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Understanding the Success of the Marlin Crawler
  1. History and Development of the Double-Row Bearing Toyota Dual Case Adapter
  2. Double Row Maximum Capacity 32-Ball Bearing
  3. Redesigned Coupler with a New Thrust Washer Detent Ball
  4. Increased Oiling Capacity
  5. New Bearing Retention System

I. History and Development


The Toyota Rock Crawling Industry, founded by Marlin Czajkowski of Marlin Crawler in 1994, has come a long way in its 12 years of growth.

Beginning in the fall of 1994, Marlin Czajkowski designed the 7-5/8" thick MC01. The MC01 was unique because it was a two-piece adapter, but it was rather long. Citing difficulties in installation, Marlin designed a shorter one-piece adapter, and the 5-1/4" thick MC03 was born. The extra length of these Crawlers allowed a forward shifting t/case to be mounted behind the Crawl Box, a very unique feature. 38 units later, Marlin had established his reputation, and with the official start of his business, the 2-3/8" thick-flanged MC05 was created in the summer of 1995. Since this time, a unique Marlin Crawler Serial-Numbering-System was implemented and is still in use today on a variety of Marlin Crawler products. These Marlin Crawler Serial Numbers are used to validate, record, and prove the performance of Genuine Marlin Crawlers.

The MC05 is a 3rd-generation Marlin Crawler Dual case, and was used until the fall of 1999 when it had reached a Serial Number just over 400. But due to reliability issues, important changes were made, and at #414, the 4th-generation Marlin Crawler was born: The MC07.

Since 1999, the MC07 has prevailed to an astounding Serial Number of #3,581 (as of 1/19/2007) and counting.


In other words, the MC07 has been sold by Marlin Crawler for over 7 years encompassing nearly 3,200 units. When compared to the out-dated and discontinued MC05, (about 400 units sold in 4 years), the MC07 has out-sold and out-numbered the MC05 by a 175% time span and at 8 times the volume. Believe me this did not just happen by chance.

Now at this point you might be wondering what was wrong with the MC05 as it only amassed about 400 units. The problem was undoubtedly a reliability concern. Clearly the most obvious change is that the MC07 uses a 1-3/16" wide Double-Row Maximum Capacity Type 32-Ball Bearing whereas the previous version used a Single-Row Conrad 9-Ball Bearing that was less than 3/4" wide. Other noticeable changes were a very important thrust washer detent ball, increased oiling, and an improved bearing retention system, all of which changes were conceived and orchestrated by Marlin himself.

But what you may not know is that when Marlin selected and approached the manufacturer in 1995, he specifically requested to have a Double-Row Maximum Capacity Type Bearing in the MC05. Remember that the MC05 was 2-3/8" inches thick. Clearly there was plenty of room to use a 1-3/16" wide bearing! According to Marlin, his request was denied with the response that such an oversized and heavy duty bearing is unnecessary and would increase the cost to produce the unit. The manufacturer insisted on using a 6209N bearing, and having no choice, Marlin agreed to use the 6209N bearing in his adapter.

Undoubtedly this was the biggest downfall in the development of the Marlin Crawler Dual Case Adapter. By 1999, just 4 years later, Marlin had gathered enough failed MC05 Crawlers (sometimes in succession), and with continuous requests for a more reliable coupler bearing, the manufacturer became aware of the inherent weakness in using a single-row bearing (the 6209N).

It is no secret that the MC05 Crawler fails in a manner that the MC07 Crawler DOES NOT. We have claimed this many, many times in the past. I have personally rebuilt or warranted 9 MC05 units in my experience working for Marlin. Our lead Transfer case technician Rocky, who has worked here for the past 7+ years, claims to have repaired over a dozen himself. This is not even including the number of failures that Marlin, Dave, Aaron, and other veteran employees have seen. There is no reason not to assume that there have been well over 50+ MC05 failures. These failures always result in stripped MC05 couplers. So why am I sharing this information with you? Because I can tell you that MC05 couplers strip out but I can NOT tell you that MC07 couplers strip out. Marlin's advice that the Single-Row 6209N bearing does not provide enough axial loading holds true, based on the fact that MC05 Crawlers often fail and MC07 Crawlers have proven extremely reliable. Out of nearly 3,200 MC07 Crawlers, only 3 MC07 Couplers have stripped out. There have been rumors of a fourth failure, however we have not seen it. There must be some reason why MC07 Couplers DO NOT STIP OUT.

Now before I go any further, I must appreciate those MC05 Crawlers still in use today. Certainly there are remaining happy customers today who are beating the odds and are still using the MC05 Crawler. Of course "using" is a relative term. All parts fail in different situations. Those who apply more mileage to the MC05 Crawler are certainly increasing the probability that the unit will fail, whereas those who limit the use thereof prolong the life expectancy. This is basic wear-and-tear 101, which brings us right back to the core issue of the Dual Transfer Case Crawler: Reliability.
There are those who are willing to save a few bucks for a less reliable Crawler, and then there are those who will not.
I have heard the usual comment where someone says, "Well I know of many people who have MC05 Crawlers that are still working", which I am most glad to hear! But what needs to be pointed out is the fact that the MC07 has out-sold the MC05 by 8-times! And it STILL has far fewer failures! That is amazing. In our experience, if you consider the 50+ MC05 failures mentioned above, then out of the 400 MC05 Crawlers sold, that is 1 failed coupler for every 8 MC05 Crawlers! And that may be a conservative estimation! If you compare that with the MC07, then its reliability has proven to be only 1 failed coupler to every 1,070 MC07 Crawlers.

The bottom-line is that, based on the above data, MC07 Crawlers DO NOT STRIP OUT.
If anyone tells you that the discontinued MC05 is just as good as the MC07, beware.
The MC05 is an outdated design that HAS FAILED MANY, MANY TIMES.

Understanding the Success of the MC07 Marlin Crawler

There are four critical design changes in the MC07 Marlin Crawler:
  1. Double Row Maximum Capacity 32-Ball Bearing
  2. Redesigned Coupler with a New Thrust Washer Detent Ball
  3. Increased Oiling Capacity
  4. New Bearing Retention System

II. Double Row Maximum Capacity 32-Ball Bearing

The 5209W Double Row Maximum Capacity 32-Ball Bearing is the most critical and important design update in the Marlin Crawler Dual Case Adapter. Marlin first requested this bearing in 1995. It was finally accepted and went into production in 1999. This feature was introduced in the 4th generation Marlin Crawler known as the MC07. Replacing the inferior 6209N bearing that was used in about 400 previous units (see above), the 5209W Double Row Maximum Capacity 32-Ball Bearing has been so successful that it is featured in the MC07-R10, MC08, MC09, MC09-R10, MC10, MC10-R10, and now the MC11. This bearing has enabled the Marlin Crawler Dual Case Setup to be at least more than one hundred times more reliable then the previous design utilizing the 6209N bearing (see above).

Some quotes from around the industry regarding the MC07:

"This model has proven to be quieter, stronger, and yet more reliable than any previous model."
- Jay Kopycinski (source:
"This new design provides more strength and smoother operation than previous designs."
- Chris Geiger (source:

Quotes from The
Timken Bearing Catalog:

"The 5209W bearing has increased axial and radial rigidity."
"The 6209N bearing is a general purpose light series bearing."

5209W (MC07) 6209N (MC05)

Maximum Capacity
Type Bearing

Angular Contact

Type Bearing


  Bearing Bore OD Width
Load Rating (ft-lbs)
Ball Count
MC05 6209N 45mm
MC07 5209W 45mm

From the table above, it is clear that the 5209W bearing is far stronger than the discontinued 6209N bearing. Marlin recalls a former competitor stating that "the MC05 Crawler uses an obsolete bearing." He wasn't joking either. Calling up three local auto parts stores, I was surprised to discover that the 6209N bearing is not in stock and is special order only. This is not to say that the 5209W is a more common bearing, but with a bearing so obsolete as the 6209N, I would surely not want it to ever fail, or even worse, cause other parts on my truck to fail.

This brings us to the most critical aspect of the bearing discussion: Coupler Failure.


Shown above are the oversized Billet Couplers used in the MC05 and MC07 Marlin Crawler. Oversized refers to the coupler's O.D. of 1.772", which is 13% larger than the factory Transfer case output shaft at only 1.575". As you can see, the MC05 Coupler is nearly 5-times longer than the Single Row 6209N bearing, whereas the MC07 Coupler is only about three-times as long as the Double Row 5209W bearing. This is extremely critical. Marlin has been a machinist since 1977. With 30-years experience, he knew that a wider bearing was absolutely necessary for the reliability of his Dual Case Crawler from the very beginning.

What many fail to realize is that the Single Row Conrad 6209N bearing has a reduced load carrying capacity and is a light duty bearing. It is only designed for light axial loads!!

On the other hand, the Double Row Maximum Capacity 5209W bearing is designed for increased axial rigidity!! The Double Row bearing looks at the Single Row bearing and completely DOMINATES when it comes to axial support!

Because of the additional row and increased number of balls, the 5209W Marlin Crawler MC07 bearing can handle radial and axial loads FAR GREATER than the inferior obsolete 6209N bearing!

As the following flash demonstration shows, the coupler bearing is the most important axial support for the coupler. Shockwave Plug-in is required to view the following illustration:

As mentioned above, the MC05 Coupler is nearly 5-times longer than it's 6209N bearing:

1 MC05 Coupler = 5 6209N Bearings

Whereas the MC07 Coupler is only 3-times longer than it's 5209W bearing:

3 5209W Bearings = 1 MC07 Coupler

Now as if having a Coupler that is 5-times longer than its bearing (which isn't even designed for axial loads) isn't enough to discredit the design of ANY 6209N BASED DUAL CASE ADAPTER, THEN PLEASE WATCH THE FOLLOWING TWO VIDEOS! THESE ARE BRAND NEW BEARINGS!!

Shockwave Plug-in Required

THAT IS AMAZING. THAT BRAND-NEW 6209N BEARING IS SUPPOSED TO HELP SUPPORT THE COUPLER?!?! UN B E L I E V A B L E!!! The Coupler is 5 TIMES LONGER THAN THE 6209N BEARING! The 6209N bearing is trying to support something that is 400% longer than itself!! Plus Single-Row bearings can not handle axial loads!! The Double Row Bearing is over 8 times more rigid than a Single Row Bearing. NO WONDER 6209N CRAWLERS FAIL!

Shown to the right is a MC05 Coupler that was removed from a broken Marlin Crawler MC05 Crawl Box. Despite the fact that the opposing end of the coupler is supported by the input pocket bearing, as you can clearly see, this coupler still stripped out. And this is no rare occurrence. This happens time-and-time again to the Single-Row-equipped Dual Case Setup. Remember that the pocket bearing has a calculated clearance and is not a pressed fit. The Coupler Bearing Is The Only Support Reference For The Coupler! The reason Single-Row couplers fail is due to a lack of axial support. Axial Support in the context of the Dual Case Coupler refers to wobble about the bearing along the center axis of the coupler as shown above. The MC05 Coupler's total length is about 3.7" long. As Marlin informed his manufacturer in 1994, it is ridiculous to use the Single-Row Narrow 0.7" 6209N bearing on a coupler that is 5-times wider!

Stripped MC05 Coupler
Note the 6209 Bearing

More info on Marlin Crawler bearings, including the stock Transfer case output shaft bearing:
Bearing Bore OD Width
Load Rating (ft-lbs)
Type Weight Ball
Conrad 396 g 9
Stock T/case
Conrad 625 g 8
Maximum Capacity 695 g 32

The 5209W Double Row Maximum Capacity Marlin Crawler MC07 Bearing is:

  • 158% Stronger than the 6209N, 98% Stronger than the 6308N
  • 59% Wider than the 6209N, 31% Wider than the 6308N
  • 76% Heavier than the 6209N, 11% Heavier than the 6308N
  • 256% More Ball Bearings than the 6209N, 300% More than the 6308N
  • The Only Toyota Dual Case Crawler with a Maximum Capacity Bearing in the world!
  • The Only Toyota Dual Case Crawler with a Double-Row Bearing in the world!
Not only is the 6209N a weaker reduced-load light-duty narrow-width bearing, but it has 256% less ball bearings, 76% less mass, 158% weaker, and 59% less contact area than the 5209W!!

Combine this with the poor track record of the 6209N Adapters, and you get a bearing that is SEVERELY UNDER-RATED compared to the 5209W. Furthermore, combine the reduced mass of the 6209N bearing with its increased load-per-area (see below), and you get a bearing that generates more heat and thus more wear than the 5209W bearing!



It is visibly obvious why we experienced 1-out-of-8 MC05 Crawlers fail and only 1-out-of-1,070 MC07 Crawlers fail.

To Recap, here is what our local competitor has said:

"The fact is that bearing failure is not something that happens very often, if ever."

I hope I have made it perfectly clear that this competitor does not know all the facts.

Before we move on to the important changes in the thrust washer, I just want to point out something that a competitor has said regarding our Maximum Capacity Double-Row Bearing,

"The double wide bearings create more heat and have a lower maximum operating rpm of 6100."
"The single wide (6209N) bearing is rated for 9200 rpm and creates less heat and rotational friction."

First I will address the RPM issue, then the Heat issue, and finally the Friction issue.

Dual Case Mainshaft Bearing and RPM
For some reason this competitor seems to be concerned about bearing RPMs FAR in excess of the achievable Dual Case Mainshaft Bearing RPMs. If you take a typical Marlin Crawler equipped truck, 37" tires with 5.29:1 differential gearing, and in the best scenario, you redline your choice of any typical Toyota Truck 4WD powerplant (best is 5,750 RPM) in 5th (0.85:1) gear HIGH RANGE, you will end up with 6,612 Coupler RPM at 141 miles per hour. Now if this competitor is correct regarding the 6,100 RPM limit on our Double-Row Bearing, then it is limited to you traveling at 127 MPH in 5th gear HIGH RANGE at 5,185 Engine RPM. So perhaps we should include a disclaimer to not operate your vehicle at speeds in excess of 127 MPH if you wish to use a Marlin Crawler (which of course is grossly against the law in the United States and is not recommended by Marlin Crawler). Now if you can show me proof of doing almost 130 MPH with 37" tires legally, then you Sir are amazing! Not to mention that once you actually engage the Marlin Crawler into Low Range (2.28:1), you'll be required to rev your engine in 5th gear to 11,820 RPM to reach 6,100 RPM at the Dual Case Coupler Bearing. Or in first gear (3.95:1), if you prefer: 54,940 RPM. Show me a 22R that can rev to 55,000 RPM!!! I am totally bamboozled as to why this competitor even mentioned what clearly isn't an issue.

The Heat Issue of the 6209N Bearing
It is interesting that this competitor defines a narrow cross section, weak bearing with less mass, less material, a reduced load capacity, and poor axial support as one that "creates less heat". Perhaps this competitor does not realize that piston-rod engines develop torque that is transferred through a drivetrain and loads the Dual Case Output shaft bearing. Please consider the following:
Test Load: 7,400 ft-lbs
6209N Bearing
(9-Ball Bearings)
5209W Bearing
(32-Ball Bearings)
Average Load per Ball 822 ft-lbs 231 ft-lbs
Difference -256%
So what we see here is that there are more balls with the 5209W bearing which means that the load per ball is greatly reduced, reducing friction, and thus reducing heat build-up on both the races and the ball bearings. Also 256% less pressure on each ball amounts to a much longer bearing life expectancy. And remember that this has little to do with the axial loads as imposed on the output shaft bearing under loading processes (such as Rock Crawling). Since the 5209W bearing is designed for axial loading (whereas the 6209N is NOT), heat buildup is reduced even more with the 5209W bearing. As I said before, this is basic wear-and-tear 101.

Increase Load per area = Increase Friction per area
Again, this competitor clearly does not understand that drivetrain bearings experience loads. If we were to compare the 9-Ball 6209N bearing with the 32-Ball 5209W bearing in a free-spinning unloaded state, then yes, the 6209N, having less balls with less contact area, would surely create less rotational friction under this zero-load state. But since drivetrain bearings experience loads, rotational friction is a function of how much force is being applied to an area. As shown above, the 5209W Double-Row bearing has 256% more balls than the 6209N bearing, thus reducing the amount of load per ball by 256% and consecutively reducing the amount of friction per area of the bearing by 256%. Since the 5209W is not 256% larger than the 6209N bearing (if that even applies), I am certain that there is more rotational friction with the 6209N bearing, Period.

III. Redesigned Coupler with a New Thrust Washer Detent Ball

UPDATE: Here is what I will be covering very soon:

Our competitor's Marketing Manager has said:
"We think the detent ball/slotted spacer concept is unnecessary,
and adds additional steps to the assembly process."

And our competitor's owner has said:
"Forcing the thrust washer to spin instead of float is creating
unnecessary heat and wear between the mating parts."

And Marlin Czajkowski from Marlin Crawler has said:

"It is rediculous to use a floating thrust washer. This was a huge mistake on the MC05 Crawler. There are no Toyota, Chevy, Ford, Dodge, Jeep, Aisin, etc. etc. etc. transmissions made with free-floating thrust washers because of the debri it will put in the oil!!"

So who is correct? Our competition or the ENTIRE AUTOMOTIVE INDUSTRY? Stay tuned for my explination using correct mechanical analysis.

IV. Increased Oiling Capacity

This section coming sooner.

V. New Bearing Retention System

This section coming soon.

Author - BigMike
Last Updated - 8/23/2007
Former Update - 1/23/2007
Bearing Load Ratings - Timken Standard Bearing Ratings
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