Question About a 6-spd. Trans. Conversion

[JDancoe]

I am looking at converting my Getrag 5 Spd. to a 6 Spd. Trans. I have a source who has an NV5600 and a newer G56. Both appear visually to be in VG condition. Is there a reason, other than price, why I might be better off with one than the other?

The G56 had a dual mass flywheel, which I am not enthused about, (my brother had a 3rd Gen with one, and it caused him a lot of aggravation and considerable expense) but I understand South Bend Clutch has a replacement for that.

Any comments would be appreciated. Thanks, Jack Dancoe

 

[cerberusiam]

The NV is a heavier trans that has few issues if you drive it right. It does not like being speed shifted or abused on shifts. The OD ratio is about the same as the current one. Big downside is they are much more expensive to repair since they are out of production.



The G56 is actually a better shifting transmission, easier to source parts for, etc. The lower OD ratio is a problem at times.

 

[gary johnson]

REALLY heavy!..... thought about the conversion on my 98 12 V with a NV4500 when 5th gear went south. 4500 weighed in at 258... . 56 i undrstand can be over500 lbs. and toooo many mods. 56 is 6 " longer than the 45 ..... another cross member to install, then lenghten the transfer case shifter. I 'm pretty sure the 56 has a 1 3/8" shaft, so watch your clutch disc and pressure plate..... then change the throwout bearing and the pilot. I just went with a reman and kept the "ol Betsy" 4500

 

[Nyoest]

The nv5600 is a good robust transmission that is impossible to find parts for. The g56 is a six speed. Mom always told me if I couldn't say anything nice.....



Are you towing heavy all the time? What axle ratio do you have? If you have 4. 10's with the six speed you can go through three gears at a light empty.



I went through this just two weeks ago with my '96 when fifth let loose. I eventually decided not to go through all the conversion crap and stick with an upgraded nv4500. If you go with nv4500 get the upgraded 1 3/8 input shaft and south bend clutch, best bang for the buck IMHO.



Have fun, any way you go will be an upgrade.

 

[KBurgoyne]

my 2 bits. ive heard better things about the 5600. its stronger and less complex than the g56 so the swap would most likely be easier, and undoughtably cheaper. as for it being heavy, the cummins powertrain is not exactly a lightweight anyway. snag a bell housing fo the 5600. i dont believe the geometry of the engine ever changed just the transmission. of course gary has a point. a built 4500 would work just fine, and be te cheapest/easiest solution to the getrag problem.

 

[Shadrach]

On my buddy's 93 W350 we installed a G56 ( the newer AE version - the ratios are slightly different than the earlier AD version ) We use the South Bend CON OFE conversion clutch and their HD hydraulic cyl. We bought all the parts from Dodge. The floor and fire wall seam need to be modified ( aka hammered ) The hole in the floor need to be moved rearward regardless of which trans you use. I believe it is a good trans but it will not take a ton of extra torque. The highest rating in a Dodge is 610 ft lbs. If you have a stock or mildly bombed 1st gen you shouldn't have a problem. He has a bombed 96 engine and a Dana 80 in it so he has to be careful as it is a service truck and is always Heavy. It works fine with the 3. 54 gears he has in it. Check this thread out https://www.turbodieselregister.com...-forum-1989-1993/192362-1st-gen-g56-swap.html Pictures start on page 4.
I also installed a G56 in My 03 in place of the NV5600 and like it, but that's another story. Shadrach

 

[RSchwarzli]

I would go 5600. Still a better transmission if you want to put some power to it. PArts are harder to find but not impossible. Blumenthals bought all the old patents and equipment from NV so they will start making more parts as demand goes up.



I have looked into both as the 1990 will be getting a 6 speed swap soon. My extensive research says 5600. Do be mindful if you have high tq, the aluminum case on the G56 flexes and that is where power problems start.....

 

[HHhuntitall]

Having done this, I'm gonna say go with either a 4500 if you don't tow a whole lot, or the 5600. The G56 is ok, and the later models used behind the 6. 7 have a higher gear ratio in 6th, rivaling the nv5600. . 72 over, where the eariler models were . 68, I believe. If using the 5600 or G56, both driveshafts will have to modified, as well. With the modified 4500 available from Blumental's, you can install it with little mods, except to the t-case shifter and floorboard, even keeping your stock clutch, if you want. The 5600 needs quite a few mods, and is a little more labor intensive. Clutches are not a problem with any of the above. Valeo is also making a Dual Mass flywheel replacement, also available from Blumenthal's, and quite a bit cheaper than the South Bends. For most 1st gens, it would work well..... I think you need the newer starter and engine adapter, though. As for parts for the 5600, they are, for the most part, readily available from Blumenthal's. The parts for the G56 are really a problem, as they are not so readily available, and typically a long time in coming. Most are not in stock, and have to be ordered from out of the country. Even Dodge... . errr, I mean R. A. M (Raw Anal Material) has difficulty in obtaining new parts, and often just replaces the whole transmission, charging extra for lube.....



I put a 5600 in my '97, and recently the 4500 in my '93. There are several clutch options available for either of those, and a few for the G56. Be sure you match the starter to your flywheel application, and have fun doing it, either way.



OH, one more thing, depending on your application, if you use the later 6 spds in your truck, if you have a 4x4, you need to watch your front driveshaft travel, and make sure it has adequate clearance on your crossmember after moving your t-case rearward.

 

[RSchwarzli]

OH, one more thing, depending on your application, if you use the later 6 spds in your truck, if you have a 4x4, you need to watch your front driveshaft travel, and make sure it has adequate clearance on your crossmember after moving your t-case rearward.

Hmmm, I moved my crossmember back 6" as the trans was 6" longer.



Is that not what you would/did do?

 

[cerberusiam]

The G56 is ok, and the later models used behind the 6. 7 have a higher gear ratio in 6th, rivaling the nv5600. . 72 over, where the eariler models were . 68, I believe.

G360 - OD . 77



NV4500 - OD . 75



NV5600 - OD . 73



G56 (early) - OD . 79



G56 (late) - OD . 74



47\48 R's - OD . 69



68RFE - OD1 . 82, OD2 . 63





I know which one I would opt for but it be SPENDY!!

 

[RSchwarzli]

You have a lot of random stuff in your head don't you? :-laf

 

[HHhuntitall]

I got those, too... . just mine aren't in order as well as Cerberusium's... I flubbed those numbers, didn't I? HA!! Didn't even get 'em in the right direction with the typo!!



I made my own crossmember in the '92 with the nv5600..... hacked the factory one for the frame brackets, and used some plate and angle iron for the center section. But can't you keep the factory crossmember with the G56, and just extend the transmission mount with a piece of flat plate? I've not done one of them, but I can see the bolt holes will definitely have to go back... ...

 

[cerberusiam]

Extensive amounts of minutiae. Random and otherwise.



Occasionally I can get it sound coherent too. :-laf

 

[JDancoe]

Everybody,
Thanks very much for the information. Tells me a lot. I may pick up the 5600, and spend the winter gathering the other misc. stuff so I can hopefully start the conversion in the spring, when the shop warms up. Thanks again, Jack

 

[Shadrach]

"But can't you keep the factory crossmember with the G56, and just extend the transmission mount with a piece of flat plate?"

That's what we did on the 93 W350. We used a piece of 1/4" thick by 2" angle iron. The only problem is the G56 stock 4x4 mount isn't designed for the weight of a heavy t case on the wrong side. It's held up so far. Shadrach