Ok, So I am new to the 4x4 world of trucks. I do know how to set my 78 F-150 into 4wd, and it did great with the foot of snow around here.

But I was wondring what were the top Speeds for the different ranges. i.e. 4Lo and 4Hi. I kept 4Lo under 25MPH, and 4 Hi under 35MPH. I was just wondering what the max was. Also for when you hit bare wet roads and still have 4WD engaged. As I ran into that scinario plenty. I know it isn't great to be doing alot of driving and turning on bare cement as sometimes that can leat to binding?

SO I was just wondering what the top speeds were. I looked in my '78 owners manual, and they just show top speeds for Manual Tranny. I have a C6 with a NP205.

 

Sounds like your right on track except 25 in low might be a little high I never run mine in low over 15. Well this is just a suggestion keep the hubs locked in and just shift the transfer to 2 until you need 4HI then the wet pavement is not an issue.

 

4WD Lo should only be used off road and in extremely bad conditions... like if you are stuck in the mud or it is very slippery never use 4WD lo on dry pavement. The reason for that is because in 4WD Lo the front drive is geared lower and if you do drive on the road with it you will cause damage to your drivetrain, as far as 4WD high is concerned as far as I know you can use that at highway speed and it will cause no harm.

 

Man you guys have some real misconceptions about 4wd use.

The front end is not geard lower than the rear, so you do not have any speed limits associated with 4wd use in low range. The output for the front through the t-case is the same as the rear. You should not not drive a part time 4wd on dry pavement, or any surface with high traction because the front and rear outputs are turning at the same rate, and during a turn on pavement the front tires and rear tires have to turn at different speeds. The inability to turn at different speeds will cause the truck to hop and bind the case. This makes it difficult to steer, and can get a little violent. NP203 transfer cases are the exception and these have a differential in the case itself that permits it to be dirven on the pavement.

Now as far as speed, why would there be a limit? I have been in excess of stupid speeds (well, my tires anyway) in 4 low and high ranges. Your front end does not work any different than the rear, and has no limits. The only limits associated with speed is the point at which you can engage 4 low. This must be done at or close to a complete stop, though I can engage low range (front or rear) up to about 5 mph. (also a 205 with a twin stick).
You might limit speed based upon gear selection, but you have the option of shifting into a higher gear and gaining some speed. In some cases you will want to go faster, and still might have to be in low range.

Here, you be the judge:

 

I drove my 78 to my buddys last night, its a few miles out of town, it was freezing rain, when I left it was crazy slippery I kicked it in 4 and ran 55 all the way to town. A couple weeks ago there was 8'' of fresh powder on the highways, no plows out yet, I put my cherokee in 4 and ran 70 for about 50 miles, I don't use 4 low on the streets.

 

Ed+wicked bronco=showoff

 

Yeah unfortunatly they don't know how to handle the snow in the Wester washington. Their plowing efforts are hit or miss at best. And it is no fun to try and hop out on a main road that is plowed where you don't need 4WD, then a mile later you need 4WD.

Really I was half tempted to buy a plow setup for my truck and go make some money. I heard that some people were wanting $90 and hour to do lots. Seeing city and county don't do private property.

 

Cool vid 75F350. I drive my 75 F100 4X4 with the full time 203 tfc to Iowa for visiting my family and its a 300mile one way drive. Drove many times at 70mph or more down the interstate in 4x4 even shifted it in and out with out slowing down. Just let off the gas a little. Never any problems.

 

Ok if there are no speeds associated with the four wheel drive let me ask why on some models of vehicles on the visor and in the owners manual do they post top speeds for certain gear configurations? The millitay also does this with its multy use equipment. Let me here the misconception explained since I have a miscoception of four wheel drive!!!!!!!

 

I know that on my dad's 01 chevy it says don't go over 35 mph in 4wd.

 

On most of our 4x4s the front axle is geared different than the rear axle. 4.10-4.11 3.50-3.54 etc. (yes, I know there are exceptions)
This allows more control when turning under power with the 4x4 engaged. The factory wanted the front axle pulling you through the turn rather than the rear axle pushing which tends to cause understeer or plowing resulting in a wider turning radius. The downside is the different ratios cause binding quickly on dry surfaces even when driven only a few feet. This led to the development of the full time transfer cases with an internal differential that could be driven on dry surfaces in 4x4.

As far as to speed in 4x4, I have never had any problem at any speed as long as it was a slick surface and within the max. RPM of the engine. I have driven many miles at 55mph on snow with no signs of excessive wear or damage.

 

This might be the maximum engagement speed for the t-case, but you can go as fast as your engine rpm/gearing will take you.

When the high range went out on the np208 in my 93 ranger I drove 45 miles in LOW range and about 55 mph. The engine was at the rev limiter but thats it. The only thing that sucked about it was the amount of fuel i burned but at least noone tried to run me over. (As if you could run a ranger w/ 39" over )

 

My 79 with c6/np205 will go about 45-50MPH in low gear with no issues at all.

 

Do you have an example of speed limits for certain speed configurations? Lets see, if I understand correctly. Is there something on a 73-79 sun visor that limits or suggests a speed limit for any given gear? This I wouldl like to see.

Is it safe to assume that even of this were true that a limit would be based upon the final drive ratio (which it is not) or might be affected by the tire size?
No limits on 4 wheel driver operation at all. There is a limit on when it can be engaged, and this is primalrilly based on whether or not the rear tires are spinning. Damage here will result, but this has to do with synchronization of the front and rear output, and not speed.

Lets see, whats next,,,,,oh. the old military must be right concept. While I am a firm beliver in the military, and spent my share of time serving, we can agree that the military is very **** about procedures, and protocol.
All I can suggest here is that military regulations prohibit "public displays of affection" and this does not mean that kissing your wife will make your lips fall off.
Just because a regulation is written, does not make it the rule, (in this case a rule about 4wd operation) it makes it the exception. As a server in the military, one must follow the regulations to the letter, but that does not mean that the regualtion is the "golden rule".
I can gurantee that even military regs (with regards to these alleged speed limitations) have been broken, and while the regs are still in place, zero damage has occured as a result.

Another example: A simple speed limit (not affiliated with 4wd use) but a simple speed limit. The Vehicle code in any state will mandate a certain safe speed for any given area, but yet, even with a "limit" we still find speeders.
Just because the limit is stated on paper, does not mean that any mechanincal damage will result if this "limit" is broken.

4wd use is not any diffrent. If your truck is capable of reaching 110 mph in 2wd, it will reach the same top speed while in 4wd. (slight drag variables will apply)
Low range will be only limited by the amount of rpm that the engine is capable of turning.

As far as different ratios from front to rear are converned, the difference between a 4.09 ratio and a 4.10 ratio is exceeded by differences in tire size, and slight variations in tire pressures. No two tires are exactly the same. This will always create a difference in total "rollout".
If these differences were so great front to rear, lockers or spools could never be run on the street, but they are every day.

4wd systems are not as fragile as many would think, or are led to believe, and thay can go as fast as horsepower will permit.
Heak, dont tell a desert racer in a 4wd class that he has to limit his speed.
Not gonna happen.

 

Very well stated

In addition: As for the military limits for speed, I am sure that those are there to reduce wear and tear on the engine/drivetrain of military vehicles. After all these vehicle see plenty of abuse on a daily basis, why subject them to even more because someone has a lead foot or is in a hurry. Most all military vehicles run multi-fuel engines (diesel), which do not like higher rpms. Given also that the vehicles usually have exremely high gear ratios it takes a lot more RPM to achieve MPH, thus risking premature engine failure.