904 Tail Shaft Seal Selection?

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Evan Dutch

Evan Dutch

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Hey guys,

I’ve got a 360 magnum and a 904 trans in my 1971 scamp. The tail shaft seal is leaking and I’m trying to source a replacement.

I’m seeing differing results and it appears there is more than one size seal.

How do I determine which seal is correct?

Thanks in advance
 
Get an original seal with the dust cover, from a Chrysler dealer. It's the only one to use. I'll look up the part number tomorrow if needed. They are not cheap but worth it. When you get one, the dust boot part has a small hole, this hole goes to the bottom when installing.
 
They've long been discontinued from Chrysler. I can certainly help you out if you have the dimensions, a picture, or both.
 
Measure the seal housing ID with a dial caliper.
 
Evan Dutch said:
Hey guys,

I’ve got a 360 magnum and a 904 trans in my 1971 scamp. The tail shaft seal is leaking and I’m trying to source a replacement.

I’m seeing differing results and it appears there is more than one size seal.

How do I determine which seal is correct?

Thanks in advance
Click to expand...
I would buy National ot Timken


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www.rockauto.com
 
Evan Dutch said:
Hey guys,

I’ve got a 360 magnum and a 904 trans in my 1971 scamp. The tail shaft seal is leaking and I’m trying to source a replacement.

I’m seeing differing results and it appears there is more than one size seal.

How do I determine which seal is correct?

Thanks in advance
Click to expand...
i think the seal changed to a larger dia in 73.
 
lemondana said:
Get an original seal with the dust cover, from a Chrysler dealer. It's the only one to use. I'll look up the part number tomorrow if needed. They are not cheap but worth it. When you get one, the dust boot part has a small hole, this hole goes to the bottom when installing.
Click to expand...
One that looks like this?

IMG_9965.png
 
If it is a 1971 904 then it's any of these numbers.
Just depends on what brand seal you want.
Chrysler #2400163
Timken # 8935s
National # 8935s
SKF #15535
The PK number on the left side of the transmission would tell if it is a 1971.
These seals can be found from many vendors including eBay and Rockauto.
 
I didn't realize that the aftermarket had the seals with the dust seal. I've seen so many rebuilt transmissions that just have a single lip seal.
 
OK, here are the extension housing seals and sizes, that were used in 904's>>>1966-1972: 2.254" OD, no dust boot, >> 1973-on: 2.375" OD>>also 1973-on 2.445" OD

Hope this helps. Your local transmission shop probably has these in their stock. Just a suggestion.
Evan Dutch said:
Hey guys,

I’ve got a 360 magnum and a 904 trans in my 1971 scamp. The tail shaft seal is leaking and I’m trying to source a replacement.

I’m seeing differing results and it appears there is more than one size seal.

How do I determine which seal is correct?

Thanks in advance
Click to expand...
See my post. Always measure the OD of the seal. According to my parts catalog, boot seals (2.375 OD) used only on 1973-on, although most shops I dealt with used the non booted seal.
 
transman said:
OK, here are the extension housing seals and sizes, that were used in 904's>>>1966-1972: 2.254" OD, no dust boot, >> 1973-on: 2.375" OD>>also 1973-on 2.445" OD

Hope this helps. Your local transmission shop probably has these in their stock. Just a suggestion.

See my post. Always measure the OD of the seal. According to my parts catalog, boot seals (2.375 OD) used only on 1973-on, although most shops I dealt with used the non booted seal.
Click to expand...
I’ll take a look at the deal later today to confirm which size it is. Or, I’ll pull the number off the trans pan rail
 
Question for transman.
All of the seals listed in post 11 have a 2.254 od with dust boot.
Do you have a part number for that od seal without dust boot?
They may exist but have never seen one.
 
My post says. 1966-1972: 2.254" OD. NO dust boot. Our part number was 12925C. That was the number we used out of our transmission parts catalog. I briefly worked for another transmission parts supplier and they used the same number. Was there another number you were looking for?
 
Evan Dutch said:
I’ll take a look at the deal later today to confirm which size it is. Or, I’ll pull the number off the trans pan rail
Click to expand...
Just pull the seal out and measure it. And then as I mentioned, go to your local transmission shop. They should be able to supply it for you.
 
OttawaCharger said:
This thread is timely. My 1985 727 suffers the same problem.
Click to expand...
OK, here are your 727 extension housing seals. The most common one>>>2.503" can come with or without the rubber boot. Most transmission shops used the non booted one, and in our Overhaul Gasket and seal kits, the non booted one was put in. Used from 1965-on. However, there are 2 not so common ones>>> 2.445" OD used with the bolt on yoke. Used from 1962-on, and the other one 2.847" OD, used on trucks with the bolt on yoke from 1987-on. Measure the OD of your seal and go from there. Again, should be a non-issue finding one. Hope this helps.
 
That's awesome Transman. Thank you. I haven't checked for bushing wear yet. It's only weeping a bit so fingers crossed!
 
This is really of little importance but the Transtar transmission catalog shows 12925B as 1966-1972: 2.254" OD. with dust boot.
Evan Dutch can ignore the following statement because it relates to the larger seal that was used on 904's starting in 1973.
Chrysler part number 3515384 with dust boot was used from 1973 thru 1982 on the 904 transmissions.
In 1983 Chrysler discontinued that number and replaced it with #4058047 which had no dust boot. Don't have any idea why they eliminated the dust boot but that's what you got at the dealership from 1983 on.
Aftermarket seals that were made starting in 1983 were available with or without the dust boot.
 
townsend said:
This is really of little importance but the Transtar transmission catalog shows 12925B as 1966-1972: 2.254" OD. with dust boot.
Evan Dutch can ignore the following statement because it relates to the larger seal that was used on 904's starting in 1973.
Chrysler part number 3515384 with dust boot was used from 1973 thru 1982 on the 904 transmissions.
In 1983 Chrysler discontinued that number and replaced it with #4058047 which had no dust boot. Don't have any idea why they eliminated the dust boot but that's what you got at the dealership from 1983 on.
Aftermarket seals that were made starting in 1983 were available with or without the dust boot.
Click to expand...
I started working in the Transmission parts industry in 1980. We had back then the 727 seals with or without the dust boot. The early 904's were non booted. We were at the time a distributor of Natpro a large transmission parts distibutor and that was our main source of parts. Chrysler part numbers mean something only to the parts guys at a Chrysler dealership. Chrysler doesn't make the seal they probably purchase them from National.
 
Interesting discussion so lets continue.
It's true that National made the seals for Chrysler.
The 904's from 1960 till 1965 had no dust boot.
Let's start with what was available from the Chrysler dealer.
If you purchased seal number 2400163 from the dealer from 66 thru 72, it came with a boot. Non booted seals from 66 to 72 could not be purchased from the Chrysler dealer.
The aftermarket produced seals with and without the boot.
#12925B seal with boot
#12925c seal without boot
Most transmission shops got there parts from transmission distributors with there own part numbers.
You would think that most people restoring Mopars would prefer to use Chrysler labeled parts when possible.
 
Last edited:
How would you determine the year of the trans based on the ID number of the pan rail?

For example, mine is 3515852A3451 6165
 
townsend said:
Interesting discussion so lets continue.
It's true that National made the seals for Chrysler.
The 904's from 1960 till 1965 had no dust boot.
Let's start with what was available from the Chrysler dealer.
If you purchased seal number 2400163 from the dealer from 66 thru 72, it came with a boot. Non booted seals from 66 to 72 could not be purchased from the Chrysler dealer.
Handled many of the old brown boxes used in the sixties with the number 2400163 which contained the booted seal. The aftermarket produced seals with and without the boot.
#12925B seal with boot
#12925c seal without boot
Most transmission shops got there parts from transmission distributors with there own part numbers.
You would think that most people restoring Mopars would prefer to use Chrysler labeled parts when possible.
Click to expand...
If you've heard of Private labeling, so you know where I'm coming from. So if I buy a seal from my local MOPAR dealer, and when I open it, it says national on it, does that mean that it can't be installed in my car I'm restoring? And if I'm rebuilding my transmission I have to purchase friction plates from Chrysler, despite the fact that my never has been apart before transmission likely has Raybestos Friction plates in it? Just because the package may say, Chrysler, GM, or Ford on it, does not mean that they made it. I get your point on getting OEM parts when you can, but a national seal is an OEM part, is it not?
 
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