Ins & Outs of Transfer Case Rebuilds

[ashyers]

Looks like I'm hunting for some parts now.

The input shaft and output gear were both killed by brinelling and the other output gear is the one with a chunk out of it. Too bad the damage could not be confined to one of the pair! The idler gear has some damage from whatever took a trip through the gear train, but it's minor compared to its mate. All the bearings looked similar and input side's shims were intact. We have not pulled the front bearing assemblies out yet.

[ashyers]

Those aren't stains! OUCH! I suspect some of the noise in Low originated here.

BrinelledOutputSmall.jpg (190.97 KiB) Viewed 4809 times

Looks like I'll be needing a pair. Too bad both are hurt, just our luck...

OutputShaftSmall.jpg (18.9 KiB) Viewed 4809 times

[ashyers]

The case is completely apart. Looks like I have 3 options:

Option A:
1 Shifter Fork, Ord 7091754 (one got a bit warm!)
1 Input Shaft, Ord 7351062 (brinelled)
1 2 Speed Driven Clutch Gear, Input, Ord 7412043 (some tooth damage/damage from fork)
2 Driven Gear Shafts, Ord 7091753 (one brinelled, one chipped)
1 Brake Band, Ord 7349062 (thin and oil soaked)
One complete set of bearings and seals.

Option B
Bush the Brinelled Driven Gear Shaft with a 660 Bronze
Rework the Input Shaft's pilot area w/ a sleeve
1 Shifter Fork, Ord 7091754 (one got a bit warm!)
1 2 Speed Driven Clutch Gear, Input, Ord 7412043 (some tooth damage/damage from fork)
1 Brake Band, Ord 7349062 (thin and oil soaked)
One complete set of bearings and seals.

Option C
NOS NP 200 w/ kit for nitrile seals so I can put synthetic lube in w/o leaks!

What we do will depend on what's available and $. With the price of some of the parts in these things it may make sense to either get creative and save what I have by bushing the input side Driven Gear (brake's gear) or picking up a NOS case.

I think a bushing may work OK, it would solve the brinelling issue and the shaft speeds would never differ by more than 2000rpm in low range (worst case scenario with my combo). I need to look up some bearing design info...

I'm curious to hear what comes back on parts prices!

Andy

ps. If anyone want's photos of something specific drop me a line. So far this thing has been easy to deal with, other than the toasted parts.

[Elwood]

If I'm remembering correctly, the input shafts (at least NOS) are unobtainium.

What about finding another used NP200 assembly, and mixing the parts to get (hopefully) one complete good one?

Or there's this one: http://www.ebay.com/itm/152292539165?ul_noapp=true

Either way, I think going with the synthetic lube is a good idea, considering how these cases are designed to operate with the power flow going through the idler gear even in two-wheel-drive mode. The synthetic will be better at heat management.

[Frank Irons]

Do not use the bushing approach, there will not be enough lubrication to make it last. The rollers allow lubricant to flow.

Frank

[ashyers]

Frank,
I'm thinking maybe oilite so I get some help in the lube department. As I see it this bushing won't get much more abuse than a typical pilot bearing, but maybe I'm missing something.

Have you tried a bushing in the past?

Andy

[just me]

The shaft rarely turns in a pilot bushing. Only when the clutch is depressed and then there is no load. (It is a pilot, after all. Not a load bearing surface.) The shafts in an Xfer are always turning and always under load. you would need to pressure feed oil to them to keep them alive.

[MSeriesRebuild]

I agree with Frank, I've seen real damage in cases we've built due to heat and then a lack of lube, in the exact area of the case you are describing. What typically happens is heat builds because of various reasons; as heat rises above the oil's ability to function properly, it begins to run away from the excessively hot area, which is where it needs to be in a big way. Soon after this point is reached, seizure takes place. Typically what happens in a bushing set up is the shaft seizes in the bushing, causing the bushing to spin in its bore. A catastrophic failure is well under way by this time causing way worse damage than you have now. Please understand, we have never used bushings as a repair method in a t/case, the scenario I have mentioned above is what I have seen in other types of gear boxes in other applications where a bad ending resulted. I can tell you that the damage you have found is already much worse than the usual NP200 we go into. I would use extreme care in checking every spec., you have an unusually high amount of damage. The area where you see the most of the damage is the area in this case that see's the highest oil temp. Fact: it takes way less oil volume to lube a needle roller bearing than it does a bushing. In a stock t/case, splash is the only oil anything in the entire case will get unless it is a low area (rear drive side) that is submerged. When we were perfecting our NP200 oil cooling system, we learned quickly where the most heat was concentrated. That lead to a decision to drill the case and install the return line exactly above the input / 2-speed component area. Result, once the oil temp warms enough to turn on the oil circulation pump and cooling fan, the oil is dumped back in directly onto these components after passing through the cooler core and the cooled oil is reintroduced back into the case. Things to consider; the input / 2-speed component area is the highest area in the case when mounted on the frame in the M37 application. None of this assembly is submerged, so oiling from splash is at best minimal, certainly too little to maintain proper lube for a bushing set up is my honest opinion. I'm not suggesting you need to follow my advice, that is your decision to make, I'm only offering an opinion. Various issues can add to the heat generated in this area other than the minimum lube due to splash only circulation. I've seen more than one case destroyed in this area due to extreme heating resulting from a too tight park brake band adjustment, or someone forgetting to release the park brake before driving. What you noted about your brake band being excessively worn could point to someone's oversight or mistake in the past with a proper band adjustment or driving with the brake engaged at some point during the life of the case. Once high heat is generated, it will cause break down of the oil, resulting in the oils inability to do a proper job of lubrication and cooling. Anytime oil is known or suspected to have been overheated, it should be drained and replaced as soon as possible.

Long story short, I would decline to build a case if I had to repair the issue by using a sleeve / bushing method, as clearly we could not warrant our workmanship on a component with such a repair in place. There are repair methods available to build up and regrind damaged shafts to spec, it is possible to build a good as new case using appropriate repair methods. This would be my next step in a situation like yours if proper repair parts were not obtainable. Crankshaft repair and regrind service facilities can do a proper buildup and regrind repair for you on the input shaft. Good luck with whatever path you choose.

[ashyers]

The upper input shaft and output gear only see relative motion in 4WD Lo, unfortunately this is likely what causes the brinelling. If there was some relative motion while in Hi range I bet the shaft and bore of the output gear would be in good shape.

[MSeriesRebuild]

The upper input shaft and output gear only see relative motion in 4WD Lo, unfortunately this is likely what causes the brinelling. If there was some relative motion while in Hi range I bet the shaft and bore of the output gear would be in good shape.

You offer another theory, this is why I still have reservations. We have built many of these cases, the damage you have found is not typical when a case is torn down and inspected. I would almost bet overheated and ruined oil that was allowed to remain in your case at some point has much more to do with the damage you see than a lack of relative motion did. Numerous issues are usually playing a part in a given outcome in these situations, so your theory may very well have played into the final result. Based on your theory about a lack of relative motion being the specific cause, I would expect similar damage would be evident in most instances, that simply is not the case based on what we see in NP200 cases.

[Tom P]

I think I would find another unit, weld and regrind the parts if unattainable.

Charles and Frank are Spot on.

Just to much heat is these gear boxes for a bushing to survive very long.
Tom

[ashyers]

There's no doubt the transfer case ran hot at some point in it's life and likely had crappy lube in it at the time. I'll post a photo later of the interior of the idler gear, it's "interesting"!

Everyone's input has been very helpful and I appreciate all the experience I've been able to draw on!

From what you guys are suggesting it looks like it's time to cut bait and look into a replacement. With the cost and availability of parts it's probably the best long term solution and also the most cost effective.

[MSeriesRebuild]

There's no doubt the transfer case ran hot at some point in it's life and likely had crappy lube in it at the time. I'll post a photo later of the interior of the idler gear, it's "interesting"!

Everyone's input has been very helpful and I appreciate all the experience I've been able to draw on!

From what you guys are suggesting it looks like it's time to cut bait and look into a replacement. With the cost and availability of parts it's probably the best long term solution and also the most cost effective.

Be careful when acquiring a replacement. A gentleman brought us a core to rebuild a while back; when we opened it up, nothing was salvageable except the case itself. Water had sat in it for years, rusted to oblivion. Looked good outside, any case, even NOS will need going through before installing it. BEWARE of government rebuilt components, the stuff is mostly very poor workmanship at best, it only goes down hill from there, I'd stay away from any component with that label.

[06boblee]

Got started.

[06boblee]

Do you think these are bad? I can't see anywhere they are cracked thru?