Ins & Outs of Transfer Case Rebuilds

[ashyers]

Hi All,
I've been looking at and listening to the T-case lately. It seems to function OK, but it leaks from all its seals and is a bit on the loud side compared to my friends M37.

I'm curious what tends to wear out in these units. The reason I ask is the price of various items involved. As I see it I have 4 options:
1) remove/clean/reseal add synthetic lube and drive it
2) all of the above plus bearings and any needed replacement parts
3) remove and replace with a remanufactured unit
4) remove and replace with a NOS unit plus a new set of modern seals

My inclination is to do the 2nd option, but I fear that it may cost as much as the 4th by the time I'm finished, without the advantage of new guts in the case. I've been driving the truck about 4000mi/yr and it's frequently driven at highway speeds w/ 4:89's.

Thoughts?

Andy

[Cal_Gary]

Hi Andy,
They usually go due to lack of oil. primarily the lower unit bearings. I still have my old one sitting on a stand awaiting rebuild after pulling the drain plug one afternoon and hearing clunk clunk clunk. Probing the drain pan with a magnet found 6 roller pins from what I assume was a destroyed bearing cup.

There is a complete bearings/seals/gaskets set on eBay regularly for $300.
Gary

[w30bob]

Hi Andy,

I guess there's a 5th option as well.........if you're concerned about cost. And that's to replace it with another used one, which seem to be all over the place when you don't need one. Certainly a crap-shoot if you can't hear it run prior, but if you get it from a trusted source (like the folks on here) you should be ok. Or you can do the redneck thing........and install a stereo and crank it up!



regards,
bob

[ashyers]

Gary,
I have magnetic plugs in the T-case and the oil's been clean after we removed the ancient lube that was in there, no metal of any kind. I'd like to think a new set of seals and bearings would keep the T-case going for the life of the truck IF the gears and shafts are in good shape, I just have no experience on how these things tend to wear the internals. If I end up buying a bunch of gears the NOS case starts looking like a much better use of $.

Bob,
I'm not sure a used T-case would work out unless I was very lucky. I suspect it would be like the one in the truck! If I found one that was local and reasonably priced I'd pick it up, but I don't see too many in my neck of the woods.

Looks like a call to Dave at DC Truck Parts is in order.

Andy

[Cal_Gary]

If this truck is the M37 I drove with you last year with the open top, I didn't notice the transfer case being any louder than mine, and mine was rebuilt just before I bought it. If your magnets are clean and you don't have any unusual wear I'd not worry about it-just keep it topped off and it should last a long time.
Gary

[ashyers]

Gary,
It's the same truck. I've only driven 2 others, one being the one we just finished sorting out. It seemed to have a much quieter t-case, which began to make me nervous! I have to do the seals and I'm concerned this will become a "while I'm in there" affair that just takes me and my wallet down the road in stages. I'd just hate to grenade the thing due to ignorance.

Andy

[isaac_alaska]

If you grenade it i have another in my garage that needs a home (and probably a rebuild)

[Elwood]

Gary,
It's the same truck. I've only driven 2 others, one being the one we just finished sorting out. It seemed to have a much quieter t-case, which began to make me nervous! I have to do the seals and I'm concerned this will become a "while I'm in there" affair that just takes me and my wallet down the road in stages. I'd just hate to grenade the thing due to ignorance.

Andy

The NP200 isn't the quietest thing in the world, especially if you're comparing them to a newer 4x4 vehicle. I think that the all gear drive is noisier than a silent chain setup.

The "while I'm in there syndrome" is understandable. I opened mine up, not knowing what I'd need other than seals, and ended up replacing every bearing, the idler gear, blasting and painting the case inside and out, redi-sleeves on all rotating shaft seals, stainless shift shafts and thrust washer from M Series Rebuild, etc. Probably not every bearing needed replacing, but I figured that as long as I have it apart, and wanting it to be at least as reliable as a new unit, I did them all.

I was fortunate in that the dog clutches and splines were in good shape, and didn't need to be replaced.

The NP200 isn't an especially complicated assembly. Probably the trickiest part is setting up the tapered roller bearings on the idler gear shaft.

[ashyers]

Hot gear lube actually works OK as a cleaning solvent. After 5K miles it's worked a large portion of the caked on mud loose and has kept a nice shine on the case :).

T-case 2.JPG (126.27 KiB) Viewed 3309 times

Check out the rock! It's been there so long it was polished smooth. Wonder where it's traveled?

T-case 1.JPG (113.86 KiB) Viewed 3309 times

Now the question is what to do with the darn thing. We'll clean it up Monday and see what lives under the crud. I'm not sure how much backlash these typically have, but if feels loosey goosey and was a bit loud. There was very little metal on the magnetic drain plug we put in 5K ago, so it's not eating itself alive, yet.

[Elwood]

That's not just some random rock. That's the excessive tilt recorder. If it falls off, you've exceeded the maximum allowable angle of approach or exit.

I've always wondered who thought it was a good idea to put the parking brake on the backside of a housing full of lubricant, contained by leather seals almost guaranteed to leak?

I don't think that there should be much free play. Might be a good idea to pull the output shaft retainer assemblies and check the pre-loads of the brake, rear axle, and idler gear tapered roller bearings. If you've got slop in the gear train, it will be hammering back and forth as the drive train loads and unloads going down the road. Eventually, that's got to cause problems.

[ashyers]

My fear is that the backlash is due to worn gears! We'll soon see.

I'll have to post a photo of the hole in the floor made by the rear driveshaft at some point. I'm sure it was rather exciting when it entered the cab !

[Tom P]

My fear is that the backlash is due to worn gears! We'll soon see.

I'll have to post a photo of the hole in the floor made by the rear driveshaft at some point. I'm sure it was rather exciting when it entered the cab !

I doubt you'll find any gear problems.
Most likely the bearings have worn over time and loosened up the preload.
Behind the bearing retainers are a number of gaskets in varying thickness to
Control the pre load.
Get NOS gaskets from one of the vendors so when going back together
You can set the preload correctly.
Tom

[ashyers]

Tom,
I hope you're right!


Does anyone have the dimensions of the various tools necessary for rebuilding the T-case?
It looks like I need a spacer to set preload and a driver/installation tool for the idler. If I can get some dimensions it will give me a nice weekend lathe project to do while it's raining.

Andy

[Elwood]

Tom,
I hope you're right!


Does anyone have the dimensions of the various tools necessary for rebuilding the T-case?
It looks like I need a spacer to set preload and a driver/installation tool for the idler. If I can get some dimensions it will give me a nice weekend lathe project to do while it's raining.

Andy

The arbor (41-A-338) for pushing out the idler gear shaft is available from 4x4 specialists, such as this one QT2013: http://www.quad4x4.com/category/TTC0/TO ... ASE/1.html. If I remember correctly, this one (which is sold for the NP205, but is essentially the same for the NP200) was a couple of thousandths larger OD than ideal, but a minute or two in a lathe (or even in a drill press) and some emery cloth will bring it down to the correct size (just clean it thoroughly before using).

I don't recall what the OD is (and don't have access to it at the moment), but if you want to make your own after you disassemble the transfer, just turn one up that's a few thousandths smaller in OD than the ID of the idler shaft hole through the case.

They also sell a seal installation tool for the shift shaft seals, but you can probably substitute something already lying around your shop.

Offhand, I don't remember the thickness of the spacer tool (41-S-3868-500) that I made up for my transfer case rebuild, but it's the thickness of the boss in the transfer case where the idler shaft comes through on the front side of the case. I measured my case, and then had a spacer made up to that thickness, then welded on a short piece of rod for a handle, although the handle isn't really needed. When I do my next one, I'll check the case thickness and if it's not the same, make up a new spacer for that case.

You can set up the bearing crush on the idler gear without the spacer tool, but it's more time consuming since you'll have to remove and install the spacer gear, bearings, and shaft until you get the right combination of spacers. Even with the spacer tool I had, I had to remove and install the idler gear assembly several times until I was satisfied with the bearing crush, but that might be because I like to see the too tight and too loose increments on either side of the final spacer combination just to know I've got it as good as possible.

[MSeriesRebuild]

My fear is that the backlash is due to worn gears! We'll soon see.

I'll have to post a photo of the hole in the floor made by the rear driveshaft at some point. I'm sure it was rather exciting when it entered the cab !

I doubt you'll find any gear problems.
Most likely the bearings have worn over time and loosened up the preload.
Behind the bearing retainers are a number of gaskets in varying thickness to
Control the pre load.
Get NOS gaskets from one of the vendors so when going back together
You can set the preload correctly.
Tom

Gaskets behind front bearing retainers have nothing at all to do with setting bearing preload. These bearings are MAX type ball bearings that do not require preload. The bearings are positioned in the case by snap rings on the outer bearing race, the retainers hold the rings tight against the front of the case, gasket thickness adjust the gap between the retainer and the case. Too much gasket thickness will allow the ball bearing to move in and out of the case. To little gasket thickness will allow the retainer to bottom out against the snap ring before the bolt ears contact the case. This condition will result in the ears being broken off the retainer when the bolts are torqued. During assembly, be sure the snap ring is against the case, hold the retainers by hand against the snap ring, while measuring the gap with a feeler gauge. Whatever the value measured by the feeler gauge, choose gasket thickness of approx. .006" thicker than the gap. This will allow good gasket compression when tightening bolts, while not breaking retainer ears.

Bearing preloading applies to the tapered roller bearings used in the idler gear, the 2-speed unit with the park brake on the rear, and the rear output shaft. This is done with metal shims placed in between the two bearing cones on the shaft until desired preload is achieved. Preload value is measured with an inch lb. torque wrench, a 1/4" drive tool works well here. Too tight or too loose preload will cause bearing damage short term, be sure it is done right, bearings will last many years and thousands of miles if the set up is correctly done and the case properly maintained.

Tooling and parts, plenty of shims in a variety of thicknesses so exact specs can be achieved during set up. A 3/4" drive torque wrench is a necessity to do things right. Correct special tools for setting the idler gear bearing preload outside the case will save much time. A HEAVY vise is a plus too.

VITON oil seals will last much longer than standard.

Gear wear, not usually a lot of visible wear, rust pit damage ruining the hardened surface on gear teeth is by far a much greater threat in the majority of cases we go into.

Good luck.