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NV4500 lockup! Can Any gurus tell me what happened here?

73k5blazer

73k5blazer

End the H1B Program!
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I was driving along in my '97 K2500, happily in 5th, towing, not shifting, just cruising 65pmh or so, and I hear a high pitched whine, by the time I turned down the radio to listen to it better, boooommm, crunch, mangle crunch, engine stall, coast down rapily like something is dragging me.
I got it home (not by driving it, engine wouldn't turn), clutch pedal went to floor, tranny was very hot to the touch, couldn't shift.
Drop the transmission, here's what I got, but I still don't get what happened. Anyone with any ideas what happened, please enlighten me.
My guess on the clutch is it just got too hot from this gear grinding and burned out the stupid hydraulic throwout bearing.
Looks to me like one of the shafts locked and burned up one of the gears, but I really can't tell. I've never been inside one of these because I've never had an NV4500 or SM465 ever have any sort of problem.
Any guesses as to how much in parts I'm in for here?

IMG_9530.JPG


IMG_9531.JPG


I havn't separated it from the transfer case yet, could something have happened back there to cause this?
 
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So, ah, I'm just doing some quick research here, like I said I know nothing of these internals, but looking at some diagrams, that looks like granny low (1st) somehow engaged and chewed itself, if I'm seeing that right.. If that's the case, how could that have happened? I was driving along cruising in 5th gear?
 
Yep, full up. It fell over to the side whist I was taking it out, that's why you don't see much in there now. But I checed the level before I removed it, came rushing out the plug as I was unscrewing it.
I always used the proper oil in the rare occasion it needed topped off. Last time I did the clutch about 50k ago, I drained and refilled. I bought from the dealer since that seemed to have been the only place to get that 'special' oil listed to use.
 
Yeah, tell me about it. Standed me to boot. First time ever. This is not supposed to happen with this transmission, this is the exact thing I was aiming to avoid when I bought this truck back in '98 with 18k miles. Me to various salesmen at the time: "I don't want an automatic, I plan to keep this vehicle a long time, and I want longevity"
This truck doesn't get abused either, it's a road truck basically. Mild towing every now and again, I rigged a small plow off my front hitch, so I can plow my driveway, but it's not near what a real plow is. It's actually an ATV plow I extended slighty and welded up some mechaniusm to mount into my 2" receiver in the front.
I'm dying to find out what happened to it.
 
I'm certainly no expert but it looks like that gear that got chewed up got much hotter than the others in the back that still have oil on them. That could have happened when whatever caused that gear to fail.

Cool carnage pics though, thanks!
 
Thats some impressive damage, It looks similar to an SM465 that I had swapped the shaft on, I didn't soak the iron bearings, I just puit oil on them when I assembled it, and first gear burnt up and siezed while cruising in 4th. I'd guess a similer thing happened to your first gear, if I remeber correctly when I had it apart, it turns the fastest while in the higher gears, it just free spins faster than the shaft its on. Its just really odd that this happened after so many miles, if there was a problem with the bearing, it would have been very quick to show.
 
Yeah, I can't tell. The shafts will turn just a little way (couple hair widths), they are not siezed completly, but I see nothing binding them, I don't know what's locked.
I think that heat came during the coasting down while in gear, because the clutch just went to floor as well. OMG did it smell bad. That's a new smell in my smell file, some people know wine smells, I know automotive smell. When I first smelled it, hmm...a little like burnt gear oil, but different. I had never smelled this before.
I took the clutch out, it looks perfectly fine. That stupid hyro throwout bearing probably just got too hot. I hate those hydro throwout bearings. Hate them. Give me the hydro slave on the side or the mechanical linkage anytime, these bearings just are not up to the task, they fail all the time. I had to remove trans/transfer case about 30k after doing a clutch job (with new hydro bearing) because it failed. Nothing like 2 days of work just to replace a $30 part. Of course I put a new clutch in too, because it was off, it's so much work, might as well.
Anyhow, I'd like to take the back part of the case off, but it looks a little more than I might want to do. DOes it come off easy? Looks like I'd have to take that 5th gear nut off. I don't know how to rebuild these, I guess I could learn, but looks like some special tools are needed, I'm debating just taking it to a shop because I'm also out of town next week, it would be nice to come back and just be able to pop that thing back in there.
Oh, the forward shift fork is half melted, probably because it was next to that forward gear there.
 
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Well, I think I see perhaps what happened.
I took the pilot bearing out and removed the tranny front bearing retainer.
The input bearing is welded to the retainer, the rollers are oval, not round, I had to beat the retainer off and the bearing pieces came with it.
The pilot bearing was shot and the front of the input shaft is all grooved up.
So I think what happened, best I can tell so far, is the pilot bearing toasted itself, in turn causing the front input bearing to toast itself and the rest is a result.
But, I can't say I've heard of that on this big stuff. I heard of, and seen, pilot beaing failure on the small engine high horsepower stuff, but that front input bearing is huge, not like a honda or porsche, if the pilot did get a little womped, it seems it shouldn't cause catastrophic failure like this.
Oh well, as soon as I got the retainer off, I was able to rotate the shaft, that's a good sign. The pilot was replaced along with the clutch about 35kmi ago. What I don't remember is what type of bearing that was, a roller or solid.
 
Input bearing failure...exactly what mine looked like, and this type of failure is why they recommend overfilling the NV4500.

Sorry dude, I spent about a grand on parts to repair this exact failure on mine. :doah:

The heat cooks the kevlar stuff off of the synchro's, and all the chunks play havoc with the rest. What's even worse is the countershaft meshes with that messed up gear and is now a paper weight too. A new countershaft is in the $300 range by itself. Add a master kit, a small parts kit, new input gear, and new synchro's plus whatever else you run into...

Rene
 
Also, from right to left...

4th, 3rd, 2nd, 1st, and reverse...5th is the very outer gear on the outside of the main case.

Rene
 
Is this the type of repair one can do in their garage, or are all the special tools really needed? I've never rebuilt one, but barring expensive tools, I'm sure I could handle it with the proper manual and general 20+ years of wrenching knowledge.
 
No real special tools, except for the socket for the mainshaft nut. I was able to 'borrow' that socket from Kyle at Northwest fab...

A press will be needed to push on the new input bearing onto the new input shaft.

It's best to disassemble the mainshaft at least partially. It comes apart from the front going back to the middle, and from the back heading forward to the middle. Good large snap ring pliers are needed, but not much else.

I used feeler guages and a digital vernier to get the shims right for counterhaft and mainshaft bearing preload. A mag base with a dial would work too.

You'll need to cut the outer bearing race off the rear countershaft bearing to get the counter shaft out. No need to remove the rest as you'll be getting a new countershaft...:doah:

i did the whole thing in a small upstairs storage room at our old townhouse...except for pressing the input bearing on. That I took to work.

Oh yeah, you'll need a large tq wrench for the mianshaft nut...it's roughly 300 ft/lbs and the socket I borrowed was 3/4" drive.

Rene
 
and this type of failure is why they recommend overfilling the NV4500.
Click to expand...

How much overfill? Do you just park it on a big inclinde to allow more oil to stay in there before you get plug back in?
 
I was told at least 1/2 a quart extra. I filled mine through the top with the cover off. From my understanding when full the level is OK, but if it does drop a pint or so the input bearing is already vulnerable to being starved of lube.

The tranny I got had run just a little low, it had a very small leak. It doesn't seem to take much...maybe they should have added some sort of a slinger to ensure adequate lube to that bearing even with low levels?

Anyways, I run an extra pint or so in mine...or will when I'm back to driving it again.

Rene
 
Take off the shifter housing off in the cab. In my 97 K2500 it's 8 sheet metal screws for the boot and insulator, and then 4 bolts and the shifter is off, leaving a nice big hole for you to pour fluid into easily. You can drink a beer while you pour :), if you have money for beer left after buying 12346190 GM Gear oil that is. :( :)
 
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