Nv 4500

I have a 95 K2500 W/ a NV4500 5 speed transmission. Everything shifts perfect (synchros) except when I am in third gear. It goes in fine, but once engaged it has a hollow knocking sound (chipped tooth?) I have had the fluid changed twice, and no metal has surfaced. When its really cold out the noise disappears, and doesnt surface again until fluid reaches operating temperature. I am running the app. fluid supplied by GM. The truck is a 4x4 and has 83000 miles. Any ideas?
If its a problem, where you do you guys prefer for aftermarket parts, or an O.R. tranny.

Possible clutch throwout bearing hydraulic assembly. Don't know for sure, but what I can tell you is that I have rebuilt a NV3500 and it sux bigtime.

The NV4500 is a good transmission. Some early versions 96-97 had a problem with 5th gear comming loose. The retainer nut would work loose from vibration and 5th gear could come loose the main shaft. If this is the case, stop driving it and take it to a good rebuilder. It doesen't cost much to fix it unless you wait for it to crater. There is an upgraded mainshaft that solves the problem. This might be the clunking noise that you are hearing.

Also, the GM fluid is ridiculously expensive. Amsoil 2000 works fine and costs a lot less. Most of the problems with this transmission are related to heat. Chevrolet routes the exhaust pipes too close to the transmission case which thins the oil and causes premature wear. Insulating the exhaust pipes solves most of the problems.

Here is some good tech on the NV4500 explaining what the 5th gear problem is. It is not limited to a few years, and New Venture never did address it correctly. There are many band-aid solutions out there, some of which just make things worse.

http://www.quad4x4.com/NV4500%205th%20Gear%20Failures%20and%20Solutions.h tm

As for the thrid gear knock...not sure.

I'm in the process of rebuilding a '95 GM NV4500 for my Jimmy. I plan on using the "Torque king 5th gear retrofit" kit on mine.

Rene