Help me decide on Transfer Case

[SteelHunterFJ80]

As the title states I am looking at transfer case options. I currently have the 1HFA freshly rebuilt and works great, shift on the fly and fully mechanical. I also have a HF2A which reportedly came from Spain along with my H151 transmission but I am unsure if it has synchros to allow 4H on the fly. Furthermore, I will need to do the 10% over and underdrive gears. I have a 1HDFT and need to drop the revs by about 10% to hit the sweet spot with the powerband and fuel usage. I would love a 15% reduction but can find anything available in that range.

So here is what I am seeking all the gurus input on. What is the best TC for all around adaptability with a truck that sees 60% street, 25% overland/desert/logging roads type driving, and 15% of wheeling and rarely anything more than level 5 moderate difficulty trails?

My options as I see them with pros and cons:

Keep H1FA:

Pros- Already in the truck and set up to work as factory. Rock solid dependability with no actuators to go out. Shift on the fly that’s super smooth. 4H 2H N 4L shift pattern.

Cons- Pin 7 mod does no longer applicable and can take a bit of movement in the truck to get disengaged from 4H increasing chance of binding in tight turns.

Locking Hubs not currently installed but in 2H does it even matter? Sure there is some wear and tear on the knuckles but its so long term does it even matter? The front drive shaft isn’t turning so no parasitic power loss there.


Put in my H2FA:

Pros- Currently sitting in my garage and would be a nice project to rebuild with 10% reduction gears. Get to use the CDL button which is easier to reach for while driving, especially with my manual gear shifter in the way. Can now use Pin 7 mod around tight corners and I imagine it has a faster engagement than manual lever. Sell H1FA which has less than 8,000 miles on it after rebuild by mud member rick_d.


Third out of the box idea, put in H2FAV:

Pros- regain AWD and VC. In the PNW this is an asset although truth be told I haven’t seen the truck not handle well in the snow in 2H provided I don’t drive like an idiot. PIN 7 mod option works.

Cons- The truck definitely handles better in real wheel drive. Much sharper, better control turns easier and coasts smoother.

Out of the box idea- Install locking hubs but no part time spool. Hubs unlocked so front drive shaft turns but without wheel/hub engagement there isn’t power to the wheels, CDL gets locked to achieve 50 50 RWD. Want AWD again, just lock hubs. My question would be how does the VC act in this case? And with unlocked wheels am I losing a fair amount of power by sending it to the front....but if there isn’t any friction with the hubs disengaged is it minimal? And would the truck still handle like its in 2H?

 

[ppc]

Take the VC off your decision tree. It's basically a liability, they're old, prone to failure and expensive to replace with very little upside. Going part time, only adding locking hubs and not addressing the the center spool is a mistake especially it this is a daily driver.

 

[SteelHunterFJ80]

Take the VC off your decision tree. It's basically a liability, they're old, prone to failure and expensive to replace with very little upside. Going part time, only adding locking hubs and not addressing the the center spool is a mistake especially it this is a daily driver.

Assume for a second that we are talking a new H2FAV unit and the VC is brand new.

Can you expand on why not having the center spool is a mistake? I would think that without the spool the CDL acts the same as before and when not locked your in Awd with hubs engaged. Is it a way to have the best of all worlds?

 

[ppc]

Others may respond but the added value of the VC is very minimal, but most guys will completely remove the VC when it fails without ill effects.
Yes, with no spool nothing changes from stock once the hubs are locked. There will be nothing gained in fuel economy because the front axles/driveshaft still spins in 2wd, ABS will not work without costly addons

 

[SteelHunterFJ80]

The ABS relocation kit is $500 and easy to install while installing part time hubs so iI'm not really cocerned about that.

Perhaps a better follow up question for the forum is if you have a H2FA or H2FAV (without the part time spool) and you have unlocked hubs up front and the CDL isn't locked are you in 2wd? And if the hubs are locked you'd be in AWD because nothing changed with the stock configuration.

My confusion on this point centers around if the front drive shaft is spinning, and if so, is power being deliver through it even though it's unlocked (certainly not the wheels but what about hubs in). I read in several articles that the power takes the easiest path.

Perhaps the experts can chine in. Thanks in advance

@DivByZero @OGBeno @mudgudgeon
@orangefj45
@cruiseroutfit
@Tapage

 

[DivByZero]

Perhaps a better follow up question for the forum is if you have a H2FA or H2FAV (without the part time spool) and you have unlocked hubs up front and the CDL isn't locked are you in 2wd? And if the hubs are locked you'd be in AWD because nothing changed with the stock configuration.

If you have the H2FA, unlocked front hubs, and CDL unlocked, if you put your foot down you go nowhere. With the CDL unlocked and the front axle disconnected from the hubs, all power goes to the front axle, which spins in place since there's no engagement on the hubs. It's the equivalent of not having lockers and having both wheels on one side of the car spinning, but in this case you've replicated it between the front/back wheels.

If you have the H2FAV, unlocked front hubs, and CDL unlocked, if you put your foot down, you move forward, and probably at quite a reasonable rate. You might even not realize you've left the front hubs unlocked at all. This is because the VC is acting as a limited slip diff, so while the front axle is spinning furiously, the rear axle also turns because some energy is transferred to the rear prop shaft via the viscous fluid in the coupler. This is actually a major problem. At this point, your front axle/prop shaft are spinning at much higher speed than intended, causing high wear and potential early failure. Before that goes though, what will happen is you'll cook your VC. You see, all the energy driving your rear axle is now being transmitted not by gears, but by friction in the viscous fluid in your coupler. That leads to extreme heat, which will melt the plates in your coupler and fuse it together. For that reason, unlockable hubs combined with a VC is a recipe for failure due to operator error.

I have the the HF1A and love it, and IMO it's the best TC for offroad use and overall reliability, due to the lack of electronics. For on-road use in wet/slippery conditions however, the AWD setup you get with the HF2A is safer. I've had two nasty on road incidents involving wet weather that would not have occurred with a HF2A transfer, in both cases due to slick road conditions around turns in the wet, one involving some kind of oil film. You've got to work out the tradeoffs here for yourself.

In my opinion, the ultimate option would be a HF2A transfer with CDL operated using the factory transfer lever. It's very viable, and that's my eventual plan here:

Thread 'New Mod - Locking centre diff using transfer shift lever (no electronics!)'

Feb 11, 2025

You're probably aware that the electronic centre diff lock in the 80 series is a bit of a weak point. At 30-35 years after manufacture, most vehicles still running have probably required work on the CDL system by now, or will shortly. This affects the full-time 4WD HF2A and HF2AV transfer cases, as well as the part-time HF1A transfer case where the electronic 4WD shift system is used. My 80 series is an HZJ80R, with the fully mechanical HF1A transfer case, so there's no electronics involved with the transfer case operation. This is how I like it. When I want to shift between 2WD and 4WD, I...

• DivByZero
• Replies: 44
• Forum: 80-Series Tech

• 

In this config, you could get pure RWD by locking the CDL and unlocking your front hubs. This would restore the default HF1A drive feel, with the only change being that the front axle is always spinning - not a huge downside IMO. If you lock your front hubs with CDL disabled, you get AWD. If you enable H4/L4, you're identical to the HF1A in H4/L4. The lack of electronics with a lever shift though makes it as rugged and reliable as the stock HF1A. That's what I'll be doing eventually.

 

[DivByZero]

Oh, and in terms of synchros in the HF2A, if it was originally fitted behind an auto transmission, it won't have one, while if it was fitted behind a manual transmission, it will. The HF1A all had them because they were all on manuals. If it's missing though, don't worry, it's easy to add during a box refurb. It's literally just a matter of installing the synchro. The mechanism is the same, it's just a question of if the synchro, which also acts as a blocker ring, is fitted or not. If you're planning to rebuild the box, it's simple to install as part of that.

 

[SteelHunterFJ80]

In my opinion, the ultimate option would be a HF2A transfer with CDL operated using the factory transfer lever. It's very viable, and that's my eventual plan here:

Thread 'New Mod - Locking centre diff using transfer shift lever (no electronics!)'

Feb 11, 2025

You're probably aware that the electronic centre diff lock in the 80 series is a bit of a weak point. At 30-35 years after manufacture, most vehicles still running have probably required work on the CDL system by now, or will shortly. This affects the full-time 4WD HF2A and HF2AV transfer cases, as well as the part-time HF1A transfer case where the electronic 4WD shift system is used. My 80 series is an HZJ80R, with the fully mechanical HF1A transfer case, so there's no electronics involved with the transfer case operation. This is how I like it. When I want to shift between 2WD and 4WD, I...

• DivByZero
• Replies: 44
• Forum: 80-Series Tech

• 

In this config, you could get pure RWD by locking the CDL and unlocking your front hubs. This would restore the default HF1A drive feel, with the only change being that the front axle is always spinning - not a huge downside IMO. If you lock your front hubs with CDL disabled, you get AWD. If you enable H4/L4, you're identical to the HF1A in H4/L4. The lack of electronics with a lever shift though makes it as rugged and reliable as the stock HF1A. That's what I'll be doing eventually

Thanks for the detailed response! I had read your mechanical conversion thread before posting as I thought there must be some way to retain AWD. Now if I drive with my CDL locked I am assuming I would lose ABS yes? And how fast is acceptable to drive with the CDL locked? I've read that it doesn't matter and many have driven for quite awhile when having a broken cv and removing the front drive shaft. I admit the allure of AWD is tempting but I know that its difficult to have something do everything.

Oh, and in terms of synchros in the HF2A, if it was originally fitted behind an auto transmission, it won't have one, while if it was fitted behind a manual transmission, it will. The HF1A all had them because they were all on manuals. If it's missing though, don't worry, it's easy to add during a box refurb. It's literally just a matter of installing the synchro. The mechanism is the same, it's just a question of if the synchro, which also acts as a blocker ring, is fitted or not. If you're planning to rebuild the box, it's simple to install as part of that.

Well that answers it and I am glad to know. My H2FA sitting in the garage came from behind an H151 transmission so I can check that off the list.

In someways I am tempted to just stick with the H1FA, the main reason I even thought of changing the TC was I need to do an under/overdrive gear change to drop my highway revs.

 

[DivByZero]

Now if I drive with my CDL locked I am assuming I would lose ABS yes?

I have to admit some ignorance on how the ABS system operates in an 80 series, as mine never had it, and I've never cared to look into how it's implemented on the 80. Theoretically, I don't believe ABS should be fundamentally incompatible with a locked CDL - it's just trying to detect wheel lockup and relieve hydraulic braking pressure on the locked wheel(s), and CDL shouldn't affect that process, but I can understand the stock electronics assuming a locked CDL = offroad driving, and assume that therefore ABS should be disabled. I assume if this feature exists (which it seems to), that it's controlled by the sensor on the transfer case that detects the locking arm position and illuminates the 4WD/CDL light on the dash. If this is the case, you could control this behaviour by installing a switch. IE, if running with a H2FA with my theoretical lever-controlled CDL, you could repurpose the CDL switch to effectively become an ABS on/off switch by making it signal to the ABS whether it thought the CDL was engaged or not, independent of whether it actually was. Since I'm largely ignorant about the realities of ABS on the 80 series though, take all this with a grain of salt. It'd be best for someone with a better understanding of the ABS system to chime in before you assume anything I've said is accurate.

And how fast is acceptable to drive with the CDL locked? I've read that it doesn't matter and many have driven for quite awhile when having a broken cv and removing the front drive shaft. I admit the allure of AWD is tempting but I know that its difficult to have something do everything.

You can drive forever with the CDL either locked or unlocked. There's no wear or issue either way. Locking the CDL just engages a sleeve that fixes the two outputs of the differential together. The mechanism is strong and stable in either state. People do recommend locking and unlocking the HF2A CDL periodically, but that's only because of worries about the electronic actuator failing/sticking. If that was removed from the equation, there'd be no need. The engagement mechanism is literally identical to the H2/H4 selection in the H1FA.

Oh, and I should note for completeness, there are in fact versions of the HF1A that used a motor actuator for H2/H4 selection, with a H4 button on the dash where the CDL button goes to enable it, rather than the lever shift. This came out in some overseas markets, but not Australia. It's a rare and odd combination with no advantages, it just brings the same weakness to the HF1A that you have on the HF2A in terms of actuator failure. I doubt your HF1A box is one of these, but I figured I'd note it here for completeness.