Was that other 4wd a fulltime 4wd, with traction control?

 

The 1979 Grand Cherokee was a full time four wheel drive, the FJ40 was manual front locking hubs, CJ7 and Pathfinder were not full time. I just do not see how a non posi diff vehicle can have both wheels have power in one direction. Take any full time "four wheel drive" and get it in dirt, put it in drive and floor it and you wll see only one rear wheel spin and dig in on each axle. Full time units will only transfer power from the center diff back and forth to the front and rear diffs unless you lock it and then front and rear diffs get equal power. This has nothing to do with what is going on in the front and rear differential. If it is not a locker or a posi unit on that axle there will be only ONE wheel getting any power and the opposite wheel will get power when in reverse. If this was not true then why would they even need a posi option if the axle automatically powered both wheels?

 

Sorry, but that's not all totally true. My old 77 K10 was fulltime, and would almost always spin all 4 tires with open diffs. On several occasions I've pulled stuck trucks out, and looked at 4 "black marks" where my wheels were spinning. I think it's when you jack the vehicle up off the ground, and no wheels are touching that you get the "one wheel up front, and one rear wheel" turning effect. I still believe that a certain amount of torque is applied to both wheels on a given axle.

So, with what you've said, and what I know.. if you have the adventure package, then that leaves you with one place to run your smaller spare. You can't run it in back if you have the locker (at least not when it's on), so run it up front. However, it's usually advised to put smaller tires on non-steering axles.. so if you have a rear locker that pretty much leaves you no great options. Now, if you don't have the adventure package.. you can run it out back... or you can elect to leave the locker off, which sort of sucks depending on your situation... seeing as it's a great advantage to have.

I really don't see the point of running a smaller tire when you already have a correct size spare.. when all you would really need to do is carry a small 12v compressor, and a tire plug kit (which take up a lot less space, and saves gas etc). Plug and fill the flat, and save the good spare for the trip home. As long as I've been wheeling, I wouldn't waste the effort to carry around something that wouldn't serve my needs 100%. I don't see your smaller spare doing that.. since you have to try and figure out where it's ok to run it.

So in the end, I just feel that it's a moot point, when theres much better options out there. I can understand carrying two spares for extremely remote locations.. like the Australian outback, or something along those lines.. but toting two around for a much shorter wheeling trip.. or everyday, is just sort of silly to me. There are better options.. and they don't include potential damage to the system. I'd sell that spare to someone who could use it, and put my money towards better provisions. But, that's just me.

 

i assume the H2 has the same type of drive system as the H3. i had all 4 tires barking on the slickrock in moab, and only the rear has a locker. maybe the bus really is retarded, but it had power to both front wheels at the same time . . . and i only had one spare, for whatever that's worth . . . .

 

I'd like to comment on the snow driving. Last year I had the joy of driving in a very heavy snow storm in Chicago. It was the night a Southwest Plane skidded off the runway at Midway Airport crushing a car and killing one person.

Anyway, I played around with the 4 wheel options to see what combo I felt worked best. Now I was in about 6-8" of snow on the road and no plows were able to keep the roads clear at this particular time. I found that running in 4 High Lock with the Stabili-Trac system turned off worked the best. Running in 4 High lock gave me the best traction and control in turning. The stabili-trac system kept trying to take over when it felt any kind of slippage whatsover so I found myself "fighting" the truck more than actually trying to drive. Now, I know that the system was just doing it's job but I prefer to use my hazardous driving skills and control the vehicle myself. That's just me.

My reccomendation to anyone that is going into the snow season is to go out to a large parking lot or somewhere where you wont crash into someone/something as soon as you get a decent snowfall or some ice and play around with the different options. It's better to be prepared and know how your vehicle is going to react when you get out into a real situation.

Mike

 

Many similar experiences. All 4 tires spin, even if you don't lock the rear diff at all, and even if its in 4-hi-open.

My dealer once described it to me as "one front wheel driven, and the opposite rear wheel is driven", as mentioned above, but i haven't seen that.

Easy way to test that might be to put the truck on a lift and "drive", just watch what happens to the wheels. I've wanted to do that for a while.

 

That's good advice. It's always best to try it out for yourself, and see what works best for you, or what feels best to you. Chances are it may actually be different for different people. As for myself, with the rare, if ever, snowfall we see.. more than likely I'd have to put it in 4wd hi-lock and hope for the best.

Also, getting back to the more than one spare subject. I mentioned carrying a 12v compressor. many of them are very pricey, but for anyone interested, here is a very good unit that will serve most people very well. They were hard to find for a while, with many off roaders buying them up .. but I believe they are back out again, although the price has gone back up a bit. This is a link to a "home test" done on the one I carry.

compressor

I think the price went back up towards the 50.00 mark, but I'm not sure. I bought two when they were still going for 24.00, one I gave to a buddy for a Christmas gift. Anyway, carrying something like this and a trail kit, flat fixer, is probably much easier, and takes up less space etc. Like I said before, if you get a flat, plug it and fill it and run it on the trail. When you are ready to hit the road again, then swap the spare onto the "flat". That way there isn't the danger of a blow out, and when you are home, you can take the tire to a tire shop and have it checked and perhaps repaired better. The compressor is also good for letting you air down a bit for better traction, and then top off the tires for the trip home. If you want to go one better, I carry a small air tank, that I fill with my home compressor, and use it as much as I can. If I use that all up, then I resort to the small compressor.

I just thought I'd post it for anyone who's interested.

 

So here's my two cents in the drivetrain subject. All full time four wheel drive vehicles (or all wheel drive) have a center differential. This diff operates just like the one in the axle, i.e. it allows for a different speed from one side to the other, not a different amount of power. Reguardless of how much power is being sent into it, only half of the power is being sent to either side; no more, no less. On vehicles with a high lock option, such as the Hummers, then essentially you are engaging a locker in the center differential. Now you have no slip between the two sides, just as when you engage a locker in an axle.
To clarify, I will talk about axles, but this all applies to the differential in the transfer case equally. Let's assume you have an open differential and an input of 100 lb/ft of torque and 100 horse power. In a strait line, you have 50 HP and 50 lb/ft going to each tire. If you turn, you still have the same power distribution, but now one side turns faster than the other because it has a farther distance to cover in the same amount of time. Now let's say you put one tire on a slippery surface and the other on a high friction surface. Both tires are still recieving the same 50 HP/50 lb/ft, but the one on the slippery surface is now spinning. It spins because the available traction is less than the power being sent to that tire, and because the traction is less than the other side. The tire with all of the traction is still getting its fair share of power, but can't do anything with it because the power required for it to move the vehicle by itself is unavailable. If you were to compare this to something that only applies power to one tire, like a go cart, then if the tire with power is on a high friction surface, the thing goes, even if the others are on a slippery surface, If that tire is on a slippery surface, then it doesn't go reguardless what the other tires have for traction.
In this scenario, in essance, as far as the components are concerned, all you have done is go around a corner. It doesn't matter which tire has what traction, they still get equal power.
To prove this, find somewhere that you can drive up onto a ramp until you have tires come off the ground, and that you can approach from the other side to get the tires that were previously on the ground in the air. You will get the right rear and left front tire off of the ground going one way, and the left rear and right front off the ground going the other. Either way, once the two tires that are being lifted off the ground see enough of a reduction in traction, they will both spin and you will quit moving. The distance traveled up the ramp will be the same for both sides. The power being sent to each tire is still 1/4 of what the engine is producing, but the two that are spinning aren't contributing their share of the work.
Now, if the vehicle has a locking differential, and you engage it, if the traction available to the two remaining tires is sufficient to move the vehicle, then you will move. If not, then you will have three tires spinning, the two on the axle that is locked, and the one in the air on the unlocked axle. If you have a locking diff in that axle, and you engage it, and the traction available to that tire is sufficient to move the vehicle, the progress continues. If not, then you have all four tire spinning. If you are in high lock or low range, then all four wheels will spin the same speed. If you manage to get in to this situation in 4 high (open) then you may notice a speed differential from front to rear, but both tires on a given axle will spin the same speed, and all four are still recieving the same amount of power as they were when they were all on the ground.

Another way to think about it is: Out of the four points of contact, and possible traction to the ground, 2 wheel drive will gaurantee one tire with the potential to move the vehicle (1 wheel drive). All wheel drive with no locking center diff will ga

 

Oh yeah, as far as the oddball spare tire, unless you plan on driving only in high open, or a 2 wheel drive, you are asking for serious drivetrain damage reguardless where you put it, because the transfer case will try to make both drivelines turn at the same speed, but that short tire will want to turn faster than everything else. It's like it is prepetually driving around in it's own private cirlce while everyone else is driving strait.

 

As to why I carry 2 spares it was because Arizona can have some very, very remote places and the roads, like up to Crown King, have very sharp shale rocks that put holes in your tires that are way too big to be plugged. I found that out in my 96 G. Cherokee with new BFG AT's. No plug kit was going to repair those flats. I figured that if I aired down the 315's and if I had to use the second smaller spare I could get the diameter of the 315's almost the same as the 285 that was pressured up.

Linus Gump - What you say sounds like what I was saying. That a four wheel drive vehicle without a locker or posi is a two drive unless it has a rear locker or posi then it would be a 3 wheel drive. My "All Wheel Drive" Subaru Legecy without a posi or locker is a 2 wheel drive vehicle for sure as was my old Internation Scout "Four Wheel Drive". I remember pulling some logs in the Scout with it engaged in low range, front hubs locked, no posi rear and getting stuck. I pulled the choke handle out so the engine would run without giving it gas and got out of the vehicle and watched as the front right and left rear wheels were spinning. So much for Four Wheel drive. A locking center diff. on the Scout, which it did not have, would make no difference to what wheels would be spinning ,only how much of the engine power they would be getting.

The only factory vehicle that I know of with real four wheel drive is the Rubicon and maybe the H1, the full size Land Cruiser which I think has a factory front/rear posi option and also maybe the Land Rover.

As far as people saying they saw both front wheels of their H3 spinning it was either from the momentum the wheel had from the time it was in contact with the road or from the slight momentum coming from the axle and other internals. No locker or posi then no power to both wheels.

Again, Linus, I think I could get away with a 2" smaller tire if I aired down the 315's and got them to be the same diameter as the 285? I just want to make it to the highway and not walk 40 or 50 miles in 100 degree heat.

ShortBus- If I was in Moab I would not be worried about a flat as the rocks there and off roads are pretty smooth. Shale rocks are like driving on knives and twice as likely to cut your tire when wet. 2" and even 3" holes are not uncommon.
And if both your front wheels were spinning then someone put a posi in the front diff while you were sleeping. Unless it was the momentum of the wheel, tire, axle, etc doing it but not with enough power to really move the H3. We should be going to Moab in a month I'll keep an eye out for a yellow H3.