My NV4500 Swap Thread

[JJorgensen52]

For the moment this is just going to be a bit of a picture dump, I'll come back and flush it out with more info this weekend (like part numbers, measurements etc):

Basic gist:
1995 NV4500 (GM) with Advanced Adapters bellhousing (manual clutch).
1990 NP241C from a Suburban (passengers drop).
Stock clutch and linkage.
Custom rear (1350 u-joints) and front (1330 double cardan / stock 1310 front yoke) driveshafts made to spec.
Modified stock SM465 tranny cross member, relocated one set of holes back
Stock Rockwell T221 T-case skidplate, relocated one set of holes back.
Big block (auto) high hump trimmed to fit NV4500 shifter with stock boot.
Mid 60's iron nose big-block high torque starter.

I still need to fabricate 4x4 shifter and linkage, and also a new shift lever for the tranny as the Nv4500 lever hits the bench and is generally just at the wrong angle.

I found that whatever combo of parts came in the Suburban my NP241 came out of happens to match mine, as my speedo (new cable, 83" length NAPA part) is actually more accurate (-1.5mph at 65) than it used to be (-5mph at 65).

This is absolutely a great swap. Truck is a joy to highway drive now, turning only about 2100 RPM at 65mph (used to be just under 3100RPM). Haven't tested 4x4 yet but I've had a NP241 truck before and it was pretty good so expecting good results.

Biggest drawback I can see is that with this particular Tcase I've lost perhaps 1.5" of ground clearance at the Tcase. Still above the pumpkins, but not so good for straddling obstacles. This is primarily a work rig so trail performance was not a huge motivator for me.

First estimate (not having totaled receipts) puts me at roughly ~$2500 for the swap, having pieced it together from various sources. A large chunk of that cost was the driveshafts. Would have been MUCH cheaper to have my factory shafts adjusted, but that's not my style. So it was on a semi-budget

I probably spent 2 solid 8 hour days on all of the fitting, fabricating and mock-ups I needed to get the install set. I probably could do the swap again, knowing what I've learned, in about 5 days start to finish.

Now on to the picture part. More or less chronological. I suspect this could have been done easily without ever removing the seat, but I needed mine out anyway and had to do some floor pan repairs so out she came.

[JJorgensen52]

[Dieselwrencher]

Nice swap and nice truck! You should really enjoy driving it now!

[treveiger]

Looks great!!! Thatll be fun in the winter.

[JJorgensen52]

Originally Posted by treveiger

Looks great!!! Thatll be fun in the winter.

You bet it was! Plowed a lot of snow this winter, that's for sure.

I have since fabricated 4x4 linkage (still not happy with it but it works) and also made a custom shifter for the trans to match the shape / style of my original, as the NV4500 stock shifter is at too extreme an angle to be comfortable.

After putting somewheres in the neighborhood of 2k on this swap, some notes:

1. I initially thought I was going to be disappointed in the change from 6.55 to 5.61 1st, but I've done a considerable amount of towing and hauling with it and found that it's actually more road friendly and it's a nice change. The change in the ratio of 2nd gear is barely noticeable, I still start in 2nd in 90% of situations.

2. For hauling off-road and plowing, the 2.72:1 low ratio in the NP241 is PHENOMENAL when compared to the 1.71:1 in the T-221. I don't abuse my truck offroad, and I have yet to have any complaints from the new case, or any troubles with it.

3. The NV4500 is not as noisy as my old combo, but it is noisy in it's own right. It was a bad idea on my part to remove the rubber isolator from the shifter, because it transmits a lot of gear noise into the cab. I am likely going to be going back to an isolated shifter in the future.

4. With my engine (307/2bbl) I can't really take advantage of 5th gear until 65mph, and I actually see a decrease in fuel mileage if I do use it because the motor lugs too much. I am planning to freshen up the motor with vortec heads and a quadrajet, I expect that will help alleviate this problem.

5. With #4 said, cruising on the highway at 70-75mph in 5th is a joy now; my oil consumption has been considerably reduced and at these speeds I do see improved mileage - I got 12.7 mpg average on a tank towing 3500lbs of car behind me, when I used to get about 10.5 - 11mpg average even unloaded on the highway.

6. I've found that the way I designed the modifications to my cross-member has a tendency to pick up road debris and snow, so I am seeing changes coming to that. It has been holding up quite well, and I haven't experienced any ground clearance issues which I had anticipated, as the center clearance is now about 2" lower than stock.

7. The NV4500 is too large to work with a stock exhaust layout - it basically is sitting on the crossover pipe and I'm not happy with how low I had to hang the exhaust to clear the new driveshaft angle. A custom exhaust system is definitely in my future.

8. This combo causes some slight interference with the parking brake - the cables basically sit on the transfer case when the brake is released. I expected to have trouble because of this, but I've found it actually works about as well as it ever did (which isn't well at all )

9. I had some initial concerns that the increased length of the case and slight increase of height at the slide yoke my cause me driveline woes (around 2.5* of angle, equal at both joints, which is probably twice the stock angle), but I've found that it actually improved overall behavior of the rear-end, a little less axle hop in general since I made the changes.

10. The adjusted geometry of the mounts changed my engine orientation slightly, which cause me to A. have fan interference (which was easily fixed by tweaking blades) and B. have firewall interference when trying to change my oil pan gasket. That is an infrequent scenario, so not much of a drawback, realistically.

11. I had some initial trouble with the clutch linkage not playing nice with me and falling out of the clutch fork, but after multiple adjustments it seems to have settled out. I think it may just have been a matter of getting all the new components seated and worked into place.

The only real con (besides the noise from my solid shifter, which is pretty easily remedied) that I've seen is that for some reason this transmission absolutely STINKS of gear oil. It is beyond my comprehension why it does this, because it doesn't leak a drop or appear to burn any fluid. I am begining to think it's supposed to have a cap instead of an open vent line ???