Rear end acted up after manuallel putting car into 4 wheel drive.

[captspillane]

A viscous coupling is like two hands interlaced. If you kept one hand still and your fingers spread apart, the other hand could move forward and backward with each moving finger passing between two stationary fingers. Inside the coupling are strips of metal connected to one output that pass in close proximity to strips of metal connected to the other output. The strips pass each other without touching, but there is a viscous fluid surrounding them. That means that if you spin one output really fast and let the other go slack, the viscous fluid will not be able to easily push out of the way. The slack output will naturally feel like spinning along with the moving output. You can always stop the slack output if you hold it still since its not rigidly connected to the spinning output, but the viscous fluid lets some degree of torque be transfered from the spinning one to the stationary one. When the viscous coupling wears out, which all of our antique transfer cases are, then there is nothing connecting the front driveshaft and rear driveshaft like any other open differential transfer case. When the viscous coupling is new, you can grab one driveshaft yoke and hold it still while slowly spinning the other driveshaft yoke, but you will feel the stationary driveshaft wanting to spin unless you exert alot of pressure.

[captspillane]

A clutch can last anywhere from 60K to 200K miles, depending on driving habits. The key to long life on a clutch is fast shifting. Thats counter-intuitive. The gripping surface on the clutch lasts forever if its cold. It sheds off material considerably faster when its warm, and insanely fast when its hot. In an exaggerated sense, the rate of wear is exponentially related to the temperature of the material. If you pull your clutch pedal back very slowly the car will smoothly start rolling. If you let the clutch out very fast, the car will jerk and toss your head around and the engine will probably stall. The smooth start requires the clutch to come into contact with the flywheel and slide against the surface, which heats it up quickly while the jerking start requires the clutch plate to contact the flywheel and almost instantly mate to it and begin spinning together without any sliding or any heat buildup.

In stop and go city traffic your clutch will heat up from many consecutive shifts. It will still last forever if you intentionally let the car gently jerk around from very fast pedal motions. It also helps if you resist the car with your brakes to slow the engine until you actually feel it throbbing from wanting to stall and then let go of the brakes just long enough for it to recover before slowing back down to a throb. The point is that you can't predict how long a clutch will last when driving techniques have a drastic impact on the rate of wear.

[Eagle1984]

A clutch can last anywhere from 60K to 200K miles, depending on driving habits. The key to long life on a clutch is fast shifting. Thats counter-intuitive. The gripping surface on the clutch lasts forever if its cold. It sheds off material considerably faster when its warm, and insanely fast when its hot. In an exaggerated sense, the rate of wear is exponentially related to the temperature of the material. If you pull your clutch pedal back very slowly the car will smoothly start rolling. If you let the clutch out very fast, the car will jerk and toss your head around and the engine will probably stall. The smooth start requires the clutch to come into contact with the flywheel and slide against the surface, which heats it up quickly while the jerking start requires the clutch plate to contact the flywheel and almost instantly mate to it and begin spinning together without any sliding or any heat buildup.

In stop and go city traffic your clutch will heat up from many consecutive shifts. It will still last forever if you intentionally let the car gently jerk around from very fast pedal motions. It also helps if you resist the car with your brakes to slow the engine until you actually feel it throbbing from wanting to stall and then let go of the brakes just long enough for it to recover before slowing back down to a throb. The point is that you can't predict how long a clutch will last when driving techniques have a drastic impact on the rate of wear.

Thanks again, so basically with a open differential is one is not engaged the power will go to it as it has the least resistance and not move compared to a closed one where it will move if one is disengaged. Does the clutch still wear out the same if it is a automatic? Are you saying that if the front axle does disengage for some reason it will not hurt anything and if it is a closed differential/transfer case even if they do disengage the front tires will still spin like they were engaged?

[captspillane]

It might suck to have to reach into your glove compartment for the emergency 9/16 wrench and have to crawl under the car in the rain along the side of Route 78 with your feet on the drivers side inches from the passing trucks to click the transfer case into 2WD. Yes indeed that does suck. No mechanical damage will occur. If your viscous coupling is strong it will make the front driveshaft spin along with the rear driveshaft but it won't matter because the wheels won't slow or restrict the movement of the driveshaft.

I'm not sure how to answer your question about a clutch wearing out in an automatic transmission. My earlier post was specific to the clutch in a car with a manual transmission.

[captspillane]

In an Automatic there are clutches, but they do a different job. The torque converter converts the engine torque into fluid pressure by using the spinning flywheel to drive internal turbines that move around fluid and imparting potential energy to that fluid. The main reason that automatics get terrible gas mileage in comparison to manual cars is that the torque converter is always putting a load on the engine and always robbing energy even when the car is sitting still. On a manual car the engine is totally disconnected from the rest of the car once the clutch pedal is depressed, so the only fuel necessary to keep it running is enough to compensate for the friction and resistance in one rotation of the crankshaft and associated internal components. That's minimal. Around each planetary assembly inside the automatic transmission is a clutch band that tightens down around the outside of the planetary to stop it from spinning or to let it spin freely, which makes the output shaft of the transmission go from stationary to spinning in a similar fashion as our differential discussion. Those clutch bands work off fluid pressure, so if the pump isn't putting out enough fluid pressure or if the throttle body can't maintain fluid pressure because of excessive leaks from antique gaskets then they can't engage fully. Clutch bands generally last for 300K+ miles but will quickly burn up and get ruined if they slip and heat up because of poor fluid pressure or a defective servo. There is also round clutch discs stacked together with steel discs in some of the internal assemblies that ease the impact of gear changes. Those also generally last forever unless they get damaged because of some other internal problem.

[mick]

Counter-clockwise is 4wd and clockwise is 2wd.