Attention: TDR Forum Junkies INSTALLING A G56 REPLACEMENT TRANSMISSION
I use my ’97 Turbo Diesel 3500 to transport trailers of all kinds all over the country. It has over 700,000 miles on the odometer. I have replaced quite a few NV4500 transmissions over the years. On average the good ones would last about 100,000 miles which wasn’t too bad, but I had two or three that didn’t make it to 12,000 miles. Of course they would always fail when I was far from home. I decided to replace the NV4500 five-speed transmission with a G56 6-speed transmission. Thanks to TDR member ewcmr2 who paved the way. The physical size of the two transmissions is shown below.
#ad
In addition to the transmission, a new flywheel, clutch and pressure plate are
needed I installed a South Bend Clutch single mass flywheel and their Con-O clutch kit.
#ad
Also needed for ‘97 and earlier two-wheel drive trucks is a speedometer interface unit
that utilizes the differential sensor for the Antilock Brake System (ABS).
I purchased the Dakota Digital SGI-5 speed signal interface from eBay. It works great and is a simple four wire installation: 12-volt power, ground, signal in from ABS, and signal out to the speedometer. For this conversion, I used output number 3 with switch numbers 3 and 4 in the up position.
On my ’97, I picked up the ABS signal from the OBD data link connector (red wire with violet tracer). The factory speedometer signal wire (white with orange tracer) was found in the big white wire connector that is under the dash in between the clutch and parking brake pedals.
The photo below shows the Dakota unit and the four terminals used. According to Dakota, a 2-amp fuse is all that is needed in the power wire, so small gauge wire is sufficient.
I used a friend’s GPS to calibrate the speedometer. I dialed it in at 30mph, at 45mph, and at 60mph. At 30mph, the speedometer read about 2mph faster than my actual speed. After continued checking, I determined that it was accurate at 60mph and was accurate at all speeds down to 45mph, which read a little fast. If the speedometer is showing 30mph I won’t get a speeding ticket.
#ad
I procured a transmission cross member from another TDR member and had it modified prior to the NV4500 removal.
Essentially, the mount has to be 1-1/2 inches lower and 3-1/2 inches to the rear of the original cross member.
#ad
Top view of completed replacement transmission cross member.
#ad
Bottom view of replacement transmission cross member.
#ad
A little sheetmetal work was required on the floorboard.
When trying to slide the G56’s transmission input shaft into the clutch, it became apparent that the truck’s floorboard was interfering with the forward movement. I placed a jack under the front of the engine and lifted the front as much as possible to tilt the engine, yet it wasn’t enough. My investigation uncovered that the square part on top of the transmission where the shift lever bolts on was still hitting the floorboard. A little sheetmetal work was required.
#ad
A view from the underside.
After the sheetmetal work, it was a normal installation. With the transmission in place there was plenty of space on top. Actually, the only real hang up was sliding the transmission under the truck. A lift would have been really nice to have. The bell housing is about 19-inches tall, so putting the transmission on the jack and rolling it under was impossible, since the jack was 10-inches tall. We had to slide the transmission under the truck, and roll the boom of my engine hoist into the cab through the driver’s side door. We dropped a rope through the shifter hole, tied it to the transmission, and lifted it enough to roll the transmission jack under it. I would never have accomplished that part had it not been for two large, strong young friends of mine.
#ad
All bolted in, thanks to the strength of youth.
After I had tightened the bell housing bolts to the proper torque, I installed the nuts for the rear mount. I actually pulled the rear of the transmission down about 1/8-inch to the cross member.
#ad
With new metric bolts and a couple of adapters, I added the Fast coolers that were on the NV4500.
#ad
I fashioned a piece of 1/8-inch aluminum to cover the hole I had cut in the floor board.
The transmission didn’t come with the orange boot for the shifter or a vent so I used the vent from my 4500 along with a formed hose in a help package from the local auto part store. I bought the boot from an ATV dealer, Moose Part No. M9206801.
#ad
I waited until the transmission was in place before I had the driveshaft modified.
I measured from the flat surface of the flange to the center of the holes where the support bearing is mounted. My driveshaft was required to be 3/16-inch longer (46-1/2 inches) than Eric’s (TDR member ewcmr2) due to minor manufacturing differences. This measurement is critical since there is no longer a slip yoke.
#ad
The interior all back together.
I’ve only driven the truck on a short test drive to Phoenix, towing a little 1,700 pound trailer and returning empty. The transmission shifts smooth, is tight, and is quiet. The engine speed at 65mph cruise is a couple hundred rpm higher than with the NV4500. I purchased the first model G56 (AD) with a 0.79 ratio 6th gear. The other version is the AE (known in some circles as a G56R).The G56R or AE transmission was discussed back in Issue 60, page 48. For a reference, these are the ratios of both AD and AE versions of the G56 transmissions along with the NV 5600 and NV4500 that I replaced:
Gear G56-AE G56-AD NV5600 NV4500
1st 5.94 6.29 5.63 5.61
2nd 3.28 3.48 3.38 3.04
3rd 1.98 2.10 2.04 1.67
4th 1.31 1.38 1.39 1.00
5th 1.00 1.00 1.00 0.75
6th 0.74 0.79 0.73 N/A
Reverse 5.42 5.74 5.63 5.04
Greg Ames (GAmes), Killeen, TX
Bill Stockard’s Note: I checked with Gary recently for a follow up. He is pleased with the G56 and has over 15,000 miles on it, including about 4,000 miles towing fifth-wheel trailers in excess of 10,000 pounds over the mountains in the western US. He says he likes the new 4th gear when climbing hills towing heavy trailers. The transmission had about 52,000 miles on it when it was installed and makes some noise in 5th gear under a heavy load or decelerating with the exhaust brake engaged. He doesn’t know if that is normal. Interestingly, Gary reports that since the G56 6th gear has a lower ratio than the NV4500 5th gear, the engine speed is 150-rpm higher and running at 2,150-rpm at 65mph, resulting in improved fuel mileage while driving empty.
I use my ’97 Turbo Diesel 3500 to transport trailers of all kinds all over the country. It has over 700,000 miles on the odometer. I have replaced quite a few NV4500 transmissions over the years. On average the good ones would last about 100,000 miles which wasn’t too bad, but I had two or three that didn’t make it to 12,000 miles. Of course they would always fail when I was far from home. I decided to replace the NV4500 five-speed transmission with a G56 6-speed transmission. Thanks to TDR member ewcmr2 who paved the way. The physical size of the two transmissions is shown below.
#adIn addition to the transmission, a new flywheel, clutch and pressure plate are
needed I installed a South Bend Clutch single mass flywheel and their Con-O clutch kit.
#adAlso needed for ‘97 and earlier two-wheel drive trucks is a speedometer interface unit
that utilizes the differential sensor for the Antilock Brake System (ABS).
I purchased the Dakota Digital SGI-5 speed signal interface from eBay. It works great and is a simple four wire installation: 12-volt power, ground, signal in from ABS, and signal out to the speedometer. For this conversion, I used output number 3 with switch numbers 3 and 4 in the up position.
On my ’97, I picked up the ABS signal from the OBD data link connector (red wire with violet tracer). The factory speedometer signal wire (white with orange tracer) was found in the big white wire connector that is under the dash in between the clutch and parking brake pedals.
The photo below shows the Dakota unit and the four terminals used. According to Dakota, a 2-amp fuse is all that is needed in the power wire, so small gauge wire is sufficient.
I used a friend’s GPS to calibrate the speedometer. I dialed it in at 30mph, at 45mph, and at 60mph. At 30mph, the speedometer read about 2mph faster than my actual speed. After continued checking, I determined that it was accurate at 60mph and was accurate at all speeds down to 45mph, which read a little fast. If the speedometer is showing 30mph I won’t get a speeding ticket.
#adI procured a transmission cross member from another TDR member and had it modified prior to the NV4500 removal.
Essentially, the mount has to be 1-1/2 inches lower and 3-1/2 inches to the rear of the original cross member.
#adTop view of completed replacement transmission cross member.
#adBottom view of replacement transmission cross member.
#adA little sheetmetal work was required on the floorboard.
When trying to slide the G56’s transmission input shaft into the clutch, it became apparent that the truck’s floorboard was interfering with the forward movement. I placed a jack under the front of the engine and lifted the front as much as possible to tilt the engine, yet it wasn’t enough. My investigation uncovered that the square part on top of the transmission where the shift lever bolts on was still hitting the floorboard. A little sheetmetal work was required.
#adA view from the underside.
After the sheetmetal work, it was a normal installation. With the transmission in place there was plenty of space on top. Actually, the only real hang up was sliding the transmission under the truck. A lift would have been really nice to have. The bell housing is about 19-inches tall, so putting the transmission on the jack and rolling it under was impossible, since the jack was 10-inches tall. We had to slide the transmission under the truck, and roll the boom of my engine hoist into the cab through the driver’s side door. We dropped a rope through the shifter hole, tied it to the transmission, and lifted it enough to roll the transmission jack under it. I would never have accomplished that part had it not been for two large, strong young friends of mine.
#adAll bolted in, thanks to the strength of youth.
After I had tightened the bell housing bolts to the proper torque, I installed the nuts for the rear mount. I actually pulled the rear of the transmission down about 1/8-inch to the cross member.
#adWith new metric bolts and a couple of adapters, I added the Fast coolers that were on the NV4500.
#adI fashioned a piece of 1/8-inch aluminum to cover the hole I had cut in the floor board.
The transmission didn’t come with the orange boot for the shifter or a vent so I used the vent from my 4500 along with a formed hose in a help package from the local auto part store. I bought the boot from an ATV dealer, Moose Part No. M9206801.
#adI waited until the transmission was in place before I had the driveshaft modified.
I measured from the flat surface of the flange to the center of the holes where the support bearing is mounted. My driveshaft was required to be 3/16-inch longer (46-1/2 inches) than Eric’s (TDR member ewcmr2) due to minor manufacturing differences. This measurement is critical since there is no longer a slip yoke.
#adThe interior all back together.
I’ve only driven the truck on a short test drive to Phoenix, towing a little 1,700 pound trailer and returning empty. The transmission shifts smooth, is tight, and is quiet. The engine speed at 65mph cruise is a couple hundred rpm higher than with the NV4500. I purchased the first model G56 (AD) with a 0.79 ratio 6th gear. The other version is the AE (known in some circles as a G56R).The G56R or AE transmission was discussed back in Issue 60, page 48. For a reference, these are the ratios of both AD and AE versions of the G56 transmissions along with the NV 5600 and NV4500 that I replaced:
Gear G56-AE G56-AD NV5600 NV4500
1st 5.94 6.29 5.63 5.61
2nd 3.28 3.48 3.38 3.04
3rd 1.98 2.10 2.04 1.67
4th 1.31 1.38 1.39 1.00
5th 1.00 1.00 1.00 0.75
6th 0.74 0.79 0.73 N/A
Reverse 5.42 5.74 5.63 5.04
Greg Ames (GAmes), Killeen, TX
Bill Stockard’s Note: I checked with Gary recently for a follow up. He is pleased with the G56 and has over 15,000 miles on it, including about 4,000 miles towing fifth-wheel trailers in excess of 10,000 pounds over the mountains in the western US. He says he likes the new 4th gear when climbing hills towing heavy trailers. The transmission had about 52,000 miles on it when it was installed and makes some noise in 5th gear under a heavy load or decelerating with the exhaust brake engaged. He doesn’t know if that is normal. Interestingly, Gary reports that since the G56 6th gear has a lower ratio than the NV4500 5th gear, the engine speed is 150-rpm higher and running at 2,150-rpm at 65mph, resulting in improved fuel mileage while driving empty.
