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Pinion seal and expansion plug help!!
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ClassicCars
Posted 2024-09-03 12:32 PM (#636811)
Subject: Pinion seal and expansion plug help!!


Regular

Posts: 68
2525
Good morning,



I'm working on my 1959 Dodge Coronet. I ordered a pinion seal from Rock Auto and was sent a National 5126. This seal has an outside diameter of 2.81 where as the original was 2.74. I could feel and see that the replacement was actually larger but I tried to install it anyways but no luck. I checked a few other places and they recommend the same National 5126. Does anyone know the part number for the correct pinion seal to fit a 1959 Dodge Coronet with a 326 engine?



Also, I'm replacing the expansion plugs in the 326 engine from this car. The original expansion plugs measure 1.61 (assuming that is the same as a 1 5/8 plug) but seem to be a flat disk (see picture). I'm not sure where to get these from as my local Napa store wanted to sell me the standard plug with a thick edge. I did find a zinc plug at Grainger part number 5MTN7 which looks like it could be it but wanted to see if anyone else had any thoughts.



(Expansion plug.jpg)



(Expansion hole in block.jpg)



Attachments
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Attachments Expansion plug.jpg (103KB - 27 downloads)
Attachments Expansion hole in block.jpg (82KB - 24 downloads)
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57chizler
Posted 2024-09-03 1:26 PM (#636812 - in reply to #636811)
Subject: RE: Pinion seal and expansion plug help!!



Expert

Posts: 3815
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Location: NorCal
The Welch plug is slightly convex when new and will flatten and expand in diameter when installed. The Grainger number is correct.

"When fitting Welsh plugs, use a solid flat punch to flatten 2/3’s of the dome area in the center only. Don’t reshape from convex to concave, just go to flat as at this point maximum size and sealing pressure has been achieved. Don’t use the ball of a hammer to butcher the plug into submission as the quality of the seal will be suspect. SIMPLY NEATLY FLATTEN 2/3’S OF THE DOME AREA IN THE CENTRE, STAYING AWAY FROM THE SEALING EDGE."

Use a hardening sealer such as Permatex #3 on the sealing edge.
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56D500boy
Posted 2024-09-03 2:16 PM (#636813 - in reply to #636811)
Subject: RE: Pinion seal and expansion plug help!!



Exner Expert 10K+

Posts: 10290
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Location: Lower Mainland BC
ClassicCars - 2024-09-03 9:32 AM
I'm working on my 1959 Dodge Coronet. I ordered a pinion seal from Rock Auto and was sent a National 5126. This seal has an outside diameter of 2.81 where as the original was 2.74. I could feel and see that the replacement was actually larger but I tried to install it anyways but no luck. I checked a few other places and they recommend the same National 5126. Does anyone know the part number for the correct pinion seal to fit a 1959 Dodge Coronet with a 326 engine?


Original Part Number (PN) for the pinion seal for a 1959 Mopar 8 1/4" rear diff is 1738 831 (or 1738831 when doing an internet search). (see listing below)

Searching for that PN turns up an number of New Old Stock (NOS) seals on eBay and also reference to the National 5126.

https://www.google.com/search?client=firefox-b-d&q=1738831+Pinion+Se...

https://www.ebay.com/itm/126150615576

Searching at Rock Auto under 1959 Dodge Coronet with 326 engine turns up a few seals including versions of the National 5126

https://www.rockauto.com/en/catalog/dodge,1959,coronet,5.3l+326cid+v...

I was surprised to see that the seal was externally flanged.



Edited by 56D500boy 2024-09-03 3:07 PM




(59MoparRearDiffPinionSealPN1738831.jpg)



(59MoparRearDiffPinionSealPN1738831_NOSseal_Front.jpg)



(59MoparRearDiffPinionSealPN1738831_NOSseal_Back.jpg)



(59MoparRearDiffPinionSealPN1738831_asNational5126.jpg)



(59MoparRearDiffPinionSealPN1738831_asNational5126_Details.jpg)



Attachments
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Attachments 59MoparRearDiffPinionSealPN1738831.jpg (137KB - 28 downloads)
Attachments 59MoparRearDiffPinionSealPN1738831_NOSseal_Front.jpg (178KB - 29 downloads)
Attachments 59MoparRearDiffPinionSealPN1738831_NOSseal_Back.jpg (183KB - 22 downloads)
Attachments 59MoparRearDiffPinionSealPN1738831_asNational5126.jpg (27KB - 29 downloads)
Attachments 59MoparRearDiffPinionSealPN1738831_asNational5126_Details.jpg (94KB - 34 downloads)
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ClassicCars
Posted 2024-09-04 12:41 PM (#636816 - in reply to #636811)
Subject: Re: Pinion seal and expansion plug help!!


Regular

Posts: 68
2525
I measured the O.D. of the yoke and it measures 1.873. The national 5126 had the right I.D. of 1.875 (just not the correct outside diameter). National 5126 is 1.875 x 2.813. My old pinion seal measured 2.744 for the O.D. So, looks like I'm looking for a 2.75x1.875. Just surprised that Rock Auto lists this as the correct pinion seal. I did try 2 of these and neither worked. Both bent as they could not compress that much.

In regards to a new old stock seal...how good is the rubber if it's been sitting that long? Is it still good? Don't know which is why I'm asking. Thanks.
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Powerflite
Posted 2024-09-04 12:55 PM (#636817 - in reply to #636811)
Subject: Re: Pinion seal and expansion plug help!!



Exner Expert 10K+

Posts: 10033
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Location: So. Cal		It depends on the history of where & how it was stored. Typically, rubber will last a long time in a more humid & cool environment. Hot, dry areas, especially stored outside the box with UV will kill it.
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