View Full Version : NV5600 Tech (My Pain is Your Gain)

03-08-2015, 10:24 PM
Well before we get down to brass tacks, errr bronzesynchronizers a little background. I have an 02 Dodge 2500 pickup with the desirable High Output options package which mainly consists of the Cummins diesel with the 245hp 505ft lbs of torque spec, NV5600 6spd transmission and Dana 80 rear axle with disc brakes. I decided to send the truck in to Greensburg Machine to have them install a new South Bend clutch since my stock style clutch was slipping. I have had some oil on the bottom of the bellhousing so I assumed the rear main was weeping (it is a Cummins afterall) and I gave them the go ahead to do that while the transmission was slid rearward to install the clutch. The NV5600 is a very stout six speed manual transmission with an integral aluminum bellhousing, cast iron main case, and cast iron transfer case adapter. It weighs nearly 500lbs by itself.

I got the call Wednesday from Mark at Greensburg Machine that my input shaft on the transmission was junk and we had to figure out what we were going to do. The input shaft on the NV5600 is a massive piece that is 1 3/8” in diameter on my spec truck. What happens is the factory flywheel has a needle bearing inside of it that the snout of the input shaft rides on. This needle bearing disintegrated due to time, poor design, and my truck having 237,000 miles on the odometer. The hub in my clutch was also torn out and due to the needle bearing failure I’ve lost the front seal in my transmission allowing the clutch to become oil soaked by transmission oil, NOT the rear main seal like anticipated. The wobbling allowed my input shaft snout to be worn out of spec.

The NV5600 is a real bastard of a transmission. Everything comes out the rear of the transmission including the input shaft which is the last thing to be removed, which you guessed it warrants a COMPLETE disassembly to retrieve it for repair. A new input shaft runs anywhere from 240-500 dollars. Runout on my worn input shaft varied from .747 down to .734 O.D. Spec is .750 I.D. on the revised South Bend sealed ball bearing in the new flywheel. The tentative plan is to disassemble the NV5600 to retrieve the input shaft, send it to a friend to get machined down to an even spec then have a bushing with a wall thickness of .125 heat shrunk to the now uniform input shaft snout to achieve a proper fit in the .750 I.D. ball bearing.


On to the tear down! This transmission weighs almost 500 lbs. It consists of an aluminum bellhousing that is integral to thetransmission, a cast iron main case with shift tower, and a cast iron transfercase adapter.


First steps are pretty clear, you must remove the boltsholding the transfer case adapter onto the main case and utilize a puller, in my case a 3 jaw I had laying around, a 2 jaw would be superior to remove theadapter. Underneath the adapter resides bearings, gears, and reverse gear and shift fork. Remove all of the loose parts and your readyto lay this behemoth horizontally again to remove all the bolts in the bellhousing.



More to follow tomorrow, i'm tired of this computer acting up...

03-09-2015, 04:46 AM
Wow that sucks - seems like alot of people have issues with those 6 speeds.

03-09-2015, 08:58 PM
Most of the issues appear to be owner induced 80% and 20% shitty design. I enjoy the way this transmission performs in the application, it's a truck transmission, it behaves in many ways like a medium or heavy duty truck transmission in the way it shifts rough and balky and long throws but it holds power plain and simple at the end of the day, especially with the heavy duty 1 3/8” input shaft diameter in my application, earlier ones were 1 ¼”.

Whelp back into the teardown of this behemoth before I digress further. We left off last night with the transfer case adapter removed, and the loose gears removed from the back of the cast iron main case, which leaves a shift fork tail exposed, and the main shaft,nut and bearing. We lay the transmission horizontally and remove all the bolts holding the bell housing to the maincase. Now we stand the transmission back onto the aluminum bell for the next steps.


The main shaft nut is torqued to 250ft lbs and is dented into a keyway onthe main shaft to retain it and keep it from spinning. You use a sharp chisel to pop the dent outand then I utilized a giant crescent wrench to grasp the nut, and a sharp toothed 3ft pipe wrench low on the splines of the main shaft to hold it tight while breaking the nut loose. The teeth on the pipe wrench fit the main shaft splines perfectly and allowed me a great grip to get the nut free no damage to the splines or the threads.


Once the nut is removed, the bearing is removed etc. And a roll pin is driven out of the aluminum shift fork in this picture, and the strange pin and discs is removed from the shift rail. Once all of that is removed we remove an 1 3/16” spring loaded detent plunger that holds a rail in place that is threaded into the main case, as well as a half inch bolt that retains a rail in position from the side of the maincase.

At this point we drive a roll pin out of the shift cup inside the shift tower of the main case and rotate the cup out of the way of the main case. Then we thread two bolts into the rear of the cast iron main case and through a 3/8” chain and lift the main case off carefully with an engine hoist or a come along from the skid loader bucket like we did. I didn’t get any pictures of this operation it kind of just happened and I was in the zone at this point. Some firm whacks from a dead blow hammer on the aluminum bell helped pop it free.

NOW we have the bull by the horns and the whole shitting mess is sitting their exposed right in front of you. Don’t celebrate yet or panic either. We MUST secure the shift forks and synchro rings all together to the rails and main shaft and countershaft so we do not lose anything. The synchros have springs and balls that rideinside the rings, each synchro has 3 balls and 3 springs, and 3 wedge lockthingy’s. Things can go to hell rapidly if you are not careful.


I used heavy mechanics wire to wire everything together. I then used an interesting clamp my brother bought for welding and fabrication work that turned out to work ok for my purpose of clamping 5th gear synchro which is the only one that isnot technically captured.

We then had to fabricate a crane tool to lift BOTH main shaft and countershaft’s and the gears as well that ride on them as one whole assembly so as not to get anything out of whack since all we are trying to do is remove the input shaft.
Once we made the tool, we hoisted the shafts, rails and everything carefully out of the bell housing, leaving the input shaft behind. Soft blows from a mallet or dead blow hammer helped free the rails from the bell housing. At this point we are done for now.


I got a picture today of my finished input shaft, which is now as good as new. I'll post a pic in a few. Reinstallation and reassembly will be tomorrow night and is the reverse of disassembly. Any questions?

03-09-2015, 09:12 PM
Repaired Input Shaft is blingin. Huge thanks to a good friend who helped me on this repair.

https://fbcdn-sphotos-a-a.akamaihd.net/hphotos-ak-xpf1/v/t1.0-9/11041801_10152777064896229_3164006890638366609_n.j pg?oh=20aa9b1caadfddfebcb44226a9037cbb&oe=5573DB73&__gda__=1435228940_e7e9a03caabc83a241579072958fe56 1

03-10-2015, 05:11 AM
That was one of the selling points of my new truck - the NV4500 was already upgraded with the 1 3/8 input and dual disc clutch (although the dual disc DEFINITELY makes the tranny shift like a big rig!)

Lookin good man, that's no joke of a project!

03-19-2015, 09:18 PM
Steve owes someone, somewhere, some money. You're not retarded after all!

That truck was in my driveway today, so I can confirm this repair was a success.

03-19-2015, 10:39 PM
^ LOL He is an ass, I'm not nearly as retarded as I can come off being, especially after I've been drinking.

So far this is day two and likely around 50 or 60 miles on this repair and the new clutch. It's shifting a little better than before, this 5600 is hard to shift period but the new input shaft machine work to true it, and the new flywheel, bearing, and clutch along with a reverse synchro ring made a huge difference in how the truck shifts. Clutch makes a little noise but pedal is same weight as stock and engagement is just as smooth as stock with much higher holding ability. The South Bend I installed is a heavy single disc. SB part #1947-OKHD rated to hold 425hp and 850ft lbs of torque. Big perk to these south bend's and using their upgraded hydraulics system for the slave setup is the adjustability of the clutch now as it wears. Stock Dodge is non adjustable clutch engagement so as it wears it doesn't allow for compensation of where the clutch releases in the pedal stroke. Valair offers a similar system to use with their clutch systems for these Dodge Cummins powered trucks.

Deadman 94 xj
03-20-2015, 09:14 AM
Good job man

03-20-2015, 07:27 PM
Nice to hear that you are back on the road... get those wheels on it yet?

03-20-2015, 08:28 PM
Yeah Josh I did, you want to part with that other set dude? I want to switch over to 16's period instead of one set of 17's and one of 16's I can get tires cheaper for 16's :)