m817 transfer case output bearing

[tobyS]

Taking out the transfer case for output bearing replacement. Has anyone been into the Rockwell that can give me a link to a thread and maybe a few words of wisdom?

Note the transfer case is the only part of my drive train that does NOT look original but has reasonably fresh brown paint.

Has anyone documented opening a Rockwell case? I haven't found one.

Any help appreciated.

 

[tobyS]

We took drive shafts off while it was in the truck and ran first the tranny, then reconnected the transfer case and ran it in low and high. In high, there was noticeable play at the emergency brake/front yoke (of rear driveshaft) and a whine. At higher speed it shook the entire emergency brake mechanism. I now attribute that noise/movement to the bearing pre-load. To tighten one must moving the cup into the housing cover, shimming or removing shims. The output had 3-4 shims, which if removed (one at a time checking pre-load), will tighten that shaft up.

All apart and the gears look like new and not a single glitch in the bearings. (This is a Rockwell T 138, not the 1138.) With the transfer case apart, I spun each bearing in it's mating cup and have absolutely no roughness. There were no leaking seals, but with output shaft play, it certainly would not take long to develop.

I noticed that 2 of the three internal shafts (output and intermediate) can have an adjustment made on the taper bearing cup, but am not sure which one to set first. If I were to use "form a gasket" and it had a very slight difference in thickness, it would not matter as all adjustment seems to be made after the main case is re-assembled...then bearing loading set.

Since this transfer case looks almost new and gears have absolutely no wear, is it possible they did not set the output shaft bearings properly, letting the output shaft have room to move at higher speed (and shake the **** out of the emergency brake setup)?

Now I'm wondering about gaskets. Mine were glued on both sides and now are destroyed. Is there a reliable form-a-gasket?

While I hate to do more work than necessary, I don't think taking it out and inspecting all components was futile...and I can't imagine setting the bearings still in the truck, although it could possibly be done if one knew EXACTLY what they are doing. I had to see it apart.

And I'm still trying to find a TM if anyone has a lead! There has to be one for setting this transfer case up...but I can't find it.

 

[tobyS]

Hasn't anybody had a Rockwell transfer case apart and successfully re-installed?

 

[glassk]

http://www.steelsoldiers.com/showthread.php?59654-M818-Transfer-Case-Upgrade-T-138-to-T-1138

I know this is not the one, but might be some info from them to help out, he knows enough to swap it out bet they know the insides also,...

 

[tobyS]

Thanks glassk,

I have read the thread and also sent a PM.

At this point, I've reassembled the case using aviation form-a-gasket, which has less thickness than the gasket. That helped to tighten things up on the tapered roller bearings. To do the final preload, the cap which has a seal pushes against the cone, tightening it on the tapered roller. So I used a small drift and tapped them in tight, checking for free movement and then put on the caps without any shims. The rear output got a bit tight so I used shims I had removed, giving it only enough to turn freely, but still tight enough to eliminate any play. I have shims left over and the case is about .030 closer than it was...so remain convinced this transfer case build did not get set up quite properly (all components look new inside). It's noticeably tighter than before.

Back to it...I have the sprag clutch to go back on and back in she goes. I sure wish I had found the proper TM but all is well (I think).

BTW, I will confirm what OPCOM says in his thread you link. That is, the transfer case from an 809 series (Rockwell T138 has a high range that is 1/1 ratio and a low range about 2/1. He states the transfer case that is behind Allison auto's in the 923 is a Rockwell T 1138 and has high ratio of .732/1 and low ratio of 1.72/1.

Thus anyone who wants highway speed with an 809 series (especially running duals), should consider swapping transfer cases. Note they do require modifications on emergency brake, but you also get rid of the sprag and go entirely to air front engagement. Sure would be nice to have lockouts too at that point, including one for the intermediate axle.

 

[162tcat]

I've always wondered if you could swap gears around to have the 1 to 1 ratio in the 1138 case. My m923 has 16.00r20s so I don't need the overdrive, 1 to 1 would be perfect for me.

 

[tobyS]

I've always wondered if you could swap gears around to have the 1 to 1 ratio in the 1138 case. My m923 has 16.00r20s so I don't need the overdrive, 1 to 1 would be perfect for me.

That would be interesting...only change out the shafts with gears. I thought about having different gears as I took it apart.

I don't think so because of the sprag clutch unit however. I think the output shaft front end drive would be entirely different (would need to compare).

This unit shows absolutely no wear on the gears or sprag and I would not hesitate to put it (entire unit) in a 923. I'm not offering however, as the dump has work to do.

I would bet with a bit of patience, you could make an even swap to someone with an 809 series...but make sure it is REAL nice.

 

[162tcat]

I have a unit from an M54a2 that I'll rip apart someday. I don't want to swap the 138 for the 1138, just the gears if possible. I want to keep my air shift.

 

[tobyS]

I have a unit from an M54a2 that I'll rip apart someday. I don't want to swap the 138 for the 1138, just the gears if possible. I want to keep my air shift.

Yea, I would want the air shift also but I think there will be a lot different for the front drive. Wonder if anybody has put an air shift from a T1138 on a T138 to get rid of the sprag?

 

[tobyS]

Ok, not knowing how the sprag works exactly has made it's assembly to the main case difficult. The air shift ring that engages the smaller outside teeth of the sprag clutch unit can be put in backward and you will find out when you go to put the air cylinder piston on, after the case is attached to the main unit. And in my case "aviation form-a-gasket" (which let go with some effort, but not too bad). Ok I admit to having it apart about 5 times and I was still left wondering why the piston of the actuator arm was up against the case on one side and against the outer cylinder end also. It works like no "piston" I have ever seen...but it is spring loaded on the inside.

 

[Ajax MD]

Hey Toby,
I think I'm having a similar issue. Did you actually fix this problem?

 

[tobyS]

Hey Toby,
I think I'm having a similar issue. Did you actually fix this problem?

I determined my TC was basically new and the 3 shafts had never had the bearings set properly. It worked sweet after I set the bearings right.