Definitive Thread on SAS
02-24-2016, 01:10 PM
#21
Senior Member
The way an open diff works is power is transmitted to the side with the least amount of traction via the spider gears. When your talking drag the process is reversed. The ring & pinion are stationery while the rotation transfers to the disconnected passenger side of the axle.
02-24-2016, 01:18 PM
#22
Senior Member
iTrader: (1)
The way an open diff works is power is transmitted to the side with the least amount of traction via the spider gears. When your talking drag the process is reversed. The ring & pinion are stationery while the rotation transfers to the disconnected passenger side of the axle.
02-24-2016, 01:20 PM
#23
Senior Member
I'd like to add an example for you. When both tires of an open diff vehicle are off the ground, you spin one tire and the other side turns in the opposite direction while the drive shaft (and ring and pinion ) do not turn at all. The rotation transfers through the spider gears to the other side without affecting the ring and pinion.
02-24-2016, 01:23 PM
#24
Senior Member
iTrader: (1)
I'd like to add an example for you. When both tires of an open diff vehicle are off the ground, you spin one tire and the other side turns in the opposite direction while the drive shaft (and ring and pinion ) do not turn at all. The rotation transfers through the spider gears to the other side without affecting the ring and pinion.
02-24-2016, 01:30 PM
#25
Senior Member
02-24-2016, 01:32 PM
#26
Senior Member
iTrader: (1)
02-24-2016, 02:07 PM
#27
Senior Member
You are correct Sir. A torsen locker will not keep the truck in 4x4.
BUT! lol
In an open diff front end, the rotating force of the drivers side tire is transferred to the open (unengaged) passenger side of the spider gears while driving. No torque or spinning motion is transferred back through the front drive shaft. When you have a limited slip or locking device, the rotational torque is sent back to the front drive shaft. Now the transfer case is disengaged so the rotational torque is cancelled on the open side if the transfer case. This still causes parasitic drag from the front right tire & will affect fuel mileage & turning radius. It also creates more possible wear on the front output shaft bearings of the transfer case and pinion bearings.
Think about it this way. If you have your truck (open diff) in 2wd and reach under it and spin the front drive shaft, it will spin freely. If you do the same with a lsd or locker present, the shaft will not spin at all. It's still engaged to the front right tire.
BUT! lol
In an open diff front end, the rotating force of the drivers side tire is transferred to the open (unengaged) passenger side of the spider gears while driving. No torque or spinning motion is transferred back through the front drive shaft. When you have a limited slip or locking device, the rotational torque is sent back to the front drive shaft. Now the transfer case is disengaged so the rotational torque is cancelled on the open side if the transfer case. This still causes parasitic drag from the front right tire & will affect fuel mileage & turning radius. It also creates more possible wear on the front output shaft bearings of the transfer case and pinion bearings.
Think about it this way. If you have your truck (open diff) in 2wd and reach under it and spin the front drive shaft, it will spin freely. If you do the same with a lsd or locker present, the shaft will not spin at all. It's still engaged to the front right tire.
02-24-2016, 02:24 PM
#28
Ok. So much got mentioned I don't know who to respond to lol. I'll just add my two cents.
Assume for a second, that a limited slip acts as a locker in the front axles and is tight through the turns.(I know it's not 100% but bear with me for a sec). The wheels won't have too much drag offroad, but will have huge issues if driven on the road, even with the transfer case is disengaged.
This was an issue after WWII with military jeeps they wished to decommission for on-road use. This is why they added manual locking hubs(see pick below). When unlocked, the manual hub releases the front wheels from the drivetrain, allowing each wheel to spin freely. The transfer case then disengages the front driveshaft. At this point, the only mpg effects come from the weight of the added parts. You could have a blown differential in the front, and the car would still drive since the transfer case is released, and the front hubs aren't connected.
If I'm not mistaken, all 4x4 f-150s 9th gen and up have electronic locking hubs, which lock and unlock when the 4x4 switch is engaged. If this is the case, then having a limited slip or locker will have zero effect on mpgs while in 2wd. If for some reason these vehicles don't have them(maybe due to all factory models having open front diffs) I believe they make kits so you can add manual ones yourself.
Assume for a second, that a limited slip acts as a locker in the front axles and is tight through the turns.(I know it's not 100% but bear with me for a sec). The wheels won't have too much drag offroad, but will have huge issues if driven on the road, even with the transfer case is disengaged.
This was an issue after WWII with military jeeps they wished to decommission for on-road use. This is why they added manual locking hubs(see pick below). When unlocked, the manual hub releases the front wheels from the drivetrain, allowing each wheel to spin freely. The transfer case then disengages the front driveshaft. At this point, the only mpg effects come from the weight of the added parts. You could have a blown differential in the front, and the car would still drive since the transfer case is released, and the front hubs aren't connected.
If I'm not mistaken, all 4x4 f-150s 9th gen and up have electronic locking hubs, which lock and unlock when the 4x4 switch is engaged. If this is the case, then having a limited slip or locker will have zero effect on mpgs while in 2wd. If for some reason these vehicles don't have them(maybe due to all factory models having open front diffs) I believe they make kits so you can add manual ones yourself.
Last edited by me1234; 02-24-2016 at 02:34 PM.
02-24-2016, 02:27 PM
#29
Senior Member
Oh I understand the whole locker keeping the drivers side engaged and the affects of it. Fyi having the front driveshaft live doesn't affect trimming radius. Mpg did take a small hit though. ( read Sig.) Just was unsure if the ls would be "tight" enough to affect the driveshaft in 2wd.
02-24-2016, 02:34 PM
#30
Senior Member
Ok. So much got mentioned I don't know who to respond to lol. I'll just add my two cents
Assume for a second, that a limited slip acts as a locker in the front axles and is tight through the turns.(I know it's not 100% but bear with me for a sec). The wheels won't have too much drag offroad, but will have huge issues if driven on the road, even with the transfer case disengaged.
This was an issue after WWII with military jeeps they wished do decommission for on-road use. This is why they added manual locking hubs(see pick below). The hub releases the front wheels from the drivetrain allowing each wheel to spin freely. The transfer case then disengages the front driveshaft. At this point, the only mpg effects come from the weight of the added parts. You could have a blown differential in the front, and the car would still drive since the transfer case is released, and the front hubs aren't connected.
If I'm not mistaken, these vehicles have electronic locking hubs, which lock and unlock when the 4x4 switch is engaged. If this is the case, then having a limited slip or locker will have Zero effect on mpgs while in 2wd.
Assume for a second, that a limited slip acts as a locker in the front axles and is tight through the turns.(I know it's not 100% but bear with me for a sec). The wheels won't have too much drag offroad, but will have huge issues if driven on the road, even with the transfer case disengaged.
This was an issue after WWII with military jeeps they wished do decommission for on-road use. This is why they added manual locking hubs(see pick below). The hub releases the front wheels from the drivetrain allowing each wheel to spin freely. The transfer case then disengages the front driveshaft. At this point, the only mpg effects come from the weight of the added parts. You could have a blown differential in the front, and the car would still drive since the transfer case is released, and the front hubs aren't connected.
If I'm not mistaken, these vehicles have electronic locking hubs, which lock and unlock when the 4x4 switch is engaged. If this is the case, then having a limited slip or locker will have Zero effect on mpgs while in 2wd.
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me1234 (02-24-2016)