The Stovebolt Site Forums The Shop Area Engine Shop NV 4500 Swap

A few months ago, I was advised by some of the fine folks on the forum to use a NV 4500 in place of the factory SM 420. I'm working on a 1967 GMC One Ton, 351 E V6. I'm wondering what types of issues may come up in doing this swap. Thank you in advance for all of your help and information. It is greatly appreciated.

The big issue will be that the NV4500 does not use the standard GM transmission bolt pattern, so it will not bolt directly to your existing bellhousing. Unfortunatly, there also is no adapter bellhousing for the GMC V6. You might be able to have an adapter plate made at the local machine shop, though.

There is a company out there that does sell adapters and all the needed parts to put NV4500s in popular trucks,I lost the info when my old computer crashed. They had all the parts to put one in my 66 F250 but I decided to go with a automatic,they even could supply a brand new trans and at the time it was about 2600.00 for everything except drive shaft modifications but its been a couple years ago.

NV4500 in a stovebolt is a fairly simple swap.

1.) Find a 1994-1997 Dodge 2wd NV4500, the lighter gas version is preferable, but the heavy duty diesel and V10 transmission will also work.

2.) Get an Advance Adapter plate to go between the bellhousing and transmission.

3.)Bolt adapter plate to bellhousing and transmission to adapter plate.

4.) Fabricate tailshaft support for transmission and have new driveshaft made.

5.) Smile when shifting through 5 forward syncro gears.

Of course it isn't exactly this simple. Here are the Monkey Wrenches...

It is likely that your bellhousing has a bore of 4.686 inches. The adapter plate that AA sels is indexed to 5.125 inches. Either the adapter plate will have to be turned down, or the bellhousing will need to be bored out by a machinest.

GM uses a 10 spline 1 1/8 inch clutch. The Heavy Duty(diesel and V10) NV4500 has a 10 spline 1 1/4 pilot shaft. The pilot shaft and the bearing retainer can be swapped with the dodge gas NV4500 to come up with the correct spline to match the stock clutch.

The part of the bearing retainer where the throwout bearing rides is a little bit thicker than the stock transmission. I believe it is 1.43 inches and stock is 1.373 inches... Don't quote me on those numbers as it has been a while since I measured. This part of the bearing retainer will have to be turned down to use the stock throwout bearing. AA might have a crossover throwout bearing that will work with the NV4500 and your clutch fork with No machining. I wanted to use as many of the stock clutch components as I could for simplicity of ordering parts, so I had a machinest turn the collar down to match the collar of the transmission that was coming out.

The pilot tip of a standard gm transmission is .590 inches. The pilot tip of the Dodge NV4500 is .750 inches. A new Pilot bearing/bushing will be needed. AA can supply this, but they will need the dimensions of the bearing you have. This was the only nonstock clutch component I used on my 1959 GMC conversion.

Why the 1994-1997 Dodge NV4500? The pilot shaft of the dodge transmission is 1 inch longer than the gm version. This allows you to use a 1 inch adapter plate to bolt it to your bellhousing. This version of the transmission is easily adapted to a mechanical speedometer. GM versions and 4wd versions do not have a speedo pinion on the transmission. There are some speedo callibration charts you can look at to get the correct speedo pinion based on tire size and gear ratio. In general adding a tooth will slow your speedo down by about 3%, and removing a tooth will speed it up about 3%. You may be able to be accurate to +/- 1%. The chart is a good place to start, and not all tooth counts are available. You will need to get a speedo pinion housing to put in place of the pulse generator the transmission will have.

A stock gm 4 speed floor shift transmission has the shifter about 4.5 inches from the bellhousing. The 94-97 dodge NV4500 shifter is about 5 inches further back, will end up being about 6 inches further back when using a 1 inch adapter.

The NV4500 is a big transmission. You might have to fabricate a humped floor cover for the transmission. My truck had a flat floor cover. I found a 4 speed floor cover that already had the hump, and simply made a hole for the shifter tower.

John

The NV4500 is a very big transmission, it will withstand over 500 ft. lbs. torque which is overkill for a GMC V6. I would suggest using a smaller, lighter gearbox, say from a Chevy pickup the Getrag I have in my 1992 GMC 1/2 ton is a very good smooth shifting transmission and would work out great for your truck with no changes to floor or crossmember needed and it also should be cheaper than the NV4500.

Advance Adapter no longer lists an adapter plate, that was the first site I checked to come up with an answer. They also do not make a bellhousing to fit the big V6.
The Getrag won't work with the V6 either, bolt pattern is wrong on the integral bellhousing and that trans is far too light for a 1 ton truck.
One option that might be considered, though, would be to use a Ranger Overdrive from Advance Adapters. No cheap, but it will bolt up to the existing bellhousing and the SM420 trans. Plus it will give 8 forward gears plus 2 reverse.

Give em a call. Here is the adapter plate needed in a kit. http://advanceadapters.com/product/3181/Adapt-Dodge-29-Spline-NV4500-to-Jeep-Dana-300-%26-GM-Small-Block-V8.html

I did the swap in 2007. I think AA charged me about $270 for the plate with shipping.

Thanks again for the information. I'd like to stay away from the getrag simply because it is only 17% overdriven. The NV4500 is out of a Chevrolet two-wheel drive. I would like to use this trans, I think it would be a very good combo with the big V6 and the 4:10 gear.

You might have to work a trade to get the dodge transmission. The chevy version has a shorter pilot shaft than the dodge version. This makes it really difficult to use an adapter plate. You also have to work around the Velocity sensor. I suppose you might be able to boar the bellhousing out to the size of the bearing retainer, and drill and tap new 1/2 inch 13 mounting holes. Is this the earlier 6.34:1 first gear transmission, or the later 5.61:1 first gear transmission?

It may be possible to switch out the pilot shaft for the later one, but not for the early one.

Just talked to the guy with the NV4500. He just bolted it up to a stock sm420 bell housing. He said it bolted right up and thinks that I shouldn't have any trouble. This adapter plate you mentioned, does it go between the transmission and my stock bell housing? Appreciate all the info!

Just talked to the guy with the NV4500. He just bolted it up to a stock sm420 bell housing. He said it bolted right up and thinks that I shouldn't have any trouble. This adapter plate you mentioned, does it go between the transmission and my stock bell housing? Is my bell housing for the v6 different from a typical manual bell housing of that era? Appreciate all the info!

If it bolted up to a stock SM420 bellhousing, it is not an NV4500. Probably either an NV3500 or a T-5. Both of those will bolt up to a stock 420 bellhousing, the NV3500 is a found mostly in 1/2 tons, Jeeps, and compact trucks, the T-5 is basically a passenger car trans, though it also is used in compact trucks as well. The bolt pattern on the NV4500 is very different from the standard GM, and it has a larger index bore ID.
Yes, an adapter plate would mount between the trans and the bellhousing. The difference in your bellhousing is the bolt pattern on the engine side, trans side is the same as standard GM.

The first chevy version of the NV4500 had a different mounting pattern than the rest of the NV4500s. I believe it also had a 5.125 inch indexing bearing retainer. This would be the one with the lower 6.34:1 first gear. As far as I know No NV4500s will bolt straight up to your bellhousing. I agree with Bill that this isn't a NV4500. It might be an SM465 4 speed, or possibly a Clark 5 speed. The Clark 5 speed would bolt up to the sm420 bellhousing, but it may or may not have OD.

As explained above... The dodge 2wd version from 1994-1997 works best for the conversion.

I thought the SM465 had a 5.125" indexing diameter?
And if your speculation is correct that the early NV4500 has the same.. Then it's not a far stretch for someone to assume it bolts up. Some extra bolt holes may have been drilled and tapped in the clutch housing?
Not saying this is all true, just that some more investigation is needed before completely discounting the claim that it is an NV4500.

Grigg