CAD (AUTO 4WD Hubs) & All About 4WD
#1
11-23-2007, 11:36 PM
CAD (AUTO 4WD Hubs) & All About 4WD
As you may have noticed, there are no hubs (manual or automatic) on the 4x4 Ram. The drivers side front wheel is permanently connected to an axle shaft which runs to the differential.
he passengers side has a two piece axle, one half permanently connected to the wheel, one half (intermediate axle shaft) connected to the differential. The two halves meet in the middle of the passenger side axle tube (that bulge on the axle tube is where the axle disconnect lives). The two halves are connected together for 4X4 operation by the Center Axle Disconnect mechanism
The inner axle shaft has a nose, which fits into a socket in the end of the outer axle shaft. The photo at the right shows the two ends which meet at the shift collar. A needle bearing in the outer axle shaft socket allows the inner and outer axle shafts to rotate independently
he passengers side has a two piece axle, one half permanently connected to the wheel, one half (intermediate axle shaft) connected to the differential. The two halves meet in the middle of the passenger side axle tube (that bulge on the axle tube is where the axle disconnect lives). The two halves are connected together for 4X4 operation by the Center Axle Disconnect mechanism
The inner axle shaft has a nose, which fits into a socket in the end of the outer axle shaft. The photo at the right shows the two ends which meet at the shift collar. A needle bearing in the outer axle shaft socket allows the inner and outer axle shafts to rotate independently
In 2WD, the axle disconnect keeps the two passenger side axle halves independent. The driver side axle happily spins the side gear in the differential, but because the differential is open and there is no solid connection on the passenger side, the side gear simply spins the diff's spider gears, which then spin the passenger side inner axle shaft backwards. Neither the differential's ring gear nor the front driveshaft will turn while in 2WD.
With me so far? OK, now when you shift into 4WD it gets a little more complicated...
- A synchronizer in the transfer case spins the front driveshaft up to speed
- The 4x4 shift lever locks into place and engages a vacuum switch
- Vacuum lines swap the High/Low vacuum signals to the vacuum solenoid on the front axle
- The vacuum solenoid (shift motor) slides the splined shift collar
- When the splines on the two axle stubs align, the collar locks into place
- Now that the axle ends are locked together by the shift collar and you have 4WD
#3
11-24-2007, 12:13 AM
Locking in 4x4
The axle disconnect does wear more than the old hubs. Basically, you are spinning everything but the diff and the front driveshaft. The outer axles spin with the wheels. The side gear on the front diff is turned by the axle on the driver's side. This side gear spins the spiders and the opposite side gear. The central axle shaft is then spun opposite to the wheels by the diff. (same action as rotating a tire on a lift and watching the other turn backwards.)
When you shift, a mechanical interlock activates the front driveshaft. This in turn slows the central axle and then rotates it in the same direction as the wheels. At this time, a vacuum line is switched that places pressure on a diaphragm behind the front axle on the passenger side (looks like a little power brake diaphragm). As the central axle reaches the same speed as the outer axle on the passenger side, the pressure on the diaphragm slides a connecting collar over the splines of the two axles and links them. Similar to the way a hub moves the splined collar over the end of the axle.
When you disengage, it all works in reverse. You don't have to stop, back-up, or anything else.
Sometimes, the 4WD light stays on, or fails to come on. This is a great indicator. What it means is that there is a difference in speed between the two axle ends, and the vacuum can't move the collar. Burping the throttle, twisting the wheel side to side, or shifting the 4WD again generally releases the pressure.
2 things. 1) It is easier to shift while moving. Even into 4LO, a slight roll makes the shift easier. If you are stuck, and it won't shift, turn the steering wheel side to side as you burb the throttle to get the axles to line up. When at a stop, it is very tough to line up non-moving splines.
Pros and Cons
Fairly strong. The size of the axle shaft at the disconnect is significantly stronger than a hub end could ever be. The outer axle splines can have a much tighter tolerance and thus distributes the load better. The weak point is the bearing carrier design instead of using discrete inner and outer bearings. In the early Jeeps, there was close to 4" between the inner and outer bearings to support side loads. In the Ram, there is only 1/8" between them. This makes rim backspace selection critical, and requires much higher tolerances in the bearings themselves. Also, with no way to service the bearings without a 20 ton press, you have no way to prevent failure without spending $300 for a new carrier.
Since the use of 4WD requires vacuum, a leak, or destruction of the lines can render the 4WD inoperative. However, the lines are fairly well protected, and failures are rare. The vacuum switch is a known weak point. The switch is a little tower on the transfer case with four lines coming from it. The switch is activated by the transfer case when a lever inside the case presses a plunger at the base of the switch. Then, a spring in the switch extends the plunger when the lever is retracted. The problem is that the plunger is rounded to ease the lever's action. This rounded part can be easily jammed inside the switch by the standard gunk in the transfer case. When this happens, the interlock and the 4WD light will not disengage. It is an easy fix by just un screwing the switch and cleaning it, but when it happens, you can feel the extra drag of the front driveshaft and associated parts.
Maintenance is very easy. A fluid change every so often is about all it requires. No spindle bearings to wear out, no dial to regrease, and no seals to leak. (actually the axle seals can leak, but it isn't too common. The part that sucks is that the passenger side seal is a bugger to replace as the seal must be pressed from inside the disconnect housing.)
This is my third vehicle with the disconnect system and I've never really had any major problems with it. Sure, I've had seals leak, and the switch jam, and other annoying things, but when I need 4WD, it has always been there.
I've also had vehicles with manual and auto hubs, and this is still an easier and more reliable system. It is only when you HAVE to get the system engaged while stopped that it can be difficult. For me, I just engage the 4WD earlier. Besides, it goes with the tread Lightly idea
The axle disconnect does wear more than the old hubs. Basically, you are spinning everything but the diff and the front driveshaft. The outer axles spin with the wheels. The side gear on the front diff is turned by the axle on the driver's side. This side gear spins the spiders and the opposite side gear. The central axle shaft is then spun opposite to the wheels by the diff. (same action as rotating a tire on a lift and watching the other turn backwards.)
When you shift, a mechanical interlock activates the front driveshaft. This in turn slows the central axle and then rotates it in the same direction as the wheels. At this time, a vacuum line is switched that places pressure on a diaphragm behind the front axle on the passenger side (looks like a little power brake diaphragm). As the central axle reaches the same speed as the outer axle on the passenger side, the pressure on the diaphragm slides a connecting collar over the splines of the two axles and links them. Similar to the way a hub moves the splined collar over the end of the axle.
When you disengage, it all works in reverse. You don't have to stop, back-up, or anything else.
Sometimes, the 4WD light stays on, or fails to come on. This is a great indicator. What it means is that there is a difference in speed between the two axle ends, and the vacuum can't move the collar. Burping the throttle, twisting the wheel side to side, or shifting the 4WD again generally releases the pressure.
2 things. 1) It is easier to shift while moving. Even into 4LO, a slight roll makes the shift easier. If you are stuck, and it won't shift, turn the steering wheel side to side as you burb the throttle to get the axles to line up. When at a stop, it is very tough to line up non-moving splines.
Pros and Cons
Fairly strong. The size of the axle shaft at the disconnect is significantly stronger than a hub end could ever be. The outer axle splines can have a much tighter tolerance and thus distributes the load better. The weak point is the bearing carrier design instead of using discrete inner and outer bearings. In the early Jeeps, there was close to 4" between the inner and outer bearings to support side loads. In the Ram, there is only 1/8" between them. This makes rim backspace selection critical, and requires much higher tolerances in the bearings themselves. Also, with no way to service the bearings without a 20 ton press, you have no way to prevent failure without spending $300 for a new carrier.
Since the use of 4WD requires vacuum, a leak, or destruction of the lines can render the 4WD inoperative. However, the lines are fairly well protected, and failures are rare. The vacuum switch is a known weak point. The switch is a little tower on the transfer case with four lines coming from it. The switch is activated by the transfer case when a lever inside the case presses a plunger at the base of the switch. Then, a spring in the switch extends the plunger when the lever is retracted. The problem is that the plunger is rounded to ease the lever's action. This rounded part can be easily jammed inside the switch by the standard gunk in the transfer case. When this happens, the interlock and the 4WD light will not disengage. It is an easy fix by just un screwing the switch and cleaning it, but when it happens, you can feel the extra drag of the front driveshaft and associated parts.
Maintenance is very easy. A fluid change every so often is about all it requires. No spindle bearings to wear out, no dial to regrease, and no seals to leak. (actually the axle seals can leak, but it isn't too common. The part that sucks is that the passenger side seal is a bugger to replace as the seal must be pressed from inside the disconnect housing.)
This is my third vehicle with the disconnect system and I've never really had any major problems with it. Sure, I've had seals leak, and the switch jam, and other annoying things, but when I need 4WD, it has always been there.
I've also had vehicles with manual and auto hubs, and this is still an easier and more reliable system. It is only when you HAVE to get the system engaged while stopped that it can be difficult. For me, I just engage the 4WD earlier. Besides, it goes with the tread Lightly idea
#4
11-24-2007, 12:15 AM
4WD Hard Low range shift
Thanks to : Mike Di Giovanni
This is a common problem with the automatic transmission. Unlike a manual with the clutch depressed, the auto is trying to spin the output shaft unless it is in park (many transmissions still "windmill" the gears even in neutral).
When the vehicle is stopped to shift into (or out of) lo range, the transfer case goes through the neutral position while the automatic transmission tries to spin the gear cluster. This causes the grinding and difficult shifting. Some people try (with mixed results) to shift while rolling at very low speed so that everything is turning. It helps to perform the shift as quickly as possible so the gears don't have time to start moving independently
When the vehicle is stopped to shift into (or out of) lo range, the transfer case goes through the neutral position while the automatic transmission tries to spin the gear cluster. This causes the grinding and difficult shifting. Some people try (with mixed results) to shift while rolling at very low speed so that everything is turning. It helps to perform the shift as quickly as possible so the gears don't have time to start moving independently
(I didn't say it was easy!)
What I have found that works pretty good is, put it in neutral and "WAIT 20-30 SECONDS" for the tranny and transfer case internals to come to the same speed, then pull or push the shifter lever aggressively. (depending if you want to apply 4lo or disengage 4lo.)
What I have found that works pretty good is, put it in neutral and "WAIT 20-30 SECONDS" for the tranny and transfer case internals to come to the same speed, then pull or push the shifter lever aggressively. (depending if you want to apply 4lo or disengage 4lo.)
#5
11-24-2007, 12:42 AM
Shifting Procedure
From Owners Manual
Transfer Case Shifting Procedure:
2H to 4H or 4H to 2H
Shifts between 2H and 4H can be made while the vehicle is moving or stopped. If the vehicle is moving, shifts can be made at any speed up to 55 mph. This shift will be easier if you momentarily release the accelerator pedal. Apply a constant force while shifting the transfer case lever. NEVER drive in 4H on dry, paved roads.
NOTE: During cold weather (below 30 F) it may be more difficult to shift the transfer case while the vehicle is moving. If so, stop the vehicle and shift. Move the vehicle slightly forward or backward to complete positive engagement of the gears.
4H to 4L or 4L to 4H
Slow the vehicle to under 3 mph (5 kmh), shift an automatic transmission to N (Neutral) or depress the clutch on a manual transmission. Shift the transfer case lever to the right and pull firmly down into 4L. Do not pause in transfer case N (Neutral).
NOTE: Pausing in transfer case N (neutral) in vehicles equipped with an automatic transmission may require shutting the engine off to avoid gear clash while completing the shift. If difficulty occurs, shift transmission to Neutral (N), hold foot on brake, turn engine off, and THEN make the shift to desired mode.
Do not attempt to shift to or from 4L while transmission is in gear or clutch is engaged.
Shifts between 2H and 4H can be made while the vehicle is moving or stopped. If the vehicle is moving, shifts can be made at any speed up to 55 mph. This shift will be easier if you momentarily release the accelerator pedal. Apply a constant force while shifting the transfer case lever. NEVER drive in 4H on dry, paved roads.
NOTE: During cold weather (below 30 F) it may be more difficult to shift the transfer case while the vehicle is moving. If so, stop the vehicle and shift. Move the vehicle slightly forward or backward to complete positive engagement of the gears.
4H to 4L or 4L to 4H
Slow the vehicle to under 3 mph (5 kmh), shift an automatic transmission to N (Neutral) or depress the clutch on a manual transmission. Shift the transfer case lever to the right and pull firmly down into 4L. Do not pause in transfer case N (Neutral).
NOTE: Pausing in transfer case N (neutral) in vehicles equipped with an automatic transmission may require shutting the engine off to avoid gear clash while completing the shift. If difficulty occurs, shift transmission to Neutral (N), hold foot on brake, turn engine off, and THEN make the shift to desired mode.
Do not attempt to shift to or from 4L while transmission is in gear or clutch is engaged.
#6
11-24-2007, 07:48 PM
4WD Hard Low range shift
Thanks to : Mike Di Giovanni
This is a common problem with the automatic transmission. Unlike a manual with the clutch depressed, the auto is trying to spin the output shaft unless it is in park (many transmissions still "windmill" the gears even in neutral).
When the vehicle is stopped to shift into (or out of) lo range, the transfer case goes through the neutral position while the automatic transmission tries to spin the gear cluster. This causes the grinding and difficult shifting. Some people try (with mixed results) to shift while rolling at very low speed so that everything is turning. It helps to perform the shift as quickly as possible so the gears don't have time to start moving independently
When the vehicle is stopped to shift into (or out of) lo range, the transfer case goes through the neutral position while the automatic transmission tries to spin the gear cluster. This causes the grinding and difficult shifting. Some people try (with mixed results) to shift while rolling at very low speed so that everything is turning. It helps to perform the shift as quickly as possible so the gears don't have time to start moving independently
(I didn't say it was easy!)
What I have found that works pretty good is, put it in neutral and "WAIT 20-30 SECONDS" for the tranny and transfer case internals to come to the same speed, then pull or push the shifter lever aggressively. (depending if you want to apply 4lo or disengage 4lo.)
What I have found that works pretty good is, put it in neutral and "WAIT 20-30 SECONDS" for the tranny and transfer case internals to come to the same speed, then pull or push the shifter lever aggressively. (depending if you want to apply 4lo or disengage 4lo.)
GOOD WAY TO BEND YOUR SHIFTER LINKAGE, I WAS SNOW WHEELING ONE DAY IN MY V10 AND WHEN I TRIED TO SHIFT TO LOW RANGE, I FORCED IT AND BANG, BENT THE LINKAGE......
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