4WH Theory & What Will Break 1st

[Mike789]

Hello (again)
I have a thread going re my 98 EB Exp as I will eventually add the Brown Wire Fix as others have too it seems. But...this is a theoretical question re the transfer case, 4WH, and so on...
I have read the 98 has a live axle, which afaik means that the F wheels turn the cv axles which turns the F differential (what I call it) which turns the axle which goes into the transfer case. Is that right ? I know a fair amount abt mechanics as mydad used to be a mechanic on a Super Modified way back, but I have not been under my Explorer to see exactly how things are working, or not.
So, afaik, the axle goes into the trasnfer case and then a clutch is used to basically connect the R wheels to the F wheels. This clutch can slip afaik, which may actuate the sensors, which may switch the 4wh to/from 2wh. I am not sure how the F wheels can slip independent from each other, as do the R wheels using any normal 'limited slip' (which I call limited traction) R differential (also called a read-end). My 95 4Runner has more of a 'locked' drive train than the Explorer does afaik. it seems when going around a slow sharp corner on gravel with the 4runner forces the outside wheel to turn less than it wants to, and the inside to turn more than it wants to. afaik, the explorer doesn't work like this, but the inside & outside wheel can slip independent from each other, aka, limited slip.
So, I am trying to understand my Explorer and how it works, and what might break 1st...

So, if my 98 is working perfect as Ford designed it, if I switch to 4WH, and drive it in a straight line 100,000mi, will something break ? IMHO, nothing should break as nothing is slipping. It might use more gas, or might not as the 98 has a live axle, but, will anything break if I drive it 100,000mi in a straight line, in 4WH ? Seems to me the only diff is that the TC clutch is locked. But, does it matter all that much since there is little to no slippage ? This assumes all the tires are the same size of course.

Another related question might be, what years of Explorer work 'better' than others related to 2/4WD ? This might mean, which years are more manual and less prone to stop working I suppose. or, are there any Explorers that have a 'solid' differential, ie, no slip from L/R wheel ? Are there any Explorers that when set to 4WD, are 'solidly' locked F to R and L to R ? I suppose one can say that AWD is the pinnacle of 4WD for those who don't care if they really have 4WD or not.

 

[410Fortune]

wow
yes the front axle is a "live axle" there are no hubs to unlock the wheels from the axle shaft
So both front tires turn the axle shafts which turn the diff which turn the front driveshaft AT ALL TIMES
(the 95-96 v6 trucks had a CAD, center axle disconnect that would "break" the pass side front axle shaft thus stopping the diff from spinning the front driveshaft, but that was only on the 95-96 v6 explorers)
The front differential is open on these trucks using spider gears, this allows one tire to travel further then the other without binding the 4wd drivetrain.

Now your 98 must be a v6 and must be control trac AWD, so your dash switch says 4auto, 4hi and 4 low.... this means that your t case has a clutch in it, that is true. It says "auto4" and that is exactly what it does, when there is a certain amount of slip detected by the speed sensors it will lock in 4wd giving you a sort of AWD system. Some of us really dislike the control trac AWD and choose to delete it from our built explorer rigs. There are non control trac t cases that can bolt into your 98 to do away with that clutch. And there are 4x4 control modules that can be wired in to still control the now non control trac t case so the truck is happy even without the control trac system in place.

The rear axle on these trucks are either open diff like the front, or limited slip, which forces both tires to spin the same, to a point, where it will then SLIP and act like an open diff.

To answer your question, yes there are some explorers that are control trac AWD like yours, and some that are full time AWD (the 5.0 96-01 trucks) and then there are some that are true 2wd, 4hi and 4 low (5 speed explorers, explorer sports and sport tracs= no control trac awd) Just like the Ranger trucks that never had control trac awd, these trucks use a real transfer case without a clutch, simply giving you all power to the rear axle or a 50/50 split, this transfer case is called the BW1354 it comes in electronic shift or manual shift

If you drive any 4 wheel drive SUV in 4 high and in a straight line, no binding will occur because all 4 tires are spinning equally.
If you start turning left and right while in 4 high on solid ground, yes binding will begin to occur and the tires will start to skip.... eventually causing damage to the 4wd system

Your 95 4 runner uses a traditional style t case, 2wd, 4hi or 4 low. Does your 95 4 runner also have a rear locker? or limited slip?
Comparing the two you need to know apples to apples
The explorer rear axle limited slip is a good unit, but it does use clutches and the clutches wear out in time.... so some explorer limited slip rear axles will work better than others, depending on how worn the clutches in the limited slip are

I hope that helps

 

[CDW6212R]

The rear LS diff's will be worn out at this age, they all need the clutches replaced. Under light use those clutches can last for many many years. But when some tires are slipping like for snow and gravel, the clutches wear faster. So they may go for ages, or just a few months if you are in very odd conditions. If they don't last that long for you, it's time to move up to a better diff.

The front diff, they are all open, the only choices there are a locking kit that drops in and is not good for road use, or the Torsen which is great but expensive($500).

 

[Mike789]

Thx for the replies and info...lots of expertise here I am grateful for !
Yes, it is a 4.0 V6.
1st issue is to get it unlocked as it seems due to the noise that it is stuck in 4WH at the moment. What I will do 1st is to unplug the wires going to the TC. I suppose while I'm under there I could take the 3 screws off some cover so I can shift it manually as I don't really need 4WD currently.
My Dad knows a lot more than I as he used to mechanic a Supermodified and has rebuilt many drive trains...but I am not so sure of what I know.
I do not understand the diff between 'open' and LS. AFAIK, there is posi (like my 69 Camaro SS had) and there is LS. I've always thought that LS means that 1 wheel may slip, then the car goes nowhere. I lived in NH until 25 so I've driven in plenty of snow.

Are you saying that my 98 Exp is not real 4WD (not that I'm sure what that is) but more like AWD ? Even in 4WH ?

How would I know if my 95 4R has a rear locker or LS ? I do know when I make a tight turn on gravel, the front wheels fight each other to do different things.

 

[96eb96]

Thx for the replies and info...lots of expertise here I am grateful for !
Yes, it is a 4.0 V6.
1st issue is to get it unlocked as it seems due to the noise that it is stuck in 4WH at the moment. What I will do 1st is to unplug the wires going to the TC. I suppose while I'm under there I could take the 3 screws off some cover so I can shift it manually as I don't really need 4WD currently.
My Dad knows a lot more than I as he used to mechanic a Supermodified and has rebuilt many drive trains...but I am not so sure of what I know.
I do not understand the diff between 'open' and LS. AFAIK, there is posi (like my 69 Camaro SS had) and there is LS. I've always thought that LS means that 1 wheel may slip, then the car goes nowhere. I lived in NH until 25 so I've driven in plenty of snow.

Are you saying that my 98 Exp is not real 4WD (not that I'm sure what that is) but more like AWD ? Even in 4WH ?

How would I know if my 95 4R has a rear locker or LS ? I do know when I make a tight turn on gravel, the front wheels fight each other to do different things.

Posi/LS are like Coke and Pepsi, cola but different brands. They accomplish a similar task, but the internals may be a bit different.

The Control Track 4wd system that was first installed on a 95 Explorer lives on Today even in 2021 Trucks on the lot. It can have 4 modes (some years of Explorer have 3). So the below can apply to a new F150 or expedition that has this system or our trucks. Some new trucks may lack 4wd auto, and just have 2wd, 4wd and 4Low.

2wd - this requires hardware to disconnect the axle. The 95-96 have a vacuum motor and slip in the front axle to break the right axle shaft. The newer trucks actually have vacuum controlled hubs, but you get the idea. No 97+ explorer has this mode.

4wd Auto - this senses wheels slipping in the rear and applies a clutch to lock the axles. When the slipping goes away(front axle speed == rear axle speed), the clutch releases. This is done with a computer and sensors. There is always though a small bias applied to the front wheels (maybe 8%). This gets it ready to lock up. Can be driven on dry or slippery pavement. The drawback is, there is a rampup time.

4wd - The clutch is ALWAYS locked. So you have True 4wd. Must be on slippery pavement.

4wd Low - Same as above, but a shift motor moves a low gear reduction gear in the drivetrain, so you get a ton of torque, but you are limited to about 30 Mph. Good for the boat ramp, offroad with very uneven terrain, or maybe pulling a house off its foundation.

AWD (like the V8 explorer, or My Lexus GS Sedan) generally is an always on system that can be driven on any pavement. There is usually some mechanical clutch that allows slippage (like the explorer) or the GS has a planetary differential with an electronic lock if things get slippery. The GS system is actually similar to the Aerostar AWD, around that age, and still used today. It is very heavy duty. A smaller tire on the AWD explorer will cause disaster, because the clutch can overheat. A differential naturally deals with differences in speed. But it needs that clutch to lock (same issue as an open diff on the rear..).

The Explorer AWD is always driving the wheels, unlike the Control trac above which acts on conditions. Remember the 4wd mode above locks the wheels so dry pavement driving is impossible. The idea of control trac was to remove the heavy and expensive center differential using software.

 

[CDW6212R]

Thx for the replies and info...lots of expertise here I am grateful for !
Yes, it is a 4.0 V6.
1st issue is to get it unlocked as it seems due to the noise that it is stuck in 4WH at the moment. What I will do 1st is to unplug the wires going to the TC. I suppose while I'm under there I could take the 3 screws off some cover so I can shift it manually as I don't really need 4WD currently.
My Dad knows a lot more than I as he used to mechanic a Supermodified and has rebuilt many drive trains...but I am not so sure of what I know.
I do not understand the diff between 'open' and LS. AFAIK, there is posi (like my 69 Camaro SS had) and there is LS. I've always thought that LS means that 1 wheel may slip, then the car goes nowhere. I lived in NH until 25 so I've driven in plenty of snow.

Are you saying that my 98 Exp is not real 4WD (not that I'm sure what that is) but more like AWD ? Even in 4WH ?

How would I know if my 95 4R has a rear locker or LS ? I do know when I make a tight turn on gravel, the front wheels fight each other to do different things.

It's an automatic 4WD, the system uses electricity to engage an electromagnetic clutch within the transfer case. For 4low and 4Hiit uses a shift motor to change the gears. In the automatic switch position, it runs in 2WD all of the time until it senses a speed difference between the front and back wheels. Then it energizes the internal clutch, which grabs the front drive shaft, making it 4WD.

 

[Mike789]

Great information, all. I am too old too admit just how old, but I have never given much thought to 4WD until now. Being an Engineer, means I will not rest ez until I know as much as I can handle...
So, I have read all the replies and still have a few questions...
It seems to me, corners are a 4WD system's 'enemy' as wheels must slip or bad things will happen eventually.
It also seems to me, with my limited knowledge so far, that 4WD systems are all different.

re my 98 Exp, in 2WH, when going around a corner on dry pavement, the inside & outside wheels want to turn at different rates, so a LS system was designed long ago. I still do not understand the reply by 9 above in an earlier post that Posi and LS are mostly the same because I have driven Posi and it does not act the same as LS at all. Posi will not let one rear wheel spin, afaik. Posi makes a car a tad harder to get thru a corner which is why most passenger cars have LS, afaik.

Back to 4WD, it seems to me that in my 98 Exp at least, when goign around a corner on dry pavement in any 4WD setting, the outside wheels MUST turn more than the inside, front and rear. This means that the differentials, F&R must slip, and do, on most 4WD systems. On my 98 Exp this is also true because the F axle is live and there is no way to disconnect the F wheels from the TC. So we have at least 2 'clutches' for this. Now, if we add 4WD to this scenario, we add another clutch, inside the TC now, so if we turn on that same corner on dry pavement, we get slippage. In total there is slippage now in 3 places. But I need to remember, the 1st 2 clutches are always slipping anyways, in this scenario, so having 4WD on only means 1 added clutch.

Now, as I want to really understand this, it seems to me that there is only slippage in the TC clutch because the F axle (that goes into the TC) is turning at a different rate than the R axle, and -not- because the inside wheel wants to turn less than the outside, as that function is done by the differential 'clutches'.

So, only because when going around a corner the F axle turns more than the R axle would the TC clutch slip. In fact, I could say when going around a L hand corner, the RF wheel turns the most, the LF turns the next lessor amount, then the RR tire turns a lessor amount, and the LR tire turns the least. So all 4 wheels want to turn a different amount for the same corner. So we have on the 98 Exp at least, 3 clutches. maybe simplified, the average of the 2 R wheels is smaller than the average turns of the 2 F wheels.

So, unless my understanding of what I've learned so far is flawed, I think I've figured what is happening and why.

The next question would be, is my 95 4Runner drive system designed differently than the 98 Exp ? I have been asked if my 4R has a locking R end but I do not know, so maybe not. If it did, does this mean that the R differential acts more like a posi rear end, with no slippage at all, than a LS rear end ? My next question would be, does any company make a 4WD system that has -real- locking differentials ? How about a 4WD system that is locked left to right and front to rear ? No slippage anywhere ? I was talkign w/a friend today and we wondered what kind of 4WD the original Hummer has. What about the real old Land Cruisers, or 4Runners...are any truly locking all the way around ? I realize a vehicle like this would have to have levers or devices to unlock/lock the system for pavement use.

Another 4WD theory question...do the old 'locking hubs' mean that when they are unlocked, the F cv-axles do not turn, so they are not 'live' axles ? Seems ike this is a better way to build a true on/off road vehicle.

Still learning...

 

[imp]

Great information, all. I am too old too admit just how old, but I have never given much thought to 4WD until now. Being an Engineer, means I will not rest ez until I know as much as I can handle...
So, I have read all the replies and still have a few questions...
It seems to me, corners are a 4WD system's 'enemy' as wheels must slip or bad things will happen eventually.
It also seems to me, with my limited knowledge so far, that 4WD systems are all different.

re my 98 Exp, in 2WH, when going around a corner on dry pavement, the inside & outside wheels want to turn at different rates, so a LS system was designed long ago. I still do not understand the reply by 9 above in an earlier post that Posi and LS are mostly the same because I have driven Posi and it does not act the same as LS at all. Posi will not let one rear wheel spin, afaik. Posi makes a car a tad harder to get thru a corner which is why most passenger cars have LS, afaik.

Back to 4WD, it seems to me that in my 98 Exp at least, when goign around a corner on dry pavement in any 4WD setting, the outside wheels MUST turn more than the inside, front and rear. This means that the differentials, F&R must slip, and do, on most 4WD systems. On my 98 Exp this is also true because the F axle is live and there is no way to disconnect the F wheels from the TC. So we have at least 2 'clutches' for this. Now, if we add 4WD to this scenario, we add another clutch, inside the TC now, so if we turn on that same corner on dry pavement, we get slippage. In total there is slippage now in 3 places. But I need to remember, the 1st 2 clutches are always slipping anyways, in this scenario, so having 4WD on only means 1 added clutch.

Now, as I want to really understand this, it seems to me that there is only slippage in the TC clutch because the F axle (that goes into the TC) is turning at a different rate than the R axle, and -not- because the inside wheel wants to turn less than the outside, as that function is done by the differential 'clutches'.

So, only because when going around a corner the F axle turns more than the R axle would the TC clutch slip. In fact, I could say when going around a L hand corner, the RF wheel turns the most, the LF turns the next lessor amount, then the RR tire turns a lessor amount, and the LR tire turns the least. So all 4 wheels want to turn a different amount for the same corner. So we have on the 98 Exp at least, 3 clutches. maybe simplified, the average of the 2 R wheels is smaller than the average turns of the 2 F wheels.

So, unless my understanding of what I've learned so far is flawed, I think I've figured what is happening and why.

The next question would be, is my 95 4Runner drive system designed differently than the 98 Exp ? I have been asked if my 4R has a locking R end but I do not know, so maybe not. If it did, does this mean that the R differential acts more like a posi rear end, with no slippage at all, than a LS rear end ? My next question would be, does any company make a 4WD system that has -real- locking differentials ? How about a 4WD system that is locked left to right and front to rear ? No slippage anywhere ? I was talkign w/a friend today and we wondered what kind of 4WD the original Hummer has. What about the real old Land Cruisers, or 4Runners...are any truly locking all the way around ? I realize a vehicle like this would have to have levers or devices to unlock/lock the system for pavement use.

Another 4WD theory question...do the old 'locking hubs' mean that when they are unlocked, the F cv-axles do not turn, so they are not 'live' axles ? Seems ike this is a better way to build a true on/off road vehicle.

Still learning...

Manual locking hubs do indeed "detach" the front wheels from the driving axles, no matter their type. Used for zillions of years successfully, but inconvenient for the Sunday drivers, so a variety of means of connecting/disconnecting, allowing slippage, etc., have been employed.

Just as two wheels separated by 5 or 6 feet of distance between them, like front or rear wheels, a set of two rears and two fronts are separated also. The fronts and rears have differentials of their own to allow speed variation between those two wheels.

Now, tie the front wheels and rear wheels together mechanically, and you have the need for a DIFFERENTIAL between front and rear, a THIRD DIFFERENTIAL. Very expensive, some have used it, though I cannot quote which, but Subaru comes to mind possibly. Various schemes are in use to allow powering both front and rear. Ford's "4X4 AUTO" switches an electronic clutch serving as a kind of third differential on and off as speed difference is detected between front and rear wheels. In case of a "shuddering" rear of the tires, the clutch may engage & disengage many times rapidly, making jarring and frightening noises, 4X4 AUTOs chief drawback, IMO. Manually switching to 4X4 HIGH locks the clutch ENGAGES until switched off again. In normal driving, 4X4 AUTO drives and runs exactly like rear wheel drive only. 4X4 LOW engages the clutch and a lower gear in the transfer case.

Ford All Wheel Drive (AWD) uses a small liquid-filled clutch something like a fan clutch, which allows apparant "slippage" to occur between front and rear wheels. It is ALWAYS ENGAGED, no electrical hookup, no choice of any kind by driver, no manual controls on the dashboard. It works, has drawbacks, like any other, but is fairly long-lived as long as tires are always kept at the same rolling diameter, all 4. This means size wise as well as inflation-wise.

 

[CDW6212R]

imp hit it thoroughly, the front and rear have differentials that handle corners perfectly. There are many kinds of LS diffs', the name is meaningless. Some allow lots of differentiation with little resistance, new LS or worn clutches give you that. Detroit Lockers lock hard and don't do well under any circumstances in corners. That locker is almost like a spool, but they do have clutches and they do allow some differentiation.

The newest common type are worm gear diffs', they resist moderately, better than LS but nothing super strong like a Detroit Locker. Most people prefer those, and that is the one type available for the front of the 95-01 Explorers, at $500(Torsen). Detroit makes one now too for most popular diff, the True Trac, that's a great unit if you can do it.

If your truck is binding up in slow cornering, noticeably, you should investigate. Under normal conditions, using 4WD will be very noticeable and harsh. That binding is from the center TC in some way locking the front and back together, question is why and should it at that time.

Driving with it binding up will hurt many things, not just one. I learned the hard way that the front differential can be destroyed. My 98 AWD I bought with no front driveshaft. I knew that and had spare parts. I replaced and repaired everything except the AWD, and it had black fluid in it. After about two years and several AWD TC fluid changes(still black), I noticed a binding that got worse quickly. I got to working on it the next week, but thinking it was a bad CV axle(both had been used from my Mercury). A new one didn't fix it, so I then did the whole front suspension(I had the parts and it needed to be done). Driving to the alignment shop I had more binding, the tighter suspension and CV's made it more obvious. The pinion gear was very loose in place, shaft moved too much. I removed the front shaft and got the alignment. Then I swapped out the whole front diff assembly, it destroyed the whole thing. I drove it like that as a 2WD for a year or so, and the trans lost 3rd/4th gears. I left it at work and still drove it on the route for two months until the water pump began making a lot of noise.

Keep equal diameter tires on the vehicle at all times if it's AWD or 4WD that you use much.

 

[410Fortune]

FYI
"POSITRACTION" is just a name GM gave their LIMITED SLIP differentials
So Posi traction and limited slip are the SAME THING

There are 3 basic types of differentials
Open
Limited slip
Locked

 

[masospaghetti]

To answer your question, yes there are some explorers that are control trac AWD like yours, and some that are full time AWD (the 5.0 96-01 trucks) and then there are some that are true 2wd, 4hi and 4 low (5 speed explorers, explorer sports and sport tracs= no control trac awd)

My 98 has the 4.0 OHV, 5-speed manual, and BW4405 control trac transfer case. Has 4Auto, 4High, and 4Low.

Edit: 4405, not 4406. Whoops

 

[410Fortune]

98 ohv with m5od 5 speed trans uses a 5 bolt control trac t case

the 4406 is a 6 bolt t case used behind the ford 1/2 ton transmissions

your 98 is a 4 door with control trac (4auto) = uses the bw 4405 torque on demand unit

1998 FORD EXPLORER 4.0L V6 OHV Transfer Case Assembly | RockAuto

RockAuto ships auto parts and body parts from over 300 manufacturers to customers' doors worldwide, all at warehouse prices. Easy to use parts catalog.

www.rockauto.com

 

[masospaghetti]

98 ohv with m5od 5 speed trans uses a 5 bolt control trac t case

the 4406 is a 6 bolt t case used behind the ford 1/2 ton transmissions

your 98 is a 4 door with control trac (4auto) = uses the bw 4405 torque on demand unit

1998 FORD EXPLORER 4.0L V6 OHV Transfer Case Assembly | RockAuto

RockAuto ships auto parts and body parts from over 300 manufacturers to customers' doors worldwide, all at warehouse prices. Easy to use parts catalog.

www.rockauto.com

Yep, mixed that up.

But still think you might off on your note "(5 speed explorers, explorer sports and sport tracs= no control trac awd)"

 

[410Fortune]

I guess I was!!!! Thanksa for pointing that out! I am not sure I have ever seen a 5 speed 4 door that had control trac, most of the 5 speeds I have seen in a 4 door were xls trucks and I did not know they were also control trac. COOL!!
I love to learn stuff.
Now lets see if it sticks!!

 

[Mike789]

Ok, so if posi and LS are the same thing, why did the 69 Camaro I have never slip, even in snow ? Only with that rear-end was I able to drive from VT to MA during the worst of the blizzard of 78. And why do most rear ends (I've always called them LS or limited traction) slip at the earliest hint of snow or lack of traction ? Why do Posi cars turn less easily ? I thought that was the whole point (for the Sunday driver) of the LS. Lots of great info here, this is the 1st thing I've read that doesn't make sense yet.

 

[CDW6212R]

I explained that in my first post. There are varying levels of locking diffs, some lock hard/fully, and others weakly or barely, depending on clutch quality(worn out or new).

The OEM Ford LS is not very strong. When new the clutches hold fairly well, but as they wear, they hold less and less strongly. Most 20+ year old LS units don't hold at all. Your old 69 Camaro had clutches in better condition for sure. There are specs to define how good a locking diff is, in torque values. The LS is IIRC in the 75lbsft range at best, what it takes to break one side from the other. That's in new clutch condition, trans in neutral and one tire on the ground. It takes a certain amount of torque to turn the tire that's in the air, to overcome the LS clutches. If you can do it by hand grabbing the tire then the clutches are fairly bad.

 

[Mike789]

Huh, I did not know that posi is really not locked up via gears, but still could slip. Does this mean, if i was so inclined, I could make most any old 70's car (I have a 74 LTD and a 76 LTD) act like it had Posi somehow ?

 

[CDW6212R]

The closest thing to actually hard locked is with a Detroit Locker. Those hold tight and in turns on dry pavement can be felt trying to keep the tires at the same speed. All differentials will allow different axle speeds, they just differ in how strong they resist. I know little about GM diffs, or the many aftermarket I haven't dealt with. I've had many LS diffs, two Torsens, and one Eaton True Track. But read around and you will find that a lot like the Auburn diff, and some Aussie is popular for 8.8 brands. Those you will find cost more than stock, and much less than the high end types. Price has a lot to do with what people have.