awalker@topaz.ARPA (*Hobbit*) (02/13/85)
Uh - This should be pointed out for the benefit of all us fo-by owners. From: jeepcj2a@fluke.UUCP (Dale Chaudiere) Case 2: If you every buy a 4-wheel drive vehicle, you must rotate the tires. Any difference in tire diameter from front to back will cause the transfer case to bind, except on the most slippery surfaces. What kind of truck are *you* driving? Any full-time 4wd vehicle has a set of spider gears in the transfer case, which let the front and rear shafts rotate at different rates. In fact the front and rear punkins are often different ratios, which makes this necessary. Naturally, if you lock the shafts together and drive on dry pavement, you'll get torque windup across the drivetrain which will undoubtely break something. Tire diameter therefore has nothing to do with what the 4wd drivetrain is doing. I have a '74 K10 Blazer into which I bolted a ''half-time'' kit that makes it full-time rear drive and switchable front wheel drive. [Especially after *losing* the front CV joint one trip back from Boston.] With this arrangement you not only save some gas, but if you lose a U-joint miles from anywhere, you can take the rear shaft completely *out* and get home on the hitherto-unused front one. _H*
williams@mhuxj.UUCP (WILLIAMS) (02/15/85)
> .............................. In fact the front and rear punkins are > often different ratios, which makes this necessary. ................... Why would the truck be designed with different front and rear ratios? Doug Williams mhuxj!williams
mike@amdcad.UUCP (Mike Parker) (02/16/85)
> Naturally, if you > lock the shafts together and drive on dry pavement, you'll get torque > windup across the drivetrain which will undoubtely break something. Naw! I've been there! If the front and rear tires are very nearly the same size and the differentials are the same ratio, you'll drive along just fine wearing the living daylights out of your tires and getting s****y mileage. But... When you get home and make that sharp turn into the driveway, Watch Out! Luckily, the windup did not break anything but I still don't know what kept me from going through the windshield. Mike @ AMDCAD
jlw@ariel.UUCP (J.WOOD) (02/16/85)
The military 2 1/2 ton truck or 6x6 has a sprag unit between the always driven quad rear wheels and the fronts. The gearing is selected such that the front wheels are driven only when the rears lose traction and start spinning faster than the fronts. This causes the sprag to lock up and the front axle to engage. Joseph L. Wood, III AT&T Information Systems Laboratories, Holmdel (201) 834-3759 ariel!jlw
jeepcj2a@fluke.UUCP (Dale Chaudiere) (02/18/85)
> Uh - This should be pointed out for the benefit of all us fo-by owners. > > From: jeepcj2a@fluke.UUCP (Dale Chaudiere) > > Case 2: If you every buy a 4-wheel drive vehicle, you must rotate the > tires. Any difference in tire diameter from front to back will > cause the transfer case to bind, except on the most slippery > surfaces. > > What kind of truck are *you* driving? Any full-time 4wd vehicle has a > set of spider gears in the transfer case, which let the front and rear > shafts rotate at different rates. In fact the front and rear punkins are > often different ratios, which makes this necessary. Naturally, if you > lock the shafts together and drive on dry pavement, you'll get torque > windup across the drivetrain which will undoubtely break something. > Tire diameter therefore has nothing to do with what the 4wd drivetrain > is doing. > I am driving one of the majority of conventional part-time 4-wheel drive vehicles that are on the road. (Jeeps, Land Cruisers, Toyotas and the majority of American makes). These conventionals rotate the front and rear drive shafts at exactly the same speed. The first versions of fulltime 4 wheel drive made by Ford, Chevy, and Dodge had only a spider gear type setup in the transfer case. (no limited slip) This allowed the power to be transfered to the driveshaft with the least resistance. Thus without limited slip in either differential, you just had a choice of one out of 4 wheels slipping instead of one out of two like a normal car. The little lever in the glove box locked the spiders in the transfer case making it behave like a conventional 4 wheel drive transfer case. The big three quit making this type of fulltime 4 wheel drive when they finally admitted the reduced gas milage, when used on hard surface roads. Jeep Quadratrack has a limited slip setup in the transfer case. I have never heard of the front and rear differentials having different ratios, except on trick sand drag rigs with small front tires and large paddles on the rear. The spider gear type setups in transfer cases were never designed to compensate different ratios front to rear. > I have a '74 K10 Blazer into which I bolted a ''half-time'' kit that makes > it full-time rear drive and switchable front wheel drive. [Especially > after *losing* the front CV joint one trip back from Boston.] With this > arrangement you not only save some gas, but if you lose a U-joint miles from > anywhere, you can take the rear shaft completely *out* and get home on the > hitherto-unused front one. > Yes and the kits I have seen for this conversion come with a new shaft for the transfer case that converts it back to a convensional setup, (no limited slip in the transfer case).
jeepcj2a@fluke.UUCP (Dale Chaudiere) (02/18/85)
> > .............................. In fact the front and rear punkins are > > often different ratios, which makes this necessary. ................... > > Why would the truck be designed with different front and rear ratios? > > > Doug Williams > mhuxj!williams They're not, see Re: Wrong!!
jeepcj2a@fluke.UUCP (Dale Chaudiere) (02/18/85)
> > Naturally, if you > > lock the shafts together and drive on dry pavement, you'll get torque > > windup across the drivetrain which will undoubtely break something. > > Naw! I've been there! > > If the front and rear tires are very nearly the same size and the > differentials are the same ratio, you'll drive along just fine > wearing the living daylights out of your tires and getting s****y > mileage. But... When you get home and make that sharp turn into > the driveway, Watch Out! Luckily, the windup did not break anything > but I still don't know what kept me from going through the windshield. > > > Mike @ AMDCAD If you read your owners manual, I believe it warns against driving with the transfer case locked in 4 wheel high on dry paved roads.
mike@amdcad.UUCP (Mike Parker) (02/20/85)
> > the driveway, Watch Out! Luckily, the windup did not break anything > > but I still don't know what kept me from going through the windshield. > > > > > > Mike @ AMDCAD > > If you read your owners manual, I believe it warns against driving with the > transfer case locked in 4 wheel high on dry paved roads. Of course, I read the manual. However, the eariler Ford full-time 4wd's weren't always that easy to shift from "center-locked" to "center-unlocked". It was possible for the little lever on the floor to be in the 2wd position while the truck was indeed in 4wd. Mike @ AMDCAD
ix1037@sdcc6.UUCP (Christopher Latham) (02/23/85)
> > > .............................. In fact the front and rear punkins are > > > often different ratios, which makes this necessary. ................... > > > > Why would the truck be designed with different front and rear ratios? > > > > > > Doug Williams > > mhuxj!williams > > They're not, see Re: Wrong!! As a matter of fact on some four wheel drive vehicles the front and rear ratios are slightly different. 4.10 to 1 as opposed to 4.11 to 1 for example. For the intended use of conventional 4WD, that is off paved roads, this does not present a problem because there is sufficient slip due to the nature of the road. Christopher Latham U.C.San Diego Dept. of Applied Mechanics and Engineering Sciences ..sdcsvax!sdcc6!ix1037
jeepcj2a@fluke.UUCP (Dale Chaudiere) (02/26/85)
> > As a matter of fact on some four wheel drive vehicles the front and rear > ratios are slightly different. 4.10 to 1 as opposed to 4.11 to 1 for > example. For the intended use of conventional 4WD, that is off paved > roads, this does not present a problem because there is sufficient slip > due to the nature of the road. > > Christopher Latham > U.C.San Diego > Dept. of Applied Mechanics > and Engineering Sciences > ..sdcsvax!sdcc6!ix1037 Because the front drive shaft is offset, the difference in differential ratios is probably to compensate for some gearing in the transfer case. The wheels would then turn at the same speed, front and rear. This makes the only sense. Since most people know so little about 4W drive train components, I am willing to go to Off-Road Mail column to get the correct answer. I am curious myself. By the way the orginal posting was about rotating tires. Every tire dealer I have talked to says you must rotate tires on a 4-wheel drive. Dick Cepek, (Largest retail off-road tire dealer) recommends rotation every 5K mi., 2.5K if you have posi. I typically get 40-45K from my mud tires. This is excellent considering the wild tread pattern. ================================================================================ I wish more people would converse on technical issues. All this debate about American vs Japanese vs German vs..., can get nowhere! Each person has his/her own opinion! If more technical subjects were discussed on net.auto people might learn something to base their opinions on. DAC
ix1037@sdcc6.UUCP (Christopher Latham) (03/01/85)
> > > > As a matter of fact on some four wheel drive vehicles the front and rear > > ratios are slightly different. 4.10 to 1 as opposed to 4.11 to 1 for > > example. For the intended use of conventional 4WD, that is off paved > > roads, this does not present a problem because there is sufficient slip > > due to the nature of the road. > > > > Christopher Latham > > U.C.San Diego > > Dept. of Applied Mechanics > > and Engineering Sciences > > ..sdcsvax!sdcc6!ix1037 > > Because the front drive shaft is offset, the difference in differential ratios > is probably to compensate for some gearing in the transfer case. The wheels > would then turn at the same speed, front and rear. This makes the only sense. > Since most people know so little about 4W drive train components, I am willing > DAC Actually the ocassional difference in ratios from front to rear probably has more to do with availability of ratios in a suitable sized differential for the load capacity. My present 4WD (Mitsubishi truck) has exactly the same ratios front and rear as do my brother's Jeep (It's been in the family since '68) and my folk's IH Travelall. Chris