Engine/Transmission (1998.5 - 2002) 4WD top speed?

[snowracer69]

I know a lot of guys launch in 4WD while racing, so I take it that it's not too bad for the system to run up to 100+MPH? I mean, obviously it's not the best thing for it, but is it terrible? Say I were to launch in 4WD, and do 1/4 mile... topping out around 80-90... will I hurt anything?



Josh.



BTW, I know... if ya can't pay if it breaks, you shouldn't race it, but it's good to know anyway

 

[Cummins4Life]

The owners manual, or the tag on the drivers sunvisor suggests not to run 4hi above 55mph, but what I've heard is that you should shift out of 4hi on the 1-2 or 2-3 shift depending on which shift you can go WOT without breaking the tires loose in 2wd. The thing I've noticed about 4wd though is that it doesnt seem to dis-engage until you let up off the throttle so you'll be running the whole distance in 4hi anyway. As far as damgage I have no idea. I doubt there would be too much wear though.

 

[athompson]

Actually, you WILL cause MAJOR damage if you CONSISTENTLY run in 4WD on pavement or any other surface that doesn't allow for wheel slip. The transfer case DOES NOT provide ANY differentiation (think spool in the axle here). MAJOR binding WILL occur. If you are lucky you will only blow out your your u-joints. If your NOT lucky, you could blow out the t-case or axles.

 

[duaneparks]

Originally posted by athompson

Actually, you WILL cause MAJOR damage if you CONSISTENTLY run in 4WD on pavement or any other surface that doesn't allow for wheel slip. The transfer case DOES NOT provide ANY differentiation (think spool in the axle here). MAJOR binding WILL occur. If you are lucky you will only blow out your your u-joints. If your NOT lucky, you could blow out the t-case or axles.

I've heard this a lot, so I have a question...



If you're running the same sized tires all around, and you're running straight down a 1/4 mile track, what will cause the bind?



The front and rear diffs have the same gearing, and the tires are the same diameter, and you're not turning (much), only correcting for drift, so the differential in speed between all 4 wheels is almost nil. What would cause it to bind up?



Duane

01 Ram 4x4 "Brandy"

 

[TomGolden]

I personally have only made one 4WD run down the strip, and I went the entire 1/4 mile in 4HI. Heck, I have enough to do shifting through 5 regular gears, I ain't got either the time or free hands to be shifting the 4WD shifter too!



My top speed that run was my fastest ever - 92. 1 MPH.



KatDiesel I think, has made a lot of 4WD launches and full 1/4 mile runs in 4WD. Or maybe it was Steve St. Laurent..... or maybe both of them.



Tom

 

[KatDiesel]

I ran about 8 times the whole way in 4wd.



After that I started shifting the lever when I get into 2nd gear or 3rd if I forget.



It "feels" better down at the other end of the track whe I do it like that.

 

[emjay]

4WD Bind

Binding up in 4WD on pavement is caused by slight differences in wheel speed from front to rear. The phase relationship of the front tires to the rear varies very slightly when you turn the steering wheel, because the a front tire moves forward or backward in relationship to the rear tire. Even slight steering movements to keep straight can cause a bind. Besides, unless the tires are exactly the same rolling diameter (which is probably never true due to air pressure, load, wear and temperature variations), the front and rear axles will bind up eventually. When the static bind torque is combined with engine torque, that's what breaks parts. To put it in perspective, a tire that has a rolling radius of 15. 25" (30. 50" diameter) makes 661. 2 rotations per mile. A tire that has a rolling radius of 15. 26" (30. 52" diameter) makes 660. 8 rotations per mile. take the difference (0. 4 roatations per mile), divide by four, and at the end of 1/4 mile, a tire that is 20 thou larger in diameter will have rotated 36 degrees in relationship to the other tire. That's a lot!

:{

 

[Texas Diesel]

Re: 4WD Bind

Originally posted by emjay

[ A tire that has a rolling radius of 15. 26" (30. 52" diameter) makes 660. 8 rotations per mile. take the difference (0. 4 roatations per mile), divide by four, and at the end of 1/4 mile, a tire that is 20 thou larger in diameter will have rotated 36 degrees in relationship to the other tire. That's a lot!

:{ [/B]

I knew I should have stayed awake in math class



How did you figure all this out????? :--)



Lets see, if Dolbert had a case of beer at morning recess and he drank 4 beers in each class and 2 at lunch, 1 on the bus ride home, and gave 2 to the bus driver, Cletis, how many would he have to give to "uncledaddy" that night?

 

[emjay]

I cheated. I used a calculator. Never cared too much for school. Actually, if you really want to know, it's not that hard:



Since there's 5280 feet in a mile, that means that there's 63,360 inches in a mile (5280*12).



The circumference of a circle (in this case, a 30. 5" tire) is 95. 82" (PI*30. 5). So each rotation of a 30. 5" tire will move 95. 82" on the ground. Take your inches per mile, and divide it by the circumference of the tire, and you get 661. 2 rotations per mile.



So, anyway, you end up with:



TireRotPerMile = (63360/(TireDiam*3. 14159))



Plug in the 30. 52" tire, you get 660. 8, a difference of 0. 4 of the circumference of the tire. Since a full circle is 360 degrees, multiply 0. 4 * 360 = 144 degrees angular difference per mile. Divide that by 4 and you get 36 degrees per 1/4 mile. Incidentally, the difference in inches traveled over a mile between the two tires is the tire circumference * 0. 4 = over 38 inches!



A lot of little things add up pretty quickly

 

[Texas Diesel]

Excellent, I saved that. Thanks!!

 

[KatDiesel]

As you said... if you are in fear of breaking it... stay in 2wd.

 

[Rockcrawler]

What's the big deal?

Has anyone actually broken anything from this? The theory makes sense and all but how hard is it really. The tires will scrub that's all.



I would'nt commute like this but for the 1/4- no harm done.



As my name implies, I'm in the rocks, a lot, competing. The rock slabs are exactly like pavement- in some cases more traction. I'm turning tight turns in 4wd all the time with torque multiplied thru low range and 7. 17 gears. we even go into rear drive low and front drive low while braking the other axle for tight technical turns.



worst case is the train gets a little bind- unload it by easing reverse and no more load. In a drag situation any tire slippage effectively unloads any bind you may be concerned about. Just do it!

 

[T. Baker]

Binding can only be as hard as the tires grip. If they slip it releases the binding. If you are spinning wheels in 2wd you are already putting harder strains on the drive line than binding could. If you are doing quarter miles you are putting way more strain on the drive line than the binding caused by running in 4wd. Don't worry about running in 4wd in the quarter mile. Worry about running the quarter. If you want everything to last a really long time don't race the quarter mile.

That being said, I have to admit I like to do a little accelerating as well. I put my truck in 4wd if I am going to do the quarter as well so I don't put all the strain on my little dana 44 rear axle. It is a short distance. Long running on pavement in 4wd is garanteed to shorten the drive line life.