio's

It's hard to predict how long ANYTHING "DC made" will remain available in "new" condition - the company seems sorta waffling in ownership at the moment - and the NV, VP-44 and a number of other former DC specific items seem to come and go at the whim of the board room...

 

[chazj]

The NV-5600 is a stout transmission, no doubt about it - just be aware that the Overdrive, like most overdrives, is intended primarily for use in lighter load situations. The engine may well feel strong towing a load up a hill in OD, but the OD shaft bearings and some other parts, will NOT like the stress of being used in operations they were not intended for!



I tow an RV at the 14-15k GCW, and DO use OD out on the flats and in minor grades - but shift into direct when grades are longer and in the 6% and greater range.



Good luck with an excellent transmission choice.

Gary: What in your experience is a "lighter load"? I tow a trailer in the 9K to 10K range with a GCWR of 17,000 Lbs (truck & trailer).



You are most correct in that the Cummins seems to have no issues in OD... but am curious if I also should be concerned when towing in OD as you describe above.



Thanks for your input.

 

[Gary - K7GLD]

Gary: What in your experience is a "lighter load"? I tow a trailer in the 9K to 10K range with a GCWR of 17,000 Lbs (truck & trailer).



You are most correct in that the Cummins seems to have no issues in OD... but am curious if I also should be concerned when towing in OD as you describe above.



Thanks for your input.

That's sorta hard to answer in a post like this - but generally speaking, if I can't easily maintain close to 1800-2000 RPM when pulling a grade, I shift down. The engine will still pull strong with my 5er in tow, but lower RPM - high torque - is a killer for OD in the 5600, and it really wasn't intended to be used in that way.



We Cummins owners - especially with added power mods - tend to think that just because the engine is running great and pulling well at lower RPM, the REST of the drivetrain must be OK too - but T'aint necessarily so, as a few unfortunate NV-5600 owners have learned the hard way!



And again, it's NOT particularly a "NV-5600 weakness", but rather owner abuse caused by not using equipment in the way it was designed to be used!



It's far easier on the transmission - and the engine too, for that matter - to maintain RPM up closer to the 2K mark when towing in the hills, than to place a lower RPM high-torque load on everything at lower RPM.



I have installed larger 285 size tires on my truck, and in pulling in the hills, this puts me at just under 2000 RPM at 55 MPH in 5th gear - the engine and rest of the drivetrain are happy - and so am I, if that gives a long lifespan for the transmission!

 

[chazj]

Thanks Gary!



My truck is stock & at 55 mph, I'm turning 2300 RPM which is close to my max torque of 505 ft. lbs. The roar of the Cummins can be a little deafening at that RPM... but that's what I guess the stereo is for... .

 

["Mad Max"]

I appreciate the inputs fellas, and I am happy to read from you what I feel is 'confirmation' about the transmission. Gary, I also concur with your advise about od. Same reasoning goes for any od too, and what I like about the 5600 is the tight gear pattern so a drop into 5th won't gun the engine but rather get it back in its happy range, and takes the stress off the od gears.



The issue with the G56 is a 1st gen thing - as far as I know the NP205 won't bolt up to a G56, and that's the critical factor for the 1st gens. I have to keep it old-school as far as the t-case goes.



More inputs are surely appreciated.



- M2

 

[AKaiser]

The issue with the G56 is a 1st gen thing - as far as I know the NP205 won't bolt up to a G56, and that's the critical factor for the 1st gens. I have to keep it old-school as far as the t-case goes.

- M2

That's unfortunate, as the G56 is a really smooth transmission. It can be a little tricky, at times, if you aren't paying attention. It's tighter pattern can cause you to try to shift into the wrong gear if you don't have your brain engaged (driving half asleep for example). It's not any different than the NV5600 as far as trying to drive it like a racecar will break it.

 

[FLynes]

Thanks Gary!



My truck is stock & at 55 mph, I'm turning 2300 RPM which is close to my max torque of 505 ft. lbs. The roar of the Cummins can be a little deafening at that RPM... but that's what I guess the stereo is for... .

You're turning 2300RPM@55MPH, and you have 3. 55's?????? I have 4. 10's and @60MPH I'm turning 2000RPM in 6th gear. You should be somewhere in the neighborhood of around 1600RPM@55MPH with your gearing, Chazj.



On the subject of the NV5600 being bullettproof, I too thought this very same thing, only to find out that the intermediate shaft bearing on the input shaft was pitted and missing pieces; I can only assume that the PO towed in 6th or left the truck sitting for long periods of time, resulting in lack of lubrication upon startup.



Keep your usable parts, boys! The NV5600 is rapidly becoming a dinosaur; parts, and the entire transmission itself for that matter, are getting harder to come by. If you're lucky enough to find one, it'll cost ya a pretty penny.



Good luck.

 

[chazj]

Hi Fred: Double checked my RPM's. Indeed 55mph was around 2250-2300

in 5th



1800 gives me 65 mph & 2000 gives me 70mph in 6th.

 

[Gary - K7GLD]

Hi Fred: Double checked my RPM's. Indeed 55mph was around 2250-2300

in 5th



1800 gives me 65 mph & 2000 gives me 70mph in 6th.

With my OEM 265 tires, my engine RPM was that as well - which leaves little useful remaining power band when towing in 5th gear. That's why I went to the oversize 285's - dropped my 5th gear RPM to about 1900 RPM or so, leaving plenty of effective remaining power band for accelerating or passing maneuvers if needed, as well as a more comfortable cruising RPM at 55 MPH.



The added "O/D" effect when out in the flats towing or empty was a plus as well!

 

[chazj]

With my OEM 265 tires, my engine RPM was that as well - which leaves little useful remaining power band when towing in 5th gear. That's why I went to the oversize 285's - dropped my 5th gear RPM to about 1900 RPM or so, leaving plenty of effective remaining power band for accelerating or passing maneuvers if needed, as well as a more comfortable cruising RPM at 55 MPH.



The added "O/D" effect when out in the flats towing or empty was a plus as well!

If you change the tire size, is there anything special one must do to keep the speedo calibrated (re-flash)... etc?



The point you describe above, Gary, is the reason behind my asking about the proper use (and thus longevity) of OD. The most effective power band & torque range just doesn't work with the stock 265 tires with the 3:55 rear end.

 

[JKinney]

If you change the tire size, is there anything special one must do to keep the speedo calibrated (re-flash)... etc?



Smarty Oo.

 

[Gary - K7GLD]

If you change the tire size, is there anything special one must do to keep the speedo calibrated (re-flash)... etc?



The point you describe above, Gary, is the reason behind my asking about the proper use (and thus longevity) of OD. The most effective power band & torque range just doesn't work with the stock 265 tires with the 3:55 rear end.

I have a Smarty programmer - so am able to recalibrate the ECM for tire changes. I fully recommend the 285's for towing, at least they sure work great with my setup!

 

[JKinney]

I have a Smarty programmer - so am able to recalibrate the ECM for tire changes. I fully recommend the 285's for towing, at least they sure work great with my setup!

Gary thanks for the tip on the amsoil airfilter... Got mine installed it then made a heat shield. . No directions with the filter, how often and how do we clean them, and no oiling right?

 

[Gary - K7GLD]

Gary thanks for the tip on the amsoil airfilter... Got mine installed it then made a heat shield. . No directions with the filter, how often and how do we clean them, and no oiling right?

Cleaning of the Amsoil/Donaldson air filters depends upon driving conditions and usage - but you're correct, no oiling - and proper recommended cleaning is stated to be carefully blowing the element out from the clean side (inside) of the filter to the outside - perhaps aided by vacuuming the dirty side for added cleaning.



I haven't enough miles on mine yet to need servicing, so can't comment on effectiveness of cleaning a dirty one...