R155F t-case gear

I've been trying to search this for a while but I can't seem to find any information on it. Does a regear kit for the T-case of a R155F exist? I can't find anything and the only thing I can find are basically completely built t-cases from marlin crawler that could potentially be mated to the transmission. Aside from having to drop 2k on one of these, they are a shift knob style which would require cutting into the body and changing the interior to fit the shifter. At the moment I'd like to keep things are stock as possible and pretty much just regear it to a 3:1 or something lower.

 

No

 

Well this is lame. I figured with Toyota's aftermarket availability there'd be something

 

You can't change gear ratios on a chain driven transfer case, the low range gears are planetary. You'd have to change the housing and all to accommodate the new gear.

 

Looked at open chain cases and it makes sense. But would something like making the input gear smaller while using a higher quality steel work? It would effectively lower the gearing, but I'm just a noob with ideas. I'm sure there's issues with that, if anyone knows what they are, other wise I'm sure someone smarter would have done it.

 

This is all I have
https://www.tacomaworld.com/threads...er-case-in-the-2nd-gen-truck-write-up.345652/

 

You can't make the "input gear" smaller. Its a planetary gear set. That means that the ENTIRE gear set would have to be changed as a unit, and that means that there would have to be *something* with a compatible gear set *and input shaft* to swap it out with... and there is no such thing.

Frankly, 3:1 isn't that far off from the 2.5:1 to make it worth the expense.

I think your best option is probably to add a "crawl box". Marlin has 2.28:1 and 4.7:1 ratios available.

A crawl box goes in between your transmission and transfer case.

Now the important thing to note, is that the crawl box shifting mechanism is mechanical linkage, 2 position. In other words, with a small amount of creativity, you could operate it with a cable (route it to somewhere that doesn't annoy you), or a servo (electric, like the factory shifter).

 

Been sitting on this idea for a while and thinking about and looking on the marlin site. Could the stock transfer case handle 4x the toque coming in from the crawl box? Sometimes youre on rocks, uphill in an awkard situation and can't risk rolling back too much and you kind of just engage the clutch hard, I'd imagine that chains in the transfer case might pop.

 

I've had the marlin crawl box in front of my chain driven case for 3 years and given it plenty of hell, no issues to date.

 

Good to know! MArlin crawl it will be.

 

There actually is one other option...
And that would be a gear ratio swap for transmission AND differentials.
I don't have my notes with me, but there is a similar transmission that Toyota makes, which has a 5th gear set that would fit in the R155, yielding a higher overdrive ratio. Combine that with a lower differential ratio, and you end up pretty close to the same place without the hit against the highway.

 

Too much work to rebuild the trans just to change one gear. I thought about the differential thing, as in over gearing the differential. But driving on the street will suck which is why I decided against it. Seems like that would only work for dedicated trucks that you can tow.

 

Its actually not a particularly big job to change out just 5th gear. Certainly doesn't need a full rip-apart. MUCH smaller job than swapping out differential gears.

5th gear is at the very back of the transmission, and is exposed immediately upon removing the back cover. You don't even need to remove the transmission from the truck to swap it out.

 

Thats interesting. Got any info on which gear and what not? The only thing I'm afraid of is the 5th being too short once the differentials are regeared. But I'll calculate it out I suppose.

 

I managed to find my notes... looks like the "doner" transmission is the R452, which can be found on a Toyota Dyna 150.
http://www.pirate4x4.com/forum/toyo...earbox-r150-r151-r452-dyna-5th-gear-swap.html
There are a lot of pictures in that thread, makes it look more complicated than it is.

That'll get you an overdrive ratio of 0.695:1

Note that we have R155, not 150 or 151. I *think* it should still be fine though...
Some threads are mentioning problems with pre-1995 R150's, but that shouldn't be an issue.

EDIT: 5th gear from an R154 is another option, which should yield about 0.75:1.
* this one is a big "maybe", since it looks like this one has a different cluster ratio.
* Another edit: scratch that one. Definitely a different cluster ratio. It would be harmful.

If you wanted to do a real *big* job, an R151F with the 5th gear from R452 would be pretty wild. First and second gears on that one are a bit lower than the other.

 

Here's some math about it;

0.805*2.54*4.1 = 8.38
0.805*3*4.1 = 9.90
0.805*2.54*3.91= 7.99 <--- this is you now
0.805*3*3.91 = 9.44 <--- this is what you are targeting
0.805*2.54*4.56= 9.32 <--- this diff ratio is pretty close
0.805*2.54*4.88= 9.98
0.695*2.54*3.91 = 6.90
0.695*2.54*4.1 = 7.24
0.695*2.54*4.56= 8.05 <-- this is where you get back to with the 5th gear swap.
0.695*2.54*4.88= 8.61

Extra:
0.58*2.54*4.3 = 6.33 <-- this is what you get with the factory 2016 6-speed AUTOMATIC, which tells me that this engine can handle about ANY ratio you can throw at it, since its higher than what you would get by throwing the R452's 5th gear on yours without any other changes.

First number is 5th gear ratio,
Second is transfer case ratio,
3rd is differential ratio.

First two lines are stock and target on <= 2015, next two lines are stock and target on 2016 (like yours, which has a higher factory axle ratio), following that is a getting there with differential gear changes instead of transfer case, last lines is where you get back to with the 5th gear swap.

The 4.56 seems to get you pretty close to where you are targeting, and with the 5th gear ratio swap, pretty much right back to the same spot. So your highway manners would be identical, and your low end freed up a whole lot.

 

Hmm, just noticed that the 2016 actually has a slightly different transmission than 2005-2015. Called the R156.
It seems to share the same (approximately) relationship with the R155 as the R151 does with the R150. Specifically, it has lower first and second gear ratios. 3rd and R are the same ratios, so same cluster, slightly different reverse, but most likely still compatible with the R452 overdrive gears.