Exploring the New MC07 XD Technology

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Exploring the New MC07 XD Technology

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To compliment our Xtreme Duty 4.70:1 Gear Set, Marlin Crawler is proud to release the long anticipated Xtreme Duty Dual Case Adapter Kit. The Xtreme Duty 4.70:1 turned the Low Range gear world up-side-down, and now it is time for the world's #1 most popular dual case adapter kit to do the same.

Originally created in 1994, the Marlin Crawler Dual Case Adapter has come a long way since its introduction as the MC01. Please take a moment to explore the technology behind the most advanced Dual Case Adapter in the world...

Marlin Crawler MC07 XD


  1. Double Row Maximum Capacity Main Shaft Bearing
  2. Chromoly Coupler
  3. Oversized Heavy Duty Cage Bearing
  4. Radiused Coupler for increased pocket bearing oiling
  5. Heavy Duty Plate Webbing
  6. Thrust Washer Lock System
  7. Shelf Oil Passages
  8. Multi-bolt Retention System
  9. Proper JIS Heavy Duty Fasteners
  10. CAD Optimized Light Weight Adapter Cut Out
  11. Unique Margasket
  12. EcoSeal Transmission Output Seal


1. Double Row Maximum Capacity Main Shaft Bearing

Marlin Crawler MC07 XD Double Row Bearing

The key ingredient in the reliability and longevity of the dual case adapter is how the coupler is supported. Knowing this important fact, Marlin incorporated a large, double row bearing into his first dual case adapter in 1994. The manufacturer at the time refused to use such a large bearing instead opting for a cheap, in-house part. Finally in 1997, Marlin had enough stripped out couplers to finally convince his manufacturer to use a double row bearing.

This was a critical turning point in the dual case adapter world. The double row bearing has been proven to be over 100 times more reliable than a single roller bearing. The double row bearing is so successful in fact, that it is used in our MC07, MC08, MC09, MC10, MC11, and MC12 dual case adapters.

  • Proven to be over 100 times more reliable than a single roller bearing design.
  • 158% stronger than competitor's single roller bearing.
  • 256% less load per ball due to its high 32-ball count.
  • The only dual case adapter in the world with a double row bearing.
  • The only dual case adapter in the world with a maximum capacity bearing.
Double Row Bearing is 8-times more rigid
8-times more rigid
double row bearing
Bearing Deflection Comparison
Minimal Deflection
Maximizes Coupler Life

How many balls do you have?

Marlin Crawler MC07 XD Double Row Bearing

2. Chromoly Coupler

Marlin Crawler MC07 XD Chromoly Coupler

You read that right: The XD MC07 Crawler comes with a Chromoly Coupler. This is Xtreme Duty, this is Marlin Crawler.

  • Chromoly Coupler adds extra strength where it is needed the most
  • Stronger material provides exceptional spline wear characteristics

3. Oversized Heavy Duty Cage Bearing

Marlin Crawler MC07 XD Oversized Cage Bearing

This is another Marlin Crawler Xtreme Duty exclusive feature. We have seen some lower cage bearings overheat in extreme conditions, such as heavy trail breaking in deep snow or mud. You might think the snow would keep the case cooler, but what happens is the snow melts around the drivetrain and then freezes into ice creating an insulating layer around the transfer cases. This prevents any air flow around the cases and, in turn, the gear oil temperature begins to rise. The Xtreme Duty Crawlers feature this MASSIVE lower cage bearing to combat this issue.

  • 84% more massive.
  • 52% stronger load rating.
  • 42% larger rollers.
  • 13% higher speed rating (not applicable in terms of crawling, but this shows it's superior heat dissipation).

4. Radiused Coupler for increased pocket bearing oiling

Marlin Crawler MC07 XD Radiused Coupler

The input pocket bearing is housed within the coupler. Because this pocket bearing is above the gear oil fill level, it is important to get the right amount of oil to the pocket bearing. Our 4.70:1 Xtreme Duty low speed gear features an innovative oil pump system, however 4.70:1 gears are generally not used in a Crawl Box. For this reason, we have designed our Xtreme Duty coupler to encourage oil flow through the pocket bearing while at the same time trimming off fat.

  • Increased pocket bearing oiling.
  • 13% lighter coupler.
  • Lighter coupler enables improved bearing support.

5. Heavy Duty Plate Webbing

Marlin Crawler MC07 XD Increased Plate Webbing

The Xtreme Duty adapter plate lives up to it's name with full flange webbing. The previous designs stopped short of each flange, but not the Xtreme Duty design.

  • More strength to hold the two flanges together.
  • Improved plate rigidity for extreme operating conditions.

6. Thrust Washer Lock System

Marlin Crawler MC07 XD Thrust Washer Lock Out

Please imprint these words into your brain: Every Toyota thrust-washer has a detent ball lock system. Period. Every main shaft in every transmission Toyota has ever built has a locked thrust washer-to-shaft system: All L-series, all G-series, all W-series, all R-series. Additionally, every transfer case they have made uses a thrust washer-to-shaft lock system including all 4-cylinder and 4-cylinder Turbo gear drive cases, and all chain drive cases including those found in Tacomas, 4Runners, T100s, FJ-Cruisers, and Tundras. Heat treated same-metals should NEVER be allowed to wear against one another.

  • Prevents unnecessary wear.
  • Reduces the amount of metal debris in your gear oil.
  • Prevents unnecessary heating of thrust washer and coupler.
  • Extends the life of the coupler, thrust washer, gear oil, gears, and bearings.

7. Shelf Oil Passages

Marlin Crawler MC07 XD Increased Oil Passage

Our adapter plates are designed with 6 oil passages between the transfer case and the Crawl Box. The upper two oil passages are above the oil fill level so only turbulent oil is able to transfer through these passages. Because of this, we've designed our Xtreme Duty Crawler plates to include shelves to "catch" and drain this oil right into the upper oil passages.

Our previous design lacked shelves and therefore relied on vehicle acceleration in order for gear oil to pass beyond the main bearing. Unlike other adapters, the Xtreme Duty adapter transfers oil under cruising conditions. This never before seen feature is only available with a Marlin Crawler.

  • Shelves catch and direct turbulent oil to flow passages.
  • Transfers oil under cruising conditions, a never before seen feature.
  • With a total of 6 flow passages, the Xtreme Duty adapter flows the most amount of oil.

8. Multi-bolt Retention System

Marlin Crawler MC07 XD Multi-bolt Retention System

When we invented the multi-bolt retention system back in 1999, we knew it would be a world class feature. That is why 7 of our dual case adapter kits use this innovative Marlin Crawler feature. Some competitors try to emulate Marlin Crawler, but the fact is Marlin Crawler has been using this design for more than a decade.

We always configure our bolt retention system with equal bolt spacing. This results in an even load distribution. This is very important because bolts that do not experience a load may easily vibrate loose resulting in catastrophic failure! Additionally, using fewer bolts results in less chance for failure.

Technically speaking, 1 bolt would suffice since the tensile strength of the grade 12.9 bolt exceeds the axial loading forces of the low speed gear, but we wanted to evenly spread the load across the snap ring while providing an esthetically appealing final product. Our design was changed from a 3-bolt system to a 4-bolt system because the larger Xtreme Duty lower cage bearing prevented an equal 120-degree 3-bolt offset pattern, but allowed for an evenly distributed 4-bolt 90-degree offset pattern. The rest is history.

  • Four equally spaced bolts result in an even load distribution.
  • Low number of bolts = low chance of one coming loose!
  • Marlin Crawler invented the multi-bolt retention system in 1999.
  • Over a decade of experience in 7 different adapter kits.
  • One bolt would be sufficient, but 4-bolts provide an appealing final touch.

9. Proper JIS Heavy Duty Fasteners

Marlin Crawler MC07 XD Proper JIS Fasteners

Marlin Crawler has used Japanese Industrial Standard (JIS) hardware since 1994 and will continue to do so. Your Toyota truck doesn't have any 13mm, 15mm, 1/2in, 5/8in, or 11/16in bolts so why should a dual case adapter have non-Toyota hardware? You drive a Toyota, you only carry tools to service your Toyota. Marlin Crawler takes great pride in using the proper hardware for the job. Additionally, you won't see us using any nylon locking nuts because it is common for the nut to lock to the stud in such a manner that the stud gets extracted with the nut. And since the adapter flanges are so close to one another, you can't get the nut off of the stud in order to get the housing off of the adapter plate! Sheesh! Also, the nylon cracks and degrades over time causing the nut to simply unthread. Toyota uses flat & lock washer combinations all over your truck so it is only natural for Marlin Crawler to use the same. Don't get "screwed" with inferior mounting hardware!

  • Using JIS compliant hardware since 1994.
  • Flat & Lock Washer combo is standard Toyota practice that far outlasts locking nuts.
  • Clearance around nuts provide access to nuts using a box-ended wrench (see image below).
  • Keep your non-Toyota tools at home!

Please consider the below image of the JIS fasteners installed into a Marlin Crawler Crawl Box. A small 14mm box-ended wrench is able to fit between the nuts for proper disassembly. The nuts are also able to fully unthread from each stud. This is not possible if non-Toyota 11/16in nuts are used. Furthermore, have you ever tried getting a huge 17mm or 11/16in hand wrench up between your transfer case and truck body? It's a nightmare! It's these sort of smart and friendly features our customers appreciate.

Marlin Crawler MC07 XD JIS Nut Clearance

10. CAD Optimized Light Weight Adapter Cut Out

Marlin Crawler MC07 XD Light Weight Design

Using the latest in computer software, we were able to reduce the weight of the adapter plate by an incredible 25% without sacrificing any strength! The adapter cut out also allows for other advanced features such as the shelved oil passages.

  • CAD optimized material removal yielded a 25% lighter product.
  • Supports advanced adapter features such as shelved oil passages not found anywhere else.

11. Unique Margasket

Marlin Crawler MC07 XD Margasket

We have been providing our very own Margaskets for over half a decade now. These gaskets are unique due to their universal nature. You don't have to second guess which gasket to use with which donor transfer case, we've taken all of the guess work out of the install process. Marlin Crawler customers appreciate the attention to detail of our products.

  • Universal Margasket fits any donor case no matter the shift style or year.
  • Removes all the guess work of which gasket to use with which donor case.
  • Eliminates the concern of oil leaks when using short gaskets on tall housings.

12. EcoSeal Transmission Output Seal

Marlin Crawler MC07 XD EcoSeal

The EcoSeal needs little introduction. This heavy duty replacement transmission output seal has a metal flanged lip to ensure a full installation into your transmission's tail-housing. This prevents installing the seal sideways/crooked, a severe installation error that reduces the life expectancy of the seal as well as the sealing effectiveness. The EcoSeal eliminates installation errors ensuring the job is done right the first time. A transmission rebuild is expensive; keep your transmission and transfer case gear oil separated.

  • EcoSeal eliminates installation errors.
  • Longer life expectancy and improved sealing.
  • Marlin Crawler has been including complementary transmission output seals since 1994.


After examining the most feature rich and technologically advanced Toyota RF1A dual case adapter kit in the world, we are certain you will agree that the new Marlin Crawler Xtreme Duty MC07 is on a completely different level far, far above all the rest. There simply is no comparing a Marlin Crawler with any other. Marlin Crawler