T-case lift FAQ (transfer case questions / answers)

[bushbasher]

Okay this is an FAQ for all those with questions on this mod. Keep in mind this isnt a thread to ask little questions in, just a reference article.

 

1.) What is the t-case mod, what advantages/disadvantages does it give, how does it work?

 

2.) What kind of fabrication/modifications are needed?

 

3.) What transfer cases can I use?

 

4.) Differentials/Solid axles.

 

5.) Differences in suspension between ea82 and ea81 models and how this relates to the t-case'd lift.

 

If anybody finds errors, correct me by PM and I will fix them so as to not clutter the thread. If you want to add something small, I can put it in one of my posts with credit to you as to keep the thing organized. Im not just trying to play FAQ GOD :-p

[bushbasher]

The t-case lift is a method of lifting your subaru with the addition of a divorced (connected to the transmission by driveshaft) transfer case, out of another 4x4, and the use of a rear diff swapped into the front suspension to drive the front wheels, instead of the transmission side outputs.

 

 

Using an extra transfer case has its advantages/disadvantages:

 

Advantages:

- Increased crawl ratio, which means that for a given RPM in your lowest gear, you will have a much slower speed, and much higher torque at the wheels. This will give you more controllability on obstacles because you can approach an obstacle with a lower speed, without having to carry momentum or ride the clutch. The chances of stalling are also much lower.

 

-Tires beyond 30" can be installed while still keeping excellent gearing off-road. Tires beyond 30" on a non tcased subaru would cause the car to be extremely gutless compared to stock, meaning burning clutches and bouncing high speed attacks at obstacles would be a way of life.

 

- The addition of a rear diff up front gives you more options for traction aids, meaning you can easily weld your front diff or install LSD. Welding the front diff is not recommended unless your vehicle has power steering and is a trail only vehicle.

 

-Also you can more easily install different diff gear ratios, choosing from 3.7:1, 3.9:1, 4.11:1. and 4.44:1 gear sets.

Disadvantages:

 

-The increased torque at the wheels in addition to the larger tires means that your axles and diffs will be stressed more than usual, leading to breakage if you are too hard on them. More info on addressing this issue will be found under "Differentials/Solid Axles"

 

-Since the motor is not dropped with the subframe as is done with standard lifts (this is to make room for the new front diff going in) the center of gravity may be slightly higher compared to a non-tcased sube. Its hard to say just how much difference this makes. I would say not much, my t-cased subaru can still lean REALLY far over.

 

HOW DOES IT WORK?

 

Okay, now how exactly is all this drivetrain going to work? We'll start at the transmission. On a stock subaru setup, the transmission has 2 splined outputs on the sides where the front cv axles are connected. Also, there is 1 rear output that normally drives a tubular driveshaft to the rear differential. This rear output only recieves power when the transmission is in 4wd mode.

 

Now, when the t-case mod is performed, the 2 side outputs on the transmission go unused, only the rear output is used. It also means that the transmission must always remain in 4wd mode if the car is to drive. Now this rear output, instead of going to the rear diff, goes to the input of the transfer case. Then a driveshaft runs from the rear output in the t-case to the rear diff. You see now the t-case is running between the transmission and differential, acting to provide extra gear reduction.

 

Now in the front end, the cv axles that used to plug into the side of the transmission are now plugged into the sides of that "rear" differential that has been mounted to the front suspension crossmember. The front axles are the same spline count as the rear diff, so it is simply a plug and play affair in that respect.

How small/big can you go with a t-case lift?

6" is about the minimum lift, even if you can get your tcase packed up high. The reason is that space is tight when fitting the rear diff into the front crossmember. So far, the biggest lift really known is about 12-13" beyond this I would say is really impractical on stock suby independant suspension.

Changes in gear ratios with a T-case:

 

Lets say that 1st gear reduction is 3.55:1, The LO range of the subaru tranny is 1.56:1 reduction, the T-case reduction is 2.00:1, and the differential ratios are 4.11:1

 

So stock subaru, tranny selector in HI range (no reduction), 1st. gear.

The reduction from the crank to the wheels is 3.55x1x4.11=14.6:1

 

Stock subaru, tranny in LO range, 1st gear.

3.55x1.56x4.11=22.8:1 This is lowest possible crawl ratio without Tcase.

 

T-cased subaru, tranny in LO, Tcase in LO, 1st gear.

3.55x1.56x2x4.11=45.5:1 This is the lowest possible crawl ratio with Tcase.

 

T-cased subaru, tranny in HI, Tcase in HI, 1st gear.

3.55x1x1x4.11=14:6:1 same as stock.

 

Actual numbers will differ a bit between different models, what diff gears you end up with, and what t-case you use.

 

As you can see a t-case can make your car crawl more than 2x slower for a given RPM, while still giving a close to stock gear ratio for road driving.

 

Okay next installment will come later, time for a break.

[bushbasher]

Heres a diagram to explain the drivetrain, courtesy of McBrat:

 

 

One thing that might be confusing is the upside down label on the front diff. The diff doesnt actually have to be flipped upside down, but is instead rotated 180* horizontally.

[bushbasher]

Skipping 2.) for now other than to say go to http://subarubrat.com , find "MY BRAT MODS". The good lift info is near the bottom.

--------------------------------------------------------------------

There are several transfer cases that can be used in your subaru:

 

 

1.) The Nissan 720 4x4 Pickup T-case.

 

This is the most commonly used T-case, probably the most convenient t-case to use.

 

-Shares subaru flanges for easy driveline work.

-Outputs are in line vertically so driveshafts line up straight with the diffs.

-Found in '80 to '85 Datsun/Nissan 720 4x4 PU's

-Fairly tall, reduces ground clearance alot. As a result an 8"+ lift is needed to get good clearance.

 

Specs: High range ratio: 1:1 Low range ratio 2.27:1

 

2.) Suzuki Samurai T-case.

 

-Range of reductions available, from stock to aftermarket 4, 6, and 8:1 reduction ratios.

-High range reduction ratio gives better gearing for big tires on the street.

-Must be clocked upright due to offset outputs, but is still shorter than a nissan t-case. Good ground clearance even with 6" lift.

-Does not share subaru flanges so custom driveline solution required.

 

Specs: High range reduction Pre/Post '85: 1.58:1/1.40:1

Low range reduction Pre/Post '85 2.5:1/2.2:1

 

 

3.) Suzuki LJ80 T-case

 

-excellent reduction ratios both in high/low range

-vertically inline outputs to line up with diffs

-easy to mount

-may be weaker than datsun or samurai case

-does not share subaru flanges

-LJ80s are very rare in the U.S.

-very small.

 

Specs: High range reduction: 3.0:1 Low range reduction: 1.7:1

 

 

4.) Lada Niva T-case

 

-compact size offers excellent ground clearance, can be used in a 6" lift

-FT4wd with difflock allows 4wd on pavement

-high range reduction helps on-road gearing

-offset outputs add to driveline angles but are still acceptable.

-funky mounting system

-shares subaru flanges

-very very rare in the U.S., as it is a russian car, imported to Canada.

-Donor car is the Lada Niva 4x4, an imported russian 4x4 similiar to a samurai but with independant suspension.

 

Specs: High range reduction: 1.2:1 Low range reduction: 2.0:1

 

Other known options are:

 

Toyota 4x4 PU t-cases with divorce kitts from OTT? Marlin Crawler?? CHIME IN PLZ but really are overkill for stock axle strength. Maybe a consideration for subarus with toyota solid axle swaps.

 

Divorced NP205 WAY WAY OVERKILL, heavier than a subaru block

 

DRIVELINES: For T-cases with subaru flanges, use datsun 720 4x4 PU drivelines and cut to required lengths.

 

For suzuki flange tcases, who knows? -Update: Information provided by ThreeEyedBandit, scroll to post #6

[JWX]

what is this "lada Niva" T-case?

[ThreeEyedBandit]

For Sami T-Cased drive lines just get the donor drive shafts and one extra flange for a subaru diff and, since the crosses are the same either one(you will need six total). If you grab all the above parts you will have everything you need.

 

 

List of materials in order of use

--------------------------------------------------------------------------

For the intermediate shaft-

 

1-Stock subaru output to transmission

2-Subaru caps and bearings to adapt the subaru output shaft to

the Samurai intermediate shaft.

1-Samurai cross

2-Samurai caps and bearings

1-Stock samurai shaft and flange to t-case

 

 

The front and rear drive shafts are the same just different lengths(2x)-

 

1-Samurai Flange

2-Samurai Caps and bearings

1-Subaru Cross

1-Subaru Drive shaft with attached u-joints and flange to the

differential.

--------------------------------------------------------------------------

 

Now with the completed drive shaft just mount the T-Case and shorten the driveshafts to their proper length.

[ezapar]

While I've not owned a rig with the divorced t-case, I've been around several and was deeply invloved in building a brat that used it. So, I gotta disagree with you a little BB.

-The tcase sitting in the center of your vehicle can reduce ground clearance somewhat in the center.

Since 8 inches of lift or more is needed to add the t-case, it will sit about par with a byb/pk 4 inch lifted soob.

Your Y-pipe is waaaaaaaaaay up there, and in my opinion, the Y-pipe is the Soob's Achilles heel offroad. You gain BIGTIME Y-pipe clearance.

WHile it may look like the Tranny crossmember is hanging, it doesn't change height, but gets higher with bigger tires.

-Power may suffer on-road from the larger tires available as well as the slightly increased parasitic loss through the extra drivelines and the t-case.

Not true. With 4lo on the Soob tranny running thru the t-case, you have some crazy low gears. Robert drove the Unhatched (the original to do the swap) more than 1000 miles to the Rubicon from Northern WA. He easily kept up 70 mph and got near 30 mpg. With 31s. In fifth gear. Several Mountain passes ta boot.

 

 

Other than those, you've done your homework well. Great write up, great idea to do so.

 

 

EZ

[bushbasher]

Thanks guys. Since I actually agree with you now that I think about it, I went ahead and deleted those bits.

[JWX]

what is this "lada Niva" T-case?

eh?

[Qman]

4.) Lada Niva T-case

 

-compact size offers excellent ground clearance, can be used in a 6" lift

-FT4wd with difflock allows 4wd on pavement

-high range reduction helps on-road gearing

-offset outputs add to driveline angles but are still acceptable.

-funky mounting system

-shares subaru flanges

-very very rare in the U.S., as it is a russian car, imported to Canada.

-Donor car is the Lada Niva 4x4, an imported russian 4x4 similiar to a samurai but with independant suspension.

 

Specs: High range reduction: 1.2:1 Low range reduction: 2.0:1

There you go.

[Sweet82]

I was curious too....

 

http://4wheeldrive.about.com/library/uc/ucgraphics/Bruttus_rusu.jpg

 

Lada Niva

 

Glenn

82 SubaruHummer

01 Forester

[JWX]

I guess I should have re-read the thread :/

[lumpycam]

Excellent job Bushbasher! I have the skills to build anything I can imagine but I lack the ability to properly present in a form wich others can comprehend.I'm glad someone took charge of making an online description of the t-case consversion.

[Adam N.D.J.]

Since 8 inches of lift or more is needed to add the t-case, it will sit about par with a byb/pk 4 inch lifted soob.

Not entirely true. You can actually install a T-case conversion into a BYB/PK 4" lifted rig. And most of the T-cased rigs are runnin with 6" lifts. And there is even a mythical beast somewhere in the PNW that has a T-case with NO standard Subaru lift, some say it has a 7" suspension lift in it. I'm sure when we get pics of bigfoot, we'll find that he drives it.

N-E-way, 6" is the typical for this install.

[bushbasher]

yes you can install a tcase in a 4" lift, but ground clearance under the front diff would be sucky. With the right t-case and tunnel cutting tcase clearance could be acceptable, but youd be down into solid axle territory with front diff clearance.

 

Thanks for the compliments on the t-case FAQ, I hope it helps people out and gets more big subes out on the trails out there (and less repeated questions on the board :-p )

[bushbasher]

just a bump and some quick q's. Hey Off-road forums mods, think this could be a sticky? I think it answers alot of questions that get asked about this stuff. Maybe we could combine it with a lift/tire faq? Just throwin around some ideas. I could write it up in a document so we could put it in the USRM.

[ezapar]

I'll add a link to the transfer case section of the Offroad FAQ up top.

 

As for a sticky, I think it would pop up pretty quick if someone did a search for transfer case

[bushbasher]

I'll add a link to the transfer case section of the Offroad FAQ up top.

 

As for a sticky, I think it would pop up pretty quick if someone did a search for transfer case

 

Thats cool, as long as the faq doesnt disappear on us. As far as the search goes, it doesnt come up right away because of the way I wrote "t-case'd" I cant seem to edit it anymore, but I would like it to be changed to simply t-case or t case. It would come up earlier then I think.

[singletrack]

Here's a good question. Running a t-case means no locked diff, right? ...as the car becomes RWD on pavement.

[bushbasher]

Here's a good question. Running a t-case means no locked diff, right? ...as the car becomes RWD on pavement.

 

You can still drive in rwd on the road with a locked diff. As long as you are gentle it will not be any worse than running fwd with a locked rear diff. Increased wear I guess, but in my experience breakage is not as common on the road as people claim it is. I drove my ft4wd turbo wagon with 28" tires, welded diff and 28" tires with no problems on the road. Keeping your rear tire pressure high helps too.

 

People dont usually daily-drive these things, and if they do it takes what, 15 min to swap in an open diff for the back, and 15min to put a welded one back in for a weekend on the trail. Thats what I plan on doing when my t-cased wagon gets on the road.

[RavenTBK]

Here's a good question. Running a t-case means no locked diff, right? ...as the car becomes RWD on pavement.

More or less correct. Just pop out one of the axles like you'd do anyways if you're welded in the rear, and run. And yes, you'd be RWD.

[ezapar]

Thats cool, as long as the faq doesnt disappear on us. As far as the search goes, it doesnt come up right away because of the way I wrote "t-case'd" I cant seem to edit it anymore, but I would like it to be changed to simply t-case or t case. It would come up earlier then I think.

 

Fixed the title for ya. If you want, maybe you could grab the answers to the questions in your original post and edit them into the post like I've done in the general FAQ. I'll go in after you and delete non-related posts to clean up the thread to make it easier to read.

[singletrack]

More or less correct. Just pop out one of the axles like you'd do anyways if you're welded in the rear, and run. And yes, you'd be RWD.

I knew somebody was gonna suggest 1wd!

[Turbone]

A small update on the afore mentioned "1WD" comment. I have a welded rear diff in mine and have driven on tarmac with one axle out.

Lets just say......its a tad squirrely? Almost unsafe.

With RWD and one axle, everytime you shift and give it gas, the car lurches to the drive side. If your really hard on the gas, its a significant lurch. Ask Qman, he drove my Hatch once like that and promptly installed the other axle. I say drive with both axles in, whether its welded or not.

[Andy FitzGibbon]

Some of the early Toyota mini trucks that were converted to 4X4 by aftermarket companies in the states used a special divorced version of the Dana 20 tcase. Another option perhaps, though probably overkill for the rest of the drivetrain.

Andy