Changing the gearing for "L" (transfer case re-gearing)

[Dharma Dude]

I read alot about changing the front/rear differential gearing to get more torque (and for larger tires) but can't the same torque increase be achieved by changing the gear ratio for the "L" transfer case gear? A bit of googling showed that for older 4runners, there exist after-market parts for doing exactly that.

It seems changing the L gear would mean you only increase torque when it's most needed (i.e. difficult terrain and climbing where you are most likely to use "L") and not affect the gearing when you're just driving on paved roads where you use mostly H, thus preserving good mpg.

The fact that nobody seems to do this on more modern 4runners and GX, and the absence of after-market support for changing transfer case gearing for more recent rigs suggests to me that there might be a sound reason against transfer case regearing. Cost maybe? Other reasons?

 

[GXO]

Usually cost is the primary factor outside of actually finding a lot that will fit in the case. There are crawler boxes that can work, but they are majorly expensive.

 

[wrmathis]

I read alot about changing the front/rear differential gearing to get more torque (and for larger tires) but can't the same torque increase be achieved by changing the gear ratio for the "L" transfer case gear? A bit of googling showed that for older 4runners, there exist after-market parts for doing exactly that.

It seems changing the L gear would mean you only increase torque when it's most needed (i.e. difficult terrain and climbing where you are most likely to use "L") and not affect the gearing when you're just driving on paved roads where you use mostly H, thus preserving good mpg.

The fact that nobody seems to do this on more modern 4runners and GX, and the absence of after-market support for changing transfer case gearing for more recent rigs suggests to me that there might be a sound reason against transfer case regearing. Cost maybe? Other reasons?

cant change the gearing in the Transfer case. its a chain driven case and there isnt any room to do it. the old trucks and 4runners you could becuase those are gear driven cases.

using a marlin/inchworm crawl box wont work in the GX/4runner/FJ becuase you will run into the gas tank

 

[GXO]

cant change the gearing in the Transfer case. its a chain driven case and there isnt any room to do it. the old trucks and 4runners you could becuase those are gear driven cases.

using a marlin/inchworm crawl box wont work in the GX/4runner/FJ becuase you will run into the gas tank

Agreed, but you can (and people have) relocated the tank. Again, MAJORLY expensive.

 

[Dharma Dude]

Definitely replacing the entire transfer case with a different set of gears would be one way to have a lower L gear but I was thinking more of replacing the gears in the transfer case, like replacing the pinion and ring gear in differentials.

In the GX, the transfer case chain connects the front shaft with the drive/rear shaft assembly. It doesn't appear to be involved in the low gearing actuation.

The L range gear is implemented by planetary gears and ring gear with teeth on the inside and outside circumference. It looks like a clutch shifts a carrier to put the planetary gear in play. So you would think that it would be possible to machine a new set of planetary gears and matching ring to implement a lower L gear. This does look like it involves a lot more "engineering" and complex fabrication than pinion/rings in the differential. So yeah...it would be expensive.

But to my simple-minded thinking, lowering the L-range gear can achieve higher off-road torque without decreasing on-road efficiency. But I don't have to resource to experiment with this, so I'll have to stick with differential gearing.

 

[wrmathis]

Definitely replacing the entire transfer case with a different set of gears would be one way to have a lower L gear but I was thinking more of replacing the gears in the transfer case, like replacing the pinion and ring gear in differentials.

In the GX, the transfer case chain connects the front shaft with the drive/rear shaft assembly. It doesn't appear to be involved in the low gearing actuation.

The L range gear is implemented by planetary gears and ring gear with teeth on the inside and outside circumference. It looks like a clutch shifts a carrier to put the planetary gear in play. So you would think that it would be possible to machine a new set of planetary gears and matching ring to implement a lower L gear. This does look like it involves a lot more "engineering" and complex fabrication than pinion/rings in the differential. So yeah...it would be expensive.

But to my simple-minded thinking, lowering the L-range gear can achieve higher off-road torque without decreasing on-road efficiency. But I don't have to resource to experiment with this, so I'll have to stick with differential gearing.

again, u can not change the gearing inside the Tcase of a chain driven case. there is not enough room to do that.

 

[Dharma Dude]

again, u can not change the gearing inside the Tcase of a chain driven case. there is not enough room to do that.

I don't really understand that. I am NOT suggesting a bolt-on like a Marlin Crawler. I am suggesting a rebuild of the entire transfer case and change the gears. So rebuilding would just replace the original L gears with new lower ones. AFAICT, the chain doesn't have anything to do with the implementation of the L gear.

 

[Arailt]

I believe he's saying that to achieve a lower crawl ratio on the low range gear, you'd need to increase the diameter of the physical gear in the transfer case, which will not fit in the factory housing.

 

[NMBruce]

a re-geared transfer case, maybe a 3.73:1 or 4:1 low range would be great.

This was something I loved about my Jeep Wrangle Unlimited Rubicon. 3:73 gears for going down the road and a 4:1 transfer case when needed, gave me around a 60-1 craw ratio

 

[wrmathis]

I believe he's saying that to achieve a lower crawl ratio on the low range gear, you'd need to increase the diameter of the physical gear in the transfer case, which will not fit in the factory housing.

this thats what i have been saying. its physically impossible to make gearing changes in the current transfer case

 

[wrmathis]

I don't really understand that. I am NOT suggesting a bolt-on like a Marlin Crawler. I am suggesting a rebuild of the entire transfer case and change the gears. So rebuilding would just replace the original L gears with new lower ones. AFAICT, the chain doesn't have anything to do with the implementation of the L gear.

where the planetary gear sits, to get a lower range would mean making the gears larger. there is no room for that in the stock case. you cant just change gears out in it to make a lower ratio

 

[Dharma Dude]

where the planetary gear sits, to get a lower range would mean making the gears larger. there is no room for that in the stock case. you cant just change gears out in it to make a lower ratio

Make sense now. Your comment now makes alot of sense after googling and finding lots of useful information about the principles behind planetary gears and transfer cases.

The only other options to lower the L gear are to add a crawl box, or install a different transfer case. Both big bucks options.