Marlin Crawl Box. Should I? (1 Viewer)

Joined
Nov 21, 2015
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512
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Needham ma
Its totally worth it. Im running a doubler with 2.28/4.7 gears and the options are awesome.

Check out Advance adapters for the doubler adapter. you can get them through poly preformance for around $370 I think.

Heres my 2.28/4.7 full 23 spline doubler to go behind a v6
BeaC6FBl.jpg


Driveshafts made from 2.5"schedule 40 fit the stock joints well.

vzYxu0Ol.jpg


Happy to answer any doubler questions, Ive done a few of them.

This is a marlin doubler that is clocked 10* that I did a few months ago.

Yqb9GrMl.jpg
Curious, what is the reason for the “clocking”
 
Joined
Mar 4, 2012
Messages
299
Location
Northfield, Vermont
x2 what z said. the 10* adapter moves the front output up about an inch. Does increase angles slightly, and a high pinion front diff will do wonders for front ds angles. It also make it difficult to use an off the shelf skid/cross member as the rear mount in 10* off. We only used it because its what came with the pile of parts he bought.

@VA.CRUISER Yes, both my 3.0/gear drive adapter and the dual case adapter is from Advance. Very happy with them. Great product and great customer service.

so.. I toasted my 4.7 gears in my rear case a few weeks ago at f&f on a blue trail believe it or not. They were 6 years old and apparently they were all done. No bearing or case falure. I was able to put the rear case in "hi" and drive out with minimal crunching.

hR8ddYml.jpg


lq3ZCOPl.jpg


I replaced with SUMO 4.7 gears ( also through advance adapters ) Shipped to my door in a week, and supposedly stronger than TG gears. I have a sumo 23 spline input in my front case for a few years now and have no complaints.


v4uzW8al.jpg


CRX6lmFl.jpg
 
Joined
Sep 28, 2006
Messages
1,457
Location
Shelton CT
I run both Cases with stock gears in my buggy with 5:29 and 39” bfgs. Plenty slow. I never take it out of low/low. 4th gear is like 1st in low only.
 
Joined
Nov 21, 2015
Messages
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Needham ma
I run both Cases with stock gears in my buggy with 5:29 and 39” bfgs. Plenty slow. I never take it out of low/low. 4th gear is like 1st in low only.
Ok cool. I just got my 5.29’s installed last week and I’m on 36 Tsl radials. So duel cases with stock gears is plenty probably since I have smaller tires too
 
Joined
Mar 4, 2012
Messages
299
Location
Northfield, Vermont
You need a gear drive top shift transfer case, or convert a front shift to a top shift. and an adapter, new drive shafts, and some floor board modification. in a nut shell.

Always fun to break down the crawl ratio.

(1st gear in trans) x (front case)x(rear case)x (axle gears)

My ratio is (r150f) 3.83x2.28x4.7x4.10 = 168.

If you had a w56, it would be 3.95x2.28x5.29 = 46 right now , stock duals 3.95x2.28x2.28x5.29 = 108 , or ultimate duals 3.95x2.28x4,7x5.29 =223

Of course it doesn't account for tire size or engine torque, but helps break it down a little.

the other nice thing about the 4.7 is it turns it into a 4 speed case. 1st is high 1:1, then stock low 2.28, 4.7 then double low of 10.7:1. 20 forward gears and 4 reverse gears. Where as with stock duals, its a 15 speed, with 3 reverse speeds.

"dual ultimate" gear layout

Black is transmission/transfercase gear ratio, red is what gear "overall"

fU1vLrml.jpg


stock duals

y5kPLipl.jpg


" . 4th gear is like 1st in low only. " looks like its closer to 2nd. lol. .

I mentioned adding gears to the front case, because my truck is a v6 so I had to convert everything to 23 spline. you wont have to do that for 4 cylinder (21 spline)
 
Last edited:
Joined
Nov 21, 2015
Messages
512
Location
Needham ma
I run both Cases with stock gears in my buggy with 5:29 and 39” bfgs. Plenty slow. I never take it out of low/low. 4th gear is like 1st in low only.
Also just found an 87 transmission and transfer case
You need a gear drive top shift transfer case, or convert a front shift to a top shift. and an adapter, new drive shafts, and some floor board modification. in a nut shell.

Always fun to break down the crawl ratio.

(1st gear in trans) x (front case)x(rear case)x (axle gears)

My ratio is (r150f) 3.83x2.28x4.7x4.10 = 168.

If you had a w56, it would be 3.95x2.28x5.29 = 46 right now , stock duals 3.95x2.28x2.28x5.29 = 108 , or ultimate duals 3.95x2.28x4,7x5.29 =223

Of course it doesn't account for tire size or engine torque, but helps break it down a little.

the other nice thing about the 4.7 is it turns it into a 4 speed case. 1st is high 1:1, then stock low 2.28, 4.7 then double low of 10.7:1. 20 forward gears and 4 reverse gears. Where as with stock duals, its a 15 speed, with 3 reverse speeds.

"dual ultimate" gear layout

Black is transmission/transfercase gear ratio, red is what gear "overall"

fU1vLrml.jpg


stock duals

y5kPLipl.jpg


" . 4th gear is like 1st in low only. " looks like some where between 2 and 3rd.

I mentioned adding gears to the front case, because my truck is a v6 so I had to convert everything to 23 spline. you wont have to do that for 4 cylinder (21 spline)
Is this the case I need?

5BC74C39-7149-4C1B-B642-2DC5080558AF.png
 
Joined
Mar 4, 2012
Messages
299
Location
Northfield, Vermont
Count the bolts on the rear output . 7 bolts for gear drive, 5 for chain. (You want 7) Thats a foward shift case (rails come out the front vs a shifter out the top) it will work, but you would have to convert it to a top shift. People make kits for that.
 
Joined
Sep 28, 2006
Messages
1,457
Location
Shelton CT
I actually run forward shift up front and top shift in back. The 94 donor truck came with forward shift That’s why it was easy to make it work. I left the shifter in stock location which is in back of transmission. Just had to weld the shift fork window closed.
 
Joined
Nov 21, 2015
Messages
512
Location
Needham ma
Count the bolts on the rear output . 7 bolts for gear drive, 5 for chain. (You want 7) Thats a foward shift case (rails come out the front vs a shifter out the top) it will work, but you would have to convert it to a top shift. People make kits for that.
Well turns out it is $50 and it is a 7 bolt which is good. But the convert kit from TG is $250! Not including shipping. Think I may pass on this one and wait for the right one ...
Thoughts?
 
Joined
Feb 19, 2004
Messages
3,377
Location
Pepperell MA
Waiting is a better choice. Look on www.car-part.com - that t-case ranges from $100-$300 here in New England.

The t-case in your pictures will also need a rebuild given the bearings being covered in dirt and dust. I've bought used t-cases from the recycler that I could use as is.

Nick
 

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