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Discussion Starter #1 (Edited)
I appreciate all the responses in advance a little or a lot of info

1965 Mustang 6 cyl 200 3 speed with 7.25 ring gear, 23 spline


Purchased a 8181NA pinion seal flanged from Oreillys. It fits, but the middle rubber seal is too short by approx. 1/4" and thus leaking.

Key things I found:
1. Seal I pulled out was not flanged and was inside of differential housing approx. 1/4".
2. I miked my shaft 1.65" and my friend said his shaft miked at 1.81"
3. My protected "rock/dust shield" is flat with no dip close to shaft and my buddy has a small dip close to the shaft on his.

Questions are:
1. Is my shaft correct size and if so, where can I buy the correct seal flanged or no flanged.
2. If my yoke wrong, where can I find the correct one with the 8181NA or equivalent.

Thank all for any help! Chris
 

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I am getting ready to replace the pinion seal on my 8" Currie unit and spoke with a rep from Currie just yesterday. I want to replace the seal with the same part as they shipped it with and he said that it was assembled with an 8181na. This is a standard seal for all Ford 8" pinions, but I don't know if it is compatible with the 7.25" diff. The NA refers to this as a National Oil Seal.
The seal is correct for your friends 1.812" pinion.
 

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Discussion Starter #3
Rhutt….thank you for your response. Maybe mine was "milled down" to fit the old pinion seal. To bad I threw the old seal away (do not throw anything away for a few days after repair...lol).
 

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According to online fitment guides, the 8181na is supposed to fit the 7.25" and 8" diffs. I don't know what pinion is in your diff, but you might want to contact the Timken Company. They produce a huge selection of pinion seals for many applications. With the proper measurements, They may be able to supply you with a seal. Good luck!


I did just find a National bearing #7457N that fits a 1.656 pinion wit a 2.627 o.d.

It fits '64 Falcon
 

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Before you drive the new seal in pack the rear side full with Vaseline. This will prevent the garter spring popping out unnoticed & leading to a frustrating leak
 

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Discussion Starter #8
UPDATE: 1965 Mustang 6 cyl 200 engine

Differential tag# WCY-E, 3 20 58C 910

I placed in C1UZ-4676-C seal and still I have leaking a lot issues.

I bought a 1965 Mustang yoke off eBay and this yoke is bigger than my small yoke and of course, the Ujoints and cup holders are bigger and wider which do not fit my drive shaft.

My yoke or the bigger ebay yoke are not pitted or grooved.

Questions: Did I place the seal in wrong or not far enough for my small yoke? Just don't know what is going on?

PS: I don't want to cut or change my drive shaft if all possible BUT, I could go with a small Ujoint on up/down and longer arms right/left to accommodate the bigger ebay yoke that might cause vibration problems???

Scratching my head on this one....
 

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I did a little research and found this:
Ford C1UZ-4676-C crosses over to a National 7457N.
Shaft size- 1.656" Bore size- 2.623".


National 8181NA.
Shaft size- 1.812" Bore size- 2.623".


The 7457N has no flange. The 8181NA is flanged. You would drive the 7457N in until it is flush with the housing. You would drive the 8181NA in until the flange is flush with the housing.


So which seal did you get- a 7457N or a 8181NA? If you got the 8181NA there is no way it will seal on your 1.65" shaft. If you got the 7457N where is it leaking? At the shaft? Or at the bore of the housing? Somebody may have boogered the ID of the housing bore getting the old seal out.
 

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Discussion Starter #10
awhtx and everyone thanks for all the info...

I got the 7457N and it was leaking at the shaft. Maybe I boogered it up getting it out. I was very careful, but ??? I do remember the old seal was approx. 1/8-1/4 of the way inside the housing. Maybe the other owner boogered it up??

Ok, so now how do I fix this or is another differential is what I need?

Oh...I purchased a yoke and it was bigger than my small one. Do you think it was for a V8 1965/1966? I did place the bigger yoke in and my leak stopped. I asked my mustang mechanic friend and he said do not use the bigger yoke because it will wear down the seal rubber and you will be back at square one. Another friend told me to get and longer vertical ujoint with a smaller horizonal ujoint to mate up with the bigger yoke and the smaller drive shaft. And of course, there is always a cut job, but I don't want to do that.

I hope all this makes sense. I don't need to loose any more hair. It is getting mighty thin up there already! lol
 

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The 7457N is the correct seal for your small pinion yoke. You state that the seal is leaking "at the shaft" which I assume means it's leaking where the pinion yoke enters the seal. If it's leaking there with a brand new seal then the sealing surface on your yoke is scored, rusted or otherwise boogered and the rubber lip of the seal can't form a leak proof seal. You need to see if there is a Readi-Sleeve or Speedi-Sleeve that will restore the sealing surface.


A lot of people drive a chisel or screwdriver into the metal part of the seal to pry it out of the differential housing. Often they don't even realize that the tip of the chisel or screwdriver may have gouged the bore that the seal fits in. The raised divot in the bore creates a pathway for gear oil to leak out. The raised divot must be removed with a stone in a Dremel or die grinder and then a blob of sealer must be smeared into the depression before driving the new seal into place. The OD of the new seal will be coated with a red or orange sealer when you remove it from the package but that sealer won't fill a depression.


If you can post some photos of your pinion yoke and the bore in the differential housing that the seal fits into we may be able to see what's going on.
 

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Discussion Starter #12
Having trouble downloading, rats!

Ok here some new info....

Bought a 66 Mustang 6 cyl 200 yoke that is almost like my 65.
Difference is:
1. 66 yoke shaft is slightly lower than my 65 shaft, but rock shield on the 66 is higher than my 65.

I installed the 66 yoke with new pinion seal in diff last night. I placed med thread lock on pinion shaft and sealant on pinion nut.
 

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Discussion Starter #13
Also there is no scoring, scuffs, or anything I could feel inside the diff housing. I placed the bearing 7457N flush up with the housing.
 

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Discussion Starter #15 (Edited)
1st pic.....small yoke from my 6 cyl 200 cc 1965 Mustang.....the big yoke is from a 1965 Mustang that I bought off Ebay. Not correct size, but both have 23 splines.

2nd pic....side view of above (#1) yokes

3rd pic....my clean silver yoke-left........right-I bought this dirty one close to me from a 1966 Mustang 6 cyl 200 cc....U_bolts, cup size, splines, yoke retainer circumference the same, BUT....dirty yoke (1966) taller and rock shield is lower when standing up

4th pic....3/4 view of both yokes
 

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Did you ever get this resolved. I ran into the same issue swapping out my 1965 Mustang, 200 6cyl with 3 spd manual to an C4 automatic from a 66 donor car. Swapping all the parts, but the driveshafts are the same as yours. the auto has a larger diameter and bigger u-joints that won't match up with the differential yoke. I couldnt locate a conversion u-joint to match the different sizes, so my brother - who has access to a lathe, turned down the larger diameter 66 yoke to same diameter as the smaller 65, fit like a charm and was able to use the entire driveshaft and u-joints plus yoke from the 66.
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