I know this isn't really the right place for this but I couldn't find an area for the 5 speed. So I lost overdrive the other day. I was cruising around town and went to shift up and it wasn't there, totally gone. It was like pushing the shifter into another neutral area, no resistance. Anyways, I tried flushing it, and just put in GL-5 gear oil until it was at the fill plug. I tried it out, and all of the other gears shift smoother (it was low before), but still the same deal with overdrive. Have any of you guys had this happen? I was doing some research and found that 5th gear is outside the main transmission case, its in the tailshaft (I think). What do you think? Thanks

Have any of you guys had this happen? I was doing some research and found that 5th gear is outside the main transmission case, its in the tailshaft (I think). What do you think? Thanks

I had a Jeep which did the same thing. 5th gear was an addon.

IF yours is the same way then, then it should be fairly inexpensive to repair. AVOID AAMCO and the other tranny chain places that charge an "inspection fee" of a few hunderd $$'s as standard practice. Find a good local shop fro tranny work and have them look at it. It was done for less than the other's inspection fee. Under $200 fixed, I believe.

Sir Veyor

Sounds like the nut on the main shaft backed off they are bad for that. The nut holds the 5 th gear on the main shaft . The 5 th is in the back end of the unit.
if the rest works ok you can pull it out and remove the rear housing and see what happened.

You used gl 5 oil , do not use with that oil for very long you will wreck the blocker rings (Synchro Ring.)

Sounds like the nut on the main shaft backed off they are bad for that. The nut holds the 5 th gear on the main shaft . The 5 th is in the back end of the unit.
if the rest works ok you can pull it out and remove the rear housing and see what happened.

You used gl 5 oil , do not use with that oil for very long you will wreck the blocker rings (Synchro Ring.)

X 2

Use GM fluid or Castrol Syntec only, There is a special 5th gear nut [repair kit] to take care of the 5th gear problem.

Do you know what is different about the oil for this trans. I have only used the GM oil, but at $28.00 a liter from GM, I would like to have another choice. Is there a special syntec just for this? what do I need to know?

had the same problem on my dodge, the 5th gear nut backed off to much. also, i believe your suppose to run full synthetic in these transmissions, i run Mobil 1 full synthetic 75w-90? i think thats the number

The GM fluid is sold in quarts , the Castrol Syntorq is sold in larger containers,5 gal or larger I believe. The problem with the NV-4500 is the factory syncros are made of some sort of fiber[don't recall if it is Kevlar] reg fluid will make the syncros soft and fall apart. Aftermarket rebuild kits often used brass syncros , if you know yours has brass syncros I believe you can use regular synthetic such as Mobil, don't take my word as gospel though, as we get remans at work and the supplier won't warranty any trans unless we use the GM fluid. Its a bite to have to pay the dealer over $100.00 for fluid, but options are limited.

On edit : I think the GM fluid is vegetable based???

special additive (friction modifer) Fiber type rings in the synchro .

The price that G M whats for that is crazy I use the amsoil it is 75-90 syn.
it is the Gl-4 the # is MTG-01 upc code is 9701226201 says for n/v 4500 trans.

I tried to run 75-90 syn oil the gl-5 type with the limited slip additive (two bottles) but in less than 2500 k's had to change the oil back to the GL-4. In the end I had to pull the unit down and replace syncho's again. Burnt them up , had very hard shifting etc.

One more thing is on any of these five speeds always run them 1/2 or so over full with oil . The 5 th gear is a little higher in the back and they do'nt get proper lub. Two ways to do this fill unit up then pour 1/2 litre in the top (shift lever) or put a elbow into the filler plug pointing up and fill to the top of that elbow. The case is pipe thread can get fitting at hardware store

good luck

Wow, thanks guys! Yeah I'm going to take it somewhere to get looked at hopefully this week. Yeah I wanted to use GL-4 but 5 was all we had laying around. I will be draining it anyway it looks like. I want to try to do the work myself but I guess I'll have to see about that. Is there anything I should do while I have it open? I mean its only got 95K but I might as well take advantage of the situation. Also, do they make a 5th gear you can buy with a little lower ratio? I think the 5th in these is .73:1 from what I read. Is there anyway to get anything like .70 or something so I can run lower rpms on the highway? Anyways thanks for all the help!!! I will be looking up that repair kit tonight.

well if you got the tranny out, i'd go ahead and put in a new clutch kit in so you aint gotta take it out later and do it. also, if the u-joints havent been replaced, i'd get some of them

thanks for the info on the oil. Anytime you take out a NV4500, always replace the output shaft bearing/bushing in the crankshaft. It is undersized and will wear out and cause clutch and output shaft damage long before the clutch itself wears out. If you do a lot of towing, it will fail sooner. GM originally used a bushing, then changed to a bearing to try to get longer life. The down side is that a failed bearing will destroy the nose of the input shaft while a bushing usually won't. I learned this from owning and wrenching three different NV4500 trucks over the last 20 plus years. There are a couple of blurry pictures of input shaft damage in my garage. If you haven't had the pleasure, an NV4500 is heavy
and smells like gear oil.

Thanks again guys! So without my knowledge, not too happy, my parents took my truck to the local dealer while I was at work, and now they are looking at it. So now I can watch the $$$ add up. If I had known, I would have dropped the tranny at home, and taken it in. Now my truck is sitting in a garage too far away from home incapacitated :(