Six speed?

[Alexe]

Just my 2 cents about a gear ratio change even though it's not on a 6.5. On my old class c camper with a 440 motor (similar torque to a 6.5 but at higher rpm).... when I went from 4:10 which was useless on the highway but pulled hills with all the cars, to a 3:54 it killed my power. Something to consider even with diesel torque down low. Wish I went with Gearvendors or a OD auto instead of the 3 speed auto with 3:54.
Anybody change 6.5 rearend gears and be happy with power/mileage? Only in Kansas I'll bet or other flatlands.

 

[6.5L]

Just an idea, but if the high RPM bothers you like ti did me, find a way around it. With my GM-3 turbo at 70mph at 2500rpm, my truck hated it and it killed mileage. I usualy had to cruise at 60mph to maintain somewhat decent mileage. I swapped over to the ATT now and at 70mph my mileage has picked up about 1-1.5mpg from where it was and she could stay there all day. Not saying it is the best approach, but it has kept me from doing a gear swap, because I enjoy the 4:10's and didn't want to swap to anything else, but the highway wasnt that good, but now I am happy with where it is at. Just my two cents

 

[GM Guy]

Your thoughts may be different, but this is how I think. Wouldn't it be cheaper to just rebuild your 4500, than to buy a new one? This IS my first diesel, and my first "big" truck, but the way I think, for the cost of a new 4500, I could probably do a complete rebuild of my old one, maybe incorporate a couple of improvements (if there are any), change the clutch/pp/brg while I am in there...

well, your decision has been made for you: new NV4500s havent been available for quite some time, so one has to rebuild their own or take it to a shop. the one improvement, if you dont allready have it, (running change in 94, so you may or may not) is the low 1st and reverse gears. if you dont trailer often, (like you said in other threads) I would only do this if you go with the 3.42 axle gears.

I know that right now, my clutch/transmission has an issue. I think there might be a synchro issue, since I have to play with the gears to get it into 2nd, while upshifting, etc. I actually think it is more of a clutch issue though, since when I put it in gear, it wants to creep on me, and 2-3, 3-4, and 4-5 shifts are sometimes a little more effort than they should be. The clutch does not slip, so I am thinking maybe a problem with the PP... maybe a problem on one side, causing it to not operate properly. If I have to pull the tranny, I will do everything I can find that needs to be done while it is out, because there will never be a better time to do those things.

master or slave cylinder most likely. try doing that first before writing off the transmission. of course check the fluid level and condition first.

Speaking of trannies, what lube is in the NV4500, and would a synthetic alternative be effective?

The NV4500 already comes from the factory with synthetic. It is very special, so make sure and use the right stuff. It is GM part number of 12346190. costs a bunch. the same damn stuff is available from dodge, and it usually costs less. Amsoil offers a compatable oil, I havent done a full change with it yet, but have topped off stuff with it, and so far no negative effects on shifting, but 88gmctruck feels that the shifts werent as smooth when he switched. but as far as aftermarket oils, the amsoil is the only one I would recommend. otherwise, GM or dodge only. The oil is actually Castrol Syntorq LT (NOT Castrol Syntec) 75w90, but is supposedly only offered in 55 gallon drums. quad4x4.com used to buy a drum and re-package the oil, but IDK if they still do. quad4x4.com is the site.

good luck!