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Old 09-30-2018, 03:35 PM   #1
rgunlock
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Grinding/binding noise from NP205 in right turn?

I've recently swapped out most of my drivetrain - front and rear axles, SM465 for NV4500, different NP205 and rear driveshaft. I don't have a front driveshaft mounted yet. Afterwards, I started noticing a loud grinding/binding noise when making right turns, generally going up a slight incline in my parking garage at work. I don't notice any noise making left turns.

I've got a device called a "Chassis Ear" where you clip microphones (I assume) at various spots and listen on each one using headphones. I took it to work with me and tried after work to identify where the noise was coming from, except that it wouldn't make the noise. I've discovered that it only makes a racket after having been driven for miles (I'm 16 miles from work).

Today I made a trip to the office so I could listen for the noise while the parking garage was empty. Basically, it sounds like the noise is coming from the rear of the NP205. I hear it more from the area with the large round cover, not so much from the u-joint for the rear driveshaft, and not from the forward facing side of the NP205.

The TC had been rebuilt by a drivetrain shop, but considering some of the issues I've had with their work I can believe that the NP205 has a problem. What I don't understand is why it would grind and bind during right turns. And it's loud. Another guy in the parking garage confirmed that he could hear it from 60-80 feet away.

I'm sure I'll end up having to swap or re-rebuild this NP205 but I'm just wondering whether anyone has a reasonable explanation for the noise. I wouldn't think that the NP205 would have any idea that I was making a sharp right turn.
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78 GMC K15 SWB, 350/NV4500/NP205/4.10s Project Thread
71 GMC 2500 350/TH400 - still deciding where to take it
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Old 10-01-2018, 10:00 AM   #2
SunSoaked
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Re: Grinding/binding noise from NP205 in right turn?

I have a similar setup. I assume this is the swb truck in your signature?
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Old 10-01-2018, 10:09 AM   #3
rgunlock
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Re: Grinding/binding noise from NP205 in right turn?

Yes, its the '78 K15.
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78 GMC K15 SWB, 350/NV4500/NP205/4.10s Project Thread
71 GMC 2500 350/TH400 - still deciding where to take it
59 Chevy SWB Stepside (next in line? Not sure now )
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Old 02-14-2019, 05:24 PM   #4
rgunlock
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Re: Grinding/binding noise from NP205 in right turn?

Going back through some of my old threads, I realized I'd never closed this one out. I was wrong about the noise coming from the transfer case. It was apparently transferring up the driveshaft from the rear end. I had just recently had that re-geared at a good drivetrain shop so it was "trusted" and I didn't specifically listen to it.

Turns out they either didn't use the right additive, or not enough of it. After filling with the correct gear oil and additive the noise disappeared.
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78 GMC K15 SWB, 350/NV4500/NP205/4.10s Project Thread
71 GMC 2500 350/TH400 - still deciding where to take it
59 Chevy SWB Stepside (next in line? Not sure now )
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Old 02-14-2019, 07:45 PM   #5
Killer Bee
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Re: Grinding/binding noise from NP205 in right turn?

glad to hear you nailed it! get 'em in here all the time, noisy diffs in turns..

drain and refill with proper GO and friction modifier and voila, noise is gone
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Old 02-15-2019, 03:27 AM   #6
mongocanfly
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Re: Grinding/binding noise from NP205 in right turn?

sometimes its just the simple things......luckily
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