My new 1990 HDJ81 (2 Viewers)

[TuffMudder]

Just stumbled upon the Pin 15 mod in an older post by @LandCruiserPhil and couldn't be happier.

It always seemed weird to me that this isnt more widely discussed. Being able to engage front and rear diffs in high (Pin 7 mod) and without the center locked (Pin 15 mod) always felt like the most usable configuration, especially when you can quickly and easily engage the CDL when you need it.

Anyway, this just moved way up on my priority list!

 

[IanB]

Just stumbled upon the Pin 15 mod in an older post by @LandCruiserPhil and couldn't be happier.

It always seemed weird to me that this isnt more widely discussed. Being able to engage front and rear diffs in high (Pin 7 mod) and without the center locked (Pin 15 mod) always felt like the most usable configuration, especially when you can quickly and easily engage the CDL when you need it.

Anyway, this just moved way up on my priority list!

I'd never seen that one before. I've done the pin 7 mod and see the utility with it, but when/why would you ever want the front and rear diffs locked without being in 4x4 (CDL locked)? It's just going to make it harder to turn...what am I missing?

 

[TuffMudder]

I'd never seen that one before. I've done the pin 7 mod and see the utility with it, but when/why would you ever want the front and rear diffs locked without being in 4x4 (CDL locked)? It's just going to make it harder to turn...what am I missing?

It may be a lack of understanding of 4wd on my part or i may be misunderstanding you, but I thought that the a locked center diff would make for more difficult turning.

My understanding of 4wd is that you would still be in 4wd without the cdl, you just wouldn't have the front and rear axles locked together. So left front is locked to right front, left rear is locked to right rear, but front and rear axles could still work independently of each other. Front and rear diffs locked without the CDL gives you added traction from AWD, but not the added binding of using the cdl. CDL gives you more traction still, but can cause additional binding and limit turn radius.

There are a lot of places i can run on high but need some extra traction, without the need to be fully locked or the additional binding that can go along with it. Usually, if i do need the best possible, I will drop into low and lock the center diff.

Ok, i've bared my ignorance to you. Please let me know if i have some aspect of this wrong.

 

[IanB]

These trucks are full time AWD, Toyota calls that 4WD in their badging and marketing, but it's not the same as 4x4. 4x4 means a 50/50 split front and rear, which requires the center diff be locked.

By adding a CDL button (comes standard on HDJ81), you can lock the center diff without needing to shift to low range. With the CDL locked you can then lock the rear, and front diffs as well, as set up from factory. In North America, only the FJ80 came equipped with a CDL button, but F&R diff locks were not available. FZJ80 got F&R lockers as an option, but no CDL came standard, meaning lockers only worked in low range as that was the only way to lock the CDL, as set up from factory.

The pin 7 mod allows you to run in low range without the CDL locked, which some like for tight maneuvering, boat ramps, etc. Having the CDL locked does impede cornering as the center diff will bind and tires will hop.

Having the front diff locked makes turning even harder, as the front tires are unable to rotate at different speeds as you turn, resulting in pushing (understeer). Being able to have the front diff locked with the CDL unlocked will fix one issue, but the other will remain.

The net effect of having locked axles and an open center diff will be that should you lose traction on either axle, the other will receive no power. Easiest example would be in winter/icy conditions, say you are trying to climb over a curb or rock and either axle spins both tires, the other axle will receive no power as it's all routed through the center diff to the path of least resistance, the spinning axle.

Newer trucks (most '93+, but not mine) have a viscous coupling that acts as a LSD in the center diff, which muddies the waters a bit, but same principles apply. In the above example of icy conditions the viscous coupling will direct some power to the axle with traction, but not the same as having the CDL locked.

Bottom line, I can't imagine a scenario where I would want locked axles but an open center diff.

 

[TuffMudder]

Ok, now.im confused. I thought the following was correct
2wd if one wheel loses traction, no traction
Awd/full time 4wd One wheel loses traction, you wheel loses traction you lose traction on that axle but not the other axle
Rear lockers if you lose one wheel on the front axle you lose traction there but you have to lose both in the rear wheels to lose traction to the rear wheels
Front and rear lockers can create binding and limit turn radius(which is why if you only lock one axle, it should always be the rear) but now you have to lose traction to both wheels. As long as you have traction. To one tire on one axle you have full traction on that axle only.
With a triple locked vehicle, as long as you have traction to one wheel, you should have traction (probably should have been saying power?) to all 4 wheels, but you worsen the issue first created by the front differential

Now all of this is changed somewhat by Toyota requiring low and locked center to engage the axles, but I thought that was an old Toyota design decision, but not a requirement for 4wd. For instance in my 2015 sequoia, I can lock rear or both diffs in high and the cdl is independent.

At this point I'm sure this is just a matter of my lack of understanding and I'm just trying to figure out where I went wrong. Sorry to belabor the point but it seems like something I should fully understand

 

[Douglas S]

You just have to think of it like 3 separate differentials (because that's exactly what it is) that all behave the exact same way depending on their locked or unlocked state. Ian's description is correct.

 

[mudgudgeon]

I agree with Ian's description above.

the Pin 15 mod is cool, but in reality, I see it having very little practical use.

I'd be interested to know if @LandCruiserPhil has seen a practical advantage over time?


Toyota's system is designed to limit the lockers to only being able to be locked in low range, and in some models at speeds below 5mph. This is to prevent possible shock loading of the diffs and locking mechanisms at high rotational speeds.

a few possible scenarios
CDL unlocked, one front wheel on ice. That wheel will spin, no drive to any other wheels.
CDL locked, one front wheel on ice, that wheel will spin, you will get drive to the rear axle
CDL locked, one front wheel, one rear wheel on ice, both wheels on ice will spin, no forward drive to wheels with traction
CDL locked, rear diff locked, one front wheel on ice, one rear wheel on ice. Front wheel will spin on ice, no drive to the other front wheel, rear wheel on ice will spin, but rear wheel with traction provides some drive
CDL locked, rear diff locked, one front wheel on ice, both rear wheels on ice. Front wheel on ice will spin, no drive to the front wheel with traction, rear wheels spin on ice, no forward drive
CDL locked, rear diff locked, front diff locked, one front wheel on ice, both rear wheels on ice. Rear wheels on ice will spin, front wheel on ice will spin, front wheel with traction provides some drive.
CDL locked, rear diff locked, front diff locked, both front wheel on ice, both rear wheel on ice. now you're fwucked, or time for the winch

 

[LandCruiserPhil]

I agree with Ian's description above.

the Pin 15 mod is cool, but in reality, I see it having very little practical use.

I'd be interested to know if @LandCruiserPhil has seen a practical advantage over time?


Toyota's system is designed to limit the lockers to only being able to be locked in low range, and in some models at speeds below 5mph. This is to prevent possible shock loading of the diffs and locking mechanisms at high rotational speeds.

a few possible scenarios
CDL unlocked, one front wheel on ice. That wheel will spin, no drive to any other wheels.
CDL locked, one front wheel on ice, that wheel will spin, you will get drive to the rear axle
CDL locked, one front wheel, one rear wheel on ice, both wheels on ice will spin, no forward drive to wheels with traction
CDL locked, rear diff locked, one front wheel on ice, one rear wheel on ice. Front wheel will spin on ice, no drive to the other front wheel, rear wheel on ice will spin, but rear wheel with traction provides some drive
CDL locked, rear diff locked, one front wheel on ice, both rear wheels on ice. Front wheel on ice will spin, no drive to the front wheel with traction, rear wheels spin on ice, no forward drive
CDL locked, rear diff locked, front diff locked, one front wheel on ice, both rear wheels on ice. Rear wheels on ice will spin, front wheel on ice will spin, front wheel with traction provides some drive.
CDL locked, rear diff locked, front diff locked, both front wheel on ice, both rear wheel on ice. now you're fwucked, or time for the winch

‘
Being part time I use it a lot for rear locker in 2wd. The next mod will being to use front locker without having the rear engaged first. Although I have not had the need much that is why it’s still on the to list.

 

[TuffMudder]

Deleted because asked elsewhere

 

[mudgudgeon]

‘
Being part time I use it a lot for rear locker in 2wd. The next mod will being to use front locker without having the rear engaged first. Although I have not had the need much that is why it’s still on the to list.

ah, fair enough, part time is a different scenario.

FWIW, in my 105, I have lockers set up so FR and RR can be switched independently, and have used FR only a handful of times.

 

[LandCruiserPhil]

ah, fair enough, part time is a different scenario.

FWIW, in my 105, I have lockers set up so FR and RR can be switched independently, and have used FR only a handful of times.

Are they factory lockers on your 105? If so i would be very interested in how you did it. On the US 80 series its not a easy thing or at least I have not be able to figure out an easy way.....yet!

 

[TuffMudder]

@Douglas S I think that's what's getting me in trouble here. I think of it as 3 separate diffs and want it to operate as 3 separate diffs instead of the stock setup where front and rears are slaved to the cdl

@mudgudgeon in your scenarios if you had cdl unlocked but front and rears locked, wouldnt that give you an advantage over just the CDL locked. In this scenario I though that with the front wheel on ice, you still get traction to other front wheel and both wheels on the rear axle, one front and one rear wheel on ice you still get drive to one wheel on each axle and you only lose forward drive by losing traction to both wheels on a single axle. This with the advantage of less wear on the drivetrain and less binding in turns? Modding pins 7 and 15 would give you the ability to run this setup in high or low and easily add the the center diff when needed.

I now understand what you are all saying about 4wd and agree. The part i don't understand is why fr-rr without cdl wouldn't be desirable. I drive on my land a lot. the trails are muddy with potholes and some rocks, but nothing technical and i can drive it in high as long as i can keep traction. I do however sometimes lose traction and it seems like rear or front and rear locked would be better than the default start point of only cdl locked without the added binding of the cdl or cdl plus front locked.

Does fr-rr without cdl somehow provide less traction than cdl only?

 

[IanB]

Awd/full time 4wd One wheel loses traction, you wheel loses traction you lose traction on that axle but not the other axle

This is the disconnect. AWD/4WD means all 3 diffs are open, power is sent to all 4 wheels, but if any one wheel loses traction all the power is routed to that wheel, it's like 2WD but for any of the tires, lol.

4X4 is when you lock the center diff, and send the power 50/50 to the front and rear axles. Now if you spin a front wheel you'll still have traction at the rear, but if you also lose traction at one of the rear wheels you're stuck.

This is why I don't understand wanting to have the truck in AWD with the front and rear axles locked...makes more sense to start with putting it in 4X4 to me, and leaving the axle lockers for if you need them.

 

[mudgudgeon]

any open diff will send drive through the path of least resistance. so with a front diff, or rear diff, if one wheel is on a slick surface, the other on good traction, the one on a slick surface will spin first.
Same with the centre diff. If one drive shaft has less resistance, it will spin, the other may not. With an open centre diff, if on wheel on an unlocked axle is on a slick surface, then that one wheel can get 100% of the driving force which equals NO forward drive.

If you lock FR and RR and leave CDL open, you can easily have a scenario with low traction on the front (ie climbing a ledge with the front already up the ledge) and high traction at the rear. in this scenario, front wheels will both spin, and get all the drive, with no drive to the rear.

for best traction with a triple locked truck, the usual sequence is lock CDL, lock rear, lock front. Occasionaly its and advantage to lock the front, and leave the rear open.
Generally, locking the CDL will give you a HUGE increase in offroad capability. With CDL locked, drive is always split 50/50 FR/RR. With CDL locked in high range, by the time you get into conditions where you need more traction, you're going to want to slow down and go to low range

 

[TuffMudder]

If you lock FR and RR and leave CDL open, you can easily have a scenario with low traction on the front (ie climbing a ledge with the front already up the ledge) and high traction at the rear. in this scenario, front wheels will both spin, and get all the drive, with no drive to the rear.

for best traction with a triple locked truck, the usual sequence is lock CDL, lock rear, lock front. Occasionaly its and advantage to lock the front, and leave the rear open.

Thank you both for sticking with me despite me being so dense on this topic. It now makes sense to me as to why I would want to start with cdl and the potential disadvantages of fr-rr without cdl. I think will put pin 15 on the back burner for the time being

Thank you!

 

[mudgudgeon]

all good. The three diffs puzzle plenty of people, me included

 

[TuffMudder]

These came in today. 12v starter hopefully arrives next week from down under, then maybe i can get time next weekend to do the conversion.

 

[Crab Sack]

I was thinking of your high egt issue and I wonder if something got jostled around in the injector pump when you went deep diving with it. The 81 always ran a bit on the rich side. You can always adjust the main fueling screw to lean it out and lower the egts. It may effect performance but worth a try. Just be sure to take a picture of it before you start for reference and then make adjustments a little at a time 1/4 turn at a time until you dial them in. I never messed with the adjustment on the injector pump but the injection shop, DFIS, may have adjusted it. There is plenty of info on how to adjust the IP in the tuning thread.

 

[TuffMudder]

Great advise. I'll take a look. Of course I have to wait until i get it back. Dropped it off Wednesday to have my $45 snorkel installed (i'll admit it, i was too much of a coward to drill the fender), and have a new air box made. They also installed the intercooler and reinstalled the transmission cooler, but they needed to order some boots, so i'll take it back in a couple of weeks to finish the intercooler. I stopped by today and taking the fender off caused a bit of a delay, so they expect it to be finished monday or tuesday. I'll see how its and wait until the intercooler is finished and then adjust the pump. I've really been loving your Land cruiser, so thanks @Crab Sack

 

[mudgudgeon]

Do you lots of reading before messing with the IP so you understand the potential impact of your tinkering.

Taking it swimming shouldn't have any effect on the IP. Keep the intake dry, and these things can be fully submerged