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  • March 01, 2024, 11:16:47 PM

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Author Topic: NP129 Output Seals  (Read 886 times)

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Offline MIPS

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NP129 Output Seals
« on: July 21, 2023, 06:20:48 PM »
Had the car in to get the two front U-joints replaced and change a leaking front output seal since they had the propeller shaft out.
Got a call a few minutes ago that the new seal doesn't fit.  :o  I don't have the full details yet. I have to bike to the shop after work to get more answers, so I'll update this thread again in a few hours.

To my knowledge my '82 has the original New Process 129. RockAuto lists SKF 18662, National 3946 and BCA NS3946 as "front" and "rear" output seals, so I'm guessing they are interchangeable. The shop ordered in a National 3946 from their own parts catalog. Not sure what could be going on unless I'm trippin' and someone in the past put a 128 in. Those that I can tell will fit a 3946 or an SKF 18771.

Offline vangremlin

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Re: NP129 Output Seals
« Reply #1 on: July 21, 2023, 07:00:57 PM »
I had my 129 worked on a few months ago and after the first go around the front seal was leaking.  I took it back to the shop and they had to put in a different front seal, said the original one they put in just wasn't fitting right.  So far the newest one seems to be working well.  I don't know if they ever told me what seal they ended up using but you're not alone with this issue!
1981 Kammback 258 - "Pepe"
1980 Coupe 258 - "Ginger
1972 Gremlin X 304
1978 Gremlin 4 cyl 121 - sold
1964 TBird 390 - sold

Offline MIPS

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Re: NP129 Output Seals
« Reply #2 on: July 21, 2023, 08:59:23 PM »
The shop couldn't really explain because they had reassembled the yokes but they simply said that it did not fit.
I'm home now. I'm under the car and yes, unless someone is playing a sick joke this is a 129.



They said as long as I don't use 4WD much it shouldn't leak too bad but it will need to be replaced before the winter.
If anyone know what magic is going on here we'd love to know.

Offline Illeagle1984

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Re: NP129 Output Seals
« Reply #3 on: July 23, 2023, 06:41:49 PM »
My records confirm a National 3946 fit into the rear of my NP129.  I don't have a part number for the front, it must have come in the rebuild kit.

Try a different brand; I try to find Timken seals whenever I can.  Even try to order another one of the same, out of the many parts I see every week, I'd say better than 2% are wrong parts in the box.
It's getting crowded down here:
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Offline MIPS

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Re: NP129 Output Seals
« Reply #4 on: July 23, 2023, 10:45:04 PM »
I asked birdman if he could check his microfiche for the part number listed by the 129 exploded diagram but he couldn't find his folder :(

BUT!
Eaglepedia has a copy of the microfiche card. Section 25.01.1

http://amceaglesden.com/guide/Section_25,_Transfer_Case

The rear output seal is part 24 - "seal" - 83502 508 (or is that 506? The scan is blurry)
The front output seal is part 46 - "seal" - 83504 434

They're different! The rear seal cross-references to National 3946 and SKF 18662. The front seal cross-references SKF 18771.
The specifications listed by RockAuto are identical, but they do not have cross-referencing interchange numbers, so they are unique.
« Last Edit: July 23, 2023, 10:46:45 PM by MIPS »

Offline djm3452004

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Re: NP129 Output Seals
« Reply #5 on: July 24, 2023, 06:10:59 AM »
My records confirm a National 3946 fit into the rear of my NP129.  I don't have a part number for the front, it must have come in the rebuild kit.

Try a different brand; I try to find Timken seals whenever I can.  Even try to order another one of the same, out of the many parts I see every week, I'd say better than 2% are wrong parts in the box.



Second to this.  I listed both the NP129 output yoke seals as National 3946, with both spline seals as Crown J8130815.  (The spline seal is the little rubber one that looks like it has teeth and goes under the yoke nut to prevent ATF seepage from around the shaft splines.)

Good luck!
David
Current Project: 1983 Eagle Wagon 258
Past AMC Project(s):  1979 Spirit Liftback 232
                                1968 Ambassador 287

Offline AMC of Houston

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Re: NP129 Output Seals
« Reply #6 on: July 24, 2023, 12:01:08 PM »
Just a further note on the AMC parts book numbers. 

What MIPS posted about the seal part numbers is of course correct - its from the '84-'88 parts book.  The older '79-'83 parts books however list the same part number for both seals (the 83502508).  So what changed if the dimensions are the same?   Who knows.  Weird!

Looking at the seal pics on RockAuto, the later seal (SKF 18771) does look more "robust" with some extra sealing rubber on the flanges.   May be worth a try.
George G.
'81 Eagle Sundancer
'85 Eagle Waggie
1960 1902 Rambler Replica
'64 American
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'77 Gremlin
'78 Pacer Coupe, '78 Pacer Wagon
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Offline MIPS

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Re: NP129 Output Seals
« Reply #7 on: July 24, 2023, 02:14:05 PM »
That's one thing that confused me. That I'm aware of the 129 and 128 use the same casting and didn't change during their lifetime. The age of the diagrams shouldn't matter for the transfer case at least. If something's different either someone has enlarged the bore to fit a larger seal or the shaft is different, meaning someone's been inside and for whatever the OE shaft wasn't available. Neither makes a lot of sense.
According to here the 129 was available on all model years except 1980 when it was still a full-time TC. The 128 is bolt-in identical but was only available for 1986. The microfiche lists when parts are specific to one or the other. (EG: the viscous coupling)
The shaft diameter, the seal diameter, the bore diameter are all otherwise identical (including when comparing to a Timken seal) but the seals themselves are visually (I'm comparing photos straight off the SKF catalog and not RockAuto in case there's a stock photo being used) different. I wonder if that is what they noticed when they removed the yoke and this isn't the first time this seal has been replaced in the time since the microfiche was updated?
I have a stack of datasheets and the microfiche printout I have to show the shop later today to see if this looks like what they were seeing.
In other news now that the shop disturbed the seal while working on the U-joints it's now leaking quite badly so I got no choice but to find a solution or I'm curbed a week before a big trip! >_<
« Last Edit: July 24, 2023, 02:19:49 PM by MIPS »

Offline MIPS

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Re: NP129 Output Seals
« Reply #8 on: July 24, 2023, 09:05:14 PM »
Talked to the shop again to book it for Thursday morning.
He's still questioning it. His secret was he measured the bore diameter, shaft diameter and a few other measurements such as yoke clearance with the old seal in place and lined up one of the new seals by eye and the new one looked like it was for a larger bore, which would rule out someone's machined the bore for a larger seal. He can't verify that unless the old seal is pulled out and doing so will destroy it so once it's out, we're committed. He'll order in a few different seals and hopefully one fits. If not then my travel plans next weekend are derailed because it's simply losing too much fluid to trust on the highway at any distance.

Offline vangremlin

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Re: NP129 Output Seals
« Reply #9 on: July 25, 2023, 05:39:09 PM »
I called the shop that worked on my transfer case to see if they had a part number for the second seal they put in and unfortunately they did not.  Since it was done as warranty work they didn't keep any records of it.  It was definitely a different size seal than what they put in the first time.  He got it through NAPA and suggested I call over there and talk to them if I needed more info.  The first seal came as part of a transfer case rebuild kit so he didn't even have any records of what that part number might be.

Good luck!
1981 Kammback 258 - "Pepe"
1980 Coupe 258 - "Ginger
1972 Gremlin X 304
1978 Gremlin 4 cyl 121 - sold
1964 TBird 390 - sold

Offline MIPS

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Re: NP129 Output Seals
« Reply #10 on: July 25, 2023, 06:45:05 PM »
I don't have the slightest idea how I would even place an inquiry for such a part through napa. Just phone them? @_@

Offline MIPS

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Re: NP129 Output Seals
« Reply #11 on: July 27, 2023, 08:17:11 PM »
It has been verified.

New Process 129 - Front output seal - SKF 18771

The shop said that Lordco, Napa and the other local parts houses all listed one or more part numbers for seals that did not actually fit the front output bore. Only the rear output seal. It was the part in the microfiche that was ultimately a correct fit.

Offline djm3452004

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Re: NP129 Output Seals
« Reply #12 on: July 27, 2023, 10:04:29 PM »
Quite curious.  The ODs between the seal they ended up using (SKF 18771, crosses to a National 710664) and the one everyone on here suggested (National 3946) differs by only 0.002".  See the attached photo.  They are both intended for a 2.750" bore.

What is even more curious is the ID/shaft diameter of the SKF seal they used in your TC is 0.011" BIGGER than the National seal that we suggested.  This implies a looser seal fit on the yoke with the SKF vs. the National.  I hope it doesn't leak.
« Last Edit: July 27, 2023, 10:06:08 PM by djm3452004 »
Current Project: 1983 Eagle Wagon 258
Past AMC Project(s):  1979 Spirit Liftback 232
                                1968 Ambassador 287

Offline MIPS

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Re: NP129 Output Seals
« Reply #13 on: July 28, 2023, 03:26:23 PM »
SKF 18662 and SKF 18771 are physically different. Their dimensions are identical save for a few thousandths but there's an extra lip, according to SKF's photographs.

Offline MIPS

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Re: NP129 Output Seals
« Reply #14 on: January 20, 2024, 07:07:36 PM »
Following up on this that the new seal has not leaked a drop so I can close this thread confirming it was the correct seal that was installed.

 

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