Rear Pinion Seal

Hello. What are the steps to replacing a rear pinion seal on a Dana rear of a 1970 Plymouth GTX? What kind if gear oil do I need to put in it? What gear oil for a 4 speed transmission? TY for any help!

That job is easy if you have the right tools. If you don't have the right tools then all you can do is lay under the car and stare at it. The torque on the pinion nut is around 250 ft-lbs so you need a big cheater bar or a big impact wrench. You'll also need a way to hold the pinion. Once you pull the pinion yoke off (takes another tool) then you just pry the old seal out and install the new seal with the correct installation tool. Then you put it back together. Takes about 20 minutes for a good mechanic with all the right tools and a lift. If you don't have any tools then you can work on it for the rest of time and never finish the job. I'm in the middle of changing the gears in my Dana 60 myself. Here is the tool I used to hold the pinion while I'll removed the nut.

I use a big pipe wrench on the pinion yoke, tighten it up so it holds well and then use 1/2 inch or if you can a 3/4 inch breaker and socket to break the pinion nut loose. I use a brass drift, punch, to drive the pinion yoke off of the pinion shaft
as far lube I like and use 75x90Wt non synthetic gear oil with a posi additive for the posi units
On the 4 speed look for Pennzoil synchromesh gear oil and use it
Summit and probably other hi Po warehouses stock and sell it if you can't find it locally like me

I think Andy is a machinist so he has nice tools. I did the pipe wrench thing for years. I final grabbed a piece of scrap 2” angle iron and drilled some holes to bolt on the yoke. I then used a torch to cut out the center slightly to get a socket on the nut. I’ve got a big Matco torque wrench that will go to 250. It was not cheap.

Here is how I break mine loose, it keeps from damaging the gears with an impac

I just did this in February. I had to take the whole axle out because I had to change the housing, because one tube was leaking(long story). Anyway, AndyF is spot on with his reply. My rear end oil is a Amsoil racing(?) brand that my friend who had rebuilt it. I know it is VERY thick stuff, not sure of the weight tho.

That's called working smarter, not harder.

Mancini has the adapter for the yoke. You'll still need a 3/4 breaker bar to fit in the tool and then a big socket and a big breaker bar for the nut. Then you'll need a big torque wrench to tighten the nut back up.
https://www.manciniracing.com/yoinreto.html

Mine was fabricated using a broken torsion bar from a Superbird.

Details at https://www.hamtramck-historical.com/NostalgiaAndOldCars.shtml

So the parking brake won’t hold the yolk? Just asking, I never tried.

FWIW I was told by a guy at a differential shop that occasionally pinion seal leaks can also be from oil migrating down the pinion gear, thru the splines, and out between the washer and or pinion nut. Once everything is wet with oil it's hard to tell where it's coming from exactly.

True, and this also applies to the crank bolt and washer. Always use a dab of RTV on the yolk splines and most of the times on the damper slot for the key. I think we even issued an ASN in the early 80’s for the 318/360 damper leaks.

Once you remove the pinion nut you'll need a way to pull the pinion off since it is a slight press fit on the splines. Here is a home made puller that I use but a two jaw puller will also work.