NP205 Experts: Knowledge Wanted!

[joeydurango]

Asked over on the general board 2 months ago but never got this figured out.

My 72 K10 (350/350) has suddenly begun spinning the front driveshaft intermittently when in 2HI. I'll be coasting along down a hill, all's normal, hit a few small bumps, and the vibration appears to cause the case to s l o w l y begin engaging the front shaft. I can hear it, and feel it, catching just the tiniest bit, then increasing engagement.

The front axle and hubs are all good, I rebuilt them a couple years back and checked them again recently. Everything else (shift linkage, all connections, u-joints, driveshaft slip joint) looks/feels completely normal and is tight and solid externally, so I've got some sort of problem inside the dang case.

What part in the NP205 t-case is responsible for keeping the t-case locked in 2HI? Is there a detent spring or something that could have broken, allowing some selection mechanism to "float" between 2HI and 4HI even when the shift lever is solidly in 2HI?

TIA!

[sweetk30]

it all just kind of floats along in 2h there is no lock feature cause if you had the hubs locked in you could brake somthing . . if your still running 75-90 or 80-90 gear oil its thick and can cause this a bit . the later 205 t-cases were atf for less drag from the factory .

other thing that might be happening is a shift rail could not be fully in the park position or the detent ball spring could be broken ( seen a few of them ) and this could be letting it kind of partly flop in front drive .

the 205 is a simple easy case to play with . i had never touched one untill i did my first full re-build and mods to 1 and they are easy . i did a step by step rebuild on the other site i am on .

my 1 old truck did just what you described and i never did play with that case .

but a few worn items like i said or thick heavy oil drag could be doing this .

also get some napa # 1370 chain and cable lube in a spray can . crawl under and spray down the 2 shifter shafts in the case with them out all the way . also do the linkage pins . then you should have a greese zerk on the bolt or body of the shifter were the bolt goes threw . hit that a few pumps . these few things help the stock shifter work better .

dont forget this thread here . http://67-72chevytrucks.com/vboard/s...d.php?t=469726 . i have not looked all the way threw it my self tho .

[joeydurango]

Thanks, that's really helpful, especially the link to that old rebuild thread - I'd seen that years ago but had forgotten!

I've been running (fresh) 80-90 gear oil for a couple years now, nothing's different there. And the shifter works pretty smooth (for a 46-year-old truck, anyway)... I'll lube it for good measure.

Sure seemed like something changed abruptly, not a wear issue, but a breakage issue - and it happened immediately after a mild 4x4 session. The internals of the 205 seem pretty bomber, so I will check the shift pattern from below, and see if I can get to those detent balls without dropping the case.

Another train of thought - maybe the case has been intermittently spinning the front shaft all along and something else in the driveline has begun making noise, so only now I notice. As noted, though, everything else appears normal!

At least I've got a couple things to work with. Thank you again.

[Bigdav160]

How do you know the driveshaft is turning?

[joeydurango]

Good question. Simple enough - I just have a mark on the driveshaft, and set it in a given position by hand.

When I don't hear the noise while driving, I look and see the mark in the same position afterwards. If I hear the noise, however, the mark has moved.

Worth noting that even if I stop immediately after hearing the noise, I can still turn the front shaft by hand - so it obviously isn't really locked in. That's where the "intermittent" and "floating" description comes from. It just comes and goes.

[sweetk30]

ya all the gears spin when moving . its just is the shift collar engaged in the low range gear or high range gear to couple the shaft to gear for power feed . when in N it holds the shaft free of power from any gear .

[dieseldude4bt]

I think your noise may be spindle bearings and not a drive shaft problem. they are SBK1 or BK1 bearings.

[joeydurango]

Spindle bearings are new as of ~5000 miles ago, along with all other bearings and seals in the front axle assembly.

Had my wife shift the case while I watched from under the truck - everything shifts cleanly and absolutely normally, and it appears the detents are firmly observed, so I think the detent balls/springs are okay.

The truck drives just fine, so this is one of those things that isn't a huge deal, I'm just someone that likes a solid truck with no strange noises I don't understand. Next step may be to film under the truck while moving to make sure that what I'm hearing is actually happening concurrent with driveshaft movement.

[Miller's Metal]

You could try running it on stands or a lift. Turning and breaking to see if you can duplicate the noise/vibration.

[jeffahart]

Originally Posted by joeydurango

Spindle bearings are new as of ~5000 miles ago, along with all other bearings and seals in the front axle assembly.

Had my wife shift the case while I watched from under the truck - everything shifts cleanly and absolutely normally, and it appears the detents are firmly observed, so I think the detent balls/springs are okay.

The truck drives just fine, so this is one of those things that isn't a huge deal, I'm just someone that likes a solid truck with no strange noises I don't understand. Next step may be to film under the truck while moving to make sure that what I'm hearing is actually happening concurrent with driveshaft movement.

Why not pull the hump off. You can see the front shaft from the hump. I just re-installed my trans and transfer. I drove it with the hump off for test driving, hump is still off. You can watch the front shaft and the shift rails as you shift from. 2Ho to 4Hi.. ect.

j

[nonstop]

Are the hubs sticking at all, and lubed properly (not too much)? I ask because it isn’t uncommon for the front shaft to slowly spin after a while of driving, driven from everything turning in the front end. It can even happen from time to time with the hubs unlocked.

[87Skier]

When I was working on my truck a few years ago I had the hump cover removed. I drove it and could watch as my driveshaft began rotating when I got to highway speed. It didn't rotate anywhere as fast as it would have if it were engaged, but it definitely rotated.

I think the important question is if your shaft is turning at it's driven speed (either by a locked hub or from the 205 being partially engaged) or if it's just some component drag (spindles, axle shafts, or even gear oil circulation).

You could put a zip tie on the front drive shaft near the U-joint and hook it to something solid like the engine cross member. If your truck breaks the zip tie, it's definitely trying to drive the shaft and you've got a problem.

[Jsfucttruck]

There is a spring loaded detent ball that hold the shift rails in position. The springs can weaken over time. If it was starting to engage the front, it will make a clicking sound as the teeth on the shift collar tries to engage.

Good luck


JB Fabrication makes adjustable detents for the 205.

[mcmlxix]

ORD is a new vendor on this board. They have knowledge and parts

http://offroaddesign.com/catalog/NP205%20Parts.htm

[sweetk30]

Originally Posted by mcmlxix

ORD is a new vendor on this board. They have knowledge and parts

http://offroaddesign.com/catalog/NP205%20Parts.htm

yep ord guys & gals know there stuff . been buying from them for years .

and yes even the ladys that answer the phone know the parts and lingo . and if not they find out .

[Doody]

I read this somewhere but do not recall where, if you used the wrong lube when assembling your hubs they may not disengage. Just my 2cents.

[Doody]

I will also add the springs (as mentioned before) could be weak, but the balls in the shift rail are hardened and the shaft is softer, so depending on how much it was used, the shaft detents wear and it wont stay in place. Now up to 3 cents. Good luck.

[BILT4ME]

Originally Posted by joeydurango

Asked over on the general board 2 months ago but never got this figured out.

My 72 K10 (350/350) has suddenly begun spinning the front driveshaft intermittently when in 2HI. I'll be coasting along down a hill, all's normal, hit a few small bumps, and the vibration appears to cause the case to s l o w l y begin engaging the front shaft. I can hear it, and feel it, catching just the tiniest bit, then increasing engagement.

The front axle and hubs are all good, I rebuilt them a couple years back and checked them again recently. Everything else (shift linkage, all connections, u-joints, driveshaft slip joint) looks/feels completely normal and is tight and solid externally, so I've got some sort of problem inside the dang case.

What part in the NP205 t-case is responsible for keeping the t-case locked in 2HI? Is there a detent spring or something that could have broken, allowing some selection mechanism to "float" between 2HI and 4HI even when the shift lever is solidly in 2HI?

TIA!

Something else to look at are the front locking hubs.

Our 70 GMC K2500 had a noise that would occur occasionally, and it took us a while to isolate and make repeatable.

It turned out that one of the original blue lockers on the RF hub was cracked and it allowed the RF hub to start to engage and rotate the front axle.

We ended up installing a set of new Warn hubs and problem was solved.

Might be worth checking.