Just Scored Unobtanium! - Marlin Crawler Rebuilt R151F Trans and RF1A T-Case (3 Viewers)

Will Van

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Last week I went to look at a 1985 Pickup for sale local to me. Seller mentioned he had a Marlin Crawler rebuilt replacement transmission "for a Supra". After a little poking around, I realized it was a Marlin Crawler R151F transmission and forward-shift transfer case. I was able to negotiate a fair deal, and the trans and t-case is now in my garage! Score!

I think the trans has the 3.83:1 1st gear, and the forward shift t-case has stock 2.28:1 gears.

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I'd like to run a dual transfer case in my project truck. My question is, what's the most efficient/economical way to build a dual case with what I have? I've read that it's best to run the 2.28:1 gears in the Crawl Box and run the 4.7:1 gears in the t-case. Plus, my forward shift case needs to be in the Crawl Box, not the Transfer Case.

Should I just buy another RF1A top-shift core, 4.7:1 gears, MC08 adapter, and two rebuild kits? Then take apart my current T-case and convert it to a forward shift Crawl Box? And convert the core to a 4.7:1 top-shift t-case?

Or can I run 4.7:1 gears in the Crawl Box and 2.28:1 gears in the t-case since the R151F output is 23 spline? Then I would just need to convert the t-case to top shift instead of forward shift (and source a forward shift Crawl Box core)?

Or is it easier to just sell the rebuilt Marlin t-case and start from scratch?
 

Will Van

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Also, on a completely unrelated note, I'm looking to buy a clean 1979 to 1985 Toyota Pickup 4x4 for a project truck.

:rofl::rofl::rofl:
 
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Your trans should have a 4.31 first gear not a 3.83. This is a turbo trans and the low gear is to give time for the turbo to spin up and get in the boost range.

Rebuilt R151 Turbo Toyota Transmission



Base SKU: MCTM-1R151F
Gear Ratio*
3.83:1 First Gear
4.31:1 First Gear
 

Will Van

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Your trans should have a 4.31 first gear not a 3.83. This is a turbo trans and the low gear is to give time for the turbo to spin up and get in the boost range.

Rebuilt R151 Turbo Toyota Transmission



Base SKU: MCTM-1R151F
Gear Ratio*
3.83:1 First Gear
4.31:1 First Gear

Yessir, the OEM R151F Turbo transmissions came with 4.31:1 1st gear. However, this transmission has been rebuilt by Marlin Crawler. The Seller could not recall which option he chose when he purchased the rebuild from Marlin. But the Seller’s truck that hte trans was supposed to go into is geared tall, because of a V8 swap. It has 3.54 diff gears. So I assumed he would choose the 3.83:1 1st gear option if he could.

But it might have 4.31.
 
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Will Van

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You can use a forward shift on the crawler box. BUT, the rear transfer case MUST BE a top shift.

Exactly. The rear t-case needs to be top shift. So I’m going to need a top-shift transfer case either way.

And I suppose I’m going to have to take apart my new forward shift transfer case either way. Either to convert it to a Crawl Box, or to add 4.7 gears and convert it to top shift.
 
Last edited:

Will Van

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I picked up an extra RF1A top-shift transfer case for my dual-case setup. I am planning on rebuilding it with 4.7 gears. should I be concerned about this nick on the mounting face?

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Stone it, file it, make it smooth and flat even to the surrounding surface. Stone it refers to smoothing and polishing things like knives and firearms triggers and parts.
 

Zor

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Stone it? I'm not familiar with that term.
Yep. Take a true and flat oil stone. Then, while keeping parallel to the rest of the mating surface, grind down that raised portion til it’s flush. A stone is slower/safer than a file. With a file you run the risk of gouging the surrounding surface, especially on aluminum.
 

Will Van

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Stone it, file it, make it smooth and flat even to the surrounding surface. Stone it refers to smoothing and polishing things like knives and firearms triggers and parts.
Yep. Take a true and flat oil stone. Then, while keeping parallel to the rest of the mating surface, grind down that raised portion til it’s flush. A stone is slower/safer than a file. With a file you run the risk of gouging the surrounding surface, especially on aluminum.

Thanks!

I’ll wait until get my Marlin dual case adapter, 4.7:1 gears, and rebuilt kit. Then address it when I dismantle for rebuild, so I can work on a flat surface.
 
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Details on the Dyna 0.68 5th gear?

What’s the trans/dual-case going into?
Mine is in a 1992 ln106
 

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