FAQ Converting HF2AV Transfer Case into Part Time Transfer Case (2 Viewers)

[OGBeno]

It's about time this gets documented and written up with the correct information all in one location. This thread will provide the necessary documentation to do this transformation at home. What will follow below is not necessarily the only way to do this conversion, but it is the way IBCRUSN and I will be doing it. We look forward to your comments, your suggestions, your criticisms, and anything else you might have to offer as we document this process.

Background:

I've been wanting to do this for a long time now: Converting the HF2AV xfer case into a part time case with the addition of manual locking hubs (Aisins) to the front axle to make the 80 series a real part time 4WD vehicle.

There have been a number of threads talking about do this and do that, but no definitive thread on how to do from start to finish. IBCRUSN and myself have been talking about this for a number of years, and Alia176 already did this to his 80 using a spool in the center diff of his xfer case.

Of course, lots of other people have converted their rigs to part time: Christo, Gary Coberly, Ali, denis, Robbie, Michael from ACC, etc. and some other forum members.

But there really is no tutorial on how to do this correctly--just lots of cobbled pics here and there, insufficient information on how to do it. This isn't rocket science and I won't pretend to be a rocket scientist. IBCRUSN and I are just shade tree guys so if we can do this conversion, so can anyone else who is interested in doing this.

We are trying to de-mystify this because we think that anyone should be able to do this at home if you have the correct tools, the space, and the money to farm things out if you do not have the correct tools or are interested in buying the Mark's kit from Christo.

DISCLAIMER: What will follow here is how we did the work and our results. We will not be responsible if you do this to your rig and your xfer case blows up or your birfs are damaged etc. We take no responsibility for what you do to your trucks.

This thread will be split into two sections:

1. Section 1 will document the conversion and work done to the HF2AV transfer case that came with 80 series Land Cruisers from 1993-1997. The "V" stands for the viscous coupler that is found in the rear extension housing of the transfer case. Section 1 will show the modifications done to the transfer case and how it was done.

2. Section 2 will document the rebuilding of a set of Aisin hubs (stock Toyota hubs available on Mini trucks, 4Runners, Land Cruisers) as well as the modification to the birfs needed if you are running birfs that were produced after April 1994. April 1994 and later vehicles have longer birf stubs which means that they need to be modified to accept Aisin hubs. Pre-4/19945 birfs will be a direct fit to the Aisins. I will be using a set of FJ60 30-spline Aisin manual hubs that I sourced locally. I will be rebuilding these with the help of a local manual hub guru and I will be then modifying my birfs to accept the Aisins.

Here is a very good thread on what Kris and I will be doing. There are great pics especially for those of us with the 8mm longer birfs that were installed into rigs starting after 4/1994. Again, it's not much rocket science here, but just getting everything correct is the key...especially when you are dealing with birfs that cost $500 or so a rattle new.

https://forum.ih8mud.com/80-series-tech/235634-longs-aisin-hubs-install.html



So, onto Section 1.

I happened to have a spare HF2AV transfer case from a 1995 80 Land Cruiser sitting in my home shop space that I will use as the test transfer case. Once I've modified it, I will be installing it into my rig which is currently sitting on jack stands at home as I do my yearly PM work on it and some other projects. The transfer case I take out will then be taken apart and modified as well and will be kept as a spare at home.

Here is the speciman:

 

[OGBeno]

First off, the whole point of getting into the transfer case is to get to the center differential (same as our front and rear diffs., except shaped different to be accepted into the transfer case housing.

The center differential on the HF2AV is located in the rear portion of the transfer case housing. The viscous coupler is also located in the rear extension housing which will be removed once the rear extension housing is pulled off. Once that is pulled off, then we go into the center differential section.

First, you'll need to remove the transfer case from the rig (this is out lined in the FSM and won't be discussed here). Drain the gear oil. Make sure you disconnect the speedo gear from the housing before you pull the transfer case.

Once you have it out and over to your shop table (xfer case weighs about 100 pounds, give or take), you begin by taking the rear extension housing off. The FSM has a schematic for the components.

To pull off the rear extension housing you will need to use a 14mm socket and pull the 9 bolts that hold the rear extention housing to the center of the transfer case area. Each bolt is a different size, so you will have to keep track of them in some way to make sure that the correct bolts go into the correct holes when you are putting everything back together again. I used a piece of cardboard and drew out the rear extension housing and numbered the different bolts in relation to where they are located. Of course, all hardware will be cleaned up and all gasket material (FIPG) will be cleaned off before re-assembly since we will be putting FIPG back onto the different sections of the gear box assembly.

Here is the template I made--very crude but effective:

Once you get the bolts out, I used a 450gram hammer to lightly tap around the housing mating surface to get the housing loose from the transfer case. There is a layer of FIPG that holds it toget at this point. I then used 2 small pry bars to pop the rear extension housing off of the rest of the case. The housing will fall off pretty easily onto the table revealing the innards.

Here is the remainder of the case looking at it with the rear extension housing off:

And here is the other side: Here you can see the viscous coupler towards the center of the pic--dark, big piece of metal on the rear output shaft. To the upper right hand corner is the oil pump for the xfer and it is under 3 screws which would reveal a rotor and housing very similar to the 1FZ oil pump on the front of the engine.

The viscous coupler is held on by a c-clip. You will need to get either a long c-clip tool, or you will have to modify one that you might have (I have the Sears version that I used a file to modify to fit into the rear output shaft area to get to the clip). Once you get the clip out, the viscous coupler slides off of the rear output shaft.

Here is the rear extension housing with the coupler removed:

The coupler was given to CDan....he always needs extra parts...

Here are some coupler pics:

That's a big hunk of metal. It'll be nice to get rid of it!!

More to come later. Gotta work for a bit then get back to the xfer case hopefully late tonight or early tomorrow morning.

Best.
-onur

 

[cool breeze]

Very cool, will be watching! Im already lucky enough to have a non VC equipped t-case.

 

[Lka1988]

About time.

Subscribed.

 

[Pin_Head]

Why not just weld up the VC? It is a lot easier than disassembling the center diff and it would accomplish the same thing. Siezed VCs are pretty easy to come by and it would be easier to reverse if desired.

 

[OGBeno]

Why not just weld up the VC? It is a lot easier than disassembling the center diff and it would accomplish the same thing. Siezed VCs are pretty easy to come by and it would be easier to reverse if desired.

A couple of things for going this route:

1. I like the idea of getting rid of 9 or so different moving gear mechanisms which just add to the general backlash issues that 80's have as they get older. When you compound the front/center/rear diffs, those are a lot of gears each with backlash going on. Getting rid of one of these would greatly reduce backlash in my opinion.

2. I have a nice donor transfer case and, to be honest, I get to learn something while I do it, so the learning part becomes a good by product of going into the transfer case.

3. I want part time xfer all the time. I am not really interested in a AWD rig since my truck sees maybe 5K a year if I am lucky.

4. I have the time and space now to do this modification.

5. CDan needed the VC...gotta keep him happy.

6. IBCRUSN has a blacksmithing friend with a nice high temp oven for this work and he will also be doing the TIG welding to the center diff.

7. s***s and giggles.

 

[silverhorse]

Thank you, thank you ,thank you ! Can't wait to get this done.

 

[IBCRUSN]

I'll throw a couple things out there straight away.

This will disable the ABS.

Unless I'm misunderstanding the service manual the transfer case shouldn't need to be removed from the truck to accomplish the removal of the tailshaft housing and the rear case half. We have the luxury of a unit sitting on the bench and Onur is anxious to swap out his his high mileage transfer case for a low mile unit. Is it me or he resembling LX_TREME a touch?

Edit: In addition to what has already been stated I do need to add that when I perform this on my rig the transfer case will remain installed in the truck and documented as such. The goal is to make this doable by nearly anyone who wishes to have a part time transfer.

I haven't been quite as lucky on the hub front and will be converting IFS hubs using Bobby Long's inner hub gears, the hubs are easier to find for a reasonable price.

I'm considering taking up an offering with the goal to purchase Onur a decent camera that has a macro setting. Dude, I had to put shades on to see the transfer case.

At any rate, as Onur mentioned the goal is to have a step by step pictorial of how to turn your HF2AV into a part time case. We'll do our best to keep this moving along swiftly.

 

[Riad]

So you're gonna have Full-Time 2H(?) 2 wheel drive after you are done with this? Then once you lock the hubs you are back to 4WD? I know this is dump question but I need to ask to clear my head; sorry .

More dumb question/comment: it sounds like this would be a great opportunity for lowering the gear ratio in the t-case. Don't know much about the availability of such gears but any plan on doing that?

 

[alia176]

can someone buy this dude a decent digital camera?

 

[silverhorse]

Maybe turn off the flash?

 

[IBCRUSN]

can someone buy this dude a decent digital camera?

No kidding, my POS Blackberry takes better pics.

 

[OGBeno]

Enough of this BS. I'll get a better camera (since I don't own one that works).

EDIT: I went and got a camera. New pictures coming soon.

Thanks.

 

[OGBeno]

So you're gonna have Full-Time 2H(?) 2 wheel drive after you are done with this? Then once you lock the hubs you are back to 4WD? I know this is dump question but I need to ask to clear my head; sorry .

More dumb question/comment: it sounds like this would be a great opportunity for lowering the gear ratio in the t-case. Don't know much about the availability of such gears but any plan on doing that?

Hey Riad:

I would love to go to low gearing in the xfer case right now, but the cost is very prohibitive (IIRC, ~$900 for the lower gears), and IIRC, there have been some issues with the Mark's low gearing kits for the HF2AV...I recall reading about them in the Oz magazines and online forums. But I haven't heard about them in a long time.

Basically, what this process will do is the following:

1. With the front hubs not engaged and the xfer case shifter in H, you are in high range with power only going to the rear driveshaft and then to the rear axles. Basically, RWD.

2. This mod calls for a center diff lock button because it will allow most of the swtiching back and forth between H and L as well as the engagement of the manual hubs. The CDan 7 pin mod is a good idea too because that will allow you to control the switching mechanism between L locked and L unlocked.

3. So, for 4H, you would leave the diff in H range, get out and lock the hubs up front and then hit the center diff switch.

4. For 4L, you would drop the xfer lever into L and then hit the center diff switch and lock the front hubs, transferring power to all 4 wheels and engaging them. With the 7pin mod and a part time case, you would have control over whether you were in L with a diff locked or L with a diff unlocked because the diff locking mechanism is controlled by the switch now, as opposed to the automatic function played by the viscous coupler, which is now removed from the xfer case.

5. Basically, this mod takes the 80 back to the old school way of engaging 4WD in trucks like a 60 or a 40. Non-NA 80 series rigs got the HF1A xfer case which was a part time case with locking front hubs. We never got them from Toyota here in North America.

Any clearer for my fellow West Virginia ?

Best.
-onur

 

[lacruiser]

Hey Riad:

I would love to go to low gearing in the xfer case right now, but the cost is very prohibitive (IIRC, ~$900 for the lower gears), and IIRC, there have been some issues with the Mark's low gearing kits for the HF2AV...I recall reading about them in the Oz magazines and online forums. But I haven't heard about them in a long time.

Basically, what this process will do is the following:

1. With the front hubs not engaged and the xfer case shifter in H, you are in high range with power only going to the rear driveshaft and then to the rear axles. Basically, RWD.

2. This mod calls for a center diff lock button because it will allow most of the swtiching back and forth between H and L as well as the engagement of the manual hubs. The CDan 7 pin mod is a good idea too because that will allow you to control the switching mechanism between L locked and L unlocked.

3. So, for 4H, you would leave the diff in H range, get out and lock the hubs up front and then hit the center diff switch.

4. For 4L, you would drop the xfer lever into L and then hit the center diff switch and lock the front hubs, transferring power to all 4 wheels and engaging them. With the 7pin mod and a part time case, you would have control over whether you were in L with a diff locked or L with a diff unlocked because the diff locking mechanism is controlled by the switch now, as opposed to the automatic function played by the viscous coupler, which is now removed from the xfer case.

5. Basically, this mod takes the 80 back to the old school way of engaging 4WD in trucks like a 60 or a 40. Non-NA 80 series rigs got the HF1A xfer case which was a part time case with locking front hubs. We never got them from Toyota here in North America.

Any clearer for my fellow West Virginia ?

Best.
-onur

Do the part time HF1A cases have a differential?

 

[OGBeno]

Do the part time HF1A cases have a differential?

Well, the HF1A is a different beast than the HF2A or the HF2AV. The HF1A will have a 3 position shift lever like the 40's and 60's: a 2H, 2L, 4L.

By taking out your viscous coupler you are in effect making your transfer case into an HF2A without the V for the viscous coupler, but it is still a 2 position transfer case.

This modification will not make the HF2AV into a 3 position xfer case, but by doing the CDan 7pin mod, by getting a center diff switch you will basically make the xfer case into a 3 position case via switching as opposed to a lever.

 

[lacruiser]

Well, the HF1A is a different beast than the HF2A or the HF2AV. The HF1A will have a 3 position shift lever like the 40's and 60's: a 2H, 2L, 4L.

By taking out your viscous coupler you are in effect making your transfer case into an HF2A without the V for the viscous coupler, but it is still a 2 position transfer case.

This modification will not make the HF2AV into a 3 position xfer case, but by doing the CDan 7pin mod, by getting a center diff switch you will basically make the xfer case into a 3 position case via switching as opposed to a lever.

OK, I've got a p/t case in mine, it was originally in a JDM diesel, and I'm pretty sure it's the HF1. It has a two-position lever, just like the US market ones, and it goes from 2 to 4 wheel drive via an electric actuator, almost identical to the CDL on the US trucks. In fact, when they did the diesel conversion on this truck, the used the CDL switch and circuitry to energize this 2/4 wheel drive motor.

I really don't know if this thing has a differential in it or not. Any idea?

 

[OGBeno]

Continuing on as we go, once the rear extension housing is out the next step is to get to the center differential in the center of the xfer case.

First, you have to remove the 5 bolts that hold the "retainer" in place. These are 14mm bolts attaching the retainer to the top of the idler bearing.

Once you get the retainer off, you will see the idler bearing.

You will also see two washers--one thin and one thick. Put those aside and remember or keep track of how those are located in the idler bearing space.

You will then need to take the top case off.

Next you have a snap ring that needs to come out. I had to modify my Sears snap ring pliers even more to get to this snap ring. I needed a nice pinch point for the removal of the snap ring.

After that, you need to remove the 8 14mm bolts that hold the center of the xfer case together. These are all the same size so you will not need to keep track of orientation as we did previously. Once the 8 bolts are out, I used a brass punch and a small 450gr. hammer to pop the case center off of the front of the housing. These areas are all held together by FIPG so you will need to clean the FIPG off well before installing the parts back together again. I used a scrapper as well as a wire brush on a drill to accomplish the cleaning and then spraying everything with brake cleaner. In fact, brake cleaner is a good friend during all of this as you get in one level after one level and it was good to use the cleaner to get a clean surface to work with.

 

[OGBeno]

Now at this point you will have the intermediate case assy. as well as the front case assy with the center diff. These are some beefy gears. It's really quite enjoyable seeing the mechanisms at play here. You will also see the shift fork as well as the long pin that engages the ends of the xfer case solenoids to indicate 4H/4L--it's the long machined piece of metal at the top center. The center differential is the large gear set to the right hand side of the case. It's beefy!

You will have to next remove the 12 14mm bolts that hold the rear case to the front case. In the middle are all of the bits of the differential. These bolts are torqued pretty high--I used a pipe attachment I have to transform my ratchets into breaker bars. I used it to break each of the bolts and then each of them were pretty much taken out by hand.

After you have the 12 bolts out, I again used a brass punch and a few small taps from the hammer on the rear case, and it pretty much fell out. Here you can see the rear case, all of the bits of the differential--side gears, thrust washers, locating pin and shaft.

These parts will not be used going forward. I did leave the rear side gear and thrust gear because those will be welded to the rear case assy.

And you can see the front case here with the front side gear and thrust washer in place. I did not remove these nor is there a reason to do so. These need to stay in place to support the front output shaft out of the front extension housing.

The next steps of the process will be heating up the rear case assy and then doing some fun TIG welding. IBCRUSN will be taking care of that portion of this process. Once the parts get back to me, then we will put everything back together and start on the front birfs and front hub rebuilds to get them ready for installation.

Stay tuned!

 

[slow91fj90]

Cant wait for the rest of this. Great write up.