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NP-205 Noise

Montoya

Sr. Member
Joined
Feb 22, 2007
Messages
518
I think I have an issue with my NP-205 but I can't quite nail it down. When I accelerate I get a clunking sound as if a U-joint is bad and its worse if I accelerate hard. I can feel and hear something metal-metal in the drive-line but my u-joints all look fine.

Is this a common symptom for an NP-205 on it's last legs? I've only ever managed to grenade them in the past, with no signs of damage before complete destruction, so this is new territory for me.
 

nvrstuk

Contributor
Just a Bronco driver for over 50 yrs!
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Jul 31, 2001
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9,384
Loc.
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Diagnosing over the keyboard is tough... let's try to eliminate some other possibilities first- like the rear driveline/CV, etc.

Is your 205 twin sticked? If so, put it in FWD only, engage your hubs and see if you get the same noise... should be able to eliminate the rear with that simple test since you say that load on it makes it worse... the rear will not have any load now...

Let us know.
 

DirtDonk

Contributor
Bronco Guru
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Nov 3, 2003
Messages
49,236
...I can feel and hear something metal-metal in the drive-line but my u-joints all look fine.

How did you test this? And those CV heads/double-cardan yokes can be very finicky and give different symptoms and make you chase your tail.
So be 100% sure it's not the driveshaft first.

how long has it been since it was all greased (all five fittings)?
Have you ever greased the semi-hidden female Zerk fitting on the centering ball?
How long have the u-joints been in use?
How old is the whole double-cardan system with yoke and centering ball?

Is this a common symptom for an NP-205 on it's last legs?

No idea. Can't remember the last time I heard anyone say they had a noise from a 205. Well, other than the explosive sounds of flying metal...

Paul
 

sanndmann3

Contributor
Bronco Guru
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Jun 13, 2007
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1,790
It could be the 205 but I kinda doubt it. They are WAY beefier than the D20 are...
I had a similar noise in my driveline. It felt like a hammer blow on the front driveshaft. U-joints looked good and felt tight but I took the driveshaft apart 1st rather than going into the T case (also a NP205). As luck would have it, it was the ujoint afterall. Not sure what the cause was, just happy that I didn't have to dive deeper into it...
 

Apogee

Contributor
Bronco Guru
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Nov 26, 2005
Messages
6,189
Assuming the NP205 has been kept well lubed during it's life, they're really tough to kill. That said, check the u-joints, double cardan, slip yokes, etc, and I bet you find your problem(s).
 

SHX669

Bronco Guru
Joined
Jan 9, 2009
Messages
1,997
Check your slip yoke for wear/looseness also the Ubolts holding your rear leaf springs to the rear axle housing.
 
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Montoya

Sr. Member
Joined
Feb 22, 2007
Messages
518
These are all great comments and that's why I love this site.

I recently (less than 3k miles) replaced the u joints in the driveshafts and everything still looks and feels great but as sandman said, it could still be it.

I was concerned about the NP because I ran it without fluid for a little bit. I know it leaks but didn't realize it was dry. That said, no whines or engagement issues and I do think it's fine after more testing.

I now think it's something in the rear but it doesn't do it when jacked up and giving it some gas. It has to do it under load.
 

DirtDonk

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Nov 3, 2003
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I recently (less than 3k miles) replaced the u joints in the driveshafts and everything still looks and feels great...
I was concerned about the NP because I ran it without fluid for a little bit.

Oh, come on now, you know the routine. You can't leave stuff like that out of the conversation! At least not and still expect an accurate answer.;)
The bit about the u-joints is important, but the other bit about running the transfer case dry is a critical bit of intel.

So how long is a "little bit" and was it ever in 4wd during that time that you know of?

That said, no whines or engagement issues and I do think it's fine after more testing.

This could be a good thing. Might have dodged that bullet for now. Or not...
The very large main bearings might live without lube, or might actually be dead and dying but not make noise under all conditions. My 3-speed didn't make any unusual noises until the moment I heard the popping and ringing sound of ball bearings shooting around the case.

U-joints can go bad quickly just like a lot of other modern parts. But for the most part, they're pretty good still. So you might be ok there.
But did you check (and more importantly, lubricate) the centering yoke? I assume so, but wanted to make sure because those things can create some very inconsistent symptoms when they're going out.

I kind of hope it's the driveshaft because it's usually easier to fix. But if you have to replace it, or the centering yoke of the CV head, it might be as expensive as rebuilding the entire transfer case (if you do it yourself) but not as expensive as something in the rear end.

Anyway, as said those main bearings in the transfer case are very robust. But if they're 45 years old, and ran long enough without lubrication (mainly the upper output bearing I think) that might have done some damage after all.

Good luck.

Paul
 
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Montoya

Sr. Member
Joined
Feb 22, 2007
Messages
518
Hi Paul,
As always you give great insight! I should have mentioned the lack of oil but honestly the thing never gets driven more than 20 miles at a time and it was filled not that many miles ago...

Turns out it leaks way worse than I thought (and the front diff, engine oil pan, rear main seal, auto trans pan, and power steering pump :p) but the underside is rust free! It's in need of a rebuild but I'm hoping to hold off for a larger rebuild project.

That said, it was in 4wd for a few miles without me knowing... My 3&5 year old kids like to play in it and I didn't catch that they had it in 4wd. It would have only been one 5 mile trip and there might have been oil in it still at that time.

I checked the U bolts on the suspension and still nothing. Going to take the driveshaft off tomorrow, maybe I just can't see a bad U joint... Fingers crossed!

If not that, I might be looking at a third member rebuild... Ugh, in my free time.

When I rotate the driveshaft by hand there is a fair amount of play in the gears... They too have an unknown number of miles on them but odds are good it's over 200k.
 
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Montoya

Sr. Member
Joined
Feb 22, 2007
Messages
518
It was the rear after all.

Somehow I damaged the ring and pinion just driving slowly around town but like I said before, I believe these parts have a large number of miles on them (the chassis has 354K miles and counting).

Thanks for all the help and happy new year to everyone.
 

DirtDonk

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Bronco Guru
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Nov 3, 2003
Messages
49,236
Well bummer that it's not a cheap and easy to fix u-joint. But maybe it's a good thing after all, as it happened near home.
And that is a lot of potential miles of wear on those gears and bearings. Might just have been time for new ones along with new wheel bearings too maybe.

Is it time to change ratios too? Or are you happy with what's in there?

Paul
 

sanndmann3

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Jun 13, 2007
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Might as well upgrade to 31 spline and lockers while you are at it... lol ;D
 
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Montoya

Sr. Member
Joined
Feb 22, 2007
Messages
518
Is it time to change ratios too? Or are you happy with what's in there?

Paul

Fortunately I'm happy with the ratio otherwise I'd be tearing into two axles. :p

I know I'm preaching to the choir but a R&P change on a 9" is relatively easy (still not cheap) compared with the same job on a Dana 44. Being able to do everything outside the truck vs underneath it makes all the difference.
 
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