Dual Transfer Cases

DRaider90

DRaider90

Uwharrie Off-Road Volunteering
Joined
Oct 23, 2007
Location
Weddington, NC
Not sure if this is quite newbie tech, but its not a topic I am very familiar with. I get the general concept of dual transfer cases for a low-low range, or even low-low-low range. Also have some idea about how drive shafts will need to be changed and other modifications. But if you stuck me in a truck with dual t-cases I would probably have to sit there and figure it out for a little while. So can anyone willing to share their knowledge about running double t-cases, difference in low ranges etc?
 
I'll try to explain best I can with my setup, Dual toyota's with 2.28 to 1 in each case. With 5.13 and 42" tires the only time I change the front case is for high use. If you put the front case in high and the rear in low or the other way around, you have the same gear reduction. Now for the confusion...If I had 4.7's in the rear case it'd be different. Front low rear high would be the same, but if I switch the order(front high rear low) the reduction would almost be as low as low low for me now, Then go low low I'd be almost double what I"ve got now. Hope this helps and doesn't cunfuse worse.
 
snappy said:
I'll try to explain best I can with my setup, Dual toyota's with 2.28 to 1 in each case. With 5.13 and 42" tires the only time I change the front case is for high use. If you put the front case in high and the rear in low or the other way around, you have the same gear reduction. Now for the confusion...If I had 4.7's in the rear case it'd be different. Front low rear high would be the same, but if I switch the order(front high rear low) the reduction would almost be as low as low low for me now, Then go low low I'd be almost double what I"ve got now. Hope this helps and doesn't cunfuse worse.
Click to expand...

So essentially with both cases having the same ratio if you put one in low and the other in high they cancel each other out (as if you only had one t-case). Now if you change it up and put 2.28s in the first, and 4.7s in the rear you start getting beyond low-low.

2.28 Low + 2.28 High = Low
2.28 Low + 2.28 Low = Low-Low
2.28 Low + 4.7 High = Low
2.28 High + 4.7 Low = Low-Low
2.28 Low + 4.7 Low = Low-Low-Low
 
DRaider90 said:
So essentially with both cases having the same ratio if you put one in low and the other in high they cancel each other out (as if you only had one t-case). Now if you change it up and put 2.28s in the first, and 4.7s in the rear you start getting beyond low-low.

2.28 Low + 2.28 High = Low
2.28 Low + 2.28 Low = Low-Low
2.28 Low + 4.7 High = Low
2.28 High + 4.7 Low = Low-Low
2.28 Low + 4.7 Low = Low-Low-Low
Click to expand...


No

Lets use your numbers
2 cases each having
2.28 HIGH ranges
4.7 Low range

With only 1 case your ratios are
2.28
4.7

With 2 cases
Case 1 2wd + Case 2 HIGH = 2.28
CASE 1 2wd + CASE 2 LOW = 4.7
CASE 1 High (2.28) + Case 2 Low (4.7) = 10.716 (2.28*4.7)
Case 1 LOW + Case 2 HIGH = 10.716
Case 2 LOW (4.7) + Case 2 LOW (4.7) = 22.09 (4.7*4.7)

1 High 2 LoW = 1 LOW 2 HIGH

Now if we change Case 2 to have 6.0 Low range
Then 1HIGH (2.28) 2 LOW(6.0) = 13.68
BUT 1LOW 2 HIGH = 10.716 again
WHILE 1low 2 low = 28.2
 
SkyHiK5 said:
No

Lets use your numbers
2 cases each having
2.28 HIGH ranges
4.7 Low range

With only 1 case your ratios are
2.28
4.7

With 2 cases
Case 1 2wd + Case 2 HIGH = 2.28
CASE 1 2wd + CASE 2 LOW = 4.7
CASE 1 High (2.28) + Case 2 Low (4.7) = 10.716 (2.28*4.7)
Case 1 LOW + Case 2 HIGH = 10.716
Case 2 LOW (4.7) + Case 2 LOW (4.7) = 22.09 (4.7*4.7)

1 High 2 LoW = 1 LOW 2 HIGH

Now if we change Case 2 to have 6.0 Low range
Then 1HIGH (2.28) 2 LOW(6.0) = 13.68
BUT 1LOW 2 HIGH = 10.716 again
WHILE 1low 2 low = 28.2
Click to expand...

So I got some of it right, but not all I guess. For clarification, the 1st 2 are still 4wd even though the first t-case is in 2wd:

2hi 1:1 + 4hi 2.28 = 2.28 (4hi)
2hi 1:1 + 4lo 4.7 = 4.7 (4lo)

4hi 2.28 + 4lo 4.7 = 10.716 (2.28*4.7) (4lo-lo)
4lo 4.7 + 4hi 2.28 = 10.716 (4.7*2.28) (4lo-lo)
4lo 4.7 + 4lo 4.7 = 22.09 (4.7*4.7) (4lo-lo-lo)

So hi + lo or lo + hi cancel each other out and you end up with the same gear reduction because both t-cases are the same. But if you put the 6:1 gears in the 2nd transfer case it changes a little, I sort of got the lo-lo-lo part the first time.

2hi 1:1 + 4hi 2.28 = 2.28 (4hi)
2hi 1:1 + 4lo 6.0 = 6.0 (4lo)

4hi 2.28 + 4lo 6.0 = 13.68 (4lo-lo)
4lo 4.7 + 4hi 2.28 = 10.716 (4lo-lo)
4lo 4.7 + 4lo 6.0 = 28.2 (4lo-lo-lo)

Just for my own clarification is this possible:

4lo 4.7 + 2hi 1:1 = 4.7 (4lo)

Giving yourself another low range putting the 6.0 t-case in 2 hi, or do you even retain the 2 hi properties of 2nd t-case? My own thought would be no its not possible, but it couldn't hurt to ask maybe I am wrong.

Thanks in advance for any answers.
 
there is no canceling out.
Just that if both are geared identical it doesnt matter which is in lo and which is in hi the net effect is the ame (although different than lo lo or hi hi)

either case in 2wd, in theory just eliminates the reduction of one case. Thee problem is if the back case is in 2wd the front d shaft isnt turned
 
So maybe canceling out isn't the right term, but either way with both t-cases having the same reduction it won't matter if one is in 4low and the other in 4high, or the one in 4high and the other in 4low the reduction will be the same.

So with 2 cases having the same ratio you end up with.

2hi
4hi (2.28)
4lo (4.7)
4lo-lo (10.7)
4lo-lo-lo (22.1)

With 2 different ratios:

2hi
4hi (2.28)
4lo (6.0)
4lo-lo (10.7)
4lo-lo-lo (13.6)
4lo-lo-lo-lo (28.2)

(the numbers varying from t-case to t-case of course depending on ratios)
 
Too much math.
A shop owner in MA has a 350 in his CJ. An Atlas ~4.3:1 and a Klune 4:1 under driver. At 1500RPM he snapped his rear drive shaft.
 
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