Diesel Suburban: Transmission Part 2
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In my last post on the Diesel Suburban project, I discussed how and why I decided to use an NV4500 5-speed transmission in this machine. The bottom line was that I could trust it, and it would work with the Suburban's body and frame.
I purchased this kit from 4BD conversions, including an Isuzu bellhousing, an adapter plate, a Dodge clutch, a bushing, and various nuts and bolts
The use of this transmission requires a number of tricks to be performed, as it has never come from a factory mated to an Isuzu 4BD1T. The 4BDConversions kit consists of a billet adapter plate, a Dodge clutch, and a pilot bushing. Because I bought the engine by itself, I included a machined Isuzu bell housing in my order. To work with this kit, the bell housing needs to be machined to clear the bolt heads on the transmission's bearing retainer. Note four spots of bright aluminum inside the adapter plate in this photo. I believe the center hole was also machined to fit the Dodge bearing retainer.
The NV4500 was used in Chevy and Dodge pickups. I used some online salvage yard search tools and got some bids on used transmissions -- because it seems that all of the yards in my area are always picked clean and I couldn't find one here. I wound up buying one out of a 2000 Chevy 2500 4x4 in North Dakota. Truck shipping wasn't as horrendous as one might guess, and I found it outside my garage on a pallet when I came home from work about a week later.
Because it came from a Chevy 4x4, the bolt pattern on the rear would allow it to bolt to the NP246 transfer case. It had 32 splines, while the NP246 had 27, though. The modification I made to the transfer case will be the subject of another posting.
This adaptation requires removing the shorter Chevy input shaft and bearing retainer, replacing them with the longer Dodge versions
Let's return this story to the front of the NV4500. I had to switch to the longer input shaft that's used when this transmission is used behind a Cummins in the Dodge pickups. This switch requires the use of the Dodge input shaft housing and bearing retainer. This photo was taken when I removed the Chevy parts. Note that I found I'd need a bearing on the new shaft and a seal in the new housing.
I picked up these parts and started to install the bearing. I tried using the snout-end of the retainer and a block of wood to push the bearing onto the shaft. I quickly found that this is a very tight fit, and that I couldn't apply enough even pressure to the appropriate portions of the bearing's inner race.
So, I made a run to Rural King(one of my favorite stores!) and visited their plumbing section. By now, they are used to seeing me walking in there with random diesel parts looking for something that fits or needs to be modified. Yes, some tractor parts have made their way into this Suburban!
This is the custom bearing pusher I used
I found a piece of pipe and a coupler that happened to be almost the right diameter to push the bearing in place. I used a bench grinder to put a taper on the coupler, ensuring that it would only contact the inner bearing race. I didn't have a hydraulic press, yet, so I set this on a piece of plywood and hit the end of the pipe with a hammer until the bearing was properly seated. Similarly, I used a block of wood to seat the race in the bearing retainer. I had to use the corner of the 2x4 to get this to seat below the retainer's surface, but this was not a super-tight fit and the approach worked fine. I also installed an oil seal in the retainer using a cheap, but perfectly functional, Harbor Freight seal driver.
I used a drill-mounted wire brush to clean up the mating surfaces. I then packed synthetic assembly grease into the bearing and coated the gear surfaces, too. Before I installed the shaft and retainer into the transmission, though, I realized I would need to use it to align the adapter plate.
Aligning the adapter plate with the modified Isuzu bell housing
I dropped the snout of the retainer through the hole in the Isuzu bell housing. You'll note that it had been pretty ugly, so I painted it my favorite color. I was happy to find that everything was a tight fit, and there was little room to misalign the components. I installed the plate and torqued the bolts.
I slipped the retainer back out and attached it, with the shaft installed, to the front of the NV4500. I used some RTV on the mating surfaces to avoid leaks.
I bolted the bell housing to the transmission. The transmission had been covered in surface rust, so I cleaned it up and painted it to match the now-pretty bell housing.
Here's a transmission from a Chevy with a Dodge input shaft and an Isuzu bell housing
To wrap up this story, I need to tell you about the clutch, throwout bearing, and fork. The Isuzu bell housing has a place to bolt a clutch slave cylinder externally, which actuates the fork to disengage the clutch. It turns out that one can use an Isuzu fork with the Dodge throwout bearing. This bearing rides on the retainer's snout, with the ability to slide forward and aft. The Isuzu fork only required a small amount of material to be removed to fit the throwout bearing -- I lightly ground it down it with a cutting wheel on my rotary tool.
This shows how the Dodge throwout bearing interfaces with the Isuzu fork
Transfer case modifications will be in another post
The Dodge clutch disk is the right diameter and is used with the Isuzu manual flywheel and pressure plate. It's amazing to me that Diesel Tim found a way to make all of these parts work together, but they are all being used the way they are meant to be used. I'm confident that there won't be any issues with this method of adaptation. Because all of these components are either found behind a stock 3.9 liter 4BD1T or a larger 5.9 liter Cummins turbo diesel, durability shouldn't be an issue.
Here the Dodge clutch is installed to the 4BD1T using an Isuzu pressure plate
The NV4500 also needed to be mated to the Suburban's NP246 Autotrac transfer case. I'll make this the subject of another post.
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