AMC 20 Thrust Block Removal - JeepForum.com
 
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post #1 of 14 Old 11-09-2015, 08:29 PM Thread Starter
Controlmech
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Cj AMC 20 Thrust Block Removal

My new 1 piece axles are binding on the thrust block. The FSM shows the differential out of the housing and the ring gear removed before removal of the thrust block. Does anyone know if you can remove the thrust block without pulling the differential from the housing?

(Moser advised either removing the thrust block or cutting the axles)


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post #2 of 14 Old 11-09-2015, 08:52 PM
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Just remove the carrier. Your axles are already out. It will be easier and its only 4 bolts.

Depending on ratio, see if your crosspin will come out with clearing the ring teeth. If not, mark the ring and carrier before you remove the ring so it goes back in the same spot.

The tricky part is popping the C clips off the crosspin. Use a magnet, cover with a rag, and wear safety glasses. IF not, it will fly across the garage.

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post #3 of 14 Old 11-10-2015, 04:18 AM
60Bubba
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Definitely get rid of that thrust block. I have 1 piece axles the PO installed, and both my axle tubes and drum backing plates look like they've been dipped in grease for years. When I pulled the axles to re-gear, I found the thrust block was still in place and they used shim stacks on both axle flanges. Not in any manual I've read...

As for getting the block out, you can do it with the carrier in if the cross pin will clear the ring gear. I think that is supposedly possible on anything numerically lower than 4.10. I can't confirm, as we just pulled the whole thing to replace with a Tru Trac.

If you decide to pull the carrier there are a few important notes:

1. Mark the side and orientation of your bearing caps. I used two punch marks on one side and a little dash made with a flat chisel on the other side. Left/right and top/bottom both matter, so make sure you can get everything back where it started.

2. My carrier hadn't been out since the factory and had mucho preload. We wrapped a rope around the carrier and attached a slide hammer. One person hammered away while the other pried with a long bar. It was still not easy. Someone who was with us suggested using my floor jack to put VERY slight pressure on the bottom of the diff housing. The carrier popped loose after just a few more slide hammer blows.

3. Make sure you pay attention to the shim stacks. It seems like the factory used one large shim on either side, so they are pretty durable. There is no guarantee you only have one shim on either side. If you already have some thin shims in there, they are a b***h to get back in without crushing them. I needed a different shim stack for the new carrier. We worked for several hours and never succeeded. I've got to try again using a case spreader to make a little room for all those flimsy little shims.

4. See the first paragraph. If you can get the thrust block out without pulling the carrier, do it!
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post #4 of 14 Old 11-10-2015, 02:26 PM
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Use pry bars at both top and bottom, pry against the ring gear bolts using the housing as the pry surface, the carrier will come out easily.
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post #5 of 14 Old 11-10-2015, 02:57 PM
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In your profile you say you have 3.31 gears. Unless you've changed the gears, there should be enough room for the cross shaft to clear the ring gear saving you the trouble of removing the diff and ring gear.
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post #6 of 14 Old 11-10-2015, 04:58 PM
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The cross shaft will come out with 3.54 gears. I know that number for a fact.
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post #7 of 14 Old 11-11-2015, 12:08 PM Thread Starter
Controlmech
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The 3.31's are still there. So does the thrust block drop out of the center section or do you have to fish it out of the end of the axle housing?

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post #8 of 14 Old 11-12-2015, 10:09 AM
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Quote:
Originally Posted by Controlmech View Post
The 3.31's are still there. So does the thrust block drop out of the center section or do you have to fish it out of the end of the axle housing?
If it doesn't drop out of the diff case, you can reach in the axle tube from the end and retrieve it with a magnet (Sears, NAPA, etc. has magnets on a telescoping extension).
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post #9 of 14 Old 11-12-2015, 05:01 PM Thread Starter
Controlmech
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Cj

Baffled now.

Pushed both axles all the way in then pulled diff cover off. Thought was if the axle binding was on the thrust block then the thrust block wouldn't move.

Well the thrust block moves back and forth about a quarter inch.
Said the hell with it, pull it out anyway and turned the carrier to get access to the lock pin. No lock pin. Spin it 180. No lock pin. What the hell???

Got a flashlight to get a better look and see there are clutch packs behind the side gears and 2 snap rings on the pinion shaft. Back to the FSM and sure enough, I've got a Trak-Lok and didn't even know it!!

Of course it needs a re-build. First time I had it up in the air a few months ago I did a chick check spinning one wheel forward and the other spun backward.

It never occurred to me that I might have a worn out Trac-Lok.
So two problems now, worn out Trak-Loc and my new 1 piece axles are binding up.

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post #10 of 14 Old 11-12-2015, 05:56 PM
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Let's go back to basics. You originally stated your new axles were binding on the thrust block, which made some sense, as it is a common issue if the thrust block is left in. What exactly led you to that conclusion? Is it possible your binding is coming from another source? Possibly too much preload on the axle bearings for example. I just spoke with Moser last week about my axles, so I can say this is about the newest info out there:

the rear race of the bearing must protrude 20-80 thousandths from the axle flange. It looks weird, but the current axle bearings (SET 9) are designed to stick out slightly. The sandwich of the bolted down seal and drum backing plate create the preload against the bearing where it sticks out of the axle flange cavity. Is it possible there is too much bearing sticking out, or maybe the bearing or the shiny spacer ring aren't square in the bore?

I'm just looking for some other possibilities for you to explore. If you bolted the axles in place and the thrust block is still moving, I agree that it doesn't seem like the thrust block could be the cause of your problems.

I also had a worn out Trak Lok with 3.31. I'll post up pictures I took last night so you can see what the end looks like. As far as I can tell, those axles should be able to bottom out right on that thrust block.

Good luck, let us know if you can see any differences between your differential and mine. If I wasn't clear, this 3.31 Trak Lok ran for tens of thousands of miles with one piece axles. I had leaky outer seals, but no binding or other bad behavior.

Case
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post #11 of 14 Old 11-12-2015, 07:11 PM Thread Starter
Controlmech
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Cj

60 - My bearing stick-out was .046 on the drivers side and 0.054 on the passengers side so should be good to go. I've been talking to Moser as well.

That's the same diff I have.

I thought about the bearing install a little too hard and pressed them on backwards. Cut those off and bought a new SET9 locally. The lock rings were thicker (0.625) but I ground them down until the lock rings were less than 0.500 but not down to the original lock ring thickness of 0.440. If the lock ring is contacting the inner seal it would bind. I'm going to check for contact with the inner seal with clay tomorrow.

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post #12 of 14 Old 11-15-2015, 05:21 PM Thread Starter
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Cj

It was the lock rings binding on the inner seal! Axles are in and spinning free. Rear brakes are replaced and all that's left is to bleed the brakes and put the wheels back on.

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post #13 of 14 Old 11-16-2015, 06:30 PM
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Good deal! I'm glad you got it figured out. I bought my SET9 bearings on Amazon, but I happened to see a post about the lock ring thickness before I go too far. I ended up buying the Crown kit with the bearing, correct thickness lock ring, seal, etc. I wrecked one of the bearings pressing it on, so I guess it was a good thing I had a spare.

Case
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post #14 of 14 Old 11-17-2015, 09:02 AM
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Quote:
Originally Posted by 60Bubba View Post
Good deal! I'm glad you got it figured out. I bought my SET9 bearings on Amazon, but I happened to see a post about the lock ring thickness before I go too far. I ended up buying the Crown kit with the bearing, correct thickness lock ring, seal, etc. I wrecked one of the bearings pressing it on, so I guess it was a good thing I had a spare.

Case
What kind of bearings came with the crown kit? Some have said they have Timkin bearings in them but I know you just did yours a week or so ago.

85 CJ7 258, borla header, Team Rush, MC2100 ,optima batt, Warn 8274, agr super box 2 & pump, T5 w/ B&M shifter, centerforce 2, superior 1 piece axles, warn hubs 2.5 in lift, 31" BFG MT

85 CJ7 258, A/C, T176, MC2100, Team Rush, Warn XD8000i, superwinch hubs, 3in lift 31" BFG AT/KO
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