AMC 20 Pinion Seal - Yoke Replacement

[hefavitzen]

I wanted to provide what I found through trial and error when replacing my pinion seal and the yoke. I had replaced the rear AMC 20 last year with a used wide-track, just before heading up to the Silverlakes meet up. You might remember that I had asked if I could get away with having one of the little tabs broken off on the yoke that holds the u-joint cap in place.

Anyway, over the last year the pinion seal had begun to leak even worse and I think the gear oil getting onto the u-joint finally lubed it all up enough for the u-joint cap to begin to work it's way off...which it did.

So, I set out to replace the yoke and the pinion seal, using Spankrjs info on doing so without rebuilding the axle. (it was WWAAAYYY easier than I thought it would be and I kick myself for no having done this sooner!)

So, I ordered all the parts I needed and when they arrived I was pretty excited. I'll post notes going forward.

Also - I replaced the U-Joint on the rear-axle end of the drive shaft, but not on the other as I had just replaced it last year and it looked fine. I now have a spare drive shaft U-Joint.

 

[hefavitzen]

So, once I got under my Jeep I marked the pinion, nut, yoke and diff for a line up reference.
- it took 15 turns to remove the nut.
- the yoke popped right off with just me pulling on it with my hand.
- As you can see, the seal was in place, but the rubber gasket had torn.

I replaced the pinion nut and yoke, so the lines weren't overly useful in the end, but I felt better having them there if I needed them.

I used Gunk Foaming Degreaser, and then just Gunk Original Degreaser to get the axle, shocks, underside of the body, brakes, etc...free of all of the gear oil that had been slung around for a year.
Two things I learned from this:
1) Neither product damaged any of the painted surfaces.
2) A grease-free work environment is absolutely, positively, swear-to-you-on-the-book-of-your-choice the best place to have to do any work!!! OMG, so thankful I degreased it all the day before and let the work area dry out. Was lovely. Like working on the Jeep in an island paradise type of lovely.

I bought some Milwaukee silver and gold sharpies from Home Depot and they worked great for marking the line! (greatly aided by the lack of oil all over everything!)

 

[hefavitzen]

So, I compared the old and new seal and found quite a bit of difference. But, in the end, I could not get the new seal to fit.

As you can see in the photos, the first two seal have a metal outer edge so it has to has to go in very gently.
Looking at the last photo, of the rubber edged seal, it has some interesting characteristics.
- It has a rubber edge over the metal body, so is a bit more forgiving when putting it into the axle housing.
- it has a metal lip that goes over the outer edge of the pinion hole in the axle housing.

Here are the measurements of each. (I used a micrometer on the first two seals. I had already installed the seal that ended up working out.)

Notes:	Brand	Part #	Inside Diameter (ID)	Outside Diameter (OD)	Width
Seal that was leaking (green seal)	SKF	18444	1.844	2.746	0.306
Initial part I tried (orange seal) Though it is barely larger than the other two, the extra .003 inches made a huge difference!! I bent it trying to install it.	Timken	470331N	1.816	2.754	0.485
Part that fit I bought at NAPA. (a little reading indicates that this is an "improvement" on the original and is a response to issues with the traditional design.)	SKF	18472	1.842	2.751	0.426

After everything, the whole job took about 1 hour from start to finish of actual working time. It was not a big deal to do and if you are leaking, have no fear!!! It's totally worth it. I hope this is helpful to someone.

 

[hefavitzen]

Another thing: When I put the new yoke on it was a VERY tight fit to get it on initially, but then "popped" on the rest of the way with a tap from the dead blow hammer. I then put the new pinion nut on and couldn't get it tight enough. (see video below).

So, I took it off and put the old yoke and old nut back on and counted the threads on the end of the pinion to get a reference of how far down the new nut needed to go. I then used my micrometer to measure both yokes to ensure they were identical. The new yoke had a machined shaft whose outer depth was a tiny bit deeper than the old one, but it wasn't what was causing my issue.

So, I put the new yoke back on and the new nut and using a pipe wrench (Spankrjs' tool of choice) and a breaker bar with a 1 1/8 socket, I was able to get the new pinion nut down far enough and finally tightened up. It does state that if your AMC 20 is still using a crush sleeve, to bear it down an extra 5 inch lbs. when putting it back together. I was able to get mine to 11 inch lbs, which is about where it was initially, but no further.

I hope that is helpful!

 

[tower210]

Nice work! Good info.

 

[jpnmaine]

Just questioning. Looking at the seal failure, are the pinion bearings good??

 

[hefavitzen]

Just questioning. Looking at the seal failure, are the pinion bearings good??

Heck if I know. It won't surprise me if they are complete garbage. I've put at least 1000 miles on the rear end since I put it in and it does a little growling, but it moves and hasn't blown up yet.

Question for you...how would you tell?

The pinion doesn't have any slop, if that would be an indicator. I have to admit, when it comes to vehicles - I'm more "Frieburger and Finnegan" than "Fred and Dave". I can do engine stuff in my sleep but axles are still somewhat of a black box for me.

 

[Ron84cj]

Heck if I know. It won't surprise me if they are complete garbage. I've put at least 1000 miles on the rear end since I put it in and it does a little growling, but it moves and hasn't blown up yet.

Question for you...how would you tell?

The pinion doesn't have any slop, if that would be an indicator. I have to admit, when it comes to vehicles - I'm more "Frieburger and Finnegan" than "Fred and Dave". I can do engine stuff in my sleep but axles are still somewhat of a black box for me.

It shouldn't growl. Other than the clicking from my locker around turns my dif is very quiet. On yours, did the yoke have any play before or after your install? How did it feel when you rotate it?

 

[hefavitzen]

It felt fine (I think) with no play to speak of, taking about 11 inch lbs of force to turn the yoke with the wheels and brakes removed. I actually tightened it up as much as I could by hand (instead of using an impact gun) as I had read that it could growl from not being tight enough. It was 10 inch lbs, now it is 11 inch lbs.

I did a pattern check last June though to be honest, I wasn't 100% on what I was looking at, but felt it wasn't bad enough to keep me from Silverlakes!

 

[Ron84cj]

Are you saying you are getting 11 inch lbs of rotational torque with it rotating the ring gear and axles? If so, I think that is too low. The AMC 20 is 14-19 with a new bearing and that's turning only the pinion gear by itself. With a used bearing a couple less. But again, that's rotating only the pinion gear. Check out my build thread "my blue jeep." I did a step by step tutorial on rebuilding the AMC 20 and the Dana 30.

 

[hefavitzen]

Are you saying you are getting 11 inch lbs of rotational torque with it rotating the ring gear and axles? If so, I think that is too low. The AMC 20 is 14-19 with a new bearing and that's turning only the pinion gear by itself. With a used bearing a couple less. But again, that's rotating only the pinion gear. Check out my build thread "my blue jeep." I did a step by step tutorial on rebuilding the AMC 20 and the Dana 30.

Thanks! I'm going to go look that up right now. I actually have a full Yukon AMC20 rebuild kit that I might just end up putting to use.

 

[hefavitzen]

Are you saying you are getting 11 inch lbs of rotational torque with it rotating the ring gear and axles? If so, I think that is too low. The AMC 20 is 14-19 with a new bearing and that's turning only the pinion gear by itself. With a used bearing a couple less. But again, that's rotating only the pinion gear. Check out my build thread "my blue jeep." I did a step by step tutorial on rebuilding the AMC 20 and the Dana 30.

Ah, so, when I say "11 inch lbs" I mean that with the axle under the jeep, the wheels and brake rotors removed, that the yoke took 11 inch lbs to rotate, including having to rotate the ring gear and axle shafts.

I can certainly try to tighten it all up more, which I assume will force the crush sleeve further in and create more tension. Is that what your saying might need to happen?

 

[Ron84cj]

Ah, so, when I say "11 inch lbs" I mean that with the axle under the jeep, the wheels and brake rotors removed, that the yoke took 11 inch lbs to rotate, including having to rotate the ring gear and axle shafts.

I can certainly try to tighten it all up more, which I assume will force the crush sleeve further in and create more tension. Is that what your saying might need to happen?

Yes. It very likely is not tight enough if you are only getting 11" lbs. rotating everything. Honestly, it's really not hard to just do it the right way. It's only 4 bolts on each side to unbolt the backing plates and slide the axles out, plus the brake line on each side. Then pop your cover off, unbolt the 4 cap bolts, and pop the ring gear/carrier out. Just keep track of the orientation of the caps. If it's giving you difficulty coming out, stuff an old rag (that's clean) in between the teeth of the pinion gear and ring gear. Simply turn the pinion and the carrier will push itself out. Then you can replace the bearings, the crush washer, and seal. It's not bad at all. If you have further questions feel free to ask here and/or I can pm you my phone number and you can call me.

 

[spankrjs]

With brakes removed, turning pinion/ring gear/differential gears/axle shafts I usually see around 25 inch pounds for rotation. The initial will be higher, but once turning it will be around 25 -30 inch pounds.

 

[jpnmaine]

Slop and noise are good indicators of an issue. As it is right now if it rotates in your hand smoothly, and feels stable side to side. I would retorque it.