Author Topic: Part Time Kit for NP203  (Read 3270 times)

Offline JohnnyPopper

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Part Time Kit for NP203
« on: January 14, 2019, 03:18:19 PM »
I bought a used Mile Marker 501 kit from a Truck recycling here in town, good guys, finally had them install it.

Started making loud racking noise in the transfer case, back into it.

Seems the kit came with the lockers for the differential but also has a radial roller thrust bearing spacer  that keeps the front axle from engaging while in 2x4.

The tech had never seen anything like that, so didn't think to install them, thus the racking noise under load.

 'CK5.COM has a write up where they illustrate the install and sure enough, they are needed.

Found some that fit, and she is running really good, It feels like I shed 500 pounds of steel!

Also found a former mechanic who had MM Supreme Locking hubs online, so she's styling.

He advised running it in 4x4 at periodic times to circulate oil into the rear tail stock. I'll do that by shifting into 4x, but not locking the hubs.

Only wish I had don't this sooner...  ;)



1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction

Offline ehjorten

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Re: Part Time Kit for NP203
« Reply #1 on: January 06, 2023, 09:11:47 AM »
Anybody know if the Mile Marker Shaft Conversion is still available for these NP203s? My 203 in my '77 is making a lot of harsh vibration noises. I don't believe it is the chain, but it could be. I had my transmission rebuilt a while back and when they were doing that, they rebuilt the transfer case as well. It was already converted to part time, but I worry that they did something wrong. It is still under warranty, so I need to get it back to their shop. I just know that the crown gears in the 501 kit wear down and cause a lot of slop in the system. Mile Marker had a shaft kit that totally got rid of the differential in the back of the transfer case and it really tightens things up.
-Erik-
1991 V3500 - Gen V TBI 454, 4L80E, NP205, 14 bolt FF, D60, 8" Lift on 35s
1977 K20 Silverado - 350, THM350, NP203, 14 bolt FF, D44, Stock Lift on 31s
1969 Chevelle Malibu Sport Coupe - EFI350, THM350
1968 Chevrolet Step-side Pickup - 300HP L6

Offline VileZambonie

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Re: Part Time Kit for NP203
« Reply #2 on: January 07, 2023, 04:42:35 PM »
I don't think so. Have you tried shifting it to see if it only does it in a particular range?
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74 GMC, 75 K5, 84 GMC, 85 K20, 86 k20, 79 K10

Offline ehjorten

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Re: Part Time Kit for NP203
« Reply #3 on: January 09, 2023, 09:07:36 AM »
It is all the time Vile. Being in 4wd (AKA Chain Spinning) doesn't make a difference. There is a certain RPM band where it is most harsh and you can hear it pinging from the rotational slop when you load and unload the drivetrain. The rear gears are in great shape and it is not coming from there. U-joint appear in good working order.
« Last Edit: January 09, 2023, 09:11:12 AM by ehjorten »
-Erik-
1991 V3500 - Gen V TBI 454, 4L80E, NP205, 14 bolt FF, D60, 8" Lift on 35s
1977 K20 Silverado - 350, THM350, NP203, 14 bolt FF, D44, Stock Lift on 31s
1969 Chevelle Malibu Sport Coupe - EFI350, THM350
1968 Chevrolet Step-side Pickup - 300HP L6

Offline VileZambonie

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Re: Part Time Kit for NP203
« Reply #4 on: January 09, 2023, 03:17:07 PM »
I actually picked up another unit and was going to rebuild it, then take mine out and rebuild that one as well. It's such an unpopular unit, there isn't a lot of aftermarket support left.
,                           ___ 
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              ⌠ŻŻŻŻŻ'   [☼===☼]
              `()_);-;()_)--o--)_)

74 GMC, 75 K5, 84 GMC, 85 K20, 86 k20, 79 K10

Offline ehjorten

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Re: Part Time Kit for NP203
« Reply #5 on: January 09, 2023, 03:43:04 PM »
Vile...I have been eyeing a NP205 and a 4L80e as a replacement option. I have that stock in my crew cab and love the overdrive! My '77 could use a little more leg with the 4.10:1 gears.
-Erik-
1991 V3500 - Gen V TBI 454, 4L80E, NP205, 14 bolt FF, D60, 8" Lift on 35s
1977 K20 Silverado - 350, THM350, NP203, 14 bolt FF, D44, Stock Lift on 31s
1969 Chevelle Malibu Sport Coupe - EFI350, THM350
1968 Chevrolet Step-side Pickup - 300HP L6

Offline VileZambonie

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Re: Part Time Kit for NP203
« Reply #6 on: January 09, 2023, 03:50:02 PM »
My only reservation on these ones is keeping it original otherwise I'd probably do something more modern as well.
,                           ___ 
                         /  _ _ _\_
              ⌠ŻŻŻŻŻ'   [☼===☼]
              `()_);-;()_)--o--)_)

74 GMC, 75 K5, 84 GMC, 85 K20, 86 k20, 79 K10