Never had a 6 speed, looking at getting an 02 with one. I dont tow alot, so is there any real reason that i should NOT want one besides having to shift the gears??? Just looking for some opinions....it has 122k on it and of course it is an H.O. thank you!!!

 

The NV5600 has great gear spacing so you always can find the sweet spot in the RPM range. The Cummins software tries to keep the engine running so backing a trailer is easy, you don't even need to use the loud pedal, just clutch and brake. You drive it like a 5 speed as you start in 2nd gear unless you're running heavy. 1st is a serious granny even in 2WD. Not for people who don't like shifting, but after spending 10 years with mine I could never go back to an auto.

 

Had mine since new and never regretted having the low 1st gear. I tow heavy and use the low gear to get the train moving. I also like it when in the sand to prevent wheel spin and hopping. G.ood for pulling the boat out on wet ramps

 

The ratio differences between a 5 speed and a 6 speed are minimal but the 6 speed has a smaller gap between 3rd and 4th which makes it a better tranny for towing heavy. The 6 speed can shift more notchy than the 5 speed which makes the 5 speed a better around town manual tranny. The 5 speed is much cheaper to rebuild than the 6 speed but the 5 speed has a weak half splined 5th gear shaft which can result in loss of 5th gear depending on driving habits. Guys will claim cheap fixes for that issue but replacing the shaft is the real fix and isnt as bad as it sounds. The 6 speeds supplied in 1998-1999 trucks have smaller input shafts than the 2000+ trucks and the same clutch as the 5 speed but the HO versions came with a 13" clutch.

Now the differences between a manual and an auto is that the auto did NOT come in HO models in the 2nd gen trucks. The auto's also have the Dana 70 differential and will have a lower GVWR than the manual trucks.

So its not only if you will get bored of shifting gears since there are mechanical differences to think about as well.

 

You won't be disappointed with the 6-speed.

The rear end ratio will make a difference. I have the 3.55's and am in a weird place in the rpm's when trying to run at 35 mph around town. In 4th I am at close to 1950-2000 rpm and in fifth its under 1500 which feels like I'm boggin it. Some say that wears the clutch prematurely.

Also, make sure you use the correct fluid in it! The Amsoil seems to rate the highest around here followed by the Redline. MTL.

Also, if you try to force shift it you will be replacing the blocker rings, which isn't cheap or easy.

 

I have the NV 5600 in my truck (6 speed). I have had great luck with mine, and im a little old school and like to shift. I have over 400,000 miles on my origional trans. I change the fluid once a year and overfill it to the total of 6 quarts. I have towed 53' enclosed car trailers, skid loaders almost daily. and plowed snow at comercial accounts for many years. At this time it shifts as well as when i first bought the truck wiht 60,000 miles on it years ago.

 

A couple more things:

Its not a race trans so you need to let things catch up to mesh when shifting, if you force it it will grind the points off the blocker rings and cause hard shifting leading to no shifting leading to rebuild.

Also, the correct fluid is an absolute must in these. The heat generated by this trans, especially when towing, is high and the wrong fluid will cook it. If it has had the wrong fluid(gear oil) in it in the past (mine did) it will need a rebuild. It should drop into gear smoothly. If it feels like you're snapping a chicken leg to get it into gear the blocker rings are shot and the yellow metal has been thru the entire trans. This will show up in a fluid drain.

The extra qt of fluid is golden advice. The early 6-speeds didn't have the passageway at the rear of the housing and the oil that got in there didn't really circulate thru the rest of the trans. The 2000 and up have a oval passage cast into the housing but you can't see it unless you pull the tailshaft. Good quality rebuilds have a couple 1/2" holes drilled thru.

 

After 20 years of driving the 5 spds I finally bought an auto a year or so ago. Just sold it because I love the 5spds. Just last forever and will run smooth from 1200 rpms up around town in 5th. I have 265k on my original trans and clutch with only having to fix the 5th gear nut problem . It;s a '98 and seems bullet proof.

 

99-00 6 spds were the small input shaft trannies. HO's were the big input shaft, '01 and '02 only. D70's were only in the auto 2500's, 3500's are still D80's. GVWR's are the same regardless of tranny.