NV4500 Transmission Teardown Guide

Transmission Teardown With Chris Mosdal

I bought a transmission on Facebook Marketplace so I could walk you through the steps of doing an NV4500 transmission teardown on your GM or Dodge truck. Following is a transcript of the video we created to help you visualize the process from start to finish.

Getting Started

The gentleman I got the transmission from said that everything worked. He just switched to a newer six-speed transmission. But third gear was a little bit chunky. So I'm going to go through this, drain the oil, take a few things apart, and we'll get into the third gear and see what we can find out.

Maybe it's something simple, maybe it's something atrocious. You can't really tell from turning the gears over, which I've already done off-camera. But we'll see when we get into it.

Removing the PTO Cover

The bottom bolt in our transmission PTO cover is going to be the easiest place to drain all your oil. One of the first things you can learn from is your oil. We've got some in there and it actually looks really clean. And we're not seeing a whole lot of fluid come out, so that's okay.

One of the easiest places to inspect a transmission is right here at the PTO cover. As you're taking yours apart, hang onto the tag because it's got information about the original build and what kind of parts are in it. We use a medium to small swing press here and get this loose from the case.

The first thing we see is that this has still got the magnet in there. A lot of these came originally with a magnet, but if somebody's been in it and cleaned it up, some people get rid of those. I have no idea why. It's a good idea to keep the magnet because it catches fine particulate matter that would otherwise go through your bearings and in between where it doesn't belong.

Right now I'm draining some more oil out of the transmission just to make this as clean a job as possible while I move it around on the table. A transmission like this weighs about 200 pounds. If you feel uncomfortable holding that much weight, get some help. (You've probably got a buddy that needs a beer.)

Once I get this drained out pretty good, I'm gonna take off the bell housing and the tail shaft housing to make the whole transmission a little bit easier to grab onto so we can get into the parts that we're inspecting.

Removing the Bell Housing

Those are 9/16" head bolts. If you end up losing some of those bolts, we've got them. As a matter of fact, we've got every bolt on this transmission. These are 3/4" bolts (3/4" head on the bolt). The bell housing on the Dodge has a different pattern than the same transmission on a Chevy. NV 4500 is used on the Chevrolets as well. The early transmissions have a different bolt pattern between the tranny and the bell housing than this later style Dodge. All the Dodges have the same style. The later style Chevy has the same housing pattern for these bolts. Now that should just pop off right back there. We'll worry about an inspection on that a little bit later.

Removing the Tail Shaft Housing

The next thing I'll pull off is the tail housing. This transmission is completely sealed when it's mated with its original style transfer case. This seal right here mates to the input gear on a transfer case and should not leak. You don't need to put that silicone in there. If it just makes you feel better, maybe just don't use that much.

These bolts on the case are 10mm 12-point socket, and they're only put in there at about 28-foot pounds if they're done right. But they can be really sticky because they're also sealed with silicone at the same time. There is no gasket that goes between the tail housing and the transfer case besides silicone.

Pro Tip #1

Hang onto those bolts – they are a particular style and they're not easy to find. But if you do lose them, you can pick them up at Torque King. There are some dowel pins in this tail housing that keep it concentric with the rest of the transmission. When you're rebuilding yours or just working on it, make sure that you've got both of those dowel pins. That's another part that we have, and it's absolutely critical.

Fifth Gear Discovery

Right here is our countershaft fifth gear, and from initial inspection, everything there looks pretty good.

Here's our fifth gear nut. Somebody's been in there. We can have a look closer right here. We can see where somebody took a chisel and they staked that nut down into the groove there. You can see this slight amount of silicone around the perimeter where the tail shaft housing was. That's just about how much you want – just enough to make sure that you're sealed up but not making a mess.

Pro Tip #2

It's a good idea to make sure you know where each of these parts that are on those bolts go to. You can take a picture and keep it for reference. It's just a good idea all around.

These are 13-millimeter bolts (13mm head). As I take them off I'm setting them aside. It's a good idea, especially if you're going to just be into a transmission briefly, to go ahead and clean around these bolt heads before you take the bolts out. That way if you're gonna put it right back together you don't get any debris into the transmission.

Removing the Top Cover

That's the last bolt is on the top cover. This top cover, like the rear tail housing, is only sealed off with RTV silicone. Also, like the rear, it has a dowel pin here and another one over here. That last bolt you saw me get loose does have a provision on either side to crack it loose in these three spots. And you can see I hadn't had it open before but that's all it took. And we're open to the rest of the transmission.

We look at the top cover here and we've got our shift forks. That's our 3-4 shift fork at the front, our 1-2 shift fork there and our 5 and reverse fork. The only one with pads is that 5 and reverse fork and it's got a plastic pad there, some sort of nylon that's made to handle the wear and tear.

The rest of this shift cover looks really good. I don't see an excessive amount of gawling or scoring on my shift forks. When I shifted the transmission on the bench off-camera, everything moved pretty smoothly. I'm going to leave that nice and clean out of our way.

Shifting Gears

We're into the transmission and we've got our 3-4 shift collar, our 1-2 shift collar and our 5 reverse collar.

This first collar is where we're expecting to look for a problem with our third gear. If I go forward, that would be like you shifting into fourth gear – the pawl inside will shift that forward to fourth gear. Fourth gear is direct, so it's a one-to-one ratio between input and output. They're going at the same speed. That's what I've got going with that right there, we're in fourth gear. Now if I shift it back into third gear, then the output shaft is going to be turning slightly slower.

This is third gear right here, which is what they said was kind of chunky, and I can see a definite wear pattern on there where it's polished on the teeth. What I'm not seeing is any problem with that part of third gear. I don't see any broken teeth or scrapes or anything like that. I don't see any uneven or unusual wear.

So we'll go and look at first and second gear. I'll shift that back into neutral. All of these gears will sit perfectly still while the rest of that main shaft turns. I haven't seen anybody else show that, but it's kind of nice to know.

Those gears can turn independently. I can't turn them independently of each other here because they're connected to the gears on the countershaft. The countershaft turns when the input shaft turns it. So it's going to move these gears all the time. Everything in here when this is turning is throwing oil all over the place and you're getting lubrication everywhere. That's what works really well with our filter or cooler system.

Pro Tip #3

Torque King has a filter and cooler kit QK 1015 that works really well here. We can put a filter here on the side but the coolers can come with a filter. When the transmission is throwing oil all over, it's a passive filter. You don't pump through it but the fluid that warms up after about five minutes of driving will push all of that fluid through that filter and keep the interior of your transmission safer quite a bit longer.

Shifting Gears

First gear is our largest gear because it's our lowest gear. Put it into first gear and everything's looking good there.

I can roll it over and that's my lowest reduction to my output shaft. Watching this gear come around, I don't see any unusual wear on the first gear either. I don't have to be shifted into gear to look at all of these gears.

I'm looking at second gear right here now, and again we can see it definitely has the wear pattern of about a three hundred thousand mile transmission but nothing looks bad – no pieces of the gear are missing.

I wasn't yet looking at the clutch collars on there for the syncros but everything that I'm looking at for second gear looks good. All my clutch hub parts are nice and pointed the way they're supposed to be. The synchro – at least from what I can see while it's still installed – looks the same way. Let's look at the next gear.

We can see a little bit in there but you kind of have to get everything out to completely check it out. What I'm seeing so far looks pretty good. We'll move on to the next step.

Input Shaft & Front Bearing Retainer

The customer told me this one already had the upgraded 1 3/8" shaft. This is the same shaft that they use for the NB5600 and the G56. They're not the same part but they are the same size so you can get a heavier duty clutch for that larger input size.

You can get plenty of heavy-duty clutches that work just fine with the original stock 1 1/4" shaft as well, but I'm guessing the reason he went this route is because he was going to go to a six-speed later. So before he could afford the six-speed and he was just putting the clutch in, he put in the clutch with that larger input.

We don't want to damage this part when we take it off. It's a little dirty and a little messy but I don't want to ding it up, so I'm going to use a small hammer to just crack it loose because it's also sealed to the case with some silicone.

I've got her pretty well cracked loose. I've got to free it of the silicone and it should come off. There may be a little too much silicone. I can tell by the way this is put on that they were definitely into this, but we've already covered that it's not the stock part, it's the upgraded version.

You only want to make up that thousandths gap with a thin film, you don't need very much.

So I'm just working this in a little bit at a time. The bearing race looks like it's in really good shape. It looks like the seal was replaced new in there (which it should be anyway). This part lifts out very easily. I'm going to lift that a little bit. I'm going to tip the transmission there. Just that little bit of extra help got it out.

It looks like everything inside that shaft is good. I don't see any wear patterns, so once we've gotten in this far, we can get to our fourth gear clutch head and synchro.

You can see that everything is looking pretty good, but to get any deeper into this, we're going to take our fifth gear nut off. The fifth gear nut tool is absolutely necessary.

Fifth Gear

The roll pins that hold this fifth gear shift fork are a mushroom headpin and so you have to have a good tool to get that out of there. I should be using a roll pin punch. i just don't have one with me today, so this regular flat punch will work. One punch to remove another punch.

We're done with that part. If we slip this off without taking the fifth gear clutch hub, my syncro struts will fly off, and we don't want that.

That's our fifth gear snap ring for the clutch hub. That part should just come out. We can see our clutch material in here on the synchro. It doesn't look burned or worn to me, and the fifth gear hub itself also looks good. Let's set that aside.

When I'm pushing on them, they grab together, which is what you want that to do. You don't want them to lock together but you want them to be able to spin smoothly. Then when you put the pressure on, they grab.

We'll try and slip fifth gear partway off. I can't get it past the fifth gear on the main shaft. So as much as I didn't want to, the fifth gear collar is coming off.

Let's have a look down here. These struts that we see right here are going to fly loose when I pop this off, so we want to make sure that we have some way to retain those somewhere to keep them.

I'm going to get a small screwdriver and I'll wiggle those into a better position before I take this the rest of the way off.

Go ahead and put that back in there. The reason I went ahead and took the shift fork off instead of just leaving it all together is to get this nut off. We're gonna have to get pretty western with it. We've got that staked-in spot on our fifth gear nut. I'm gonna get a chisel underneath it and lift that back up a little bit so that when I put my tool on there I can spin that nut off.

I'm going to put this into two gears at one time, and that effectively locks that shaft into place. Now when I turn on that it's not going to go anywhere. I still need to get that nut loose.

I still need to raise that a little bit. All I found so far was a nice little punch but since I'm just trying to lift it, it should work. You might wonder if it's so easy to lift that little nub out of there, did it do any good at all? I'd say yes, it did. It didn't go anywhere that I could tell, but also it doesn't take very much to hold something in place. It takes a whole lot more to break over that first initial loosening point before everything starts to go.

We're about ready to swing on this. Get my tool on there. This has been beaten on pretty badly already. This tool can work with either a ratchet or you can swing on it just like I did there. That came loose pretty easily. I don't think they were all the way up to that 300-foot pounds that we recommend in our book.

Pro Tip #4

If you want to know how to go through this whole transmission, we've got the TM1003, which is the manual that was done in-house on the NV4500. It's got a lot of great information.

The Shaft

Okay, it looks like we're dealing with a stock shaft. It's a good thing I pulled this apart. I've got a whole lot of rust in there, and that's unusual. Partway into reverse and partway into first gear. Now I can take my fifth gear off the back here and there's a bearing in there that looks good and the thrust washer also looks good. There's also an anti-rotation pin. That little pin right there keeps that thrust washer from spinning independently on the shaft to reduce wear.

So we'll take these plates off (I think I'll just take my main shaft plate). Here we have our shims. When you're putting the transmission together you'll have the input shaft in. You'll have everything put into place and this shim stock holds this bearing right there snug into the right spot to keep your 4 1/2 to play within spec. You want 2-6 thousandths front-to-back play. Take up the difference with those shims.

Pro Tip #5

Torque King has shim packs. The main shaft shim is a QU10009. The countershaft also uses shims, and that's a QU10008 shim pack.

Now that we've got everything loose here, I'll go ahead and take this bearing cup out. I see a little bit of gawling and pitting. It'll be good to put new bearings in here. We'll set that aside.

Now we're going to try and take our main shaft out. I pulled that out – that's the bearing race that the shims line up against. Then the bearing at the back of the main shaft here slid right off. They're not supposed to slide off, it should be pressed on. But if you get the book (the TM 1003) you can read like I did that several aftermarket shafts that have tried to fix the fifth gear nut problem have a slip fit bearing. The whole reason for that is so that you can get this shaft in and out and work on it more than once.

Inside the Transmission Case

Now with that bearing out of the way, I can lift this past the countershaft and get my whole main shaft out. Let's look down inside the transmission case. It looks like my countershaft gears, my reverse gear there and that also runs my first gear and there's my second gear and third gear. That's just the countershaft main gear. Everything in there looks really good.

I can see a little wear right there where the machining stopped in the final polish on that gear, but it rolls over beautifully. So with a fresh set of bearings and some new synchros, I think we'll have a good transmission.

There's our fourth gear synchro and our friction material looks good and our clutch hub looks good. It looks like it's a little unevenly worn there. I might need to replace that. If you look close that should be shaped more like a symmetrical house, but it's not – it's worn more on one side than the other. Maybe I'm wrong. I'll consult the book. We'll look at a brand new one once we've got the rest of this torn down. We'll also take a look and decide what other pieces we can use from this transmission and which need to be replaced. I'm going to start setting pieces down. I'm getting my struts out of there, we've already got one that's in the case.