Is one better? I know they are 6spd trans.whats the dif.?thx.

 

The NV5600 is Cast Iron and the G56 is Aluminum.

Reverse in the G56 is far Left and down. IIRC the 5600 is far Right and up.

Most guys think the G56 is weaker because its Aluminum.

IIRC the G56 is used in trucks up to 60k GVWR.

 

The g56 is a more modern design, aluminum case, Mercedes unit that is easier shifting and has a lower 6th gear ratio.

The 5600 is a more traditional cast iron box. Heavy. Harder to re-build from what I've read (never done it). Slower shifting, but has a great top gear ratio. I'm wondering if it will become harder to get parts for the 5600 before the g56?

I'm considering a change from my auto to a six speed and I will go with the g56 if I do. Others know more about them than I do.

 

on't know about now, but 2 years ago I had to rebuild my 5600 and the guy quoted me $2,800 for the job. An hour later after he had called to order parts he called me back to tell me that he did not realize part prices had shot up and that this rebuild was gonna be $3500 and should he continue. They were getting hard to find since they stopped making them, but I have heard that there are companies picking up the slack now.

 

they all will break have broken the nv4500 g56 and probably the nv5600 but the truck got totaled before i could put the miles on it. the g56 should last if you change the fluid often since it runs on atf. the overdrive ratio does stink tho even on the newer ones compared to the nv my .02

 

There's many threads about this question, do a search. It's subjective to what people wants to believe. I just bought a rebuilt NV5600 for $ 2800 and it's a great unit.

 

That sounds like a great way to go providing the rebuild is with quality U.S. made parts. I would have no problem swapping a broken g56 for a reman NV5600. Add two drive shafts, hydraulics, new uni's etc?

btw, I read about some parts for the NV5600 imported from china? Any truth to that?

 

I've had one of both. The NV's overdrive is considerably higher but mine was rough shifting. The G I have now makes a bit more gear noise, but it shifts better. The lower 6th is also nice when towing, but a bit too low for empty freeway running IMHO.

Lastly, the G comes with the dual mass flywheel...

 

Really they are both strong. The G56 uses a dual mass flywheel, so its more money to get a good clutch..

In 2007 the G56 had a ratio shift, all 6.7's have the new ratio, rare to find with a 5.9.

Ratio's are
NV5600: 5.63, 3.38, 2.04, 1.39, 1.00, 0.73
G56 (early AD): 6.29, 3.48, 2.10, 1.38, 1.00, 0.79
G56 (late AE): 5.94, 3.28, 1.98, 1.31, 1.00, 0.74

The early G56 was the best towing 6 speed. You got the advantage of the 3.73 ratios in lower gears, where it takes less power per mph, so each gear lasted longer.. But the same final drive as a 5600 w/ 4.10; which makes all the difference at 55-65mph towing thru the hills. The few extra rpm's keep the AD G56 from having to downshift.

My dad has a 06 AD G56 and I have a 05 NV5600, he can pull larger hills in 6th than I can... It takes about 1900 rpms for me to not have to downshift on all but the biggest hills with my TT, thats 66mph for me, but only 61 for dad. So at 65 he is at 2000 and thats plenty to never have to slow down.

Some people thing the NV5600 or AE G56 get the best mileage but my dad and I get similar mileage, negligible to quantify anything based on 2000 vs 2175 rpms at 70 mph.

 

That's kind of my experience. My 06 revs a bit higher on the freeway, but it doesn't seem to effect MPG much and it tows very well.

Actually, when I was on some narrow curvy mountain roads, I ran in 5th for a long time. It seems to me that RPM (within reason) doesn't change MPG much, but road speed does.

 

That's some good info, I knew 6th was different was different with the old and new G56's but didn't know every gear was different. I know I wish I was revving a little lower on the highway.

 

And I wish I was revving a little more while towing

 

I've never understood why anyone wants to tow in OD. The weakest gear in any manual transmission.

I tow a 10k lbs 5th wheel in 5th gear (1:1) never going into 6th. NV5600, 3.73 gears, stock 265/70R17 tires.

In 5th gear, with the trailer on the back I cruise at 60mph/100km/r, which is perfect at about 2200rpms.
No need to downshift up hills, EGT's are just fine, no lugging & in the straight-thru 1:1 5th gear.
For me this is the sweet spot for comfort & fuel mileage.
I can go faster but my fuel mileage goes down & decreases the safety factor with the trailer on the back.

Just my thoughts.. Joe..

 

If I'm revving too high in 6th, why would I go into 5th?
For best fuel economy you need to keep the revs below 2000 RPM.

 

Sorry Fisherguy, my post about cruising in 5th gear was meant for towing only. Not cruising empty.

When I'm cruisin empty, 6th gear in my NV5600 brings my rpm's down to about 1900 rpm which is fine empty & about 65mph/110km/r.

..Joe