Midnight Metalworks D300 Transfer Case

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woody

eternal noobie
Staff member
Oct 12, 2010
1,852
56
Toquerville UT


The stock Dana 300 works decently enough....but mine has always been a bear to shift, and even with the portals reducing the load to the case, they aren't known for strength. So, in comes the Midnight Metalworks D300 transfer case.

DIY guys, like me.....there are a few important details to pay attention to when assembling the MMW300:

The biggie is the centerpin....aftermarket chromo pins are out, unless they "match" the design of the OEM crosspin. Additionally, the OEM pin is notorious for some variance in length, so double-triple check that the case closes "easily" with the pin in place. Simply, as you look into the "deep" half of the case, the center pin opening is keyed at the bottom to prevent the pin from rotating....a little red grease on the pin and tap it in, then install the backside of the case and be SURE it sets down easily. If there is ANY resistance, then the crosspin needs to be shortened a touch. Getting the pin out once installed is a PITA, a simple seal puller and some luck allowed me to get it in/out a few times as I mocked things up.

This pic is the empty front half being test-fit into my JHF Trail chassis....seat clearance, room for shifters, clocking etc were all planned out here. I ended up with the front output clocked down to roughly the same spot as my stock case, and the seat JUST clears the top. No seat rail changes needed :)

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Purchased the Atlas stud kit and used that....they all needed a die across the stud threads, and will get a little blue loktite before being snugged down.

The input is TIGHT....you must remove the gear for it to install as well, so get out your snap ring pliers and remove that. It's an interference fit....I'm considering putting it in the press for final install, snugging it down with the 6 little bolts seems like a disaster waiting to happen.

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If you've torqued lug nuts or beadlock rings, you'll know the routine....star pattern, a little at a time. This was more annoying than beadlock rings....

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1/4 drive ratchet and time....lots of time...painstaking time...

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And finally, the gear gets reinstalled.

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Shift rods....the 3 hole is an earlier design, the current design is a single hole for the set screw. I had an earlier design and there have been changes, and I'll note what the old versus current stuff is as I go thru.

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Cover plates need to be match-marked so they orientate correctly....I originally did not, and as snug as this fit, rotating to get the 6 bolts in was a PITA....the punch points will make it obvious in the future.

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Center pin in place, front shift fork/collar in place. Grease the seals before installing the rods, both case halves. The Midnight uses 3 shift pads and AR plate...no deflection is a good thing.

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Note in the pic above: the FRONT shift rail is in the REAR position....so it switched. Don't make that mistake. :)
 
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So, fun with linkage ideas....

There are 3 types of levers....most t-cases use a Type 1 where the fulcrum/pivot is in the middle and the "work" is at one end. However, the shift rods on the case will drive straight into the seat mount area, so space is tight...or you make a drop-bracket off the shift rods and deal with that little bit of side loading every time you shift. I'm hoping to avoid that.

Type 2 levers position the fulcrum at one end and the "work" in the middle. The force needed is actually less than a Type 1 for the same resistance applied over the same lever length, but the distance of throw on the lever is greater. Considering the shift rods move about 1" and the fulcrum is about 3" from the rods, it shouldn't be too bad from a throw standpoint....but I'm still in mock up stages.

The GREAT part about this is space....everything is on the t-case itself. The "big" nuts are 3/4" thick and mimic the adapter plate thickness (and the curve). I'll switch out the two bolts in the front output cover for studs, and tack spacers in place instead of washers. The plate is 1/4" thick. The tab has a 1/2" hole for the fulcrum point, and the slots in the primary levers are .26 side so a 1/4" rod (or bolt cutoff) will be welded to the 7/16-20 coupling nuts. Still determining a few things.

Round rods will then be welded to the front edge of the two primary levers and bent to clear the seat and locate them in the cockpit.

If you look close, you can see the black sharpie mark on the top/front edge of the case that denotes the outside edge of the seat rail.

Install will suck however, since the fulcrum plate needs to be installed with the t-case only partially into the trans adapter, otherwise there isn't space to slip it over the studs. Time will tell on how big a headache it is....

Oh, and if this works, I'll post up the dxf files. I did have to overdrill the four 3/8" holes to get it to drop into place, so it's only 98% perfect...lol

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This is a closeup of the centerpin pocket in the back (thin) half of the case. You can see where the cross pin oils have coated MOST of this cavity, which helps confirm that the cross pin is not too long.

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Case internals installed, and about ready to mate the back half. Another note: the thrust washer for the center pin MUST orientate correctly so it catched properly on the case slots. If it doesn't, the case won't close and/or the gears won't spin freely as you soft-fit the rear cover.

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Thrust cover for the front output. I gently sanded down the outside diameter of an old race to allow for easier test-fitting and shim setup. The race DOES come out, but using an old test one never hurts.

Note that the latest case production setup includes seals on both this thrust cover AND the front output cover. No sealant required on either.

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This is another pic of the case ready to have the cover installed, and a shot of the anaerobic sealant I used for the front input and for the rear output. Something like this is needed to help keep the tolerances correct.

BTW: in earlier pics, I had an old beat up input installed with RTV....that came out and I went thru the D300 stash and found a much nicer one....used the Permatex to seal it up. Found this on the bottom shelf at my local O'Reilly Auto.

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Shift rails in the PROPER place (LONG slot for the rear output) and the thrust washer tab orientated up. Next up, install the cover.

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Do you find using the anaerobic sealant is better than plain 'ol RTV? Just had this discussion a couple days ago.
For this type of machined/flanged surface, I think its a better option....especially since tolerance between the case and the input/output pieces is SO tight. On looser fitting items where the tolerances aren't so critical I'll stick to the grey RTV.
 
Installed!!

I bench-filled the case with 2 quarts of Amsoil Severe Gear 75W-90. Use that everywhere else, so no point in using anything different...and IMO thicker lube - harder shifting.

NOTE: In this and other photos, you'll notice that the detent block is upside down....the case backhalves have been redesigned with the fill opening slightly lower so the adjusting screws for the detents are on the bottom. Because of clearance, mine is upside down.

Rob is custom machining one for me so it installs correctly. Customer Service for the win :)

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Engine hoist install, just fits thru the window opening. Using the shiftrails to suspend worked perfectly, and made aligning/clocking super simple. Permatex 27037 was liberally globbed around the input to seal it to the adapter.

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Bolted up! The shift plate required a shade of grinding on the curve, my bench mockup was off a bit. Easy fix, but had to hustle so the Permatex didn't harden too quickly (or the trans fluid leak out....lol) Again, the shift cover is upside down....

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Pic of what I used between the case and adapter. There is supposed to be a seal in there, but the one I took out was destroyed, so Optimum Max Flex for the win :)

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DXF files of the shifting mechanism, I DID overdrill the holes slightly and DID have to grind on the curve to install...it's not perfect, but might get someone started.
 

Attachments

  • Shift Plate.dxf
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  • Shift Arm.dxf
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Detent adjustments:

Tools: 11/16 combo, 7/32 allen

Note: mine is upside down...

First the ball, then the spring. Then finger-snug the allen set screw. I added 1/2 turn with my allen wrench and then locked into place with the nut and combo wrench. This is a good starting point for setting that tension.

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Nice write up. How did it shift and were you happy with it after todays ride. How did it feel compared to the Stock 300. I know mine was night and day when I switched cases.
 
I thought i would warn everyone we have to raise our prices but you have till the end of the week to get a case at the current price. We have been absorbing the increased raw material price for as long as we could hoping the markets would come back down.
 
Raised the fulcrum position by 1-1/2". This means a longer throw but improved ratio. Hope to get some trail time in tmrw to test.

And no, I opted to not cut off the old points just yet.... #hack101 ;)

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BTW, the new fulcrum point "breaks" around 10#....this is running the latest 220# detent springs too (previous were 100#) These were cut to about 75% max length to allow for sufficient jam nut threads.


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