Transfer case gearset compatibility; telling if one set is "better" and differences

I don't know where to start on figuring this out. Hopefully someone just has general amazing-ness and knows...

I have a gearset for a 30 tooth Dana 18 (tooth count being of the input/bull/main gear, aka trans output shaft gear) (the 30t variations only existed in overseas Jeeps). I also have a gearset for a 29 tooth Dana 18. I can not tell the functional difference between the two. Logic says that there must be a difference, but I have no clue what to look for. What do I measure to ensure that the parts are interchangeable (that I can use a 29t input gear with the intermediate and output gear from the 30t set)?

Or maybe an easier question to answer that might make the problem moot, would the US gears be a step down in quality or strength? Here are two exemplary pictures, 30t gear on left, so shiny:

And the nice machining for the splines of the sliding gear (30t gear on right):


I've put more pictures online here: photobucket/j54mitsu




Here's the longer story. I ordered an Overdrive from Herm. Herm didn't have a 30t gearset to test/compare anything with, so after talking with Herm he sent me a 29t gearset and a 29t OD. The plan being to loose the oddballish 30t gearset and make future parts replacement easier. But here I am wondering if I can use my Mitsu gears if the US gears are "worse"; I'd hate to make a step backwards when I thought that I was taking a step forward. Herm has been very helpful, but understandably reserved about giving advice when he can't be confidently accurate (bc he doesn't have a 30t set to compare with).

Here's some observations:
-Overall the Mitsu's gears' teeth are shorter, yet they appear to be the same thickness of the Dana gears' teeth at that height, so I do not know if this has any functional difference, or just evidence of later/better machining technology.
-The Mitsu teeth look like the bowl gear of the OD that Herm sent, implying further that there may not be any functional difference. Herm may have suggested sending the 29t set bc he had no 30t set to know that they might be the same.
-The output gears appear to be the difference, which is weird to me since that would imply that the intermediate must be different too (but it's not from what I can tell). The inner diameter to the trough of the Dana output's teeth is about 1mm greater than the Mitsu, but it's also narrower, like it was just cut deeper to provide more tolerance of poor machining.

Horribly specific question that possibly seeks annoyingly technical answer... Thanks for any help and advice.

 

Re: Transfer case gearset compatibility; telling if one set is "better" and differenc

My take: That 30 tooth gear will not like the standard stock D18 intermediate gear and although it may physically fit, the probability of it lasting a normal life will be minimal.

As to the gear quality, the Dana/Spicer's are second to none I know of-even the aftermarket sets. Yes, some of the non-critical machining is, let's say, not real refined, the surfaces that matter are well machined and the hardening is top notch.

 

Re: Transfer case gearset compatibility; telling if one set is "better" and differenc

Well, the gear diameters have to be complementary and the angle of the teeth has to match between gears.

Here's a chart that shows the various transfer cases and their part numbers: http://www.novak-adapt.com/knowledge/transfer_case_gears_grid.htm Notice that "18-8-xx" numbers are given, as well as the Jeep Corp PNs (like 9xxxxx). I see an 18-8-xx number cast into one gear and stamped into the other.

One's an 18-8-24, which is a Bronco gear. The chart says 29 teeth, and I count 29 teeth, not 30.

The cast number is 18-8-6, which may be the casting number and not match anything. Look for another number on the other gear.

 

Re: Transfer case gearset compatibility; telling if one set is "better" and differenc

OK, the one on the left has 28 teeth, and the one on the right has 29 teeth.
one on the left has 29 spaces for teeth and the one on the right has 30 spaces for teeth.
Counted 4 times.
I am confused.

 

Re: Transfer case gearset compatibility; telling if one set is "better" and differenc

Holey jamoley, you're right. Boy do I feel blind. Well that's a hhhhhhhuuuuggeee difference. This pretty much seals the deal to do the swap, but one remaining riddle: the intermediate gears do not appear different. When stacked together all teeth align perfectly. The Dana has .25mm deeper teeth gaps (when measured from the gear's center). I'm going to go stare at them some more to make sure I wasn't blind while I looked at them as well...





The 30t reference was confusing. It's referring to the set that matches the 30t drive gear (the gear that I'm replacing), if you're curious it's here.

Duffer, thanks for the vote of confidence on the quality. I couldn't help but make sure I've thought through my options, there's something satisfying about using the old girl's original parts if possible, especially when they're still good looking.

 

Re: Transfer case gearset compatibility; telling if one set is "better" and differenc

Tim, thanks for the Novak link. I wish that they'd include foreign alternatives. Advance Adapters sells the Mitsu drive gears, so I the industry must know the data. Assuming that the 29t gearset that Herm sent has always been together, it is 18-5-9, 18-8-22, and 18-8-6 so possibly from a truck, wagon, or behind a V6 (the Bronco had a different sliding gear that doesn't match the one I have).

 

18-5-9, 18-8-22, 18-8-23, and 18-8-24 are the gear numbers that are used in the 29 tooth 18 transfer case and the "T" shift early Bronco case that shares the same gear ratio. The Bronco also had an 18-8-37 slider not used in the 18 transfer case. These numbers are for the "T" shift (earlier) Early Bronco transfer case and not the later "J" shift.
As was mentioned, you need the complimentary gears to convert your transfer case. Tooth count and pitch are if paramount importance. I wouldn't try to mix and match your Mitsu gears with the Dana/Spicer gears.
My experience has been the same as Duffer's. while somewhat crude appearing the materials and hardening of the Spicer stuff is some of the best I've come across.


Sent from my iPhone

 

Re: Transfer case gearset compatibility; telling if one set is "better" and differenc

I fully agree with Duffers post in all regard
Whenever a helical gear tooth count changes the tooth pitch also changes.
You cannot expect helical cut gear sets to correctly mesh if either the driver or driven tooth count is changed by even one single tooth.
This holds true for any and all helical cut gear sets.
In this instance a "gear set" specifically refers to the driving gear and its mating driven gear.

 

Re: Transfer case gearset compatibility; telling if one set is "better" and differenc

Thanks all for the help. I'll be putting in the Dana gears. Prudence and following advice is outweighing my capability to research this until I learn enough to make what is seemingly black magic become understandable.

For instance, the drive and output gear of the US 29t set are the same diameter---which makes sense. However, the Mitsu 30t drive gear is 4mm wider than its set's 28t output gear. I'm not sure how everything is meshing right unless the Mitsu engineers played with some sort of calculated tolerance that the intermediate gear will accept. Perhaps this is why the Mitsu intermediate teeth appear stubier/different beyond just the Dana gears showing more wear. I haven't measured the tooth pitch on both intermediates yet, I'll probably compare them to satisfy some curiosity. Too bad none of the Mitsu gears have numbers stamped on them as a foot in the door for googling something or submitting to Novak to possibly extend the compatibility chart in the future.

timgr and nickmil, I appreciate the deeper history that you two gave on where the Dana gearset came from.

 

Re: Transfer case gearset compatibility; telling if one set is "better" and differenc

Scroll back to the very last pic that you posted.
Here we see a pic of two very similar yet different intermediate driven gears.
Note that both the upper (Spicer) gear and the lower (Mitsu) gear both have 29 teeth.
Note how the upper (Spicer) gear teeth are more sharply pointed than the lower (Mitsu) gear teeth.
That is the result from a change of the pitch.
That difference specifically indicates that these two helical gears utilize different driving gear tooth counts.

In order to accept the 29 tooth O.D. bowl gear you will also need to change out the Mitsu intermediate gear.
You might want to consider changing all transfer case gears over to Dana Spicer just to insure complete gear compatability.
In truth the metalurgy used by the different manufacturers is unlikely to be problematic, yet as an unknown it remains as a remote possability.

In that case it should be more cost effective just to buy and install a complete Dana Spicer transfer case.

 

Re: Transfer case gearset compatibility; telling if one set is "better" and differenc

Ken, thanks for that point to identify a difference. I have a complete Dana/Spicer gear set and an OD, so all tcase gears will be changed.