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 move the transfer shifter. This means the shifter has four positions, not three like the motor driven versions:
So last year when I worked out some H150F gearbox upgrades, I had a second project planned, which I've just started looking at now. What if we could adapt HF2A and HF2AV transfer cases to also have four positions, and use the transfer shift lever to lock the centre differential? This would allow us to discard the electronic lock motor, the 4WD ECU, and the CDL button. In its place, we just shift the transfer lever. We'd still have the CDL light on the cluster, directly driven by the sensor on the transfer case as before.
Why am I interested in this? I've driven a part-time 80 series for a long time now. The main thing I like about the HF1A is the fact that it's fully mechanical. This is why I wanted it, and this is what I still want. But the HF2A, and especially the HF2AV, are a superior transfer. Having a selectively lockable centre differential is better than just being able to switch between RWD and locked 50:50 ratio 4WD. My 80 is my DD, so I do a lot of on-road driving as well as off-road. I've taken to running most of the time with my front hubs locked, so I can switch to 4WD when taking off at the lights in the wet, or tackling slippery, dicey roads. If I had a centre diff, off-road it would be locked, but on the road, it would help a lot with traction issues, and the HF2AV moreso with its viscous coupler, giving an LSD effect. The only thing I would "lose" is the ability to not have the front driveshaft spin, but I'm not worried about that, as I usually have my hubs locked these days anyway as I said, in which case it's spinning anyway, and if I really want to get RWD only, which is fun sometimes on the loose stuff, I can still do it by locking the centre diff and disengaging my front hubs.
Now you may think getting the transfer shift lever to lock the centre differential would be a very hard mod to achieve, but I don't actually think it is. In fact, I think it's literally just swapping a handful of parts. Unlike in the US, I have relatively easy access to HF1A transfers. I also have the "New Car Features" manuals which describes the internal operation of the HF1A, HF2A, and HF2AV transfers. This manual is very useful and really should be scanned, but here's a couple of pages out of the 50 or so related to the transfer:
What's important to note is that the mechanical operation of the centre diff lock in the HF2A/HF2AV is identical to the H2/H4 selection feature on the HF1A. Both employ a shifting fork and sleeve to lock a hub in the front extension housing. The only real difference is that there's a different shaft connecting to the shift fork, and an adapter plate that connects it to the shift lever rather than being gear driven by the motor. Since the HF1A had two variants of H2/H4 selection, one motor driven and one lever driven, it follows that the assemblies are fairly interchangeable, and the lever-driven mechanism should also be able to drive the centre diff lock on the HF2A/HF2AV, with the appropriate parts changes. The manual excerpts themselves alude to that above. What I couldn't tell for sure from the parts catalog or the manual alone though, was whether there were clearance issues with the different shaft and the alternate shifting fork used for the high/low selection on the H2FA/HF2AV version.
Today I dragged a spare HF1A (from a 105 series) and a HF2A onto the workbench (which I had just lying around because I'm a parts hoarder), cracked them open and took a look:
HF1A on the left, HF2A on the right. From what I can determine, the parts should just drop right in. There's definitely no clearance issues with the alternate shifting mechanism inside the main case, and I know there's no issue in the front housing extension, since it's the same part number used across all variants of the transfer. What this means is, I'm pretty sure you can order a handful of parts from Toyota, which I believe are all still available, and convert a HF2A/HF2AV to use the transfer shifter to lock the centre diff. You could then optionally change the housing over to the HF1A version without the holes drilled for the centre diff lock motor, or fabricate a cover plate to block it off. You could change the shift lever retainer over to get the "lift for N/L4" feature of the part time transfer, or leave it as-is to have a straight shift between Unlocked H4, Locked H4, N, L4. You could swap the shift knob over too or leave it. In terms of the important parts changes though, it's really just the shaft, the joining plate, then a couple of springs, clips, etc. Almost nothing.
I'm probably going to attempt to move the parts over and bench test this soon. I probably won't be putting it into the vehicle, as I'm waiting on getting a HF2AV version before I do that switch, but it's easy to test on a workbench and verify the change works. I'll report back when I find the time to do that. In the meantime, anyone else interested in this mod idea?
So last year when I worked out some H150F gearbox upgrades, I had a second project planned, which I've just started looking at now. What if we could adapt HF2A and HF2AV transfer cases to also have four positions, and use the transfer shift lever to lock the centre differential? This would allow us to discard the electronic lock motor, the 4WD ECU, and the CDL button. In its place, we just shift the transfer lever. We'd still have the CDL light on the cluster, directly driven by the sensor on the transfer case as before.
Why am I interested in this? I've driven a part-time 80 series for a long time now. The main thing I like about the HF1A is the fact that it's fully mechanical. This is why I wanted it, and this is what I still want. But the HF2A, and especially the HF2AV, are a superior transfer. Having a selectively lockable centre differential is better than just being able to switch between RWD and locked 50:50 ratio 4WD. My 80 is my DD, so I do a lot of on-road driving as well as off-road. I've taken to running most of the time with my front hubs locked, so I can switch to 4WD when taking off at the lights in the wet, or tackling slippery, dicey roads. If I had a centre diff, off-road it would be locked, but on the road, it would help a lot with traction issues, and the HF2AV moreso with its viscous coupler, giving an LSD effect. The only thing I would "lose" is the ability to not have the front driveshaft spin, but I'm not worried about that, as I usually have my hubs locked these days anyway as I said, in which case it's spinning anyway, and if I really want to get RWD only, which is fun sometimes on the loose stuff, I can still do it by locking the centre diff and disengaging my front hubs.
Now you may think getting the transfer shift lever to lock the centre differential would be a very hard mod to achieve, but I don't actually think it is. In fact, I think it's literally just swapping a handful of parts. Unlike in the US, I have relatively easy access to HF1A transfers. I also have the "New Car Features" manuals which describes the internal operation of the HF1A, HF2A, and HF2AV transfers. This manual is very useful and really should be scanned, but here's a couple of pages out of the 50 or so related to the transfer:
What's important to note is that the mechanical operation of the centre diff lock in the HF2A/HF2AV is identical to the H2/H4 selection feature on the HF1A. Both employ a shifting fork and sleeve to lock a hub in the front extension housing. The only real difference is that there's a different shaft connecting to the shift fork, and an adapter plate that connects it to the shift lever rather than being gear driven by the motor. Since the HF1A had two variants of H2/H4 selection, one motor driven and one lever driven, it follows that the assemblies are fairly interchangeable, and the lever-driven mechanism should also be able to drive the centre diff lock on the HF2A/HF2AV, with the appropriate parts changes. The manual excerpts themselves alude to that above. What I couldn't tell for sure from the parts catalog or the manual alone though, was whether there were clearance issues with the different shaft and the alternate shifting fork used for the high/low selection on the H2FA/HF2AV version.
Today I dragged a spare HF1A (from a 105 series) and a HF2A onto the workbench (which I had just lying around because I'm a parts hoarder), cracked them open and took a look:
HF1A on the left, HF2A on the right. From what I can determine, the parts should just drop right in. There's definitely no clearance issues with the alternate shifting mechanism inside the main case, and I know there's no issue in the front housing extension, since it's the same part number used across all variants of the transfer. What this means is, I'm pretty sure you can order a handful of parts from Toyota, which I believe are all still available, and convert a HF2A/HF2AV to use the transfer shifter to lock the centre diff. You could then optionally change the housing over to the HF1A version without the holes drilled for the centre diff lock motor, or fabricate a cover plate to block it off. You could change the shift lever retainer over to get the "lift for N/L4" feature of the part time transfer, or leave it as-is to have a straight shift between Unlocked H4, Locked H4, N, L4. You could swap the shift knob over too or leave it. In terms of the important parts changes though, it's really just the shaft, the joining plate, then a couple of springs, clips, etc. Almost nothing.
I'm probably going to attempt to move the parts over and bench test this soon. I probably won't be putting it into the vehicle, as I'm waiting on getting a HF2AV version before I do that switch, but it's easy to test on a workbench and verify the change works. I'll report back when I find the time to do that. In the meantime, anyone else interested in this mod idea?
